November 17, 2011
Impacts Of Deforestation Varies By Latitude
Scientists from 20 institutions around the world said that the impact of deforestation on global warming varies with latitude.
Researchers say these new findings, which were published in the journal Nature, call for new climate-monitoring strategies.
"It depends where the deforestation is," UC Davis atmospheric science Professor Kyaw Tha Paw U, a study co-author, said in a press release "It could have some cooling effects at the regional scale, at higher latitudes, but there's no indication deforestation is cooling lower latitudes, and in fact may actually cause warming."
"Because surface station observations are made in grassy fields with biophysical properties of cleared land, they do not accurately represent the state of climate for 30 percent of the terrestrial surface covered by forests," the study says.
The researchers found that deforestation in the boreal region, north of 45 degrees latitude, results in a net cooling effect.
Cutting down trees releases carbon into the atmosphere, which increase the area's albedo, or reflection of sunlight.
Surface temperatures in open, non-forested, high-latitude areas were cooler because these surfaces reflected the sun's rays, while nearby forested areas absorbed the sun's heat.
Without the albedo effect, open land at night would continue to cool faster than forests, which force warm turbulent air from aloft to the ground.
"People are debating whether afforestation is a good idea in high latitudes," Xuhui Lee, the study's principal investigator and professor of meteorology at the Yale School of Forestry & Environmental Studies, said in a press release. "If you plant trees you sequester carbon, which is a benefit to the climate system. At the same time, if you plant trees you warm the landscape because trees are darker compared to other vegetation types. So they absorb solar radiation."
Paw U said that the findings should not be viewed as a "green light" to cut down forests in high latitudes.
"The intent is to clarify where we can see these regional effects using actual temperature measurements," he said in a press release. "Besides absorbing carbon dioxide, forest ecosystems have a number of other valuable qualities, even if at certain latitudes they may be warmer than open areas."
The team said that north of Minnesota, which sits above 45 degrees latitude, deforestation was associated with an average temperature decrease of 1.5 degrees Fahrenheit.
Deforestation of North Carolina, which is below 35 degrees latitude, appeared to cause warming.
The team collected temperature data from a network of specialized weather stations in forests ranging from Florida to Manitoba and compared results with nearby stations situation in open grassy areas.
"The cooling effect is linear with latitude, so the farther north you go, the cooler you get with deforestation," Lee said in a press release.
David Hollinger, a scientists with the USDA Forest Service and study co-author, said that another way to look at the results is to see that the "climate cooling benefits of planting forests is compounded as you move toward the tropics."
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