A nomad woman walks past a desert tree near Chinguetti, Mauritania. Research shows a host of trees retreating from an arid region south of the Sahara Desert over decades, with trees losing ground to more arid species.

Washington ? Some climates may disappear from Earth entirely, not just from their current locations, while new climates could develop if the planet continues to warm, a study says.

Such changes would endanger some plants and animals while providing new opportunities for others, said John W. Williams, an assistant professor of geography at the University of Wisconsin, Madison.

Using global change forecasts prepared for the Intergovernmental Panel on Climate Change, researchers led by Williams used computer models to estimate how climates in various parts of the world would be affected. Their findings are being published in this week’s online edition of Proceedings of the National Academy of Sciences.

The IPCC, representing the world’s leading climate scientists, reported in February that “warming of the climate system is unequivocal, as is now evident from observation of increases in global average air and ocean temperatures, widespread melting of snow and ice and rising global average sea level.”

Tropical regions may face unexpected changes, particularly the rain forests in the Amazon and Indonesia, Williams’ researchers concluded.

This was surprising, Williams said in a telephone interview, since the tropics tend to have little variation in weather.

But that also means temperature changes of 3 or 4 degrees in these regions might have more impact than a change of 5 to 8 degrees in a region that is accustomed to regular changes.

Species living in tropical areas may be less able to adapt, he said, adding that that is speculative and needs further study.

Areas like the Southeastern United States and the Arabian Peninsula may also be affected, the researchers said.

And they said mountain areas such as in Peruvian and Colombian Andes and regions such as Siberia and southern Australia face a risk of climates disappearing altogether.

That doesn’t mean these regions would have no climate at all – rather their climate would change and the conditions currently in these areas would not occur elsewhere on Earth.

That would pose a risk to species living in those areas, Williams observed.

If some regions develop new climates that don’t now exist, that might provide an opportunity for species that live there, Williams said. “But we can’t make a prediction because it’s outside our current experience and outside the experience of these species.”

Alan Robock, a professor of environmental sciences at Rutgers University welcomed the report, calling it the first he has seen “that not only looks at species extinctions, but also looks at regions where novel climates will appear.”

“The potential consequences and how these new regimes will be populated are poorly known, and the potential for new threats to humans through disease vectors could be a real danger,” he said.