Climate change scenarios are tough to predict because the Earth is such a complex system. But scientists can point to several weak links in parts of the planet where climate change could bring about the sudden, catastrophic collapse of important ecosystems, even at a rise of 3C.

· If we continue to burn fossil fuels at current rates, levels of carbon dioxide in the atmosphere will reach 550 ppm (parts per million) - double pre-industrial levels - by around 2050. A 2001 report by the Intergovernmental Panel on Climate Change, the group of climate experts who summarise the latest thinking in climate science for policy makers, said this would increase global temperatures by between 1.4 and 5.8C by 2100, and that sea levels would rise by between 0.09 and 0.88 metres (3.5 to 35in). This rise could lead to several major catastrophes.

· The Greenland ice sheet, which holds about 2.6 million cubic kilometres of fresh water (around 6% of the world`s supply) will start to melt. At 3C, it will begin releasing all that water - currently resting on land - into the north Atlantic Ocean. According to scientists at the Hadley Centre, the UK`s foremost experts in climate modelling, sea levels around the world would rise at 5mm (0.2in) a year (compared with 1-2mm a year at the moment). This is in addition to any sea level rise due to other effects of global warming.

· Methane hydrates are structures made of frozen methane gas locked in water ice. More than twice the amount of carbon present in fossil fuel reserves is stored in these blocks of ice living at the bottom of some of the coldest oceans. The Hadley Centre says that even any global temperature rises could penetrate deep into the oceans and, even if they destabilised a small fraction of the methane, it could lead to a rapid increase in global warming.

· The giant West Antarctic ice sheet, up to a kilometre thick in places, might not disappear completely as some might fear but recent history should be a warning. Two years ago, a vast chunk, the Larsen B ice shelf, fragmented into icebergs. In just 35 days, about 3,250 square kilometres of ice was lost. The size of the entire shelf is now roughly 40% the size at which it had previously stabilised. It will not take huge increases to continue this decline. If the entire sheet melted, sea levels around the world could rise by 6m, putting many coastal towns and habitats under water and raising the risk of flooding in others.

· In February, the IPCC warned that estimates of temperature increase might be underestimating the problem. Their previous estimates suggested increases of between 1.5 and 4.5C but new computer models have foreseen rises as high as 11C.
(The Guardian, 15/04/2006)
http://www.guardian.co.uk/climatechange/story/0,,1754291,00.html