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

of protea species would become threatened or endangered, whilst four would become completely extinct.

      In North America too, one degree of climate change could push a threatened species over the brink to extinction-and this one is cute and furry According to WWF, pikas-small, hamsterlike creatures with rounded ears and bushy whiskers-are the first mammal to be endangered by climate change. Pikas live in broken rock on high mountains in the western US and south-western Canada, and are notable not just for being cute and furry, but for their agricultural activities: these small relatives of the common rabbit cut, sun-dry and then store vegetation for winter use in characteristic ‘haypiles’ on top of rocks. (As a charismatic species, pikas have acquired quite a cult following: check out www.pikaworks.com for everything from pika music to pika mouse mats.)

      However, as the climate warms, pikas-timid beasts, which never stray more than a kilometre from their nests-are set to become increasingly isolated in ever-smaller geographical islands as temperature zones migrate upwards towards the summits. Already local extinctions have been documented at sites in the United States. As the ecologist and pika enthusiast Dr Erik Beever puts it: ‘We're witnessing some of the first contemporary examples of global warming apparently contributing to the local extinction of an American mammal at sites across an entire eco-region.’

      It has become something of a cliché to talk about the ‘canary in the coal mine’ when discussing climate impacts on the natural world-but one group of animals more than any other exemplifies this point: the amphibians. With their moist skins and early lives in water, frogs, salamanders and toads are particularly vulnerable to changes in their environment. Indeed, an amphibian-the Costa Rican golden toad-is often cited as the first known case of a global warming extinction.

      Once the ‘jewel in the crown’ of Costa Rica's Monteverde Cloud Forest (to paraphrase the scientist and author Tim Flannery), this Day-Glo orange amphibian was observed in its hundreds back in 1987, gathered around pools in the forest in preparation for mating. But there were already signs of danger: the amphibian expert Marty Crump, who witnessed this last golden toad mating frenzy, also watched the resulting eggs get left behind as the forest pools dried. Only twenty-nine tadpoles lasted out the week, whilst 43,500 eggs were left desiccated and rotting. The following year Crump found only a single, solitary male, and a year later, in 1989, the same male was back once more. That day, 15 May 1989, was the last time anyone saw a golden toad. The species was eventually listed as extinct in 2004. The cause of death seems to have been the general lifting of the mist that nourishes the forest with moist cloud droplets: as the air surrounding the mountains warmed, the cloud base simply rose too high above the forest, allowing the golden toad's spawning pools to dry out.

      This memorable animal may be the first, but it is no longer the only amphibian to have gone extinct because of rising temperatures: frog populations have crashed all around the tropics, with more than 100 out of 110 tropical American harlequin frog species having disappeared-even in seemingly pristine forests far away from direct human disturbance. No one knows exactly why: some biologists blame the chytrid fungal pathogen, which is invading new areas and may be causing sudden population crashes. Others blame mystery diseases which are so far undiscovered and unidentified. But experts are largely agreed on one thing: rising temperatures are central to the extinction epidemic, either by helping the new diseases spread, or by stressing amphibian populations and making them more susceptible to die-offs. In this particular murder scene, the weapon may still be in dispute but the overall culprit is clear.

      Nowhere, it seems, is safe. One degree of global warming will have severe impacts in some of the world's most unique environments, adding to the biodiversity crisis which is now well under way for reasons unrelated to our changing climate. Pushed out to the margins and isolated in smaller and smaller pockets of natural habitat by ever-expanding zones of human influence, vulnerable wild species will find it impossible to adapt to rapidly changing temperatures by migrating or altering their behaviour.

      Whilst coral reefs have a vital role in protecting coastlines from storms and nurturing fisheries, no one can reasonably claim that pikas, proteas and harlequin frogs are essential for global economic prosperity. Their value is intrinsic, not financial. But the world will still be a much poorer place once they're gone.

       Hurricane warning in the South Atlantic

      With all the headlines about hurricanes hitting the United States, there is one storm that stands out above all others in the way that it caught the scientific community off guard. It wasn't Katrina, which devastated New Orleans and killed over a thousand people. It wasn't Rita, another Category 5 monster which reflooded parts of the city only a month after Katrina struck. Nor was it Hurricane Wilma, which bombed in a single day from being a minor tropical storm into the strongest hurricane ever recorded in the Atlantic basin. No, the storm that really made the forecasters scratch their heads occurred a year earlier, in 2004. And it hit in a part of the world that isn't supposed to experience hurricanes. It was called Catarina, and it struck the coast of Brazil.

      Received scientific wisdom holds that hurricanes can only form where sea surface temperatures top 26.5°C. As well as warm oceans, tropical storms also need low ‘wind shear’: cross-winds at high altitude which can cut the vortex of a developing storm in half. These conditions, as any weatherman can tell you, only occur in the North Atlantic tropics. Not a single South Atlantic hurricane had ever been documented-that is, before March 2004. Indeed, when a strange swirl of clouds began to form off the Brazilian coast on 20 March 2004, local meteorologists couldn't quite believe their eyes. So unheard of was a South Atlantic hurricane that many of them were still refusing to employ the term ‘hurricane’ when Catarina-complete with 95 mph winds and torrential rain-swept ashore near the town of Torres, damaging 30,000 houses and killing several people. Many of those who suffered, because they also refused to believe that hurricanes were possible in Brazil, had neglected to take shelter as the storm barrelled towards the shore.

      In the inevitable meteorological post-mortem, it did indeed look as if the storm was simply a freak, a once-in-a-lifetime experience for those who suffered it. What was strange was that sea temperatures had not been unusually high when it began to gather strength. Instead, what really gave Catarina a boost was a very rare combination of other atmospheric factors which meant that the storm's vortex experienced very little of the deadly wind shear which normally precludes hurricane formation in the South Atlantic. It's a complex picture, but raises an obvious question: will global warming, as well as making the seas warmer and therefore more likely to spark hurricanes, lead more regularly to the conditions which allow tropical cyclones to gather strength in new areas like the South Atlantic?

      Two Australia-based meteorologists, Alexandre Bernardes Pezza and Ian Simmonds, addressed this question in their forensic dissection of Catarina which was published in August 2005 by the journal Geophysical Research Letters. Their conclusion was tentative, but contained an alarming prospect: it did indeed seem as if the warming atmosphere would favour the conditions which allowed Catarina to form in such an unusual place. ‘Therefore,’ they wrote, ‘there is evidence to suggest that Catarina could be linked to climate change in the southern hemisphere circulation, and other possible future South Atlantic hurricanes could be more likely to occur under global warming conditions.’

      Given that if just 0.8°C of global warming so far has already allowed one hurricane to form, a further degree of global warming could make storms in this vulnerable region much more likely in the future. Not only will Brazilians have to batten down the hatches-and perhaps evacuate large areas of their heavily populated coastline-more often, but hurricane-forecasting services will need to be extended to a whole new oceanic basin.

      The hurricane season in the following year, 2005, also contained a surprise, which suggests that Brazil is not the only area which will have to keep an eye out for tropical cyclones in our globally warmed future. On 9 October 2005 a new tropical storm appeared about five hundred miles south-east of the Azores, in the East Atlantic, and rapidly gained strength to hurricane status as it drifted past Portugal's Madeira Islands. Hurricane Vince luckily weakened before it made landfall near Huelva in Spain, but set a new record as the first tropical cyclone ever to affect Europe.

      Again, conventional wisdom has it that tropical storms can only form over warmer waters thousands of kilometres to the southwest