WASHINGTON : The most significant harm from climate change so far has been in the world ' s polar regions , but 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 is because some tropical species , insects as an example , are living near their maximum temperatures already ; 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 does not 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 is 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 will not work for everyone ; species already living on mountaintops will have no place to climb . The study provides an important illustration of the potential risk to tropical species from global warming , Jens - Christian Svenning of the University of Aarhus , Denmark , and Richard Condit of the Smithsonian Tropical Research Institute note in a commentary on the findings . " These numbers suggest large risks , " but are likely to be controversial because there remain large gaps in the knowledge of species ' sensitivity to climate change , added Condit and Svenning , who were not part of the research team . Meanwhile , a separate paper in Science reports that warming climate already has scrambled the ranges of small mammals in Yosemite National Park in the northwestern United States . Ranges for some high - elevation mammals such as the alpine chipmunk have shrunk , while animals living at low elevations , such as the harvest mouse , have expanded their ranges into higher reaches , Craig Moritz of the University of California , Berkeley , and colleagues report . Early this year a study of 171 forest species in Western Europe showed most of them are shifting their favored locations to higher , cooler spots . For the first time , research can show the " fingerprints of climate change " in the distribution of plants by altitude , and not only in sensitive ecosystems , said Jonathan Lenoir of AgroParisTech in Nancy , France . His team found " a significant upward shift of species ' optimum elevation , the altitude where species are the most likely to be found over their whole elevation range . "