New research in Nature has a surprising conclusion; the impact of deforestation on global warming varies with latitude, which at least explains a frustrating lack of warming in the U.S. even though global warming has been measured higher overall.

The researchers calculated that north of Minnesota, or above 45 degrees latitude, deforestation was associated with an average temperature decrease of 1.5 degrees Fahrenheit. On the other hand, deforestation south of North Carolina, or below 35 degrees latitude, appeared to cause warming. Statistically insignificant cooling occurred between these two latitudes.

The researchers collected temperature data from a network of specialized weather stations in forests ranging from Florida to Manitoba and compared results with nearby stations situated in open grassy areas that were used as a proxy for deforested land.

So deforestation in the boreal region, north of 45 degrees latitude, results in a net cooling effect. While cutting down trees releases carbon into the atmosphere, it also increases an 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. 

At night, without the albedo effect, open land continued to cool faster than forests, which force warm turbulent air from aloft to the ground.

"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 authors write.

"People are debating whether afforestation is a good idea in high latitudes," said Xuhui Lee, the study's principal investigator and professor of meteorology at the Yale School of Forestry&Environmental Studies. "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."

It doesn't mean there is a "green light" to cut down forests in high latitudes, trees have benefits besides carbon sequestration, you just might not know it if you read media reports of the last ten years. "The intent is to clarify where we can see these regional effects using actual temperature measurements. 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 cooling effect is linear with latitude, so the farther north you go, the cooler you get with deforestation." 

David Hollinger, a scientist with the USDA Forest Service and study co-author, wanted to make sure the results of the new study were framed properly to reaffirm that deforestation leads to global warming, and 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."