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.