Copyright

In Memoriam

Paul and Joan Rimmer

Together again

Contents

1  Cover

2  Title Page

3  Copyright

4  In Memoriam

5  Contents

6  Foreword

7  1 Degree

8 2 Degrees

9 3 Degrees

10 4 Degrees

11 5 Degrees

12  6 Degrees

13  7 – The Endgame

14  Acknowledgements

15  Notes

16  Index

17  Also by Mark Lynas

18  About the Author

19  About the Publisher

LandmarksCoverFrontmatterStart of ContentBackmatter

List of Pagesiiiivvixxxixii1345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596061626365676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117119121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163165167168169170171172173174175176177178179180181182183184185186187188189190191192193194195196197198199200201202203204205206207208209210211213215216217218219220221222223224225226227228229230231232233234235236237238239241242243244245246247248249250251252253254255256257258259260261262263264265266267268269270271272273274275276277278279280281282283284285287288289290291292293294295296297298299300301302303304305306307308309310311312313314315316317318319320321322323324325326327328329330331332333334335336337338339340341342343344345346347348349350351352353354355356357358359360361363364365366367368369370371372ii

Foreword

When I started writing this book I thought that we could probably survive climate change. Now I am not so sure. As you will read in these pages, we are already living in a world one degree warmer than that inhabited by our parents and grandparents. Two degrees Celsius, which will stress human societies and destroy many natural ecosystems such as rainforests and coral reefs, looms on the near horizon. At three degrees I now believe that the stability of human civilisation will be seriously imperilled, while at four degrees a full-scale global collapse of human societies is probable, accompanied by a mass extinction of the biosphere that will be the worst on Earth for tens or even hundreds of millions of years. By five degrees we will see massive positive feedbacks coming into play, driving further warming and climate impacts so extreme that they will leave most of the globe biologically uninhabitable, with humans reduced to a precarious existence in small refuges. At six degrees we risk triggering a runaway warming process that could render the biosphere completely extinct and for ever destroy the capacity of this planet to support life.

In the UN Paris Agreement signed in 2015, world leaders vowed to hold global temperature rise at 1.5°C, or, failing that, 2°C. So far they have entirely failed to keep their promises. To meet the 1.5°C target we would have had to cut global emissions by nearly half within a decade, and reach net zero by mid-century. Instead, emissions have reached a new record-setting high every year since the agreement. Many countries have offered their ‘Paris pledges’, but even if these were to be fully complied with, their combined effect on emissions is so trivial that they would still take us headlong into the four-degree world. That is why I wanted to write a completely new, fully updated version of Six Degrees, my book that was first published in 2007, because while the world’s scientists have done an amazing job in conducting research and writing papers over the last two decades, somehow the full import of the science has failed to register on our political system. Each chapter of this book makes abundantly clear what every successive degree-by-degree rise in temperature will mean for human society and the planet’s natural systems. The situation has become desperately urgent, and nobody who reads this will be able to say they didn’t know what was coming.

Even as I was writing this book, I could see the climate emergency continuing to escalate. When I began, Australia was still a normal country. Following the devastating wildfires of January 2020, which themselves followed record-breaking high temperatures that seared a drought-stricken nation, it no longer is. Millions of Australians endured weeks of living under a pall of smoke, as 12 million hectares of bush and farmland were incinerated in catastrophic mega-fires. The human death toll, currently standing at 33, is tragic enough. But spare a thought for the estimated billion wild animals that have also lost their lives. And remember too that there can be no return to normal. Normal has gone, for ever.

I can’t tell you with any precision when the globe will reach different temperature levels in the future. This is not so much because the science is uncertain – although to an extent it is – but because the rapidity of warming this century will depend on decisions yet to be made about how far and fast carbon emissions continue to rise. If we stay on the current business-as-usual trajectory, we could see two degrees as soon as the early 2030s, three degrees around mid-century, and four degrees by 2075 or so. If we’re unlucky with positive feedbacks (more on them later in this book) from thawing permafrost in the Arctic or collapsing tropical rainforests, then we could be in for five or even six degrees by the century’s end. On the other hand, if politicians make serious and determined efforts to implement the Paris targets, with the United States coming back into the fold as part of that effort, we can still hold off two degrees until the latter part of the century, and stop three degrees or higher temperature rises from ever happening at all.

As to which of these two outcomes is more likely, I am sorry to say that I am now substantially more pessimistic about the future than I was when Six Degrees was first published. Back then I believed that if only enough people could be better informed about the reality of climate change, then surely the world would be moved to act. While there have been positive shifts, such as declining coal use in some countries and cheaper renewable energy, these are dwarfed both by rising emissions and an alarming trend towards denialism. By this I don’t just mean the overt climate denial of some US politicians stupid enough to call global warming a ‘hoax’ on Twitter. Nor am I simply referring to the populist backlash that seriously threatens liberal democratic values and has brought the political far right back into international ascendancy for the first time since the defeat of Hitler. (2007 already seems a much gentler world.) I’m talking, in addition, about the kind of denial that we all practise, the ‘implicatory denial’ of climate change that allows us to keep on living our lives as usual despite the obvious implications of what climate scientists are telling us. It’s as if we don’t really believe them.

After all, it’s still possible – just – to pretend that the world isn’t warming, or that the rate of change is nothing exceptional, or that the warming we see could be the result of ‘natural cycles’ or some such. Even the UN’s Intergovernmental Panel on Climate Change (IPCC) admits this. In its 2014 report, IPCC experts stated that rising greenhouse gas concentrations in the atmosphere due to human activity are only ‘extremely likely’ to have been the dominant cause of observed warming since the mid-20th century. In IPCC-speak, ‘extremely likely’ translates to a precise numerically quantified meaning of 95–100% probability. So yes, that does allow for a 5% probability that climate change is either natural or inexplicable with current knowledge. However, in 2019 a team of scientists re-evaluated these probabilities. Looking at three datasets of observed atmospheric temperatures combined with climate model outputs, they concluded that there is only a 1 in 3.5 million chance that current global warming is natural. That translates into about a 0.00003% chance that the US Republican Party is right. As the scientists wistfully conclude: ‘Humanity cannot afford to ignore such clear signals.’

I agree, and the task I set myself in writing this book was to make the science so clear that nobody will have any excuse for ignoring it. I have spent years combing through long-forgotten issues of obscure glaciological journals. I have spent whole days lost in the small print of the citations in IPCC reports. In the process I have read hundreds upon hundreds of scientific papers – all so that you don’t have to. So if you want to know the truth about climate change, here it is. I offer this not with optimism, for there is little enough cause for that, but with hope. Even when all else seems lost, hope remains. I can see it now, lighting a way to the future.

1°

Headline of the century

It happened in 2015. The event made the news, although only for a day or two, before normal service – terrorism, politics, sport, celebrity gossip – resumed. You could therefore be almost forgiven for not having noticed what might be considered the most important news story of the entire century so far.

To its credit, the Met Office (the UK’s meteorological service) did put out a press release. This noted that, ‘for the first time, global mean temperature at the Earth’s surface is set to reach 1°C above pre-industrial levels’ (‘pre-industrial’ was defined by the Met Office as 1850–1900). Human activities had, the scientists pointed out, now managed to cause a degree of global warming over and above what would have been the planet’s natural temperature otherwise. There was no mystery about the main driver: look no further than the two trillion tonnes of carbon dioxide gas (henceforth CO2) that have been poured into the Earth’s atmosphere mainly through the combustion of fossil fuels since the start of the Industrial Revolution.

With one degree already in the bag, some historical comparisons are in order. In just over a century of unbridled fossil fuel use, humanity has returned atmospheric CO2 concentrations to levels last seen in the Pliocene, around three to five million years ago. As a result, global surface temperatures can be expected to go on rising for a long time yet, but the thermal inertia of the planet – the centuries to millennia it takes to warm the abyssal depths of the oceans and melt the colossal bulk of the Greenland and Antarctic ice sheets – means that the temperature rise lags some way behind the ‘forcing’ effect of increased greenhouse gases. As we will see, there is much more still to come.

Most of the global warming has gone into increasing the heat content of the oceans. The latest estimates published in 2019 by the IPCC are that about 6 zettajoules of additional energy are accumulating in the upper oceans every year. A zetta is a big number: 621 is a 6 followed by 21 zeroes, or 6,000,000,000,000,000,000,000 joules. For comparison, humans use about half a zettajoule per year in our total global energy consumption. A better visualisation might be to quantify all this extra energy in a more evocative unit: the heat released by the Hiroshima atomic bomb. Six zettajoules of energy equates to the same amount of heat as three Hiroshima atomic bombs exploding in the oceans every second. Count them: 3, 6, 9, 12, 15, 18 …

In late November 2018 the World Meteorological Organization (WMO) confirmed the UK Met Office’s preliminary diagnosis. Based on five independently maintained global temperature data sets, the WMO in its annual State of the Climate report revealed that the global average temperature between 2014 and 2018 was 1.04°C above pre-industrial levels. In other words, we are now definitively living in the one-degree world. For me, seeing this announcement was a particularly significant moment, because when I wrote the original Six Degrees book nearly a decade and a half ago this one-degree world still lay in the future. For the purposes of this book it is as if we have moved forward a chapter: what was once the future is now the present. If we don’t succeed in cutting back carbon emissions in time, the increasingly terrifying impacts detailed in later chapters – of two, three, four degrees and even higher – will also one day become our present. This really is our final warning.

The view from Mauna Loa

Mauna Loa, the gigantic shield volcano that sits at the centre of the Big Island of Hawai’i, is so tall that its summit protrudes above most of the island’s active weather. On the east side of the mountain, as the trade winds hit and are forced to climb the slopes, they cool, form clouds and drop torrents of tropical rainfall. This makes Hilo, the island’s biggest town, one of the wettest settlements in the United States. Drive through the glassy lava flows on the long haul up the flanks of the volcano, however, and you will quickly leave the rain clouds far below you. Conditions close to the summit are sub-Arctic, with only an inch or two of precipitation each year, much of that in the form of snow.

The paved road ends at the 3,200-metre contour line, where a group of antiquated buildings scattered across the volcanic debris together comprise the Mauna Loa Observatory. The Observatory is not as high as the solar telescopes that cluster atop the 4,207-metre summit of Mauna Kea, visible seemingly floating above the cloud layer 40 kilometres to the north. It is, however, arguably more historic, certainly from an earthly perspective. It was here that atmospheric chemist Charles Keeling first began collecting samples of airborne CO2 in 1958, seemingly on a whim and with little official support, using pioneering monitoring equipment that he designed himself.

Keeling had found that measuring CO2 lower down in the atmosphere was pointless, because the levels fluctuated constantly as a result of emissions from car exhausts, industrial chimneys, vegetation growth and so on. Thanks to its elevation, Mauna Loa rose above all that day-to-day noise, and Keeling’s measurements were the first in the world to show that CO2 mixed at high altitudes through the whole global atmosphere was increasing, in a sawtooth upwards seasonal pattern now known as the ‘Keeling Curve’ (probably the most famous global warming-related graph of all time). Charles Keeling died in 2005, but appropriately his efforts have been continued by his son Ralph, also an atmospheric chemist. Ralph Keeling has made his own subsequent discoveries, such as that the oxygen content of the air is decreasing commensurately with our consumption of fossil fuels, as airborne O2 is combined with carbon extracted from underground to form the gas CO2.

When Charles Keeling began his measurements in 1958, the rarefied air atop the lava fields of Mauna Loa contained CO2 at a ratio of 315 parts per million (ppm), already substantially higher than the pre-industrial concentration of about 278 ppm. On 10 May 2013 the Scripps Institution for Oceanography, which maintains the Observatory, made a landmark announcement. For the first time ever in human history, CO2 levels had briefly touched the 400 ppm threshold. ‘There’s no stopping CO2 from [permanently] reaching 400 ppm,’ commented Ralph Keeling sadly. ‘That’s now a done deal. But what happens from here on still matters to climate, and it’s still under our control. It mainly comes down to how much we continue to rely on fossil fuels for energy.’ Perhaps no one was listening, because at the time of writing the atmospheric concentration of CO2 has hit 408 ppm. This figure will already be out of date by the time you read this book. You can follow the relentless upwards progress of the Keeling Curve in real time on Twitter, via @Keeling_curve.

The Keeling Curve is a useful reality check, one that cuts through all the noise and confusion of the climate and energy debates. Unlike the slopes of the huge volcano on which it is measured, the initially gentle upward curve gets steeper the higher you go. That means that the rate of CO2 accumulation in the atmosphere is steadily increasing, from roughly 1 ppm in the early years to about 2 ppm annually today. There is no visible slowdown, no sudden downwards blip, to mark the implementation of the Kyoto Protocol, still less 2009’s Copenhagen ‘two degrees’ commitment or the landmark Paris Agreement of 2015. All those smiling heads of state shaking hands, the diplomats hugging on the podium after marathon sessions of all-night negotiating – none of that actually made any identifiable difference to the Keeling Curve, which is the only thing that actually matters to the planet’s temperature. All our solar panels, wind turbines, electric cars, lithium-ion batteries, LED lightbulbs, nuclear plants, biogas digesters, press conferences, declarations, pieces of paper; all our shouting and arguing, weeping and marching, reporting and ignoring, decrying and denying; all our speeches, movies, websites, lectures and books; our announcements, carbon-neutral targets, moments of joy and despair; none of these to date have so much as made the slightest dent in the steepening upward slope of the Keeling Curve.

