Mapping impact of snow and ice feedbacks on climate

NASA Earth Observatory Image of the day has some powerful figures created with data from a new paper by Mark Flanner and others Radiative forcing and albedo feedback from the Northern Hemisphere cryosphere between 1979 and 2008. in Nature Geoscience. They use satellite data to estimate how changes in snow and ice in the Northern Hemisphere have contributed to rising temperatures over the last 30 years. They found that these changes in albedo have warmed the planet more than expected from models.

NASA Earth Observatory writes:

The left image shows how much energy the Northern Hemisphere’s snow and ice—called the cryosphere—reflected on average between 1979 and 2008. Dark blue indicates more reflected energy, in Watts per square meter, and thus more cooling. The Greenland ice sheet reflects more energy than any other single location in the Northern Hemisphere. The second-largest contributor to cooling is the cap of sea ice over the Arctic Ocean.

The right image shows how the energy being reflected from the cryosphere has changed between 1979 and 2008. When snow and ice disappear, they are replaced by dark land or ocean, both of which absorb energy. The image shows that the Northern Hemisphere is absorbing more energy, particularly along the outer edges of the Arctic Ocean, where sea ice has disappeared, and in the mountains of Central Asia.

“On average, the Northern Hemisphere now absorbs about 100 PetaWatts more solar energy because of changes in snow and ice cover,” says Flanner. “To put it in perspective, 100 PetaWatts is seven-fold greater than all the energy humans use in a year.” Changes in the extent and timing of snow cover account for about half of the change, while melting sea ice accounts for the other half.

Flanner and his colleagues made both calculations by compiling field measurements and satellite observations from the Moderate Resolution Imaging Spectroradiometer (MODIS), Advanced Very High Resolution Radiometer, and Nimbus-7 and DMSP SSM/I passive microwave data. The analysis is the first calculation of how much the energy the entire cryosphere reflects. It is also the first observation of changes in reflected energy because of changes in the entire cryosphere.

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