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.