This does not make us powerless prisoners of fortune. No trend continues for ever, and just because recent history has been all one way does not mean the future must necessarily follow suit. These emissions are not extra-terrestrial – they come from our everyday activities. Indeed they are an inescapable part of modern civilisation itself. We can get a sense of the sources, and the magnitudes, from the annual Global Carbon Project report. On average, every year over the last decade we humans transferred 35 billion tonnes of CO2 from the geological reservoirs (that’s coal, oil and gas) into the atmosphere. This was augmented by 6 billion tonnes of CO2 from ‘land-use change’ (that’s deforestation, ploughing up new farmland and so on). About 9 billion tonnes of this new CO2 dissolved in the oceans, and 12 billion tonnes was taken up on land by vegetation and soils. That left a remainder of about 18 billion tonnes to accumulate in the atmosphere and drive the relentless upward climb of the Keeling Curve. (The imbalance of 2 billion tonnes is due to uncertainties.)

There are small changes in the carbon budget year on year, which sometimes cause great excitement. In 2014, 2015 and 2016, for example, there was little to no annual growth in fossil fuel emissions, which seemed to have stabilised for the first time. Cue some premature celebrations. But had the world reached an early peak in emissions? No. In 2017 growth resumed again, reaching a new high of 36.8 billion tonnes despite a record installation of 161 gigawatts of renewable generating capacity in 2016 alone. In 2018 emissions continued to accelerate, however, increasing nearly 3% on the previous year and pushing CO2 levels to a new historic high. In 2019 growth slowed somewhat, to 0.6% above 2018, thanks to a reduction in coal use in Europe and the US. But what we need is carbon cuts, not slower growth – urgently.

So what’s going wrong? Well, it’s a matter of scale. The world is hungry for new energy: primary energy demand keeps on increasing, and 80% of that increase is supplied by new fossil fuels. Overall, renewables (not including hydro) in 2019 accounted for only 4% of global primary energy, still much too small a proportion to have any discernible effect on the upward trend in overall emissions. This is why solar and wind have so far not measurably dented the Keeling Curve. According to recent estimates, the installation rate for clean energy sources would have to increase tenfold to arrest the annual growth in fossil fuels.

Meanwhile, as the measurements conducted in the Observatory buildings continue to show relentlessly rising CO2, Mauna Loa itself is experiencing the effects of the resulting climate warming. Temperatures are gradually rising, and night frosts are rarer than they were when Charles Keeling first began to keep records with his home-made equipment. Mauna Loa may sit above most weather, but no part of the world can entirely escape global heating. Snowfall is less frequent – and the snow melts earlier in springtime – while plant life on the slopes of the mountain is changing with every year that passes. In 1958 Charles Keeling had to design complex and sensitive equipment to discern subtle changes to the Earth’s environment. Now these changes are plain for all to see.

Back to the future

With its official average temperature just over one degree above pre-industrial levels, 2015 was the warmest year on record. But what about much longer ago, before humans invented thermometers and started taking measurements? You have probably heard of the Little Ice Age spanning the 17th to 19th centuries, when frost fairs were held on the frozen River Thames in London, or the Medieval Warm Period, when the Vikings colonised Greenland. These are sometimes cited by climate sceptics as evidence of previous variations in the climate, with the accompanying assertion that today’s high temperatures are therefore not caused by humans (a logical fallacy: whatever changed climate in the past is not necessarily what is changing it today) and are nothing to worry about.

However, a 2019 Nature paper using temperature records from corals, lake sediments, glacier ice, sea shells and trees, collected across the globe from Antarctica to Australia and from Canada to Chile, demonstrates convincingly that these earlier temperature fluctuations were regional phenomena and not globally coherent. So while it is a historical fact that frost fairs were held on the Thames from the 1600s to the early 1800s (our romantic myth of the ideal white Christmas dates from this period), colder European winters at the time were balanced out by simultaneous warmer temperatures in the western half of North America that no one now remembers. This was not a global cooling event, just as the Viking occupation of Greenland or the Romans growing grapes in Britain is not evidence of pre-historic global warming. In fact, according to these multiple data sources, today’s global high temperatures are unprecedented for at least 2,000 years.

That’s just two millennia, however. What about even longer ago? One study, combining data from 73 different sources around the world, concluded that the early Holocene, from 10,000 to 5,000 years ago, was just over half a degree warmer than the pre-industrial era. Given that temperatures since 2015 have been one whole degree higher than then, it is reasonable to conclude that the globe is now almost certainly warmer than at any point since the end of the last ice age, 18,000 years ago. Indeed, to find an analogue for today’s anomalous warmth, you have to look beyond the last ice age to a period of time between 116,000 to 129,000 years ago often referred to by scientists as the Eemian.

In the first Six Degrees, I included studies about the climate of the Eemian in my second chapter, corresponding roughly with two degrees of warming. But more recent studies suggest that the Eemian was only about one degree warmer than the pre-industrial Holocene. In other words, it was roughly equivalent to global temperatures we are already experiencing now. Yet the Eemian world was radically different: the Arctic tree line was much further north and hippopotamuses bathed in rivers in southern England. The Eemian isn’t a perfect match with today, because with humans still confined to cave dwelling, atmospheric CO2 remained at pre-industrial levels of about 270 ppm. Why was it then so warm? Probably because slight variations in the Earth’s orbit changed the distribution of incoming solar energy, warming the higher latitudes but leaving the tropics little changed or even slightly cooler than now. Studies of preserved dead midges in lake sediments have found that local summer temperatures in parts of Greenland were somewhere between 5°C and 8°C higher than today, but it seems that there was still plenty of sea ice in the Arctic Ocean.

Perhaps the most ominous lesson from the Eemian is that even with CO2 at around 135 ppm lower than today, and worldwide temperatures about the same as modern averages, sea levels were six to ten metres higher than at present. Evidence from the Eemian suggests that about five metres of this sea level rise originated from the partial melting of the Greenland ice sheet, which shrank down to a largish remnant in the north-east of the landmass. The implication is pretty clear: it suggests that today’s temperatures are already high enough to eventually melt the majority of the Greenland ice sheet and deliver a multi-metre rise in sea levels. This seems hard to believe, until you travel to Greenland and witness what was once a frozen wasteland currently undergoing rapid, epochal change.

Greenland’s lakes

Greenland is turning blue. Hundreds of thousands of iridescent blue lakes now dot the fringes of the rapidly melting ice sheet throughout the summer months, and the melt area has been creeping steadily upwards and inwards towards the interior as global heating bites. The direct impacts of this increased thaw can be dramatic – in late July 2012 so much meltwater was sluicing off the south-western portion of the ice sheet that a bridge was washed away on the Watson River, which empties into a fjord just to the south of the town of Kangerlussuaq. Footage shared on YouTube shows a grey-brown torrent resembling a tsunami washing away a tractor and tearing through the bridge and the road leading up to it in just a matter of minutes.

This episode is more than just a revealing anecdote. Meltwater flows in the Watson River have been steadily rising in recent years, and on average are now nearly 50% higher than they were in the 1950s. The tattered, debris-covered edge of the giant ice sheet lies just a few kilometres up the valley from Kangerlussuaq, and most of the hundreds of blue lakes that pepper its surface in summer drain into the Watson River, which is fed by a 12,000-square kilometre catchment across the south-western portion of Greenland. In terms of annual averages, the three largest discharge years on record are 2010, 2012 and 2016, with the largest single discharge peak coming in July 2012, explaining why it was then that the bridge over the Watson at Kangerlussuaq succumbed to the dramatic flood.

The timing of this glacial torrent was no great mystery either. For the first time in living memory unprecedented melting had penetrated right up to the summit of the giant ice sheet, located at 3,216 m in altitude. Summit is classed as a polar desert, an inhospitable place of frigid thin air and snow as dry as dust. On 12 July 2012, however, temperatures edged above freezing at the summit for the first time in recorded history, and the automated weather instruments permanently located there were surrounded by slush. Lower down, on the western side of the ice sheet, climate researchers were forced to rebuild their camp when snow and ice supports melted away. Things were no better in North Greenland where Danish scientists logged six consecutive days of above-freezing temperatures at the surface between 10 and 15 July. It even rained on 11 and 13 July, with melt and rainwater percolating down into what had previously been permanent snow.

When the first satellite data came in about the July 2012 melt event, scientists analysing it thought their instruments must have malfunctioned. Later visuals showed the entire ice sheet coloured deep red, indicating pervasive melt conditions. When the scientists checked their data with output from other satellites, they found that on 8 July the temperature of about 40% of the ice sheet surface was above freezing. On 12 July the figure was 98.6%. Virtually the whole of Greenland was in the melt zone, the first time any of the scientists studying the colossal ice sheet had seen such a thing.

Longer-term data show that all-Greenland melt events are extraordinarily rare. A December 2018 paper concluded that the 2012 melt rates were exceptional and ‘likely also to be unprecedented over the last 6,800–7,800 years’. The same paper stated that there has been a 500% increase in melt intensity at the ice core site in just the past 20 years. The latest data show that the fastest-expanding melt zones are now in the northern portion of Greenland, in what should be the coldest area closest to the North Pole.

Once the domain almost exclusively of ice and snow, Greenland has begun to see more rain, even in the depths of winter. While fresh snow is brilliant white, reflecting most of the sun’s radiation back out to space, thawing slush is less reflective, and the bare ice sheet with snow removed is darker still. All around Greenland the snowline has retreated uphill, exposing more uncovered ice to the full heat of the summer sun. As the fringes of the ice sheet gradually shrink inland, bare rock and glacial debris are revealed, leading to an increase in dust storms. Plants have begun to colonise new areas, and are now coming into leaf a week or two earlier as spring temperatures rise.

It has long been clear from ice core records that the climate in Greenland can do sudden and strange things. About 11,700 years ago, at the end of a colder period called the Younger Dryas, temperatures shot up by 15°C over a few decades. A similarly dramatic warming, of 9°C in less than 70 years, took place 14,760 years ago during the last ice age. Scientists fear that Greenland may currently be crossing a similar threshold of rapid climate change, one that could lead to the eventual loss over centuries of the entire ice sheet. Mean annual air temperatures are already 3°C higher than they were a few decades ago. But these shifts did not happen gradually: they came about in sudden jumps, of 2°C in 1994 and a further 1.1°C in 2006. This is a rate of change that, if sustained over decades, easily matches the major climate tipping points of the distant past.

And 2019 was another epochal year. Temperatures across Greenland soared to 12°C above the late July average, and the summit of the ice sheet saw another thaw between 30 and 31 July 2019. This time temperatures at the highest point topped the record set in 2012, and stayed above freezing for longer over a two-day period. In response to these rapid changes, some scientists have begun to warn that the projections for 21st-century sea level rise may need to be revised upwards. According to one researcher, the current melt rates weren’t supposed to happen until 2070. In the first Six Degrees I reported that Greenland’s contribution to sea level rise was about 0.3 mm per year. In 2019, according to preliminary estimates, the melt rate may have been as high as 1.5 mm, a fivefold increase. If that’s not a tipping point, I don’t know what is.

Arctic on thin ice

Signs of increasingly rapid global warming are now evident throughout the Arctic, where temperatures are rising at a rate two to three times the global average. In late December 2015 at the North Pole itself temperatures rose close to freezing. Under normal circumstances, air temperatures at the pole would be averaging around -30°C during the frigid polar nights of late December. On this occasion temperatures shot up by 25°C in just one day as a deep low-pressure system wafted in sub-tropical air from the south. Although no one was there to witness it directly, it seems likely that it was even raining at the North Pole for a brief period at the height of the Arctic winter.

This extreme Arctic warming event lasted for 40 days between 29 December 2015 and 6 February 2016, during which the entire polar Arctic above 66°N saw temperatures 4–6°C above average. Scientists studying the event called it ‘unheard of’ and ‘super-extreme’ – but the following December it happened again. ‘A weather buoy about 90 miles south of the North Pole registered a temperature at the melting point of 0 Celsius early Thursday,’ reported the Washington Post, adding: ‘Santa may need water skis instead of a sleigh this year.’ Temperatures throughout a broad area of the Arctic were 20°C or more above normal in November and December. At a time when the Arctic sea ice should have been regrowing due to winter cold, it actually shed another 50,000 square kilometres (19,300 square miles), an event unprecedented during the entire satellite period. The high Arctic temperatures of October and November were ‘off the charts’, said baffled experts.

To test whether the event could have been caused by chance, scientists at the World Weather Attribution network plugged the temperature data into climate models and compared the results with ‘natural’ conditions without global warming. None of them showed Arctic events as hot as 2016 in the simulated world without human carbon emissions.

So what’s going on? Part of the answer comes from the long-term trend in declining Arctic sea ice, which has been shrinking in area by 13% a decade (in its minimum summertime extent) since satellites began measuring it in 1978. That means half the entire Arctic’s stock of sea ice has disappeared since the late 1970s, and what remains has become about 85% thinner. In fact the thinning trend has become so extreme that scientists now struggle to find thick enough ice floes on which to deploy their measuring instruments. All this new open water has transformed the atmospheric dynamics of the Arctic region, allowing warm, moist winds – whose energy would previously have been dissipated by ice – to penetrate right up to the pole itself.

Other researchers have confirmed that the extreme polar heat of 2016 would not have been possible without the extensive disappearance of Arctic sea ice. While 2018’s Arctic ice minimum was only the sixth lowest in the satellite record, the overall trend continues irrevocably downwards, equating to 82,300 km2 lost on average every year, an area four times the size of Wales. Cumulatively this adds up to a vast total: the extent of Arctic summer sea ice lost since the 1980s would be sufficient to cover 40% of the contiguous United States. And the 2019 September sea ice area, at 4.15 million square kilometres, was the second-lowest since the beginning of the satellite era in 1979. Nature reported that 13 of the lowest Arctic sea-ice extents have been recorded in the last 13 years.

