University of Michigan study indicates Earth's shrinking snow and ice cover exacerbate global warming more than models predict
A new University of Michigan study indicates sea ice and snow cover in the Northern Hemisphere responded more to global warming over the last 30 years than was predicted by models, according to U-M assistant professor Mark Flanner.
“The Northern Hemisphere sea ice and snow cover has responded quite sensitively to warming over the last 30 years,” Flanner said of his findings.
Flanner said the research relied on satellite data to analyze changes to the Earth’s cryosphere — the planet's layer of snow, sea ice and permanent ice sheets — from 1979 to 2008. He said snow cover and sea ice in the Northern Hemisphere are “bright and reflective, and reduce the amount of solar energy Earth absorbs."
The analysis was conducted over the last year, he said.
Flanner’s article, “Radiative forcing and albedo feedback from the Northern Hemisphere cryosphere between 1979 and 2008,” can be accessed online here.
"If the Earth were just a static rock, we could calculate precisely what the level of warming would be, given a perturbation to the system. But because of these feedback mechanisms, we don't know exactly how the climate will respond to increases in atmospheric carbon dioxide," Flanner said in a U-M news release. "Our analysis of snow and sea ice changes over the last 30 years indicates that this cryospheric feedback is almost twice as strong as what models have simulated. The implication is that Earth's climate may be more sensitive to increases in atmospheric carbon dioxide and other perturbations than models predict."
In the Northern Hemisphere, the average temperature rose by about 0.7 degrees Celsius since 1979, whereas the global average temperature rose by about 0.45 degrees, Flanner said in the release.
According to the release, “For every 1 degree Celsius rise in the Northern Hemisphere, Flanner and his colleagues calculated an average of 0.6 fewer watts of solar radiation reflected to space per square meter because of reduced snow and sea ice cover. In the 18 models taken into consideration by the International Panel on Climate Change, the average was 0.25 watts per square meter per degree Celsius over the same time period.”
The news release continues, “Flanner points out that the models typically calculate this feedback over 100 years — significantly longer than this study, which could account for some of the discrepancy. Satellite data only goes back 30 years.”
"People sometimes criticize models for being too sensitive to climate perturbations," Flanner said in the release. "With respect to cryospheric changes, however, observations suggest the models are a bit sluggish."