The researchers calculated that north of Minnesota, or 45 degrees latitude, the temperature decreased by an average of 1.5 degrees Fahrenheit.On the other hand, deforestation south of North Carolina, or 35 degrees latitude, appeared to cause warming. In addition, Lee said that “statistically insignificant” cooling occurred between these two latitudes.
The researchers collected temperature data from a network of weather stations in forests from Florida to Manitoba and compared results with nearby stations situated in open grassy areas that were used as a proxy for deforested land.
“The cooling effect is linear with latitude, so the farther north you go the cooler you get with deforestation,” said Lee.
David Hollinger, a scientist with the USDA Forest Service and study co-author, said, “Another way to look at the results is that the climate cooling benefits of planting forests is compounded as you move toward the tropics.”
The researchers call for new climate-monitoring strategies. “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 study, “Observed Increase in Local Cooling Effect of Deforestation at Higher Latitudes,” can be viewed on Nature's website
. The study was supported, in part, by grants from the U.S. Department of Energy and the Yale Climate and Energy Institute.