Ice Sheet Height

Ice sheets form when layers of snow are compressed into thick, dense masses of ice over time. For example, the Greenland ice sheet is about 1.7 million square kilometers (656,000 square miles) and about 3 kilometers high at its thickest.

A positive feedback loop occurs as an ice sheet grows and increases in elevation. Because the air temperature is colder at higher altitudes, more ice forms as the ice sheet grows taller.

Likewise, when an ice sheet starts to melt and decrease in height, the top of the ice sheet is exposed to warmer air temperatures; because the ice sheet is now exposed to warmer air temperatures, more ice melts, which leads to further melting and causes the height of the ice sheet to drop.

Click to see larger version

The graph shows the average rate of ice melt, in meters per year, from 1958–1987 and 1988–2013. The shading represents the 95 percent confidence interval, the range within which 95 percent of the values fall. 2010 and 2012 were years with exceptional melting.