Arctic ice provides more than just homes for fish and mammals — it also slows global warming.
Dwindling sea ice in the Arctic Ocean is creating large areas of relatively dark ocean surface that reduce the albedo, or reflectivity, of the polar region. More open water causes the Earth to absorb more of the sun’s solar energy rather than reflect it back into the atmosphere. A new study by researchers at Scripps Institution of Oceanography, UC San Diego, has found that the impact this phenomenon is having on global warming has likely been substantially underestimated.
“It’s fairly intuitive to expect that replacing white, reflective sea ice with a dark ocean surface would increase the amount of solar heating,” Kristina Pistone, a graduate student at Scripps who participated in the research, said in a statement.
However, the study, published Monday in the Proceedings of the National Academy of Sciences, used direct satellite measurements for the first time rather than computer models to determine that the magnitude of surface darkening has been two to three times as large as found in previous studies.
“Scientists have talked about Arctic melting and albedo decrease for nearly 50 years,” Veerabhadran Ramanathan, a distinguished professor of climate and atmospheric sciences, said. “This is the first time this darkening effect has been documented on the scale of the entire Arctic.”
According to the researchers, the Arctic has warmed by 2°C (3.6°F) since the 1970s, with the summer minimum Arctic sea ice extent decreasing by 40 percent during the same interval. The study found that the Arctic grew 8 percent darker between 1979 and 2011.
“That extra absorbed energy is so big that it measures about one-quarter of the entire heat-trapping effect of carbon dioxide,” the study’s lead author, Ian Eisenman, a climate scientist at the Scripps Institution of Oceanography, told the Associated Press.
At its peak melt in September, Arctic ice has shrunk on average by nearly 35,000 square miles per year since 1979, an annual decrease of nearly the size of Maine.
“Although more work is needed, a possible implication of these results is that the amplifying feedback of Arctic sea ice changes on global warming is larger than previously expected,” said Eisenman.
Even without the aid of a weakened albedo, the Arctic is warming — and melting — at an alarming rate. An NOAA-led study from last month found that “climate model projections show an Arctic-wide end-of-century temperature increase of +13° Celsius [23°F] in late fall and +5° Celsius [9°F] in late spring if the status quo continues and current emissions increase without a mitigation scenario.”
The study found that “it is very likely that the Arctic Ocean will become seasonally nearly sea ice free before 2050 and possibly within a decade or two:”
“Temperature increases in response to greenhouse gases are amplified in the Arctic due to large-scale changes in the ability of the Arctic to reflect sunlight. As atmospheric temperatures increase, ice and snow decline, which opens up larger areas of water and land to the sun. Open water and snow and ice-free land absorb and store heat at a much higher rate than snow and ice, which reflects sunlight and heat. This physical process is known as Arctic amplification.”
These two studies coming in quick succession amplify Arctic concerns and emphasize the need for increased research and immediate action. In another nod to this reality, last week the U.S. State Department announced plans to create an Arctic representative position. “The Arctic has enormous and growing geostrategic, economic, climate, environment, and national security implications for the United States and the world,” Secretary of State John Kerry said in a statement about the position.