Did you know that polar sea ice grows during the winter months and melts during the summer?
Covering about 9.6 million sq. miles of the Earth, its bright white surface reflects sunlight, which helps keep the polar regions cool. But as temperatures rise, Arctic Sea Ice melts more quickly. Not only does the extent of ice coverage shrink, but the ice becomes thinner. Less ice cover means that fewer of the sun’s rays are reflected and more energy is absorbed by the polar oceans. With the continuous cycle of warming and melting, even small increases in temperature can have a major impact, making Earth’s polar regions the most sensitive regions to climate change (1).
Scientists can observe changes in sea ice using satellite imagery (Figure 5). By comparing the minimum Arctic Sea Ice extent which usually occurs in September, they can analyze the percent of ice cover that has been lost over time.
How much ice has melted? Based on satellite data, scientists estimate that the extent of Arctic Sea Ice has declined more than 40% since the 1970’s(2). The record low occurred in 2012, when the minimum sea ice extent measured 1.2 million square miles (3). In comparison, the average minimum extent between 1979-2010 was 2.37 million square miles. Check out this animation from NASA (http://climate.nasa.gov/vital-signs/arctic-sea-ice/) to see changes in Arctic Sea Ice over time.