As ice in the Arctic circle retreats, darker surfaces on the planet Earth are absorbing more of the sun’s energy, according to researchers at the Scripps Institution of Oceanography. Their findings are published in the Proceedings of the National Academy of Sciences.
A bright white field — such as snow, or ice — effectively reflects the sun back into space. That's the albedo effect, and nearly a half-century ago, scientists hypothesized that the loss of ice was diminishing it in the Arctic region.
Scripps researchers are now able to measure Arctic reflectivity by using satellite data. According to graduate student Kristina Pistone, the team used actual satellite measurements of both albedo and sea ice to verify the hypothesis, and quantify the amount of heat the Earth absorbs as a result of the loss of ice.
"It was quite encouraging to see how well the two datasets – which come from two independent satellite instruments – agreed with each other,” Pistone said, in a written release.
It’s the first time scientists have used actual observation to quantify this phenomenon – before, they were using modeling.
“Scientists have talked about Arctic melting and albedo decrease for nearly 50 years,” said Scripps professor of climate and atmospheric sciences V. Ramanathan. “This is the first time this darkening effect has been documented on the scale of the entire Arctic.”
Calculations of Arctic reflectivity show it has dropped significantly over the last 30 years. Albedo is represented with a percentage; fresh snow typically has an albedo value between 80 and 90%. Scripps researchers say the Arctic's albedo diminished from 52% to 48% since 1977.
Forty-five years ago, atmospheric scientists hypothesized that ice melt in the Arctic could amplify global warming. A warmer earth can accelerate the speed at which ice melts.
The Scripps team says its work suggests something else: it might be that melting sea ice is having a bigger contribution to a warming planet than previously expected.