Weeds likely to thrive.

WASHINGTON AP - If you can't stand global warming, get out of the tropics. While the most significant harm from climate change so far has been in the polar regions, tropical plants and animals may face an even greater threat, say scientists who studied conditions in Costa Rica.

"Many lowland tropical species could be in trouble," the team of researchers, led by Robert K. Colwell of the University of Connecticut, warns in Friday's edition of the journal Science.

"The tropics, in the popular view, are already hot, so how could global warming harm tropical species? We hope to put this concern on the conservation agenda," Colwell said.

That's because some tropical species, insects are an example, are living near their maximum temperatures already and warmer conditions could cause them to decline, Colwell explained.

"We chose the word 'attrition' to emphasize slow deterioration," he said. "How soon that will be evident enough for a consensus is difficult to say."

But the researchers estimated that a temperature increase of 5.8 degrees Fahrenheit (3.2 Celsius) over a century would make 53 percent of the 1,902 lowland tropical species they studied subject to attrition.

That doesn't mean today's jungles will one day be barren, however.

"'Tis an ill wind that blows nobody any good. Some species will thrive," Colwell said. "But they are likely to be those already adapted to stressful conditions," such as weeds.

What of the others?

There are few nearby cooler locations for tropical plants and animals fleeing rising temperatures.

In the tropics in particular, going up rather than out may be an answer.

That's because tropical species with small ranges would have to shift thousands of kilometers north or south to maintain their current climatic conditions. "Instead," Colwell said, "the most likely escape route in the tropics is to follow temperature zone shifts upward in elevation on tropical mountainsides."

For example, moving uphill, the researchers said, temperature declines between 9.4 degrees Fahrenheit (5.2 C) and 11.7 degrees (6.5 C) for every 3,280 feet (1,000 meters). To get a similar reduction moving north or south, species would have to travel more than 620 miles (1,000 kilometers).

Of course moving won't work for everyone; species already living on mountaintops will have no place to climb....