Six Degrees: Our Future on a Hotter Planet

Unless spurred on by a major hurricane or storm surge, the end for atoll countries will not be rapid or cathartically dramatic. Instead it will be death by a thousand cuts, an incremental dimin-ishment of each nation's ability to support itself, as young people lose confidence in the future and old people sink back into comforting dreams of the past. Each bit of beach lost, each vegetable garden invaded by salt water, each undercut coconut tree which topples into the waves will add to the inevitable toll. Decades before the last bit of coral disappears under the sea, community services will decline, children will emigrate, schools will close, and the fabric of a nation will begin to unravel.

Bear in mind that as future chapters of this book unfold, unacknowledged and mostly forgotten, atoll nations will be submerging-bit by bit.

2° (#u002bc48c-dd26-5651-a20b-e9e5578ccf07)

2 TWO DEGREES (#u002bc48c-dd26-5651-a20b-e9e5578ccf07)

China's thirsty cities

Take a train from Hohhot to Lanzhou in northern China, and you pass through a strange area of heavily eroded badlands, where steep gullies and cliffs crowd in around the railway track as it weaves its way through a narrow river gorge. At many points caves have been hacked out of the cliffs-their history is murky, but perhaps they were used by vagrants, or people expelled from the cities, or even by Communist dissidents exhorting the peasantry to rise up against the Nationalists during the 1930s. A more prosaic explanation is that they were carved out by railway construction workers as they laboured to lay track through cold, windy and inhospitable territory.

These badlands are the edge of China's loess plateau, a gigantic area of compacted dust many hundreds of metres deep, deposited over thousands of years by dust storms and strong winds roaring down from the Gobi Desert of Mongolia. This dry plateau may not be much good for agriculture, grazing or anything else (bar digging caves) but it is a treasure trove for palaeoclimatologists, who use its finely preserved layers of dust and sand to reconstruct the fluctuations of ancient climates across the whole region of northern China.

It was with this purpose in mind that a team of Chinese scientists based in Lanzhou trekked out to four sites on the loess plateau in 1999, drilling more than 30 metres down into the compacted soil before carefully extracting their sections and carting them back to the lab. Near the base of each section was the target of the research: a layer of prehistoric soil-‘palaeosol’ in the jargon-dating from the Eemian interglacial, the previous warm period before the start of the last ice age. The weather records preserved in this inauspicious red-brown layer would prove to hold clues not just about the past, but also about the future.

Like Africa and the Indian subcontinent, northern China is subject to an annual monsoon cycle. In summer, moist air blows in from the ocean, bringing heavy rainfall to the south. In winter, however, the pattern reverses and strong winds sweep down from the north, bringing dust and freezing temperatures. The Lanzhou scientists, using complex techniques to measure particle sizes and magnetic data from the palaeosol section, were able to draw conclusions from their sample about changing monsoon strength 129,000 years ago, as the Eemian climate gradually warmed up. Because of how long it takes the oceans to absorb heat, it appeared, the dry winter monsoon responded much more rapidly than the summer one to the changing conditions. The result was a period of drought and continental-scale dust storms, before the summer monsoon pushed far enough inland to bring significant rainfall to the loess plateau.

So could such a mechanism plausibly repeat in the two-degrees-warmer world? Studies of Pacific sea floor sediments suggest that the height of the Eemian interglacial saw global temperatures about 1°C higher than today's, making this period a potentially useful analogue for a warmer climate in the future-particularly as regional temperatures in a large continent like Asia would in turn have been a degree or so higher than the global average. And if it did take China's monsoon climate longer to make the transition from cool/dry to warm/wet 129,000 years ago, as some scientists believe, this does suggest a possible cause for the droughts and rising temperatures that have struck northern China in recent years. So whilst southern China can expect more flooding as the climate warms, the oceanic time lag means that it may take much longer for the rain-bearing summer monsoon to reach the drought-stricken north. With China split between two extremes, agriculture will inevitably suffer, and water-stressed cities like Beijing and Tianjin will continue to experience shortages-particularly as economic growth spirals upwards and underground aquifers are pumped dry. The Chinese government has begun construction of a massive water transfer project, which aims to take billions of cubic metres of water from the Yangtze River in the south to the thirsty cities in the north. However, even this mega-project-the largest ever constructed on the planet-will (if it works, which many doubt) have difficulty keeping the taps running. With a chronic shortage of water, China will not just struggle to develop a more affluent lifestyle, it will struggle to feed itself too.

