Warming climate may slam many species.

Expected increases in global temperature could eradicate from a sixth to a half of the plant and animal species across large areas of the globe, scientists say.

Climate change over the past 30 years has produced significant shifts in the population sizes and the geographical distributions of many species, says Chris D. Thomas, an ecologist at the University of Leeds in England. He and his colleagues recently used mapping techniques to discern population and distribution trends of 1,103 selected plant and animal species that live in parts of Mexico, Australia, South Africa, Europe, and the Amazon rain forest. The areas studied account for 20 percent of the Earth's land surface.

If the average global temperature rises between 0.8[degrees]C and 1.7[degrees]C by 2050--the minimum expected change, say the researchers--13 percent of the species studied could become extinct or so reduced in number that they couldn't recover. Those figures assume that all of the plants and animals would be free to move to suitable habitats in the new climatic regime. If species couldn't migrate because of factors such as habitat fragmentation, then up to 31 percent of the species studied could be wiped out.

For global temperature increases greater than 2[degrees]C, the picture is grimmer: About one-third of those species that move to more suitable settings could still succumb, and a whopping 52 percent could eventually become extinct if no migration were to occur.

Assuming the species in the study are representative of most plants and animals in the areas studied, even the least deadly cases of climate change could wipe out more than 1 million species, the researchers warn in the Jan. 8 Nature.--S.P.