Because there is now dark-coloured open water during the summer rather than highly reflective snow and ice, solar heat absorption has increased fivefold since the 1980s in the once-frozen seas north of Alaska and Canada, introducing vast quantities of additional energy into the Arctic system. I wrote about the Arctic albedo feedback in the first Six Degrees: ‘While bright white, snow-covered ice reflects more than 80% of the sun’s heat that falls on it, the darker open ocean can absorb up to 95% of incoming solar radiation. Once sea ice begins to melt, in other words, the process quickly becomes self-reinforcing: more ocean surface is revealed, absorbing solar heat, raising temperatures and making it more difficult for the ice to re-form during the next winter.’ This change in albedo (how much sunshine gets absorbed by darker coloured surface versus how much gets reflected from brighter surfaces) has now been measured directly by satellites, and its impact is dramatic. Averaged globally, the heating effect is equivalent to pumping another 200 billion tonnes of CO2 into the atmosphere.

Global warming makes us all responsible for this dramatic on-going transformation of the Arctic, and in a surprisingly direct way. Scientists have found a linear relationship between cumulative CO2 emissions and the September sea ice minimum. It turns out that every metric tonne of CO2 implies a sustained loss of 3 m2 of Arctic ice. Given the disparities in emissions between countries, that means that every American is on average responsible for the loss of nearly 50 square metres of ice each year, while a British person is responsible for just under 20 m2 of annual ice loss. This compares to 22 m2 of disappeared ice for each Chinese, 5 m2 of loss for each Indian but under 1 square metre each for the low fossil fuel-consuming inhabitants of east Africa. For Antarctica the equivalent figures are even more dramatic: each kilogram of released CO2 is responsible for melting two metric tonnes from the much larger ice cap over the South Pole.

This transformation of the Arctic is also having serious effects on the wildlife of the polar region. That most emblematic symbol of global warming – the polar bear – is facing population declines because it depends on the sea ice on which to hunt seals. Less ice means fewer seals can be caught, which translates to fewer cubs able to survive into adulthood, and more hungry, skinny adult bears scavenging on ice-free coastlines during the summer. Body-fat samples recovered from polar bears shot by Inuit hunters – who together typically harvest a couple of hundred bears per year across Canada – show a strong seasonal correlation between the availability of sea ice and the condition of the polar bears. ‘We’re restructuring a whole ecosystem,’ says polar bear ecologist Andrew Derocher. ‘Sea ice is to the Arctic what soil is to the forest. Without sea ice we’ll still have an ecosystem but it won’t include polar bears and many other species.’

It’s not yet too late to save the polar bear. Scientists have determined that dramatic emissions reductions and the stabilisation of CO2 at 450 ppm could still retain enough summer sea ice to prevent the polar bear becoming extinct in the wild. Polar bears are not the only species highly dependent on sea ice; walrus, bearded and ringed seals, bowhead whales, beluga and narwhal all need ice for part or all of their life cycles. And the changing Arctic ecosystem brings other new threats. Those marine mammals that survive the loss of ice face being chopped up by boat propellers thanks to the increase in shipping traversing the newly open Northern Passage. The rapid warming affects the oceans too, with Arctic fish species retreating north towards the pole as Atlantic and Pacific migratory fish move in.

These ecological shifts can have tragic effects. For example, the summer sea ice edge has retreated 400 km further away from the nesting grounds of the black guillemot on Cooper Island, off the north coast of Alaska. The guillemots’ primary prey species, Arctic cod, has retreated with the ice, and the majority of chicks now starve to death. Seabird die-offs have also been recorded thanks to low ice conditions in the Bering Sea. With more moisture in a warmer atmosphere, heavy snow can also be an issue – in the summer of 2018 so much snow was left lying across the high Arctic that scientists documented a near-total collapse in the food web of north-east Greenland. Plants failed to flower until late in the season, while migratory shorebirds had only a few eggs hatching. Those nestlings that did fledge would not have had enough time to grow to full size in time to survive the return southward migration. Some shorebirds even starved to death. There were no Arctic fox cubs, and almost no muskox calves. This was the ‘most complete reproductive failure encountered in the terrestrial ecosystem during more than two decades of monitoring’, scientists reported.

The ongoing reorganisation of the Arctic system is also beginning to have ricochet effects on weather patterns across the Northern Hemisphere. Record-breaking wildfires in California, for example, have been linked to changes in atmospheric circulation possibly triggered by the disappearance of Arctic sea ice. These changes are one of the factors behind the devastating multi-year drought that has parched much of the south-western United States, making the area tinder-dry and extremely prone to wildfire outbreaks. This drought has also led to declining yields of crops in the United States, thereby fingering faraway Arctic sea ice as a factor in falling food production thousands of kilometres away. One study published in May 2019 suggests an additional relationship between reductions in sea ice in the Hudson Bay and more frequent heatwaves across the southern Plains of the United States. Another points to a ‘regime shift’ towards ice-free conditions taking place in the Barents Sea in 2005 that may have subsequently ‘contributed to the increasingly frequent extreme weather events experienced over Europe in the past decade or so’.

Several studies have also suggested a possible Arctic amplification fingerprint in ‘planetary waves’ – large-scale wave-like meanders in the Northern Hemisphere jet stream that can remain nearly stationary for long periods of time and cause devastating weather extremes, from summer heatwaves to floods or even winter cold events. Although some experts urge caution in assigning blame, multiple studies have linked these waves to events as diverse as the 2003 European heatwave, the Russian heatwave and Pakistan floods of 2010, the 2011 Texas drought and the persistent lack of rainfall in California, evidence that is now supported by climate models. These ‘blocked’ weather patterns have also contributed to record cold extremes in the Eurasian and North American continents in recent years. Warming of the Arctic Ocean may have helped weaken and shift the ‘Polar Vortex’ of extremely cold, high-pressure air, bringing intense winter conditions across Eurasia and North America. The evidence linking this shift with the changing Arctic is increasingly strong: one study showed a clear link between anomalous warmth in the newly ice-free Barents–Kara Sea region of the Arctic Ocean and severe winters in East Asia, and also linked extreme cold in North America to extra heat in the Chukchi Sea north of Alaska. Another group of meteorologists assessed the record-breaking cold and blizzards that hit parts of North America in the winter of 2014/15, and found that reduced Arctic sea ice might have helped drive the ‘anomalous meander of the jet stream’ which led to the extreme cold.

Teasing out the relative contributions of the different factors is incredibly complex, but one thing is clear: the Arctic circulation that has been established for millennia is breaking down, and this must be having impacts further afield as well. As Chris Rapley, professor of climate science at University College London, told the Guardian:

What happens in the Arctic doesn’t stay in the Arctic. By upsetting the energy balance of the planet we are changing the temperature gradient between the equator and the pole. This in turn sets in motion major reorganisations of the flow patterns of the atmosphere and ocean. The consequences are emerging and they are disruptive, and likely to become even more profoundly so.

In the summer of 2019 the Arctic even began to burn. In mid-June more than a hundred wildfires were burning above the Arctic Circle across Alaska, Siberia and Canada. Even Greenland saw wildfires erupting on fenlands scorched by unusual summer heat. But most importantly of all, the Russian wildfires were not just burning trees. They were also smouldering in dried-out peat, much of it formerly immobilised in permafrost. By the end of July it was estimated that the blazes had released more than 120 million tonnes of CO2 – an all-time record, and more than the total annual emissions of Belgium. All this extra carbon can only do one thing: accumulate in the atmosphere and cause more warming. These weren’t just wildfires, they were positive feedbacks, showing that the heating of the Arctic is threatening to run out of control.

Gulf Stream collapse

The winter blizzards of recent years were as nothing compared with the icy onslaught that hit Europe about 12,000 years ago during the Younger Dryas. During this brief return to near ice age conditions, thawing glaciers in the British Isles and other parts of northern Europe suddenly re-advanced. The remains can be seen all around the peaks of Britain’s now ice-free hills, such as the Lake District, the Scottish Highlands and Snowdonia, where tell-tale hummocks of grassed-over moraines testify to the final extent of these long-disappeared small glaciers. The cause of the sudden cold snap is still disputed, but the driver may have been a shift in the strength of the critically important Atlantic current popularly known as the Gulf Stream. Even longer ago, during the depths of the last ice age, abrupt periods of extreme cold – during which armadas of icebergs were launched across the North Atlantic – have also been blamed on fluctuations of this gigantic ocean current.

Today, the ‘Atlantic Meridional Overturning Circulation’ (AMOC, of which the true Gulf Steam is but a small component) continues to have an outsized impact on Europe’s climate. It is thanks to the AMOC that north-western Europe is roughly 6°C warmer than equivalent maritime latitudes on the Pacific coast of North America. This mighty current carries sub-tropical surface water equivalent in volume to the flow of all the world’s rivers north via the Gulf Stream to the British Isles and Scandinavia. The AMOC is so big that it even has its own unit, the Sverdrup (Sv), equivalent to one million cubic metres of water moving at one metre per second. The AMOC has an average strength of around 17 Sv in the North Atlantic; compare this with the flow of the Amazon – the world’s biggest river – at a paltry 0.2 Sv. It transports oceanic heat of 0.9 petawatts, equivalent to the output of half a million or so nuclear power stations from the tropics to the higher latitudes. For this reason alone, the Northern Hemisphere as a whole is warmer than the Southern Hemisphere, because ocean heat is transported from the south across the equator and into the North Atlantic. A fictionalised AMOC shutdown was the scenario depicted in the 2004 film The Day After Tomorrow; while the giant tsunami hitting New York might have been stretching things a little, it is widely agreed that a total AMOC collapse has the potential to plunge Europe back into decades of sub-zero winters and destabilise weather across the globe.

Whether the AMOC is beginning to weaken – and if so, whether human global warming is to blame – is currently the focus of intense debate. The driving forces behind the AMOC are the areas of very salty, colder water that form offshore from Greenland, Iceland, Scandinavia and Arctic Canada during the winter. This water has a higher density than warmer, fresher surface water and consequently sinks to the ocean floor, where it begins a long journey south to restart the process, like a gigantic heat conveyor belt. Although there is substantial variability year to year, recent data from ocean sensors shows that the strength of the AMOC has already slowed by 15% since the mid-20th century, making it weaker now than probably at any point in the last 1,500 years.

Studies based on data gathered by ocean arrays found that the AMOC’s strength declined by 0.6 Sv per year – that’s three River Amazons’-worth – between 2007 to 2011, and that this weaker state still persists today. It is possible that this is just part of a longer natural fluctuation, as one later study suggests. However, concerns have been growing that the weakening of the AMOC current is linked with the huge quantities of fresh water that are now sluicing off the thawing Greenland ice sheet every summer. This meltwater, combined with increased rainfall, is diluting the waters of the north Atlantic, reducing its salinity. Less saline water is less dense and heavy, and therefore does not sink into the depths and drive the movement of the current.

Climate models also disagree about whether and how the AMOC will collapse, making this issue one of the classic ‘known unknowns’ in the climate debate, a potential shift that could have huge impacts through global weather destabilisation. Whether the current weakening trend will continue is highly uncertain. But one thing we do know: AMOC collapse has happened before, and it had drastic impacts on the climate of the entire Northern Hemisphere. Any prolonged shutdown would have equally disastrous effects today.

Antarctic icebergs

They called it B-46. This was not a code name for a new bomber or some other piece of military hardware, but something potentially much more significant. B-46 was huge, 300 km2 in area – a gigantic iceberg spawned in November 2018 by one of Antarctica’s biggest glaciers, Pine Island Glacier (PIG). And B-46 was not even a record, being substantially smaller than the more than 500 km2 monster that floated away from the same Antarctic glacier in 2015. PIG, the mothership for these mega-bergs, is one of the largest ice streams draining the West Antarctic Ice Sheet (WAIS) and has consequently been the focus of intense study in recent years. Something big is happening to PIG: from 1974 to 2010 it accelerated by 75% to a forward speed of 4 km per year. At this speed an observer standing on land at the edge of the glacier would almost be able to see the massive stream of ice grind by with the naked eye. Its rate of annual ice loss in the same period increased from 6 billion tonnes per year to 46 billion tonnes, an increase of a whopping 750%. The accelerating rate of melt now makes PIG the largest single glaciological contributor to sea level rise in the world. This one glacier now adds a tenth of a millimetre each year to the height of the global oceans.

Although the front of the glacier is floating on the ocean, its grounding line – where the glacier’s base is attached to the seabed – has retreated by 30 kilometres inland since 1992, and herein lies the problem. Like its neighbour, the even bigger Thwaites Glacier, the bed of PIG slopes downhill towards the centre of the West Antarctic Ice Sheet, where it is anchored over 1,500 metres below sea level. Many scientists fear that a process of irreversible collapse has already been triggered, with a positive feedback seeing warming waters penetrating further and further towards the centre of the vulnerable ice sheet in a process of unstoppable melt that will continue for centuries to come.

All-told, the WAIS has enough ice to raise global sea levels by more than three metres. However, this massive meltwater pulse would not be released overnight. Currently the whole WAIS is adding about 0.3 mm per year to global sea levels, but this rate is increasing as the massive glaciers that drain into the warming ocean shed more and more mass. In May 2019 Antarctic scientists published their latest data; this showed that both Thwaites and Pine Island glaciers have thinned by up to 122 metres in places and that rates of ice loss have increased fivefold since surveys began in 1992. They concluded that nearly a quarter of the entire West Antarctic Ice Sheet is now in ‘structural imbalance’. Scientists fear that a ‘wave of thinning’ is spreading rapidly across some of Antarctica’s most vulnerable glaciers, driving up sea levels around the planet.

