— Climate change maps, showing that novel climates are projected for tropical and subtropical regions, and disappearing climates are predicted to be concentrated in tropical mountains and the poleward regions of continents (Image: John Williams et al)
Within a century, half of the world's climates as we know them will have vanished forever as a direct result of global warming, taking thousands of species with them.
These are the gloomy projections of John Williams at the University of Wisconsin at Madison, US, and colleagues, who have carried out the first global assessment of how all of the Earth's local climates will be affected as the world heats up.
New, previously unseen types of climate will also emerge, they say, with hotter temperatures and more rain.
Its the coldest climates that would be replaced, Williams says. They would be similar, in 100 years time, but several degrees warmer, so glaciers would retreat and ice would disappear from mountains such as Kilimanjaro in Tanzania.
New types of climate would emerge in more tropical regions, particularly the Amazon and Indonesian rainforests. What were concerned about is what happens to the species in these regions, says Williams. The only options are migrating or adapting, but some will have nowhere to migrate to, or will be out-competed by invading species.
Williams's team assessed the effects of warming on local and global climates using the latest projections developed by the Intergovernmental Panel on Climate Change for high and low emissions of carbon dioxide, the main greenhouse gas.
Comparing best and worst outcomes, the team estimates that 20% to 39% of the worlds land would develop completely novel climates, and existing climates would vanish in 20% to 48% of land area. Theres a big difference, so reductions in carbon dioxide do give cause for hope, says Williams.
A previous study, carried out in 2004, estimated that 15% to 37% of the world's species would be committed to extinction by the year 2050 (see Global warming threatens millions of species).
"The new study extends that  analysis and uses the latest climate change projections to highlight areas where current climates might disappear and novel climates may arise," says Andrew Watkinson, a climate researcher at the University of East Anglia in the UK, who was not involved in the research.
"As expected, disappearing climates are likely to be concentrated in tropical mountain regions and towards the poles, while novel climates will develop primarily in the tropics and sub-tropics."
Watkinson says that protecting biodiversity in the face of a changing climate is an enormous challenge, especially as climate change is not the only stressor. "Many of the areas highlighted in this paper are also subject to some of the greatest land use changes, especially in terms of deforestation."
Journal reference: Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas.0606292104)