Acidic oceans

Greenhouse gases released over the last hundred years or so have not only changed the climate; they have also begun to alter conditions in the largest planetary habitat of all-the oceans. At least half the carbon dioxide released every time you or I jump on a plane or turn up the air-conditioning ends up in the oceans. This may seem like a good place for nature to dump it, but ocean chemistry is a complex and delicate thing. The oceans are naturally slightly alkali, allowing many animals and plants which inhabit the seas to build calcium carbonate shells.

However, carbon dioxide dissolves in water to form carbonic acid, the same weak acid that gives you a fizzy kick every time you swallow a mouthful of carbonated water. That's great for a glass of Perrier, but not so good if it's beginning to happen on a gigantic scale to the whole of the global ocean. And it is indeed beginning: humans have already managed to reduce the alkalinity of the seas by 0.1 pH units. As Professor Ken Caldeira of the Carnegie Institution's global ecology department says: ‘The current rate of carbon dioxide input is nearly 50 times higher than normal. In less than 100 years, the pH of the oceans could drop by as much as half a unit from its natural 8.2 to about 7.7.’ This may not sound like much, but this half point on the pH scale represents a fivefold increase in acidity. And because the oceans circulate only very slowly, even if atmospheric carbon dioxide levels are eventually stabilised-perhaps because humanity wakes up to their warming effect-these changes in ocean chemistry will persist for thousands of years.

This fast-moving area of scientific research was the subject of a major report by the Royal Society in June 2005, which identified some of the main concerns that are increasingly keeping marine biologists awake at night. First and foremost is the possibility that even with relatively low future emissions during this century (equating to two degrees or less of temperature warming), large areas of the Southern Oceans and part of the Pacific will become effectively toxic to organisms with calcium carbonate shells after about 2050. With higher emissions, indeed, most of the entire global ocean will become eventually too acidic to support calcareous marine life.

The most important life-forms to be affected are those that form the bedrock of the oceanic food chain: plankton. Although individually tiny (only a few thousandths of a millimetre across), photosynthesising plankton like coccolithophores are perhaps the most important plant resource on Earth. They comprise at least half the biosphere's entire primary production-that's equivalent to all the land plants put together-often forming blooms so extensive that they stain the ocean surface green and can easily be photographed from space. The places where phytoplankton thrive are the breadbaskets of the global oceans: all higher species from mackerel to humpbacked whales ultimately depend on them. Yet coccolithophores have a calcium carbonate structure, and this makes them especially vulnerable to ocean acidification. When scientists simulated the oceans of the future by pumping artificially high levels of dissolved CO

into sections of a Norwegian fjord, they watched in dismay as coccolithophore structures first corroded, and then began to disintegrate altogether.

Acidification will also directly affect other ocean creatures. Crabs and sea urchins need their shells to survive, whilst fish gills are extremely sensitive to ocean chemistry-just as our lungs are to the air. Mussels and oysters, vitally important both as economic resources and as part of coastal ecosystems worldwide, will lose their ability to build strong shells by the end of the century-and will dissolve altogether if atmospheric CO

levels ever reach as high as 1,800 ppm (parts per million: this ppm measure means, very simply, that for every million litres of air there are 1,800 litres of carbon dioxide). Tropical corals, already badly hit by bleaching, will more and more be corroded by this increasing oceanic acid. Walk out to sea on a reef in 2090, and it may crumble beneath your feet. Ships, rather than being torn apart when they strike rocky coral, may find themselves ploughing through weakened reefs like sponge. Indeed, it's difficult to overstate just how dangerous an experiment we are now conducting with the world's oceans. As one marine biologist says: ‘We're taking a huge risk. Chemical ocean conditions 100 years from now will probably have no equivalent in the geological past, and key organisms may have no mechanisms to adapt to the change.’ Phytoplankton are also crucial to the global carbon cycle. Collectively they are the largest producer of calcium carbonate on Earth, removing billions of tonnes of carbon from circulation as their limestone shells rain down onto the ocean floor. There's nothing new about this process: the chalk in the cliffs and downs of southern England originally formed as the limey sludge from countless billions of dead coccolithophores back in the Cretaceous era. But as the oceans turn more and more acidic, this crucial component of the planetary carbon cycle could slowly grind to a halt. With fewer plankton to fix and remove it, more carbon will remain in the oceans and atmosphere, worsening the problem still further.

