More warming in the Arctic

From a study at UC, Berkeley: Trees invading warming Arctic will cause warming over entire region, study shows:

As the Arctic warms, shrubs and other plants are moving in, making the area more amenable to trees. One way they do this is through local warming: snow, and the bare ground replacing the snow, both have higher albedo, that is they reflect more sunlight, than do the darker plants moving in. Now another cause of Arctic warming has been found. Trees add water vapor to the Arctic air.

“Broad-leaved deciduous trees are not as dark as evergreen trees and so are generally assumed to be less important. But broad-leaved trees transpire a lot more water through their leaves and are actually able to change the water vapor content and increase the greenhouse effect. As the air warms, it can hold more water vapor, and the greenhouse effect increases further,” [UC Berkeley graduate student Abigail L.] Swann said. “So, broad-leaved trees end up warming the entire Arctic.”

More importantly, the researchers’ model predicts that the increased water vapor would melt more sea ice, resulting in more absorption of sunlight by the open ocean and dumping more water vapor into the atmosphere. This positive feedback will warm the land even more and encourage faster, more efficient tree growth and perhaps a faster expansion of trees into the Arctic.

All told, the model predicts an additional 1 degree Celsius increase in temperature over the Arctic as a result of this effect. Global warming already is predicted to increase temperatures in the Arctic between 5 and 7 degrees Celsius within the next 100 years.

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