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

police managed to clear the area of holidaymakers just before the mass of rocks and mud washed by.

      When he heard about the two near-disasters, the glaciologist Wilfried Haeberli had no doubts about the cause. ‘The Matterhorn relies on permafrost to stay together,’ the Zurich University scientist told reporters. But Switzerland had just been suffering its strongest-ever heatwave. With the fierce summer heat having melted all the winter snow much earlier than usual, the permafrost and glaciers themselves were beginning to melt down. Once that process begins, Haeberli warned, ‘water starts to flow, and large chunks of rock begin to break away from the mountain’.

      Most ground in the Alps above about 3,000 metres remains permanently frozen throughout the year, and is anchored, as Haeberli says, by permafrost. But in the summer of 2003 the melt zone reached as high as 4,600 metres-higher than the summit of the Matterhorn, and nearly as high as the top of Mont Blanc, western Europe's highest mountain. And whilst the Matterhorn climbers were lucky to get down safely on 15 July, at least fifty other climbers were less fortunate during that boiling summer-most were killed by falling rocks.

      Haeberli, a world expert on permafrost, has since co-written a scientific paper on the impacts of the 2003 hot summer in the Alps. He and colleagues calculated that the thaw experienced during that heatwave outranked anything the mountains had suffered in recent history, and that most rock fall as a result took place during the hottest months of June, July and August.

      They also found that the 2003 thaw penetrated up to half a metre deeper into the rock than any thaw during the previous two decades.

      Surprisingly, however, the worst rockfalls didn't take place on sunny slopes where the direct heat was strongest, but on shaded northern faces, where the high air temperature penetrated the mountain. Ominously, the study concludes that with one degree of further global warming, more permafrost degradation in the Alps is unavoidable. ‘Widespread rockfall and geotechnical problems with human infrastructure are likely to be recurrent consequences of warming permafrost in rock walls due to predicted climatic changes,’ Haeberli and his colleagues warn. ‘The extreme summer of 2003 and its impact on mountain permafrost may be seen as a first manifestation of these projections.’

      As mountain slopes thaw out and fail, whole towns and villages will be at risk of destruction in the Alps and other mountain regions. Some towns, like Pontresina in eastern Switzerland, have already begun building earthen bulwarks to guard against deadly landslides from the melting slopes above. But many more will remain unprotected and unprepared-until the worst happens, bringing death crashing down from above, suddenly and with no warning. Moreover, this won't be the only danger associated with mountains in the warming world: as later chapters show, just as dangerous will be the likelihood of running out of life's most precious resource-water.

       Queensland's frogs boil

      No one could accuse the Australian authorities of not taking their responsibility to protect the Queensland Wet Tropics rainforest seriously. Visitors must stay on walking tracks at all times. Fuel for stoves must be brought in, as campfires might disturb the delicate nutrient cycle of the forest. Every tuft of moss, leaf and twig is protected: removing living materials is a criminal offence. Dogs and cats are banned, as are soap, toothpaste and sunscreen, in case these chemicals leach into streams and harm aquatic animals. And you're most certainly not allowed to swing from vines in the trees.

      There is good reason for this intense conservation focus. Recognised since 1988 as a UNESCO World Heritage Site, seven hundred species of plants are found nowhere else on Earth. The Wet Tropics ecosystem contains many species that are unique relicts from ancient rainforests which once grew on the Gondwanan supercontinent 120 million years ago. Many of the same fern species which are still found there today were once grazed by dinosaurs. Amazing carnivorous plants-like pitcher plants and sundews-poke out from the forest floor. Pythons wind around branches, whilst skinks and geckos scurry across rocks and up tree trunks. Thirteen mammal species-including tree kangaroos and ringtail possums-are also unique to the Wet Tropics region. Overall the area is home to a quarter of Australia's frogs, a third of its freshwater fish, and nearly half of its birds-all on a fraction of 1 per cent of the continent.

      Yet there is one threat which the Australian authorities are powerless to prevent-and indeed have actively conspired to ignore. It comes not from feral pigs or cane toads, nor even from a thousand swinging, littering, tooth-brushing humans. This threat comes as the climate which sustains the forests-in some areas with a staggering 8 metres of annual rainfall-gradually begins to warm up. It turns out that the Queensland Wet Tropics rainforest is one of the most sensitive areas on the planet to climate change. Just one degree of warming will have devastating impacts on species diversity and habitats.

      The reason lies in the unusual topography of the Wet Tropics area. Unlike the Amazon forest, which covers a huge, flat basin until it rises into the eastern slopes of the Andes, the Queensland rainforest comprises hilly terrain-starting from the white sands fringing the ocean to heights of 1,500 metres or more in places. Many of the species which are unique to the area are found only above certain heights: there's a ring-tailed possum which is only found above 800 metres in altitude, and many birds, reptiles and frogs only live at the tops of mountains. As the climate warms, temperature zones rise up the mountainsides, squeezing these species into diminishing islands of habitat-and eventually leaving them with nowhere to live at all. They, like the polar species in the Arctic, will have been literally pushed off the planet.

      Dr Steve Williams, of James Cook University's School of Tropical Biology, has been warning for years about the dangers that even small degrees of climate change pose to the Wet Tropics rainforest. Williams-who leads teams of Earthwatch volunteer helpers on his survey trips-has conducted 652 bird surveys, 546 reptile surveys, 342 frog surveys, and at various times set around 50,000 night traps to catch small mammals. Armed with this voluminous wildlife data, he ran a computer model representation of the area under a changing climate and studied the results to see what happened. Even with just a one-degree rise, the results were dramatic. In particular, 63 of the 65 modelled species lost around a third of their core environment. One species of microhylid frog, which instead of having tadpoles in ponds lays its eggs in moist soil, is predicted to go extinct altogether. With higher degrees of warming, rates of biodiversity loss become increasingly dramatic, adding up, in Williams's words, to ‘an environmental catastrophe of global significance’.

      Nor are animal species the only ones affected. A similar modelling study by David Hilbert of the CSIRO Tropical Forest Research Centre concluded that one degree of warming would reduce the area of highland rainforest by half, wiping out the habitat of many of the rare animal species mentioned above. Rainforests as a whole won't disappear from Queensland as long as the region receives high rainfall, but without these precious throwbacks to an ancient supercontinent, today's world will be immeasurably poorer. Moreover, Australia's national government, which refused for over a decade to take global warming seriously, will have failed in its international duty to protect a UNESCO World Heritage Site.

      Just a few miles offshore from the sparkling white sands of the Queensland coast lies another threatened World Heritage Site: the Great Barrier Reef. This is the biggest and most pristine of all the world's coral reefs, a massive subsea wall of coral which is the largest natural feature on Earth, stretching more than 2,300 km along the north-east coast of Australia. One of the most spectacular and diverse ecosystems on the planet, the reef is home to 1,500 species of fish, 359 types of hard coral, 175 bird species and more than 30 types of mammal. It is one of the last refuges of the dugongs (sea cows) and hosts six of the world's seven species of threatened marine turtle.

      But the oceans around the Great Barrier Reef are warming-as they are all over the planet-threatening to tip this unique ecosystem into irreversible decline. Coral reefs are actually the external skeletons produced by billions of tiny coral polyps, which secrete calcium carbonate into branches, fans and globes. These constituents in turn combine over thousands of years to form a reef. Each polyp contains algae, tiny plants which live in symbiosis with their animal hosts. Both parties benefit-the coral gets the sugars which the algae produce by photosynthesising light (turning it into energy), whilst the algae derive fertility from the polyp's waste products. But this cosy relationship can only continue in the right aquatic conditions: once the corals' thermal