Rapid changes are taking place elsewhere in Antarctica too. A huge 100-metre waterfall of meltwater now pours off the edge of the Nansen Ice Shelf into the ocean during the Austral summer. Although melting on Antarctica is not new – streams and ponds were also documented by early explorers – researchers now envisage a gradual transformation towards a melt regime closer to that of Greenland. Indeed, in September 2019 researchers reported having spotted more than 65,000 lakes all around the margins of the East Antarctic, many in areas previously thought too cold to allow substantial summertime thawing. One of the new lakes was more than 60 kilometres long, and meltwater pools were spotted as far as 500 km into the interior of the vast ice sheet and as high as 1,500 metres in elevation.

In March 2015 the tip of the Antarctic Peninsula registered the highest ever temperature recorded on continental Antarctica, a balmy 17.5°C, an event classed as an ‘extreme Antarctic heatwave’ and which helped trigger yet more melting across nearby ice shelves. Some ice shelves have been suffering periods of intense melt even in the dead of the Antarctic winter. Ocean waves now reach exposed glacier fronts that were previously protected by sea ice, promoting rapid disintegration. The Larsen C shelf may in fact be the next to disintegrate, following on the heels of the collapse of Larsen A in 1995, Larsen B in 2002 and Wilkins in 2009. Larsen C reduced in size in 2017 by 10% following the calving of a single colossal iceberg of 5,000 km2 in area, larger than the US state of Rhode Island and ten times bigger than anything that PIG could produce.

Overall, the latest survey – published in the journal PNAS in 2019 – shows that the rate of ice loss from the continent has increased sixfold over the last four decades, from an estimated 40 billion tonnes to 252 billion tonnes per year. Although the majority of the melt comes from the more immediately vulnerable West Antarctic ice sheet, East Antarctica is now a ‘major participant in the mass loss’. This is noteworthy both because East Antarctica contains the vast majority of the continent’s ice, and because it was previously thought too cold to lose significant mass. This melt has added about 14 mm to global sea levels since 1979, an amount that would have been even higher were it not for the fact that rising temperatures are increasing snowfall and accumulation rates in the interior of the frigid continent. ‘I don’t want to be alarmist,’ Eric Rignot, lead author of the 2019 PNAS paper and an Earth-systems scientist for the University of California at Irvine and NASA, told the Washington Post, ‘[but] the places undergoing changes in Antarctica are not limited to just a couple of places. They seem to be more extensive than what we thought. That, to me, seems to be reason for concern.’

The current melting in Antarctica may sound huge, Rignot added, but actually it is ‘just the tip of the iceberg, so to speak’. The future is a much greater concern. ‘As the Antarctic ice sheet continues to melt away, we expect multi-metre sea level rise from Antarctica in the coming centuries.’ All round the continent, grounding lines where glaciers meet the ocean are retreating, as experts have long feared. Although the ice-sheet models project relatively slow melt rates, recent evidence suggests that glaciers in contact with the warming oceans may thaw much more rapidly than expected. This would not just be two or three times faster, either. ‘The observed melt rates are up to two orders of magnitude greater than predicted by theory,’ the experts reported. If Antarctic tidewater glaciers all increase their melting rate a hundredfold over what has so far been predicted, expect much quicker impacts on the world’s coastlines.

Melting mountains

‘El Nevado Pastoruri estuvo aquí en 2015,’ announces the sign (‘The Pastoruri Glacier was here in 2015’). All around are rocks, and the front of the receding mass of ice is now hundreds of metres away. Welcome to Peru’s famous Ruta del Cambio Climático – Climate Change Route – that winds its way up to the rapidly thawing snows of the Cordillera Blanca in Huascarán National Park. Once famous for its ice caves, this easily accessible glacier has split in two and now mostly turned into a lake. Tourists are requested not to climb on the ice or break pieces off; where once Peruvian high-school students used to slide down on plastic bags, most of the glacier is now roped off to protect it from further damage.

The ice-clad peaks of the Cordillera Blanca are sacred places for me. A chapter in my first book detailed my journey to a remote glacier on the eastern side of the range above the small town of Huari, retracing the footsteps of my father’s team of geological surveyors, who made the trek back in 1980. When I visited in 2002, the glacier I was looking for – a huge wedge of ice that tumbled down a precipice and calved icebergs into a lake – had disappeared. I haven’t been back since, but Google Earth shows that the parent glacier has receded well back from the top of the slope, and will now be out of sight of my 2002 vantage point at the lakeside below. One of my favourite photos from this expedition was of our bivouac site high on the ridge to the north, on a lovely round tongue of snow that protruded from the upper-level glacier. That seems to have gone now too; indeed the whole ridge looks denuded and bare.

The ice on these peaks has more than just sentimental value for climbers like me mourning its loss. The high mountains are sacred to local people as an abode of the Incan spirits and for their very practical value as a source of freshwater. Most communities in the area depend on glacial runoff for much of their water, and this diminishing resource is beginning to spark conflicts between settlements. Huaraz, the main town in the province and a climbers’ mecca within sight of Peru’s highest peak, depends on glacial runoff for 90% of its water during months of drought. The water from glaciers on the western side of the Cordillera runs off into rivers that then enter the Pacific via an intensely arid coastal plain (water on the eastern slopes ends up in the Amazon). Without this freshwater for irrigation, the majority of Peru’s agricultural production – not to mention its hydropower – would disappear. The sprawling capital city Lima is also dependent on mountain runoff for its fresh water, part of which originates from glacial melt. In neighbouring Bolivia, the high-altitude capital La Paz gets about 15% of its annual average water supply from surrounding mountain glaciers, but this rises to as much as 85% during dry months.

Peru’s glaciers are now critically endangered. The Cordillera Blanca has lost a third of its area in recent decades, and other Peruvian glaciated mountain ranges are suffering similar losses, as are those elsewhere in the Andes. Overall, the South American Andes have shed nearly 23 billion tonnes of ice since the year 2000, contributing more to sea level rise than even the Himalayas. The melt rate on mountain glaciers around the world is now so rapid that, combined, they now add nearly as much to sea level rise each year as the whole Greenland ice sheet, totalling an estimated 335 billion tonnes of melted ice.

Glaciologists do not tend to communicate in overly emotive language, but the latest publications suggest that even they are beginning to panic. ‘Rates of early 21st-century mass loss are without precedent on a global scale, at least for the time period observed and probably also for recorded history,’ wrote a team of authors from the World Glacier Monitoring Service recently in the Journal of Glaciology. With a few short-term regional exceptions, every major mountain range in the world is rapidly losing glacial mass.

It is not just glacier ice that is disappearing; snow cover is vanishing too. California, the most populous state in the US, with the world’s sixth-largest economy and producing a quarter of all the country’s agricultural produce, depends for 30% of its freshwater on the Sierra Nevada winter snowpack. This is because most of the state’s precipitation comes in the winter, accumulating in the high mountains as deep snow cover. This snowpack then gradually melts during the dry spring and summer months, keeping the rivers flowing and irrigating the vegetable and fruit crops that flourish in the state’s Mediterranean climate. However, with more winter precipitation now coming in the form of rain, less and less snow is accumulating to keep the rivers flowing during the summer dry season. On 1 April 2015, for example, after four years of record-setting drought, scientists calculated that the Sierra Nevada snowpack was at only 5% of its historical average, a low that they declared ‘unprecedented in the context of the past 500 years’.

Other mountain ranges have also suffered from strange wintertime climate shifts. In the European Alps sudden warming events have become increasingly common. In December 2015 an unprecedented ‘winter heatwave’ hit the eastern Alps, with temperatures rising above freezing even as high as 2,500 metres in altitude, removing lying snow and even melting the glacier ice underneath – something previously unknown in winter. In January 2018 high temperatures – again in the Alps – brought heavy rain that melted lying snow, causing landslides and debris flows in French and Swiss alpine valleys. Higher up the slopes more than five metres of snow fell, adding to the risk of huge avalanches hitting roads and villages, and leaving tourists stranded in major ski resorts.

In lowland areas across Europe, meanwhile, snow cover is now ‘dramatically decreasing’, in the words of one 2018 study published in the journal Geophysical Research Letters. The authors found that the average snow depth in Europe had decreased by more than 12% per decade since the 1950s, and that this trend had accelerated after the 1980s. Memorable cold extremes can obscure these longer-term trends; where I am based in the UK, the winter of 2017–18 saw heavy snowfalls and prolonged freezing temperatures during an Arctic blast dubbed the ‘Beast from the East’. The following winter, temperatures hit an all-time high, reaching 20°C in mid-February. This latter event – much more unusual in a historical context than a couple of weeks of blizzards – was quickly lost to memory.

The heatwave that came in the summer of 2019 won’t be so easily forgotten. France set a new all-time temperature record, with daytime highs of a sort normally seen in North Africa rather than Europe. Up in the French Alps, the high temperatures melted out a new glacial lake below the spectacular summit of the Dent du Géant in the Mont Blanc massif. Alpinist Bryan Mestre’s Instagram photo of a turquoise-blue pond entirely surrounded by ice, 3,500 metres up the mountain, quickly went viral. The climber himself was perturbed: ‘I have been up there a fair amount of times, in June, July and even August, and I have never seen liquid water up there.’ Mestre might have compared his photo with similar ones from melting mountain ranges around the world, from the Himalayas to the Andes – even perhaps to tourist photos taken in Peru’s Cordillera Blanca, where at the end of the Ruta de Cambio Climático an even bigger lake is steadily replacing what is left of the once-famed Pastoruri Glacier.

Fickle floods

Not all climate impacts in our one-degree world are as clear-cut as the melting glaciers in the Alps and Andes. So it is with the vexed issue of floods. The IPCC’s most recent summary is a masterpiece of studious equivocation. After reviewing a number of sources, it concludes: ‘In summary, streamflow trends since 1950 are not statistically significant in most of the world’s largest rivers, while flood frequency and extreme streamflow have increased in some regions.’ In 2012 the IPCC released a special report on extreme events, which looked at how climate disasters were impacting society and how those impacts could be mitigated. It acknowledged that while there have been increases in heavy rainfall events, there was ‘low confidence’ in any resulting changes in flooding. A year later, in 2013, the IPCC’s Fifth Assessment Report assessed the situation similarly, admitting that confidence remained ‘low’ about any potential increases in flooding.

The IPCC’s caution was well justified. The most comprehensive recent review of river-flow trends at the global scale, published in 2016, investigated 50 years of changes on the world’s largest 200 rivers. Out of these rivers, those exhibiting negative trends in flow rate (totalling 29) slightly outnumbered those showing positive trends (26). All the largest rivers – the Amazon, Congo, Orinoco, Chang Jiang, Brahmaputra, Mississippi, Yenisei, Parana, Lena, Mekong, Tocantins and the Ob – showed peaks and troughs over the period, as might be expected from natural climate variability. But there were no obvious upward trends in any of them that might indicate increased runoff or more severe flooding. Indeed, for the vast majority, 145 out of 200, any long-term (1948–2012) trends were statistically insignificant. A second study, published in 2017 and investigating changes in water flows at 9,213 river-monitoring stations, found ‘more stations with significant decreasing trends than significant increasing trends’, confirming the 2016 analysis.

This situation might seem perplexing because of frequent media reports about flood disasters around the world, which are often attributed to the changing climate. Plus, as all these reports acknowledge, there is unambiguous evidence that global warming is leading to heavier and more frequent intense precipitation events across much of the globe. This observed increase in precipitation intensity fully accords with climate physics. Warmer air can hold more water so as climate change accelerates, there is potentially more vapour available in a warmer atmosphere to be condensed into clouds and fall as rain, hail or snow.

For heavy precipitation, therefore, the IPCC offers no equivocation. ‘The observed record suggests that increases in precipitation extremes can be identified for annual maximum 1-day precipitation and consecutive 5-day precipitation [events],’ it stated in 2018. In other words, short-term cloud bursts and long-term deluges have both got worse. According to one recent assessment, a quarter of the land mass on Earth has experienced a definitive increase in heavy rainfall events. Extreme precipitation has been found to be increasing far faster than the average, and the number of record-breaking rainfall events is also clearly increasing.

Evidence is now stacking up from around the world. A 2019 study found an intensification of storm rainfall totals in the south-western United States, while a 2017 Nature Communications paper reported a ‘threefold increase in widespread extreme rain events over central India during 1950–2015’. Perhaps counter-intuitively, arid areas are just as affected as wet regions by this increase in extreme rainfall. For example, a recent study found a tripling in the frequency of extreme storms in the dry Sahel region of West Africa since the 1980s. Flash flooding is often followed by ‘flash droughts’, sudden and intense dry periods combined with extreme heat; such events have tripled in incidence in southern Africa over the last 60 years.

Researchers also found that the extreme rains that hit Wuhan, China, in June and July 2016 are now ten times more likely in the one-degree world. These storms dropped over a metre of rainfall, causing severe flooding, the loss of 237 lives and $22 billion in economic damage, making them the second-most expensive weather-related disaster in China’s history. In the United States, the strongest type of large-scale storm – the ‘mesoscale convective systems’ that often generate destructive tornados and large hailstones – are becoming more frequent and lasting longer. When it comes to heavier rainfall, therefore, the jury is no longer out.