Phytoplankton are also hit directly by rising temperatures, because warmer waters on the surface of the ocean shut off the supply of upwelling nutrients that these tiny plants need to grow. As with acidification, changes are already detectable today: in 2006 scientists reported a decline in plankton productivity of 190 mega-tonnes a year as a result of the current warming trend. Together these two factors, warming and acidification, represent a devastating double blow to ocean productivity. As Katherine Richardson, professor of biological oceanography at Aarhus University in Denmark, says: ‘These marine creatures do humanity a great service by absorbing half the carbon dioxide we create. If we wipe them out, that process will stop. We are altering the entire chemistry of the oceans without any idea of the consequences.’

Wiping out phytoplankton by acidifying the oceans is rather like spraying weedkiller over most of the world's land vegetation, from rainforests to prairies to Arctic tundra, and will have equally disastrous effects. Just as deserts will spread on land as global warming accelerates, so marine deserts will spread in the oceans as warming and acidification take their unstoppable toll.

The mercury rises in Europe

Under normal circumstances, the human body is good at dealing with excess heat. Capillaries under the skin flush with blood, allowing the extra warmth to radiate into the air. Sweat glands pump out moisture, disposing of heat through evaporation. Heat can even be lost through panting, and the heart works overtime. During exercise, the normal body temperature of 37 degrees Celsius can rise to 38 or 39°C with no ill effects.

But 2003 was not a normal summer, and the heatwave experienced in Europe during the three months of June, July and August did not produce normal circumstances. In Switzerland the mercury climbed above 30°C as early as 4 June, rising to a maximum of 41.1°C in the south-east of the country on 2 August-the sort of searing temperature more often associated with the Arabian Desert than temperate central Europe. Across the continent, records tumbled: in Britain temperatures reached 100° Fahrenheit for the first time. Beaches were packed as holidaymakers enjoyed the summer heat, but in big cities like Paris, a hidden disaster was unfolding.

The first symptoms of heat stress may be minor. An affected individual will feel slightly nauseous and dizzy, and perhaps get irritable with those around. This needn't yet be an emergency: an hour or so lying down in a cooler area, sipping water, will cure early heat exhaustion with no longer-lasting symptoms. But in Paris, August 2003 there were no cooler areas, especially for elderly people cooped up in their airless apartments. It wasn't so much the high temperatures of the day, but the fact that things didn't cool down enough at night to give the body time to recover. The effects were cumulative, and the most dangerous-and often fatal-form of heat stress then became much more likely: hyperthermia or heatstroke.

Once human body temperature reaches 41°C (104°F) its ther-moregulatory system begins to break down. Sweating ceases, and breathing becomes shallow and rapid. The pulse quickens, and the victim may rapidly lapse into a coma. Unless drastic measures are taken to reduce the body's core temperature, the brain is starved of oxygen and vital organs begin to fail. Death will be only minutes away unless the emergency services can quickly get the victim into intensive care.

These emergency services failed to save over 10,000 Parisian heatstroke victims in the summer of 2003. Mortuaries quickly ran out of space as hundreds of dead bodies, mainly of elderly and marginalised people, were brought in each night. The crisis caused a political furore as people accused politicians and municipal administrators of being more concerned with their long August holidays than with saving lives in the capital. Estimates vary, but across Europe as a whole, between 22,000 and 35,000 people are thought to have died.

The heatwave and drought also devastated the agricultural sector: crop losses totalled around $12 billion, whilst forest fires in Portugal caused another $1.5 billion of damage. Major rivers such as the Po in Italy, the Rhine in Germany and the Loire in France ran at record low levels, grounding barge traffic and causing water shortages for irrigation and hydroelectric production. Toxic algal blooms proliferated in the denuded rivers and lakes. Melt rates on mountain glaciers in the Alps were double the previous record set in 1998, and some glaciers lost 10 per cent of their entire mass during the heat of that one summer. Meanwhile-as described in chapter 1-melting permafrost caused rockfalls in mountain areas like the Matterhorn.

It wasn't long before questions were asked about global warming's possible contribution to the disaster. Meteorologists who investigated past hot spells found that the 2003 heatwave was off the statistical scale-a one-in-several-thousand-year event. According to an analysis by UK-based climatologists, twentieth-century global warming has already doubled the risk of such a heatwave occurring. Right across Europe, according to research published in 2007, the frequency of extremely hot days has tripled over the last century, and the length of heatwaves on the Continent has doubled. The conclusion is stark: the 2003 summer hot spell was not a natural disaster.

