One of the most dramatic signals of Earth’s recent warming has been the precipitous decline of the Arctic sea ice. While the sea-ice decline is in response to warming ocean and atmosphere, it also has an important feed-back on the climate itself.
Solar radiation and albedo
Earth’s main energy source is solar radiation. This solar radiation is either absorbed in the atmosphere or at the surface of the planet, or it is reflected back into space. The measure of how reflective a surface is is called its albedo. Sea ice, being white, has an extremely high albedo, compared to the ocean. Therefore when the sea ice declines, more solar radiation is absorbed by the planet, leading to more warming.
Shrinking sea ice decreases the albedo of the Arctic
Our image of the week shows a figure based on data presented in Pistone et al (2014), produced by the NASA/GSFC Scientific Visualization Studio. It shows how the declining Arctic sea ice has decreased the average albedo in the Arctic, with darker colors indicating a declining albedo and therefore warming of the Arctic Ocean. Based on satellite estimates of the sea-ice extent since 1979, the authors were able to constrain that the impact of the sea-ice retreat alone has led to an amount of global warming that is more than 1/4 as strong as the effect due to increased C02 in the atmosphere.
An animation of the annual Arctic sea ice minimum with a graph overlay showing the area of the minimum sea ice in millions of square kilometres.(Credit: NASA/GSFC Scientific Visualization Studio)