So why has this not translated into clearly observed increases in flooding? A 2018 study examining this question acknowledged that there is a clear ‘dichotomy’ between the trend towards heavier rainfall events and the ‘lack of corresponding increases in floods’. The truth is that there are many confounding factors influencing whether increased frequency of heavy rainfall translates into worsening floods. In many parts of the world, for example, snowmelt is an important part of river basin hydrology, and a warming climate means less snow accumulating during the winter and suddenly melting in spring – hence, less early-season flooding. Many rivers are also now interrupted by dams, which means that flows are directly controlled by human managers. Others have been dredged, channelled, diverted or otherwise altered in recent decades, while runoff has also been affected by changes in land use, urbanisation and forest cover. In addition, large amounts of water are withdrawn into reservoirs or pumped out of the ground for irrigation and direct human use. Some rivers – such as the Colorado and the Yellow rivers – have so much water abstracted for farming and industry that they sometimes fail to reach the sea at all. An increase in their annual flows, whatever the changing climate, is therefore unlikely to be registered over recent decades.

There is one type of extreme event, however, where the magnitude of rainfall changes is becoming so enormous that its effects on flooding are much more evident. The immediate impacts include the submergence of whole areas, resulting in disastrous economic damage and tragic loss of life. These storms form over warm ocean water, and strike fear into the hearts of people living close to the sea throughout the tropics and sub-tropics. I am talking, of course, about hurricanes.

Houston’s hurricane

‘GET OUT OR DIE!’

As a warning message, written in all caps, it was unsubtle but effective. So was the message that preceded it, also written by Tyler County judge Jacques Blanchette as Hurricane Harvey loomed over Texas on 29 August 2017: ‘Anyone who chooses to not heed this directive cannot expect to be rescued and should write their social security numbers in permanent marker on their arm so their bodies can be identified,’ wrote Blanchette. ‘The loss of life and property is certain.’

The judge’s warning was no exaggeration. As the floodwaters eventually receded after nearly a week of torrential deluge, the bodies of six family members – including four children – were pulled from a van that had been swept off a Houston bridge into a bayou. During the disaster itself, a shivering three-year-old girl was found clinging to the submerged body of her drowned mother. In all, at least 68 people died from the effects of Hurricane Harvey, the largest number of direct deaths from a tropical cyclone in Texas since 1919. The fatalities included a veteran Houston police officer, who drowned in his car in a flooded underpass while dutifully attempting to reach his place of work.

The scale and intensity of the deluge was staggering, even for seasoned meteorologists. Houston’s branch of the National Weather Service reported an almost unimaginable 250 mm (9.92 inches) of rain in a single 90-minute period at a station in the southern suburbs of the city. Harvey deposited around 22 cubic kilometres of rainwater in total across the south-eastern coastal United States, an amount equivalent to the flow of Niagara Falls for 110 days. The weight of all the water was sufficient, scientists calculated, to depress the Earth’s crust by two centimetres over the affected region. It took five weeks for all this extra water to flow back into the sea and for the land surface to gradually rebound.

Harvey was the wettest hurricane in United States history, with several places reporting 1,300–1,500 mm (50–60 inches) of rainfall. The totals were so high that the US National Weather Service had to add two new shades of purple to its flood maps to represent such extreme amounts of precipitation. ‘After more than 50 inches of rain over four days,’ reported the Washington Post, ‘Houston was less of a city and more of an archipelago: a chain of urbanized islands in a muddy brown sea. All around it, flat-bottomed boats and helicopters were still plucking victims from rooftops, and water was still pouring in from overfilled reservoirs and swollen rivers.’ About 300,000 buildings in the region were flooded, along with half a million cars. According to the Federal Emergency Management Agency, 30,000 water rescues took place during Hurricane Harvey’s catastrophic deluge.

Even before the storm came ashore, speculation was rising about a possible role of climate change in the anticipated disaster. ‘What you can and can’t say about climate change and Hurricane Harvey,’ read the headline of a Washington Post piece by the newspaper’s climate specialist Chris Mooney on 25 August (the storm hit later that evening). ‘Did climate change impact Hurricane Harvey?’ asked CNN, as the flood waters reached their peak on 28 August. ‘The Specter of Climate Change Hangs Over Hurricane Harvey’, suggested the New York Magazine. The Sydney Morning Herald, publishing on the same day, took a more moralistic tone: ‘Houston, you have a problem, and some of it your own making’ read the headline. The author asserted – after wishing the state’s residents well during the ongoing catastrophe – that ‘as the self-styled “world capital of the oil and gas industry”, there’s a connection between rising global greenhouse gas levels and the extreme weather now being inflicted that some of your residents have understood for decades and had a hand in.’

Watching the disaster unfold, albeit from hundreds of miles away on the other side of the Atlantic, was a strange experience for me because the spectacle was frighteningly reminiscent of the scenario I painted of a monster hurricane hitting Houston in the first Six Degrees. As I wrote in an imaginary scene: ‘The first of [the hurricane’s] rain bands advances under the cover of darkness, dumping torrential downpours across coastal Texas, from Corpus Christi in the south right up to the border with Louisiana. The storm is enormous, and Houston is right in the middle of its projected track … The surge is now moving up the river, the first water pouring around the buildings on the eastern edge of Houston itself. With blinding rain now pounding all of Harris County for several hours, Houston’s long-tamed river, Buffalo Bayou, begins to return to the wild. First to flood are underground car parks and malls. Storm drains suddenly start spouting floodwater. Manhole covers blow off with no warning, releasing fountains of foam five metres into the air. Abandoned vehicles float down the rapidly rising river, together with wind-blown debris washed out of flooded streets.’

All this bore an uncanny resemblance to the scene as it unfolded in Houston, not in my imagined future of August 2045 but right there in August 2017. Moreover, I had set this scene in my Three Degrees chapter because at the time I felt the science was not clear about whether or not hurricanes were already getting observably stronger, but that in a three-degree-warmer world ‘any lingering doubts about the connection between global warming and stronger hurricanes will have been dispelled by the brutal realities of a more energetic atmosphere’. In that sense, Hurricane Harvey came 30 years too early. Like many computer climate models, I had been proved unduly conservative by real-world events.

The deluge of rain was shortly followed by a virtual avalanche of scientific papers analysing the possible contribution made to the disaster by climate warming. A November 2017 paper in PNAS by hurricane expert Kerry Emanuel concluded that Harvey was a one-in-2,000-year event for Houston because of the sheer magnitude of its rainfall. Emanuel wrote: ‘By the standards of the average climate during 1981–2000, Harvey’s rainfall in Houston was “biblical” in the sense that it likely occurred around once since the Old Testament was written.’ Emanuel calculated, using both observations and climate models, that the annual probability of Harvey had already seen a ‘sixfold increase since the late 20th century’. A subsequent paper, published a month later in Environmental Research Letters, determined that the three-day rainfall total of just over one metre recorded at Baytown was a staggering one-in-9,000-year event, and that global warming made the rainfall about 15% more intense and the storm overall three times more likely.

Hurricanes are fuelled by warmth in the oceans, and the ocean heat content in the Gulf of Mexico was the highest on record in 2017, helping drive Harvey’s strong winds and intense rain. Harvey was also particularly destructive because the storm stalled over Houston, dropping enormous quantities of rain in one place over an extended period. There may be a climate change factor here too: a 2018 paper in Nature reported that tropical cyclone forward movement speed has slowed by 10% over the last half-century, increasing local rainfall totals that would previously have been spread over a wider area.

A similar stalling of an intense hurricane also led to the devastating flood-related disaster visited on the Bahamas by Hurricane Dorian in September 2019. This time the monster storm parked itself over the vulnerable islands for more than a day, resulting in nearly 1,000 mm of rainfall deluging the islands, accompanied by a multi-metre storm surge. As reported in Scientific American: ‘This slow motion and extreme intensity allowed Dorian to subject the Bahamas to the most fierce and prolonged battering by an Atlantic hurricane of any populated place in recorded history.’ By the time the cyclone finally drifted away to the north-east, Abaco and Grand Bahama islands were virtually flattened. With sustained wind speeds of 185 mph and gusts up to 220 mph, Dorian was ‘truly exceptional … Winds of this strength would make Dorian worthy of a category 6 rating, if it existed.’

Despite Dorian’s fury, 2019 was not as intense an Atlantic hurricane season overall as 2017. That year saw 17 named storms (the average is 12), 10 hurricanes and 6 major hurricanes. These included Irma and Maria, which devastated islands across the Caribbean. A 2019 study that investigated Maria found that the 2017 storm produced higher average rainfall totals than any of the 129 storms that have hit Puerto Rico since reliable records began in 1956, and that this extreme precipitation has become much more likely in recent years due to climate change. The combined storms generated ‘accumulated cyclone energy’ that was 245% above normal, thanks to hotter sea temperatures in the tropical North Atlantic. Hurricane Maria was the most deadly Atlantic hurricane for over a decade, causing – directly and indirectly – nearly 3,000 fatalities and leaving Puerto Rico’s infrastructure devastated, with nearly all power lines, many buildings and 80% of crops destroyed.

Scientists are now beginning to wonder if something has permanently changed in hurricane climatology. Coastal North Carolina has experienced three extreme tropical cyclone-driven flood events since 1999, with experts left fearing that they are seeing the impacts of a ‘regime shift’ towards a permanently higher risk from hurricane-related floods. Climate models do seem to suggest that the disasters caused by hurricanes like Katrina (which submerged New Orleans in 2005), Irma and Maria would simply not have been so destructive in a pre-industrial climate that had not been altered by accumulating greenhouse gas emissions. In other words, these destructive storms were the different creatures we can now expect in our one-degree world.

Some studies have also detected a human climate-change fingerprint in the rapid intensification and peak windspeeds reached by some tropical cyclones: both Maria and Irma underwent rapid intensification in the tropical Atlantic prior to landfall. The latter achieved Category 5 status and maintained that highest category longer than any storm anywhere in the world since reliable records began. Scientists have now found, for the Atlantic at least, a ‘detectable increase’ in tropical cyclone intensification rates as a result of global warming. Over in the eastern Pacific, in 2015 Hurricane Patricia broke records as the most intense tropical cyclone ever to form in the Western Hemisphere, with estimated sustained peak wind speeds of 185 knots, which equates to an extraordinary 212 mph. Patricia intensified explosively from a weak tropical storm to a strong Category 5 monster in just 48 hours, a rate of intensification so rapid and profound that it has probably also never been observed before in the modern era.

Underlying all these changes is the huge increase in ocean heat driven by global warming. In the western North Pacific, meteorologists have seen a doubling or even tripling of the numbers of Category 4 or 5-equivalent typhoons affecting eastern China, Taiwan, Korea and Japan over the last few decades. While the overall numbers of tropical cyclones have not changed much, those that do form are increasingly intense.

There is also evidence that the extent of the Earth’s surface affected by tropical cyclones is increasing. Research shows that the main cyclone-generating regions have migrated poleward in both hemispheres during the last 30 years, consistent with broader changes in atmospheric circulation driven by global warming. This process is likely to continue. In 2017, for example, Hurricane Ophelia – the largest-ever recorded hurricane in the East Atlantic – made it all the way to the coast of Ireland, bringing strong winds and heavy rain, and causing coastal erosion.

This means that in decades to come it will not just be the coastal residents of places like Taiwan and North Carolina who will have to batten down the hatches for hurricane season. As the Irish found out in 2017 as Ophelia loomed up from the south-west, bringing strong winds, tropical warmth and peculiar yellow skies, areas that have previously been considered too cold to be at risk of landfalling tropical cyclones will increasingly find themselves in the line of fire. As if to presage this change, in late September and early October 2019 Hurricane Lorenzo blew up in the Atlantic, setting new records as it became the most northerly and easterly Category 5 storm ever recorded. ‘This is something totally unusual for this kind of environment,’ said Miguel Miranda, president of the Portuguese Institute of the Sea and Atmosphere. Hurricane Lorenzo ‘is not normal’, he added. Fortunately the storm largely dissipated before hitting the British Isles – but there will be many more ‘abnormal’ storms to come.

High tides

Rising seas, of course, make the threat from hurricanes even worse. Sea levels have risen by nearly 6 cm since I wrote my first book in 2004. I took its title, High Tide, from my experience on the threatened island nation of Tuvalu in the Pacific. I was entranced by island life and the rhythms of the day- and night-time activities, from catching tuna fish to drinking beer and dodging fights in the capital Funafuti’s sleazy afterhours bar. Life was rapidly modernising – the majority of people wore jeans and T-shirts most of the time, but island traditions continued nevertheless. Most older men still wore coloured wraparound skirts, and we all gathered one evening for traditional dancing in the open-walled maneapa communal house, sharing plates of fish and taro. Sea level rise was impacting the community in Funafuti already, however: waves were washing into people’s properties, and ‘king tides’ led to water bubbling up in the centre of the island and running through the streets. Things have only got worse since then, with Tuvalu experiencing a rate of sea level rise three times the global average.

The leaders of Tuvalu and other small island states are not suffering in silence as their survival is threatened. At UN meetings and climate change conferences representatives of the ‘Association of Small Island States’ (AOSIS) do their best to communicate their nations’ plight to the rest of the world, demanding action on greenhouse gas emissions that is rapid and sustained enough to save them from drowning. I worked with AOSIS for several years in my capacity as climate advisor to President Nasheed of the Maldives, which as a coral atoll nation composed of hundreds of tiny islands is one of the countries most vulnerable to the rising seas. Nasheed was the first democratically elected president in the Maldives, and he made headlines early on in his administration when he and his ministers donned scuba gear and held an underwater cabinet meeting to illustrate the threat posed by the rising oceans. I worked with Nasheed on plans for the Maldives to lead the way towards a cleaner economy by becoming the world’s first carbon-neutral country, a policy commitment announced in 2009. It has not all been plain sailing since then; a coup interrupted plans in 2012, with Nasheed forced from power and even suffering several months in prison at the hands of an autocratic new president. Fortunately, democracy has since returned, with Nasheed’s Maldivian Democratic Party winning elections comprehensively in 2018.