The intensity of the heatwave also tells us something about the future. Averaged across the whole continent, temperatures were 2.3°C above the norm. So does that mean that in the two-degree world, summers like 2003 will be annual events? It seems so: in the UK-based study mentioned above, scientists used the Met Office's Hadley Centre computer model to project future climate change with increasing greenhouse gas emissions, and concluded that by the 2040s—when temperatures globally in their model are still below two degrees-more than half the summers will actually be warmer than 2003.

That means that extreme summers in 2040 will be much hotter than 2003-and the death toll will rise in consequence-perhaps reaching the hundreds of thousands. Elderly people may have to be evacuated for months at a time to air-conditioned shelters, and outside movement during the hottest part of the day will become increasingly dangerous. Temperatures may soar to highs commonly experienced today only in North Africa, as rivers and lakes dry up and vegetation withers across the entire continent. Crops which require summer rainfall will bake in the fields, and forests which are more accustomed to cooler climes will die off and burn. As a result, catastrophic wildfires may penetrate north into new areas, torching broadleaved forests from Germany to Estonia.

Here again the summer of 2003 gives us a glimpse of things to come. Europe-wide monitoring systems showed a 30 per cent drop in plant growth across the continent, as photosynthesis began to shut down in response to the twin stresses of high temperatures and crippling drought. From the deciduous beech forests of northern Europe to the evergreen pines and oaks of the Mediterranean rim, plant growth across the whole landmass slowed and then stopped. Instead of absorbing carbon dioxide from the air, the stressed plants instead began to emit it; around half a billion tonnes of carbon was added to the atmosphere from European plants, equivalent to a twelfth of total global emissions from fossil fuels. This is a positive feedback of critical importance, because it suggests that as temperatures rise-particularly during extreme heatwave events-carbon emissions from forests and soils will also rise, giving a further boost to global warming. And if these land-based emissions are sustained over long time periods and large areas of the Earth's surface, global warming could begin to spiral out of control, as the next chapter shows.

We may have come dangerously close to that point during the 1998-2002 mid-latitudinal drought in the northern hemisphere, which left plants withering through regions as far afield as the western US, southern Europe and eastern Asia. One study showed that carbon emissions which would normally have been taken up by plants instead accumulated in the atmosphere, explaining the abnormally large jumps in the atmospheric CO

concentration in following years. (Jumps which caused jitters among many climate change watchers about whether runaway positive feedbacks might have already begun.) Over a billion tonnes of extra carbon poured out of plants and soils in response to the drought and heat.

At the time of writing, the heatwave of 2003 has already begun to fade in people's memories, and the ‘normal’ summers of the following two years will have begun to soak up some of the extra carbon that entered the atmosphere during that deadly hot spell.

But we forget at our peril. The summer of 2003 was a ‘natural experiment’ whose conclusions should be taken very seriously. This wasn't just some output from a computer model, whose assumptions and projections can be legitimately challenged. It actually happened. Moreover, the near-repeat of the 2003 heatwave in the summer of 2006 suggests that if anything the models are underestimating the likely frequency and severity of future heatwaves.

We have been warned.

Mediterranean sunburn

Perhaps the most striking images from 2003's hot summer came from Portugal, where gigantic forest fires swept through the tinder-dry landscape, destroying orchards, torching houses and killing eighteen people. In total an area almost the size of Luxembourg was devastated. The conflagrations were so huge that they cast palls of smoke right over the North Atlantic, with both fires and smoke easily visible from space. The fires must have been particularly shocking for tourists, many of whom flock to southern Portugal from northern Europe-more in search of the sun than several days of smoke inhalation.

However, one study shows that such wildfires are going to be an increasingly common sight for holidaymakers to southern Europe and the Mediterranean. Climate change simulations show the region getting drier and hotter as the subtropical arid belt moves northward from the Sahara. In the two-degree world, two to six weeks of additional fire risk can be expected in all countries around the Mediterranean rim, with the worst-hit regions being inland from the coast where the temperatures are highest. In North Africa and the Middle East virtually the whole year will be classified as ‘fire risk’.

These fires will be driven on by scorchingly hot temperatures.

The number of days when the mercury climbs over 30°C is expected to increase by five to six weeks in inland Spain, southern France, Turkey, northern Africa and the Balkans. The number of ‘tropical nights’, when temperatures don't cool off past 20°C, will increase by a month, and the entire region can expect an additional four weeks of summer. A doubling of what the study calls ‘extremely hot days’ is also projected, whilst land areas around the Mediterranean can expect three to five additional weeks of ‘heatwaves’ (defined as days with temperatures over 35°C). Islands such as Sardinia and Cyprus only tend to escape the worst because of the cooling influence of the sea.

