by James Randerson

By the end of the century up to two fifths of the land surface of the Earth will have a hotter climate unlike anything that currently exists, according to a study that predicts the effects of global warming on local and regional climates. And in the worst case scenario, the climatic conditions on another 48% of the land surface will no longer exist on the planet at all.The changes - which will have a devastating affect on biodiversity hotspots such as the Amazonian and Indonesian rainforests - will wipe out numerous species that are unable to move to stay within their preferred climate range. These species will either have to evolve rapidly or die out.

"There is a real problem for conservation biologists," said the lead author, John Williams, at the University of Wisconsin in Madison. "How do you conserve the biological diversity of these entire systems if the physical environment is changing and potentially disappearing?"

Studies already suggest that the ranges of species are shifting towards the poles at around six kilometers a decade, but what will happen when the rate of change intensifies?

His team used emissions scenarios set out by the Intergovernmental Panel on Climate Change (IPCC) - the international scientific group that advises policymakers - to predict where changes in temperature and precipitation will occur.

As is already happening, the analysis predicts that as the planet warms climate zones will move north and south towards the poles. To work out the significance of these changes, the team compared them with the climate variation that occurs naturally. They attach greater weight to changes in regions that are relatively stable. This suggests that some of the worst impacts will happen in tropical and subtropical regions as they shift to new climatic conditions not currently seen.

"That's one of the things that really surprised us," said Professor Williams. "The tropics have very little variability from year to year in temperature, they are a very stable climatic zone. So species that live in those climates expect a limited degree of variability." Other studies have suggested that the Amazon basin, an extremely biologically rich region, will be at increased risk of forest fires because of its hotter and dryer climate.

"One of the things that comes from our paper is that because the species that live in the tropics are adapted or have evolved for a reduced range of variability, it may be that a two to three degree temperature change in the tropics may be more significant than say a five to eight degree change in high latitudes," he added.

Up to now, much of the focus of the impact of global warming has been on polar regions because this is where the climate is changing fastest." At the other end of the scale are climatic regions that will be lost from the planet altogether.

The climate model predicts that these disappearing climates will be lost mainly from tropical mountains and the edges of continents nearest the poles.

As the Earth warms, these climate regions simply have nowhere to shift to. Some of the losers are the tropical Andes, the African Rift mountains, the Zambian and Angolan highlands, the South African Cape region, south-east Australia, parts of the Himalayas and the Arctic.

The team reports in Proceedings of the National Academy of Sciences that by 2100, between 12% and 39% of the land surface of the Earth will have a new climate, while the combination of climatic conditions on 10%-48% of the planet will have disappeared altogether. This is using one of the IPCC's business-as-usual global development scenarios. Using a different scenario that assumes more environmentally friendly development, the corresponding predictions are 4% to 20%.

The true effect on species may be more than these numbers suggest, though, because even if a climate still exists somewhere, it is no use unless a species can migrate fast enough to follow it as it shifts. One study published in 2004 predicted that 15% to 37% of species could be driven extinct between now and 2050 assuming moderate climate warming. Globally, this would mean the loss of more than 1 million species.
© Guardian News and Media Limited 2007