NASA satellites see Arctic surface darkening faster


This image shows a visualization of Arctic sea ice cover on Sept. 12, 2013, with a yellow line showing the 30-year average minimum extent. A new study shows that the magnitude of surface darkening in the Arctic (due to the retreat of sea ice) is twice as large as that found in previous studies. Credit: NASA Goddard’s Scientific Visualization Studio/Cindy Starr

The retreat of sea ice in the Arctic Ocean is diminishing Earth’s albedo, or reflectivity, by an amount considerably larger than previously estimated, according to a new study that uses data from instruments that fly aboard several NASA satellites. As the sea ice melts, its white reflective surface is replaced by a relatively dark ocean surface. This diminishes the amount of sunlight being reflected back to space, causing Earth to absorb an increasing amount of solar energy.

The Arctic has warmed by 3.6 F (2 C) since the 1970s. The summer minimum Arctic sea ice extent has decreased by 40 percent during the same time period. These factors have decreased the region’s albedo, or the fraction of incoming light that Earth reflects back into space — a change that the CERES instruments are able to measure.

Scripps graduate student Kristina Pistone and climate scientists Ian Eisenman and Veerabhadran Ramanathan used satellite measurements to calculate Arctic albedo changes associated with the changing sea ice cover. Albedo is measured as a percentage. A perfectly black surface has an albedo of zero percent and a perfectly white surface has an albedo of 100 percent. The albedo of fresh snow is typically between 80 and 90 percent whereas the albedo of the ocean surface is less than 20 percent. Clouds and other factors, like aerosols and black carbon, also influence the albedo of Earth.

The researchers calculated that the overall albedo of the Arctic region fell from 52 percent to 48 percent between 1979 and 2011. The magnitude of surface darkening is twice as large as that found in previous studies. They also compared their results to model simulations to assess the capability of computer models to portray and forecast albedo changes. Edited from NASA satellites see Arctic surface darkening faster

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