A new video from the European Space Agency explains how changes in climate are causing sea levels to rise around the world.
There are three main causes for this change in global sea level, according to the video: thermal expansion of oceans, the melting of ice sheets and glaciers, and changes in land-water storage. The agency uses satellite data to measure how much each of these individual components attributes to the sea level increase.
Meltwater from glaciers accounts for about a 6.6 millimeter (0.26 inches) sea level rise every decade, the video says, which accounts for 20 percent of the total change between 2003 and 2013. Greenland’s ice sheet accounts for 8.3 millimeters (0.33 inches), or about 25 percent of the total, while the Antarctic ice sheet contributes 3.6 millimeters (0.14 inches) or 11 percent of the decade total. Changes in land-water storage (such as lakes) contribute 3.3 millimeters (0.13 inches) or 10 percent, and ocean thermal expansion adds 9.9 millimeters (0.39 inches) or 30 percent.
Water expands when it freezes into ice, and contracts when it melts; but above a certain temperature water begins to expand as it warms, according to the National Oceanic and Atmospheric Administration.So as the ocean accumulates "the excess heat caused by greenhouse gas emissions," its volume increases and the sea level rises.
Scientists can also measure sea level rise independently, using satellite altimeters to determine where on Earth the water is rising most, according to the video. Comparing these measurements with how much each individual component contributes to the sea level rise helps scientists better understand the sea level budget — the discrepancy between how much the water is actually rising and how much it should be rising according to models that take into account the various causes of sea level change.