Global Sea Ice Loss

Sea ice is simply frozen ocean water. It forms, grows, and melts in the ocean. In contrast, icebergs, glaciers, ice sheets, and ice shelves all originate on land. Sea ice occurs in both the Arctic and Antarctic. According to NSIDC (National Snow and Ice Data Center), on an average, sea ice covers about 25 million square km of the Earth, or about two-and-a-half times the area of Canada.

These are main reasons why sea ice is important:

• Sea ice has a bright surface, so much of the sunlight that strikes it, is reflected back into space (an effect known as albedo). As a result, areas covered by sea ice don't absorb much solar energy, so temperatures in the Polar Regions remain relatively cool. As gradually warming temperatures melt sea ice over time, fewer bright surfaces are available to reflect sunlight back into space, causing more solar energy to get absorbed at the surface, and raising temperatures further. This chain of events starts a cycle of warming and melting. The cycle is temporarily halted when the dark days of the polar winter return but starts again in the following spring. Even a small increase in temperature can lead to greater warming over time, making the polar regions the most sensitive areas to climate change on Earth.
• By regulating polar heat, sea ice also affects weather worldwide. That's because the oceans and air act as heat engines, moving heat to the poles in a constant quest for balance. One way is atmospheric circulation, or the large-scale movement of air. Another, slower method occurs underwater, where ocean currents move heat along a "global conveyor belt" in a process called thermohaline circulation. Fueled by local variations in warmth and salinity, this drives weather patterns at sea and on land.
• It insulates the air - As cold as the Arctic Ocean is, it's still warmer than the air in winter. Sea ice acts as insulation between the two, limiting how much warmth radiates up. Along with albedo, this is another way sea ice helps maintain the Arctic's chilly climate. But as sea ice melts and cracks, it becomes dotted with gaps that let heat escape. "Roughly half of the total exchange of heat between the Arctic Ocean and the atmosphere occurs through openings in the ice," according to the NSIDC.
• It keeps methane underground - Scientists have long known that the Arctic tundra and marine sediments contain large, frozen deposits of methane, posing a climate risk if they thaw and release the potent greenhouse gas.
• And last but not least, the Arctic supports native people and wildlife.

The monthly Sea Ice Index provides a quick look at Arctic-wide / Antarctic-wide changes in sea ice (ocean area where there is at least 15% sea ice coverage). It is a source for consistently processed ice extent and concentration images and data values since 1979.

This graph shows monthly ice extent anomalies plotted as a time series of percent difference between the extent for the month in question and the mean for that month based on the January 1981 to December 2010 data. The anomaly data points are plotted as plus signs and the trend line is plotted with a dashed grey line.

Source: NSIDC, Treehugger, NSIDC Data

This graph shows monthly ice extent anomalies plotted as a time series of percent difference between the extent for the month in question and the mean for that month based on the January 1981 to December 2010 data. The anomaly data points are plotted as plus signs and the trend line is plotted with a dashed grey line.

Source: NSIDC, Treehugger, NSIDC Data