During my time working with the Maldives and other small island states, it often seemed like the United States was the enemy, holding back progress at the UN and vetoing attempts to forge a global treaty on climate change. Now perhaps the US will need to think about joining AOSIS. Its east coast suffers some of the fastest relative rates of sea level rise in the world – about three to four times the global average – with a combination of tidal shifts and land subsidence making the 1,000-km-long, highly populated coast north of Cape Hatteras in North Carolina a ‘hotspot’ of accelerated sea level rise. Up and down the coast thousands of hectares of ‘ghost forests’ can be found in tidal estuaries and wildlife areas, where trees that have stood for decades or longer have been killed by gradually intruding saltwater. Scientists comparing the modern seashore with old maps from the 1850s suggest that 40,000 hectares of coastal forest may have died around the edges of Chesapeake Bay alone. ‘Much of the dead forest has now been replaced by marshland, while former marsh areas are now open water,’ reports Climate Central.

Coastal communities are now experiencing a new threat, of so-called ‘sunny day flooding’, where seawater inundates streets and parkland even on fairweather days without high onshore winds. According to the US agency NOAA, Boston, Massachusetts, and Atlantic City, New Jersey, both experienced 22 days of flooding in 2017, while Galveston, Texas, saw seawater invade its streets on 18 separate days. On 27 September 2015 ‘sunny day’ high tides in the Miami region flooded several coastal communities with 0.57 metres of ocean water. Although this was only the sixth-highest water level measured in the area, the previous five flood events had all been associated with landfalling hurricanes. The NOAA report revealed that the frequency of high tide flooding on US coastlines has doubled in the last 30 years.

This is still only the beginning. Sea level rise has been accelerating in recent decades, from 1.4 mm/year before 1990 to 3.6 mm/year in the latest IPCC assessment. There are now numerous reports coming in from low-lying areas all around the world of the resulting impacts. A study of one part of the Solomon Islands in the western Pacific found five out of twenty vegetated reef islands ‘have been totally eroded away in recent decades’. A further six islands are experiencing severe shoreline erosion, which at two sites has destroyed villages that have existed since at least 1935, forcing people to relocate. A study in New Caledonia in the south-western Pacific found numerous islets in a ‘critical situation’ and likely to disappear within just a few years. The picture is complicated, however. Global assessments show that larger islands have been remarkably resilient in the face of rising seas, with most inhabited islands not yet losing land area. Smaller atoll nations are uniquely vulnerable, however, including where I have worked in the Maldives.

Globally, 700 million people live in low-lying areas and 200 million are already within the range of extreme sea level rises. In southern Florida, weather forecasts now come with tide warnings, and stranded fish are a regular sight on flooded roads. Every year the waters rise, and residents know that while they can temporarily fight back with engineering projects and other adaptation measures, ultimately the oceans will win.

Paradise lost

It was ‘like the gates of hell opened up’, reported the newspaper USA Today. Except that this wasn’t supposed to be hell – it was supposed to be Paradise. That was before the Camp Fire, however. The paper reported how the wildfire disaster that struck the small California town with the heavenly name on 8 November 2018 unfolded: ‘As true darkness fell – smoke had clogged the air all afternoon – residents jammed onto winding, hilly two-lane roads. Witnesses reported blackout conditions, the smoke too thick to see through. Drivers collided, went off embankments, slammed into signs and trees as embers rained down upon them, setting trees and houses and cars alight.’ The heat was so intense that windows were blown out, and streams of melted aluminium ran down the roads from burning vehicles. People stuck in traffic jams were burned alive in their cars as fiery tornados raged around them. ‘It just looked like Dante’s Inferno,’ evacuee John Yates remembered. ‘Black and red was all you could see.’

By the time the wildfire was finally brought under control ten days later, little remained of Paradise but a few charred foundations, with the survivors of its original 27,000 residents scattered into shelters and evacuation centres. The official death toll of what had become the nation’s deadliest wildfire for a century climbed to 85 people. ‘A whole town was wiped off the face of the Earth in a matter of eight hours,’ one traumatised resident told CNN. As survivors began to return to the smouldering wreckage, they were warned to keep an eye out for bone fragments, all that might remain of residents who had not managed to escape in time. Other evacuees and relatives provided DNA samples to assist in the identification of any additional human remains.

After the fire burned out, attention moved to the role potentially played by climate change. Climate scientist Daniel Swain from the University of California, Los Angeles, explained on Twitter: ‘If Northern California had received anywhere near the typical amount of autumn precipitation this year (around 4–5 in. of rain near the Camp Fire point of origin), explosive fire behaviour & stunning tragedy in Paradise would almost certainly not have occurred.’ Reuters reported: ‘Paradise had not seen significant rain for 211 days, and the town, on a ridge in the foothills of the Sierra Nevada mountains, was surrounded by a potential bonfire of dry or dead trees following a five-year drought that ended in 2017.’ Swain’s own work has shown that more of California’s annual precipitation is coming in the winter months, leading to a drying trend in the summer and autumn, when fires tend to break out.

Later scientific work confirmed these preliminary conclusions. Studies show that between 1972 and 2018 California experienced a stunning fivefold increase in burned area. Each subsequent year seems to be setting new records: in 2017 modern state records were set for the largest individual wildfire (Thomas Fire, at 114,078 hectares) and for the most buildings destroyed by an individual wildfire (Tubbs Fire, 5,636 structures, leading to 22 fatalities). Both these records were to fall in 2018. In that year the Mendocino Complex Fire set a new record for the largest individual wildfire, turning 185,800 hectares to ashes. The deadly Camp Fire set a new record of 18,804 structures destroyed as it levelled the town of Paradise, and a state record was also set for the total area burned: 676,312 hectares. The costs were immense. In those two years California spent over $1.5 billion on fire suppression, itself also a new record. An analysis published in July 2019 showed that the major cause of the increase in summertime wildfires is the drying effect of rising temperatures, which have shot up by 1.4°C since the 1970s in California. Direct human influences – such as urbanisation, suppression of natural fires (which can lead to a build-up of unburned fuel wood) and so on – are potential contributory factors, but climate change is the big one.

This summer-drying trend has been measured over a large proportion of the forested areas of the western United States since 1979, and is strongly correlated with fire occurrence elsewhere as well. The number of large fires has been increasing: over the last quarter-century each year saw an average of seven additional large fires and an increase in burned area of 355 km2 in the western US, according to one recent study. ‘The geographically broad and coherent nature of fire and climate trends across much of the study area implicates climate as a dominant driver of changing fire activity in the western U.S.,’ the authors reported. Another study, published in PNAS in 2016, also concluded that human-caused climate change has been drying out forests across the western part of the US, lengthening the period of ‘high fire potential’ by nine days on average. Between 1984 and 2015 climate change doubled the area affected by forest fires, with an additional 4.2 million hectares burned.

Canada has also seen an increase in devastating fires. The Alberta Fire that levelled a fifth of the city of Fort McMurray in spring 2016 burned for two whole months before being finally extinguished on 5 July. By that time, 2,400 buildings had been destroyed and 590,000 hectares of land burned. With 90,000 residents affected, the Alberta Fire resulted in the largest-ever wildfire evacuation in the province. Fortunately no one was killed, although the fire was the costliest economic disaster in the country’s history, with an eventual price tag of 4.7 billion Canadian dollars. Ironically, perhaps, one of the fire’s impacts was to shut down oil sands production in the north of Alberta province, taking one of the most carbon-intensive and environmentally destructive source of liquid fossil fuels offline, at least for a few days. A year later it was the turn of neighbouring British Columbia, which saw a record 1.5 million hectares (an area three-quarters the size of Wales) burned and 65,000 people displaced during the most extreme fire season on record. A study by Canadian scientists concluded that the 2017 disaster was made two to four times more likely by climate change, which also increased the area burned by a factor of seven to eleven.

Wildfires everywhere seem to be increasing both in frequency and destructive power. The year 2017 saw extensive and severe fires in Chile, the Mediterranean, Russia, the US, Canada and even Greenland, where fires were spotted burning in the tundra along the western coast. Across the world as a whole, researchers have found that the average fire season has lengthened by nearly a fifth, with half of the Earth’s entire vegetated surface area seeing an increase in fire weather conditions during the last fifteen years. As the unfortunate residents of the Californian town of Paradise found out in the 2018 disaster, wildfire can strike with unprecedented ferocity and deadly speed – at one point the Camp Fire was spreading at the rate of a football field every single second.

In the first Six Degrees I used the image of Dante’s Inferno, describing each degree rise in temperature as a descent into one of the successive circles of hell. This was meant to be just a metaphor. But from California to Canada, as smoke rises, it seems that we are entering the Inferno for real.

Heat refugees

Everywhere temperatures are rising, as ever-higher concentrations of greenhouse gases in the atmosphere trap heat at the Earth’s surface. When I was beginning to write about climate change in the early 2000s, extremely hot summers might have been expected to occur twice a century. Now they are expected twice a decade. The shift is clear, even in temperate England where I live, with a two- to threefold increase in heatwaves since the pre-industrial period and week-long extreme heat events seemingly getting more intense each year. On 25 July 2019 a new UK all-time high-temperature record of 38.7°C was set at Cambridge University Botanic Garden, beating the previous record – set in 2003 – of 38.5°C. This seemed pleasantly cool by French standards, however. A month earlier, in June 2019, while much of western Europe baked in an unprecedented heatwave, thermometers in the southern French town of Gallargues-le-Montueux read a stunning 45.9°C, setting a new all-time record. A later study of the 2019 French heatwave found that it had been made five times more likely because of climate change.

This is what one degree of global warming looks like. Just the previous year, in the summer of 2018, almost the entirety of the Northern Hemisphere experienced drastically elevated temperatures, with extreme heat in Europe, North America, Asia and North Africa. In Oman, the coastal city of Quriyat experienced a 24-hour temperature that never dropped below 42.6°C, most likely setting a record for the highest minimum night-time temperature ever observed on Earth. In the Algerian Sahara, a high of 51.3°C was measured on 5 July, probably a new all-time record for the continent of Africa. At one point temperatures were as hot in Arctic Scandinavia as they were in southern Spain. Japan, too, set a new temperature record, with the city of Kumagaya, 65 kilometres from Tokyo, seeing 41.1°C. All around the world, records tumbled like dominoes.

A June 2019 study concluded that it was ‘virtually certain’ that the 2018 Northern Hemisphere heatwave – which affected a fifth of the populated and agricultural areas of the northern mid-latitudes concurrently – could not have happened in the absence of human-caused climate change. ‘Virtually certain’ means 99–100% probability in IPCC parlance; it is extraordinarily rare to have this level of confidence declared in any scientific finding. The authors also stated that heatwaves like that of 2018 were ‘unprecedented prior to 2010’. The human fingerprint has become very clear in modern-day temperature rises – one modelling study suggests that there was only a one-in-a-million chance that the high global temperatures recorded in 2014, 2015 and 2016 could have come about through natural variability.

High temperatures may not seem as immediately dramatic as floods or storms, but they are just as deadly; more than 70,000 additional deaths were recorded in Europe during the extreme heat of August 2003, with those losing their lives primarily being the elderly and most vulnerable. According to a 2018 health review published in the leading medical journal The Lancet, vulnerability to extremes of heat has risen steadily since 1990 in every region, with 157 million more people exposed to heatwave events in 2017 compared with 2000. The death tolls for the 2018 and 2019 heatwaves have not yet been calculated, but they will likely be in the many thousands. Preliminary estimates are worrying: in northerly Sweden, for example, the heatwave of 2018 was associated with 635 excess deaths. In Japan, medical authorities reported more than 34,000 cases of heat-related emergency transportation during the 2018 heatwave, with nearly 100 people found clinically dead upon the arrival of the emergency medical services.

But there is another, more subtle, way in which heat kills people. Rising temperatures increase the risk of drought, and in less fortunate parts of the world drought can lead to food shortages and a loss of livelihoods, which exacerbates conflict. Drought risk is particularly increasing in the sub-tropics due to the widening of the tropical belt, a long-predicted and now observed feature of a warming planet. The Sahara is expanding both northwards and southwards, threatening the livelihoods of tens of millions more people living in the increasingly arid zones of West and North Africa. Across the Mediterranean in southern Europe, scientists have calculated that it is more than 95% likely that climate change has increased the probability of drought years. The Levant region – Palestine, Israel, Lebanon and Syria – suffered 15 years of drought between 1998 and 2012, again due to the expanding zones of sub-tropical dry air consistent with global warming. Scientists have studied tree ring data from the region to try to estimate how often these kinds of droughts occurred in the past; they found that the recent decade was probably drier than any comparable period over the last 900 years.

The impacts on the inhabitants of the region have been utterly devastating. During the worst part of the drought after 2009, 1.5 million people were displaced from agricultural areas in Syria and forced to migrate to cities as harvests failed and livestock herds died from thirst and starvation. This led to a doubling of food prices and a dramatic increase in childhood undernutrition. ‘The rapidly growing urban peripheries of Syria, marked by illegal settlements, overcrowding, poor infrastructure, unemployment, and crime, were neglected by the Assad government and became the heart of the developing unrest’, reported an assessment for PNAS, with this unrest later becoming a full-scale civil war. The failure of the Assad dictatorship to initially address the agricultural crisis, and the dire conditions suffered by millions of displaced people and refugees who were living in terrible conditions on the edges of cities, were therefore important factors in the Syrian uprising that began in 2011. This obviously does not mean that Assad’s decision to drop barrel bombs and poison gas on civilian populations can be blamed on climate change. The Syrian regime’s war crimes remain its own responsibility, albeit shared with the Russian and Iranian governments that propped up the blood-soaked Syrian dictator.

