Melting Arctic sea ice has contributed considerably more to warming at the top of the world than previously predicted by climate models, according to a new analysis of 30 years of satellite observations.

 

Sea ice helps cool the Arctic by reflecting incoming solar radiation back into space. Because of its light color, sea ice has what is known as high albedo, which is the percentage of solar radiation a surface reflects back to space. Dark ocean water left behind by melting sea ice, on the other hand, has a low albedo, usually measuring less than 20 percent, whereas bare sea ice generally measures between 50 and 70 percent, according to the National Snow and Ice Data Center.

 

Since as early as the 1960s, scientists have hypothesized that melting sea ice amplifies global warming by decreasing Arctic albedo. Researchers have since devised climate models to demonstrate this phenomenon but, until now, nobody had relied entirely on satellite data to confirm this effect through time.

 

Now, scientists based at the University of California, San Diego have analyzed Arctic satellite data from 1979 to 2011, and have found that average Arctic albedo levels have decreased from 52 percent to 48 percent since 1979 — twice as much as previous studies based on models have suggested, the team reports today in the journal Proceedings of the National Academy of Sciences.

 

The amount of heat generated by this decrease in albedo is equivalent to roughly 25 percent of the average global warming currently occurring due to increased carbon dioxide levels, the team reports.

 

Previous models of Arctic albedo have suggested the reflectiveness of white cloud cover could potentially mitigate a portion of albedo loss due to melting ice; but these new observations show that cloud cover has had a negligible effect on overall Arctic reflectivity, the team says.

 

While Arctic sea ice will not likely return to 1979 values in the near future, the ice does change from year to year and might still experience some comeback this century, though the extent to which this might happen remains unclear.