Six Degrees: Our Future on a Hotter Planet. Mark Lynas

of Iberia. At the time of writing, tropical meteorologists have yet to dissect the unusual combination of factors responsible for Vince, but again the implication is clear: as global warming accelerates, past experience about areas of hurricane formation is not necessarily a reliable guide to the future. Many more hurricane forecasters may be left scratching their heads before they finally admit that not just Brazil but now Europe is already vulnerable to these terrifying storms.

      Indeed, there is now evidence for how this might happen: a paper published in July 2007 by Spanish and German climatolo-gists, looking at simulated storms in a computer model, suggests that the whole of the Mediterranean may soon come into the firing line as sea temperatures climb to levels able to spark off genuine tropical cyclones-in a region which has never seen them before. The greatest number of virtual cyclones appeared in the hottest part of the Mediterranean, between Italy and Libya, and once formed, the powerful storms lasted for a week or more.

      One computer-generated hurricane formed in the eastern part of the Mediterranean, and then wandered westward all the way to the southern coast of France-much to the amazement of the watching scientists. Another storm formed a tight, symmetrical eye of torrential rain, just as real tropical cyclones do. The idea that once-placid coastlines from Spain to Cyprus could be at risk of landfalling hurricanes in a globally-warmed future has to be one of the most striking projections ever to come from the climate modelling world.

      But already real-world evidence is fast emerging that hurricane characteristics are changing as the world's oceans warm up. One of the grandfathers of tropical cyclone physics, Massachusetts Institute of Technology's Kerry Emanuel, recently published a paper in Nature that caused its own academic storm. In contrast to the usual view that global warming is still too small a signal to have a measurable impact on tropical cyclones, Emanuel looked again at the data and concluded that storms were in fact getting more intense and lasting for longer, due in large part to rising sea temperatures driven by global warming. The storm intensity index hadn't simply gone up by a few percentage points over the last 30 years, either, it had actually doubled-a far greater increase than either theory or modelling had predicted.

      Emanuel's data and methods have since been challenged in an academic discussion too technical to analyse here, but it is worth noting that his conclusions are supported by a second piece of work, this time published in Science by a team of experts based at the Georgia Institute of Technology in Atlanta. Analysing much of the same storm data-collected by aircraft, satellites and ships over the past three decades-this scientific team identified a large increase in the number and proportion of those hurricanes reaching the strongest categories 4 and 5, despite an overall decrease in the number of cyclones.

      Like Emanuel, the team were looking at data from the Pacific as well as the Atlantic Ocean in order to build up a global picture. And like him (though using a different statistical measure), they found a near-doubling in the number of the strongest storms between 1970 and 2004. The Georgia team concluded that the upswing in Category 4 and 5 hurricanes is unlikely to be the result of natural climate cycles, but instead is probably connected to rising temperatures in the tropical oceans.

      A year later, after the record-breaking 2005 Atlantic hurricane season-which left 1,000 people dead, 1 million homeless, and caused $200 billion of damage-two leading climatologists tried to settle the argument about whether or not global warming had contributed to the run of disastrous storms. Noting that the warm sea temperatures measured that year-the highest ever-undoubtedly contributed to the ferocity of Katrina, Wilma, Rita and the other 2005 storms, Kevin Trenberth and Dennis Shea used complex maths to figure out how much of the Atlantic warming signal was due to global warming, and how much to natural cycles. Their conclusion should be a wake-up call to us all: at least half of the extra warmth had come from human-caused global warming. As so many people suspected at the time, Katrina was only partly a natural disaster.

       Sinking atolls

      I hate to put this so bluntly, but in all probability nothing can save the Pacific island of Tuvalu. Like a slowly boiling kettle, the oceanic system has very long response time to changing conditions, and the seas will go on slowly rising for centuries even if all greenhouse gas emissions stopped tomorrow. With Tuvalu already experiencing regular flooding events due to past sea level rise-as I documented in High Tide-this extra rise in the world's oceans will sound the death knell for this fascinating and lively island society.

      Tuvalu, with only 9,000 inhabitants, is actually one of the smallest of the five atoll nations which will shortly cease to exist. The others are Tuvalu's sister atoll group Kiribati, with 78,000 population, the Marshall Islands, with 58,000 people, tiny Tokelau (2,000 people; a dependent territory of New Zealand) and the Maldives, the largest and most densely populated of all the island groups, with 269,000 inhabitants. Together with people displaced from coastal areas of other non-atoll islands, this already totals about half a million people who-suddenly divorced from their cultures and their origins-will need to find new homes. New Zealand has hesitantly offered to take a small number of Tuvaluans, but no other nations have yet stepped up to offer themselves as places of refuge, least of all those rich countries who have done most to cause the problem in the first place.

      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°

2 TWO DEGREES

       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