However, there is evidence that climatic calamities do correlate with armed conflict, at least in the most ethnically divided countries. The authors of a recent study note that ‘about 23% of conflict outbreaks in ethnically highly fractionalized countries robustly coincide with climatic calamities’. This is not a simple cause-and-effect relationship, but it does seem like the disruptions brought on by climate heating play out in ethnically divided countries ‘in a particularly tragic way’. The ensuing conflicts can have impacts far afield, as – in the case of Syria – millions of refugees flee to neighbouring countries.

The moral challenge of climate change is writ large in the fate of refugees. Given that the richer countries have done most to cause global warming, I would argue that they have an especially strong responsibility to assist people who are suffering the impacts of drought-related conflicts like that in Syria. One of the proudest moments of my life was speaking to a crowd of 2,000 people at a ‘refugees welcome’ rally a small group of us organised in 2015 at a few days’ notice in Oxford. The spark that made us act, and prompted so many people to come along to show their support, was the photograph of the Syrian toddler Alan Kurdi washed up drowned on a beach in Turkey. Kurdi was a victim of climate, conflict – and callousness: that of European leaders who closed their nations’ borders and refused aid to millions of people in distress, forcing the young boy’s family to attempt a dangerous night-time crossing to Greece in an open boat. We are all human, and as climate impacts accelerate in decades to come, maybe one day Western readers of this book will be the refugees. I hope – and it might be a forlorn hope – that we can summon up the will to address future climate impacts in a spirit of mutual solidarity rather than division. Otherwise I fear there will be many more Alan Kurdis washed up on the world’s beaches in the years ahead.

Against nature

It is not only humans who are suffering from the impacts of ongoing climate breakdown. Global heating is now an increasing factor in wildlife declines and even the outright extinction of species as plants and animals lose their habitat due to shifting climate zones. According to the IPCC, ‘the geographical ranges of many terrestrial and freshwater plant and animal species have moved over the last several decades in response to warming: approximately 17 km poleward and 11 m up in altitude per decade.’ In terms of annual distance, that corresponds to 1.7 kilometres per year – or nearly five metres per day – that species are having to shift their ranges to keep up with rising temperatures in our one-degree world. And this is only an average: in many places climate zones are moving much faster.

It may be obvious that plants, which are generally rooted to the ground, will have difficulty keeping up with this increasing ‘climate velocity’. But even those species with wings are lagging behind. One recent study found that birds and butterflies were running up ‘climatic debts’ by lagging 212 and 135 kilometres respectively behind the ongoing speed of climate change. When they do move long distances, butterflies may find themselves stranded in a suitable climate but without food to raise their caterpillars, if their larval host plants are slower to disperse into new areas. Birds which then depend on absent insect larvae to feed their chicks may find their own offspring facing starvation. One example is Baird’s sandpiper, a species whose migration into the high Arctic used to be timed exactly to coincide with the peak of insect abundance during the short tundra summer. Insects are now emerging earlier as springtimes advance, meaning less food later in the season for hungry sandpiper chicks. Another migratory bird is the pied flycatcher, whose populations have crashed in Holland as the bird arrives from Africa too late to exploit the peak supply of caterpillars. Research has also found an increasing mismatch between the supply of caterpillars in UK oak forests and the demands from nestlings of birds such as blue tits, great tits and pied flycatchers. Such is the reality of unravelling food webs across the world as temperatures rise.

Animals and plants in mountain areas are particularly vulnerable because they are finding themselves squeezed uphill in contracting areas towards mountain summits as temperatures rise. Dubbed the ‘escalator to extinction’, this topographical effect is particularly worrying among mountains in the tropics, because species would have to travel thousands of miles to higher latitudes to find the same kinds of cooler regions that currently exist in tropical highlands. There is evidence that this is already happening; in 2017 a team of biologists visited a remote and densely forested Peruvian mountain ridge called Cerro de Pantiacolla, returning to an area that had been originally surveyed for birds back in 1985. With temperatures having risen nearly half a degree in the intervening period, the scientists expected to find that bird species had shifted their ranges uphill in order to stay in the same temperature zones. What they found was even worse. ‘Several high-elevation species seem to have disappeared, and those that persist have generally shifted upslope and now inhabit smaller distributions with lower abundances,’ the scientists reported, concluding that ‘high-elevation birds on the Cerro de Pantiacolla are indeed riding an escalator to extinction.’

It is not only changing temperatures that are a concern. In California’s Mojave Desert researchers found that numbers of bird species have ‘collapsed’ since the early 20th century, with reduced rainfall amounts being the most likely cause of an observed 40% decline. A 2016 study surveying 976 species around the world found that climate-related local-area extinctions had already occurred in nearly half of them. The casualty list included fish, insects, birds and mammals, with tropical species suffering the most. A total of 460 species had been driven out of previous habitat by rising temperatures.

When species are already under threat and restricted to very small areas, a single disaster can wipe out the entire global population. This is what is thought to have happened with the world’s first documented climate-driven mammal extinction – that of the Bramble Cay melomys, a small rodent restricted to a single island in Australia’s Torres Strait. With extreme high tides driven by sea level rise inundating the island and destroying vegetation, the animal lost 97% of its habitat. The last individual was seen by a fisherman in 2009, and in 2019 the government of Australia recognised it as officially extinct. ‘The Bramble Cay melomys was a little brown rat,’ the Wilderness Society told the Sydney Morning Herald. ‘But it was our little brown rat and it was our responsibility to make sure it persisted. And we failed.’

Climate change is only one factor among many driving the on-going epidemic of global biodiversity loss. The Bramble Cay melomys was one of three Australian vertebrates known to have gone extinct between 2009 and 2014. One of the others was also a mammal, the Christmas Island pipistrelle bat, which disappeared alongside another Christmas Island species, the forest skink. The last individual of the latter species, a female lizard nicknamed Gump, died in captivity on 31 May 2014. The immediate cause of the species’ deaths is not known for certain, but is likely to involve predation from introduced species such as cats or snakes.

Whether caused by invasive species on islands, hunting for bushmeat in Africa, the destruction of tropical forests or rampant industrial overfishing, the ongoing wave of destruction is affecting pretty much the entirety of life on Earth. Take wild herbivorous mammals, 60% of the species of which are threatened with extinction. These include the Bactrian camel, of which only 950 survive in the wild, Przewalski’s horse (population 310), the pygmy hippopotamus (2,500), our close relatives the Eastern gorilla (5,900 are left), and the mountain tapir (2,500). The total population of Javan rhinoceros is just 50, while the Sumatran rhinoceros numbers only 280 individuals.

As these dismal numbers indicate, even where species do not disappear entirely, so few individuals are left in the wild that a species may be ecologically dead anyway. Marine biologists are now observing the proliferation of ‘empty reefs’, ‘empty estuaries’ and ‘empty bays’. This drastic reduction in wildlife numbers – termed ‘defaunation’ – means that 40% of mammal species and 32% of all vertebrates have experienced severe population declines in recent decades. Scientists writing in PNAS in July 2017 described this as ‘biological annihilation’, part of what has now become the ‘sixth major extinction event’ in the Earth’s history.

The statistics are so overwhelming as to be almost numbing. In September 2019, for example, a team of biologists reported in Science that since 1970 bird populations in the US and Canada have declined by nearly a third. These declines are seen not just in rare and threatened species but in familiar backyard birds seen across the North American continent. The total number of birds lost was a staggering three billion individuals, including sparrows, warblers, finches and swallows – which, as BirdLife explains, are ‘common, widespread species that play essential roles in food webs and ecosystem functioning, from seed dispersal to pest control’.

One of the biggest factors driving the decline of once-common bird species is an underlying fall in the numbers of insects. The term ‘Insectageddon’ is now used in the media to describe the rapid declines in insect numbers measured around the world. This seems to be happening even in areas that are not obviously directly impacted by humans; a study in German nature reserves found a 75% decline in ‘total flying insect biomass’ over 27 years, while in relatively undisturbed Puerto Rican rainforests another team found that insect biomass had declined by between 10 and 60 times between the 1970s and today. Not surprisingly, parallel declines were observed in the populations of insectivorous lizards, frogs and birds. A 2019 paper found that global rates of decline are now so dramatic that 40% of the world’s insect species may be driven to extinction within the next four decades. Another recent study in the US Midwest found that a third of butterflies had disappeared in just 20 years.

Habitat loss due to agriculture is the number one concern identified by the researchers, followed by pollution from fertilisers and pesticides, and invasive species. However, climate change is probably now a significant factor behind insect loss too, as ecological zones shift and food webs fray. Direct impacts of heat may also be affecting insect reproduction. A 2018 study found that simulated laboratory heatwaves could damage sperm production in beetles, suggesting that this ‘male reproductive damage under heatwave conditions provides one potential driver behind biodiversity declines and contractions through global warming’. The researchers found that a single heatwave (defined as a 5–7°C rise in temperature for five days) halved male fertility in the beetles, while a second heatwave almost sterilised them.

Climate change can also interact with disease. Amphibians – frogs and salamanders in particular – have suffered catastrophic population collapses worldwide in recent decades as a result of the rapid international spread of an infectious skin disease caused by the chytrid fungus. At least 501 amphibian species have been pushed into decline by the resulting chytridiomycosis disease, with 90 species confirmed or presumed extinct in the wild and a further 124 experiencing declines of more than 90% in abundance. While the global amphibian trade may have helped to spread the disease rapidly, even into protected nature reserves far from direct human disturbance, rising temperatures may also be a factor. One study looking at the critically endangered Panamanian golden frog – a native of cloud forests in central Panama – found that individuals showed especially high mortality rates when the chytrid fungus was combined with higher temperatures.

If you go trekking in the Panamanian jungle today you won’t find any golden frogs. The only specimens left alive are within captive breeding programmes in zoos and conservation centres, protected behind glass and plastic walls, and isolated from the external environment by strict biosafety protocols. Annual Golden Frog Festivals – for the beleaguered amphibian is Panama’s national animal, no less – feature parades, sponsored runs, and trips to see the few remaining captive animals. Much of the frog’s former territory is protected in the hope that it might one day return, perhaps after the climate has been stabilised and the current wave of extinctions has passed. But for the moment the Panamanian forests that once echoed to the sound of the frog’s distinctive whistling mating calls lie silent.

Global browning

For Chapman’s Baobab the end came suddenly. On 7 January 2016 a loud cracking sound, followed by a mighty groan, echoed across the Kalahari. All seven trunks of the mighty tree – one of the largest and oldest in the world – suddenly split apart at the base and crashed to the ground, leaving them splayed apart in opposite directions like corpses on a battlefield. Tellingly, while the disaster arrived with no warning, it came after Botswana recorded its hottest-ever day, and following two years of punishing drought. This gigantic tree, which had stood for at least a thousand years and was one of Botswana’s best-known landmarks, had died of thirst.

Ancient and stately, baobab trees have stood sentinel-like on the plains of southern Africa for millennia. Known as the ‘tree of life’, the baobab – with its bulbous trunk and frequently hollow base – is instantly recognisable, even from a far distance. Several individuals have been measured at over 2,000 years old. And yet these antique specimens, the oldest angiosperms (flowering plants) on the planet, have begun one by one to topple over and die. In 2018 a research team led by the Romanian ecologist Adrian Patrut, an expert on baobabs, reported that nine of the thirteen oldest, and five of the six largest individuals have died or begun to collapse in the past twelve years. They include Namibia’s Homasi tree, which had stood since the end of the Roman empire and fell on 1 January 2005. Many of the trees are immensely historic; Chapman’s Baobab, for instance, had initials on its bark carved by the 19th-century explorer David Livingstone. The oldest of all was Panke, a sacred baobab located in a remote part of Matabeleland, Zimbabwe. Patrut and his team carbon-dated samples from its trunks after the tree fell in 2010, finding it to be an incredible 2,400 years old. No wonder it was sacred.

‘The deaths of the majority of the oldest and largest African baobabs over the past 12 years is an event of an unprecedented magnitude,’ wrote Patrut and his team in Nature Plants journal. There was no evidence of an epidemic of disease, they made clear, and yet numerous mature baobabs had all died suddenly in a short space of time, making climate change a leading suspect. Other experts are more blunt. ‘One would imagine such behemoths had survived many climatic vicissitudes over their vast lifetimes,’ forest ecologist Bill Laurance told environment writer John Vidal. ‘But in a climatically changing world, their great stature is a curse. They struggle to get water up to their foliage without suffering dangerous embolisms in their vascular systems. Droughts can be fatal. In a world with more drought and with higher temperatures, it does not take much to push them over the edge.’

Africa’s baobabs are not the only arboreal casualties. From Spain to New Mexico, and from Argentina to Australia, there are now multiple examples of large-scale forest die-offs associated with drought and high temperatures. In Algeria, the majestic blue-green Atlas cedars have begun to dry out and die, while in Australia acacias have been dying back over large areas. In New Zealand and Patagonia one casualty is Nothofagus (southern beech), while across western India numerous tree species in dry tropical forests have suffered sharply increased mortality. In Europe, spruce, beech, fir, oak and pine have all experienced die-offs in the wake of heatwave and drought events. Across huge areas of the American West conditions are now too dry for ponderosa pine and Douglas fir seedlings to re-establish after wildfires, leading to fears that these iconic forests may be passing a threshold where they will eventually disappear completely. Forest experts are concerned that widespread tree death due to drought and heat may now be a worldwide phenomenon directly resulting from our one-degree world.

