Global warming affects tropical life more

SEATTLE, Oct. 7 (UPI) -- Global warming is greatest in the Northern Hemisphere but its impact on life could be much greater in the tropics, a U.S. study says.

Even with smaller increases in temperature in the world's tropical zones, those regions could see greater impacts on life, ranging from shifting geographic ranges to species extinction, says Michael Dillon, an assistant professor of zoology and physiology at the University of Wyoming.

A study focused on ectothermic, or cold-blooded, organisms, those whose body temperature approximates the temperature of their surroundings.

Researchers charted temperature increases from 1961 through 2009, then examined the effect of those increases on metabolism. Metabolic changes are key effects of climate warming because a higher metabolic rate requires more food and more oxygen, study co-author Raymond Huey, a University of Washington biology professor, says.

"Metabolic rate tells you how fast the animal is living and thus its intensity of life," Huey said.

Since metabolic rates for cold-blooded animals increase faster as temperatures rise, organisms in the tropics show greater effects from global warming because they start at much higher temperatures than animals in the Arctic.

Research has shown that small temperature changes can push tropical organisms beyond their optimal body temperatures and cause substantial stress, while organisms in temperate and polar regions can tolerate much larger increases because they already are used to large seasonal temperature swings, scientists say.

"Just because the temperature change in the tropics is small doesn't mean the biological impacts will be small," Huey said. "All of the studies we're doing suggest the opposite is true."