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.