Polar bears fighting for survival in the face of a rapid decline of polar ice have made the Arctic a poster child for the negative effects of climate change. But new research shows that species living in the tropics likely face the greatest peril in a warmer world.

A team led by University of Washington scientists has found that while temperature changes will be much more extreme at high latitudes, tropical species have a far greater risk of extinction with warming of just a degree or two. That is because they are used to living within a much smaller temperature range to begin with, and once temperatures get beyond that range many species might not be able to cope.

"There's a strong relationship between your physiology and the climate you live in,"

"In the tropics many species appear to be living at or near their thermal optimum, a temperature that lets them thrive.

above the thermal optimum, fitness levels most likely decline quickly and there may not be much they can do about it."