The high temperatures will be aggravated by drought, with areas in the southern Mediterranean projected to lose around a fifth of their rainfall. Spain and Turkey will also be badly affected, whilst northern areas on average see a 10 per cent decline in rainfall and a corresponding two-to three-week increase in the number of dry days. Up to a month extra of drought can be expected in southern France, Italy, Portugal and north-west Spain. The seasonality of rainfall will also change, playing havoc with agricultural practices: in southern France and Spain, for example, the dry season is projected to begin three weeks earlier and end two weeks earlier.

Air-conditioning may not always be an option: with peak power demand occurring during the driest part of the year when reservoir levels are already low, hydroelectric power outages could lead to blackouts during the worst heatwaves. Tourists-especially the elderly-will need to stay away because of the danger of heatstroke, whilst Mediterranean locals might actually prefer to spend summers far away in northern Europe in search of cooler temperatures. Lifestyles will have to change, with people perhaps adopting more Middle Eastern or North African living routines to cope with the heat.

Water shortages will become a perennial problem around the whole Mediterranean basin, particularly as some of the most arid coastal areas of Spain and Italy are also some of the most densely populated. Rich Germans and Britons thinking of retiring to Spain might be well advised to stay put. With searing heat and little fresh water to cool things off, perhaps the lure of the sun won't be so strong after all. The mass movement in recent decades of people from northern Europe to the Mediterranean is likely in the two-degree world to begin to reverse, switching eventually into a mass scramble to abandon barely habitable temperature zones-as Saharan heatwaves sweep across the Med.

The coral and the ice cap

Back in 1998, three Canadian geologists took a trip to the Cayman Islands. They were not there to sunbathe or launder money (two activities for which the islands are justly famous) but to investigate a strange raised limestone platform in the Rogers Wreck area of Grand Cayman island. The platform-known to geologists as the Ironshore Formation-is about 20 metres thick, and includes layers of ancient coral hundreds of thousands of years old. The formation sparked the scientists' interest because if they could date the coral accurately, its height above sea level today would help them solve a mystery about how sea levels had changed in the past. Tropical coral reefs form in shallow seas, so if old coral is now above sea level, only two explanations are possible: the land has risen, or the sea level has fallen. After meticulous investigation, the three scientists-Jennifer Vezina, Brian Jones and Derek Ford of the University of Alberta's Earth and Atmospheric Sciences department-ruled out land uplift and concluded that sea levels during the previous Eemian interglacial period were many metres higher than they are now.

The Canadian scientists' conclusion chimed with other studies from around the world, which have also suggested that sea levels were 5-6 metres above present during the Eemian, 125,000 years ago. Given that global temperatures were then about 1°C higher than now (though slightly higher in the Arctic, thanks to the polar amplification effect), this in turn raised another question: where had all the extra water come from?

First to come under suspicion was the West Antarctic Ice Sheet. Glaciologists had long suspected that it might be sensitive to small changes in temperature, and in total it contains enough ice to raise global sea levels by 5 metres. Indeed, as early as 1978 a paper in Nature warned that the ice sheet posed ‘a threat of disaster’-a warning which is even more pressing today, as chapter 4 reveals. But attempts to model ice sheet collapse had proven inconclusive, and in 2000 an entirely different contributor to sea level rise was proposed: Greenland.

The Greenland ice cap contains enough water in its 3-kilometre-thick bulk to raise global sea levels by a full 7 metres, and when scientists investigated cores drilled from the summit of the ice sheet they reached a surprising conclusion. Greenland had indeed shrunk significantly during the Eemian-so much so in fact that most of the southern and western part of the landmass had been completely free of ice for thousands of years. Indeed, evidence has recently emerged that Greenland was once forested in regions that are now under two kilometres of ice-although this may have been in an earlier (and slightly warmer) interglacial than the Eemian. With a lower summit, steeper sides and a drastically reduced extent, the Eemian ice sheet would have contributed, the scientists concluded, between 4 and 5.5 metres to higher global sea levels at the time. This, together with smaller contributions from Antarctica and other glaciers, plus some thermal expansion of seawater, would seem to explain the high sea levels.

The study raised a few academic eyebrows at the time, but its implications didn't really begin to sink in until several years later. In retrospect, this is perhaps surprising: it contained clear evidence that a climate only a degree or so warmer than today could melt enough Greenland ice to drown coastal cities around the globe, cities that are home to tens of millions of people. Nor was it just a one-off: more recent work confirms that Greenland's contribution to the higher sea levels of the Eemian was indeed somewhere between 2 and 5 metres.