During California’s epic 2012 to 2015 drought, tree mortality increased tenfold, from tens to hundreds of dead trees per square kilometre, a death toll that rose dramatically in the fourth year of the drought. According to a study published in July 2019, conifer trees throughout the southern Sierra Nevada had found themselves with soil moisture exhausted as deep as 15 metres into the ground, far below accessible root level. As well as direct death from thirst, the drought made trees vulnerable to bark beetle outbreaks and wildfires. While California has seen droughts before, the higher temperatures accompanying the recent record-breaking rainfall deficits seem to have been the final straw for millions of trees.

With the world’s forests under threat, the next generation of climate models may have to be retuned. It has long been supposed that rising CO2 levels in the atmosphere will have a fertilising effect on the world’s plants, and that the land biosphere will therefore continue sucking up increasing amounts of carbon right through until the end of the century. Certainly CO2 fertilisation is real, and is why some growers pump waste CO2 into greenhouses to ramp up tomato production. And for a long time it was also the case that large areas of the Earth’s surface were greening, partly in response to elevated levels of CO2. The phenomenon used to be talked up by climate change deniers, who a decade ago ran a now-defunct coal industry front group called the ‘Greening Earth Society’ to tout ‘the benefits to plant life from carbon dioxide fertilization’ to the unwary. No more. The most recent satellite data, published in August 2016, show that a threshold was passed in 1999, after which the greening trend in many areas reversed. The culprit seems to have been a parallel post-2000 decline in relative atmospheric humidity, which has been drying out forests faster than water can evaporate from the world’s oceans. Thanks to this increasing water vapour shortage, greening Earth became browning Earth instead.

If the CO2 fertilisation effect has indeed been overplayed in climate models, it means that more carbon will remain in the atmosphere to generate further warming rather than being taken up by plants. Moreover, if sudden forest die-offs continue to be seen over large parts of the world, not only will the biodiversity crisis accelerate but new carbon may appear as ecosystems collapse. In the worst-case scenario, the land biosphere will become a net source of carbon. If that happens, the falling Chapman’s Baobab – which echoed like gunfire across the arid plains of the Kalahari on the morning of 7 January 2016 – may have been the opening shot in a much wider war.

Ocean heatwaves

Rising CO2 has major effects in the ocean too. Most directly it causes ocean acidification as carbon dioxide dissolved in seawater generates carbonic acid. Since pre-industrial times, surface ocean pH has decreased by around 0.1, a change already harming shell-building organisms – from corals to plankton – that use calcium carbonate. This pH drop may not sound like much, but it is estimated to be taking place an order of magnitude faster than any natural event for hundreds of millions of years. So much human-made CO2 has now entered the oceans that the seafloor is even starting to dissolve in several locations around the world. As the authors of a recent PNAS paper point out, this ‘chemical burndown’ is beginning to alter the geological record of the deep sea, and ‘will intensify and spread over vast areas of the seafloor during the next decades and centuries’ as ocean acidification accelerates.

CO2 of course also causes warming, and the laws of physics dictate that hotter water holds less oxygen. The slowdown of ocean circulation – also driven by warming – means that less surface oxygen is transported into the depths. Thus global warming is beginning to deoxygenate the oceans, depleting the dissolved oxygen in seawater that is essential for the survival of virtually all forms of life. Over the last half-century the ocean has lost 2% of its oxygen content, which equates to a loss of 77 billion metric tonnes of oxygen. In the open ocean so-called ‘oxygen-minimum zones’ have expanded by 4.5 million square kilometres, equivalent to the size of the European Union, while the volume of fully anoxic water (seawater that is completely devoid of oxygen) has quadrupled. In addition, more than 500 dead zones now persist in coastal waters around the world. Although these smaller coastal dead zones are caused largely by nutrient pollution from agricultural runoff and sewage, the worldwide loss of oceanic oxygen bears the unmistakable fingerprint of global heating.

Ocean warming is having a direct and sometimes devastating effect on species and ecosystems. One tragic example was the ‘marine heatwave’ that struck the Pacific coast of North America between 2014 and 2015 and led to a mass die-off of seabirds. Populations of the robin-sized Cassin’s auklets were particularly badly hit. The US Fish and Wildlife Service collected 250 carcasses on a single stretch of Oregon beach and left as many behind. ‘You’d find them piled up in clusters on the wrack line, where the tide leaves sea grasses and debris,’ the biologist recalled. ‘Most were in these states of decay, but every now and then we’d see tracks coming out of the water and find a bird that was just barely clinging to life. They were just skin and bones.’ By April 2015 more than 9,000 carcasses had been recorded on beaches from California to Washington State. ‘It was so distressing,’ recalled one bird-spotting volunteer, who had patrolled the beaches of Washington State looking for dead or stranded seabirds. ‘They were just everywhere. Every ten yards we’d find another ten bodies of these sweet little things.’ Scientists found that the carcasses were emaciated – ruling out toxic pollution or oil spills, they concluded that the little birds had starved to death in huge numbers.

The mass-mortality event closely tracked the appearance of hotter-than-usual waters over a huge area of the coastal north-east Pacific, famously dubbed ‘The Blob’ by Washington’s state climatologist Nicholas Bond. Warmer temperatures had drastically reduced the numbers of tiny invertebrates, called copepods, that are the primary food source for Cassin’s auklets, and the tiny birds had starved in their thousands as a result. The species was already listed as of conservation concern following long-term population declines, and scientists warn that marine heatwaves on the scale of the 2014–15 north-east Pacific event ‘may well represent a global population precipice’ for the vulnerable seabird. ‘I’ve never seen anything like this, ever, and I’ve been here since 1985,’ David Nuzum, of the Oregon Department of Fish and Wildlife, told National Geographic.

It wasn’t just birds that were affected. The Blob was also implicated in a cetacean ‘Unusual Mortality Event’ (UME) that saw 46 whale carcasses – mostly fin and humpback whales – stranded on the coastlines of British Columbia and Alaska. Another UME was declared at the same time for fur seals and California sea lions, with malnourished, starving and dead animals washing up along the entire California coast from January 2015 onwards. Those that could be saved were taken to rehabilitation centres where malnourished pups were provided with nutrition and hydration so that they could be re-released when conditions improved. Fisheries were also affected, and a harmful algal bloom led to toxins contaminating shellfish along the coasts of Washington, Oregon and California. All told, scientists writing in the journal Nature Climate Change concluded, ‘it is possible that the northeast Pacific warm anomaly of 2014–15 is the most ecologically and economically significant marine heatwave on record.’

Other marine areas have been hit by their own versions of ‘The Blob’. On the Atlantic coast of South America a 2017 marine heatwave brought the hottest-ever recorded sea temperatures over a wide area, causing mass mortalities of fish and a toxic algal bloom just a few miles offshore from Uruguay’s capital city. In 2010 to 2011 a marine heatwave off the coast of Western Australia damaged huge areas of ecologically important seagrass meadow and led to a long-term decline in the population of bottlenose dolphins. Marine heatwaves ‘have already become longer-lasting and more frequent, extensive and intense in the past few decades’, a 2018 Nature Climate Change paper concluded, reporting data showing that marine heatwave days doubled between 1982 and 2016. Another 2018 paper, published in Nature Communications, found that ‘from 1925 to 2016, global average marine heatwave frequency and duration increased by 34% and 17%, respectively, resulting in a 54% increase in annual marine heatwave days globally.’ The explanation was straightforward: a rise in average ocean temperatures. In other words, the culprit was global warming.

A more recent paper, published in March 2019, concluded that marine heatwave days have increased by 50% in recent decades as compared with the first half of the 20th century. Lead author Dan Smale compared the impact of hotter oceans on marine ecosystems to wildfires on land. ‘You have heatwave-induced wildfires that take out huge areas of forest, but this is happening underwater as well,’ he told the Guardian. ‘You see the kelp and seagrasses dying in front of you. Within weeks or months they are just gone, along hundreds of kilometres of coastline.’

Bleaching corals

The oceanic ecosystems most endangered by marine heatwaves are tropical coral reefs, which are experiencing devastating bleaching episodes as they are swept by ever-hotter waters. In 2016 and 2017 Australia’s Great Barrier Reef suffered back-to-back mass bleaching events that virtually wiped out large areas of this 2,300-km-long ecosystem. Terry Hughes, a world expert on corals, surveyed 900 sections of the reef during and immediately after the 2016 bleaching event from the air. ‘I showed the results of aerial surveys on bleaching on the Great Barrier Reef to my students,’ he tweeted on 19 April 2016. ‘And then we wept.’

Hughes and colleagues subsequently published a paper in Nature that detailed an ‘unprecedented ecological collapse, extending southwards from Papua New Guinea for up to 1,000 km’. In the worst-hit northern 700-km section of the reef, where heat exposure was most extreme, 50% of coral cover on reef crests was lost within eight months. With the staghorn and tabular corals suffering a ‘catastrophic die-off’, the three-dimensionality and ecological functioning of nearly a third of the 3,863 reefs that together comprise the world’s largest coral reef system was transformed. Mass bleaching was easy to spot from the air, with large sections of reef converted into areas of deathly white visible through the clear water. The southern section of the reef was only saved from the same fate by pure luck, when cooling wind, cloud-cover and rain from a passing tropical storm rescued it from the rising temperatures that were devastating corals elsewhere.

Any lingering optimism about the longer-term fate of the reefs must surely be misplaced. Coral bleaching was virtually unknown in the world’s oceans before the mid-1980s. This means that corals have evolved little protection to rising heat that might help them adapt or speed ecological recovery. For example, a bleaching event in 1998 killed large areas of staghorn coral surrounding Orpheus Island off the Queensland coast. Now, 18 years later, photographs of the same site show it still covered with muddy debris and exhibiting no sign of recovery. Even when some ecological rebound does take place, bleaching events are now arriving too frequently for the reefs to recover anything like their previous diversity before the next event strikes. The latest studies now show that marine heatwaves are becoming sufficiently intense to skip the bleaching process altogether and kill coral organisms directly. The exposed reefs, left vacant by the dead coral polyps, are draped with a layer of algae within a few days, and later begin to dissolve.

The 2016 worldwide bleaching event, as well as devastating the Great Barrier Reef, also had ‘catastrophic impacts’ – according to scientists later reporting in Nature – in the Red Sea, central Indian Ocean and across the Pacific Ocean and the Caribbean. In some areas corals were bleached right down to what should be much cooler areas 90 metres below the sea surface. In the Arabian Gulf, where corals were assumed to be reasonably accustomed to higher sea temperatures, reefs spread over 350 kilometres of the southern basin of the Gulf were bathed in lethally high temperatures for over a fortnight. Mass bleaching ensued, and two-thirds of corals were killed outright. By the next year, just 7.5% of the original coral cover was left. Reef scientists were particularly shocked at the scale of this loss because the Gulf corals were supposed to be more resistant to bleaching as they were used to higher temperatures. Yet they still died.

The coral die-off has transformed once thriving reefs into ‘more degraded systems, with just a few tough species remaining,’ scientists report. No wonder so many coral experts are in despair. A recent feature in Nature reported that many marine biologists who work on the Great Barrier Reef are experiencing ‘ecological grief’ at witnessing the real-time breakdown of one of the world’s most beautiful and valuable ecosystems, something that they have loved and studied throughout their careers. Researchers also feel the weight of knowing what has been lost, and the reality that their children will never enjoy the pristine and thriving reefs that they themselves remember.

Meanwhile, the extinction clock is ticking. The final demise of the reefs may come sooner than even many scientists expect, not just because of increased bleaching or thermal stress, but because corals are increasingly failing to reproduce at all. Researchers have found that juvenile corals, which need a solid anchor point on the seafloor to start growing, cannot establish new colonies on a bed of algae and mud-covered rubble. Although new coral colonies are moving poleward in a desperate effort to stay within thermally tolerable waters, studies have found a more than 80% reduction in their worldwide reproductive success since the 1970s. Recent work on the Great Barrier Reef found a 90% collapse in the reproductive capacity of the corals, though perhaps this is hardly surprising since most of the sexually mature adults over large areas are already dead.

Coral reproduction used to be one of the great wonders of the world. Despite being unable to communicate directly, corals are somehow able to spawn over hundreds of kilometres simultaneously on a single night, this miraculous synchrony coordinated through a complex combination of environmental cues and the phases of the moon. Eggs and sperm can only survive in the water for a matter of hours, so successful fertilisation depends critically on coral colonies all releasing their sexual material at the same time. However research conducted in the Red Sea, published in Science in September 2019, suggests that this system, which evolved over millions of years, is beginning to break down in the face of record-breaking sea temperatures. Corals are losing their spawning ‘synchrony’ – in other words they are going out of tune, with colonies spawning in an irregular way over different nights or even failing to spawn at all. This synchrony breakdown drastically reduces the probability of successful fertilisation, which in turn reduces the numbers of young corals and may eventually ‘drive aging populations to extinction’.

I don’t know whether the researchers wept when they saw what was happening to coral spawning in the Red Sea. But it would be strange not to suffer ‘ecological grief’ at the sight of billions of coral eggs dispersing uselessly into the warming ocean, and at the thought that the prospects of the next generation of these spectacular corals has been stolen. This is a future stolen ultimately not just from tropical corals, Cassin’s auklets or golden toads. It is also stolen from our own children, who will never know the amazing and spectacular world that we enjoyed when we were young. Already, at one degree, our globe is becoming impoverished and reduced. We might all weep for what we have done.

2°

Конец ознакомительного фрагмента.

Текст предоставлен ООО «ЛитРес».

Прочитайте эту книгу целиком, купив полную легальную версию на ЛитРес.

Безопасно оплатить книгу можно банковской картой Visa, MasterCard, Maestro, со счета мобильного телефона, с платежного терминала, в салоне МТС или Связной, через PayPal, WebMoney, Яндекс.Деньги, QIWI Кошелек, бонусными картами или другим удобным Вам способом.