The 700,000 square kilometers of glaciers and ice sheets in the world make up 10% of Earth's total land area and are located on every continent except Australia. Glaciers typically develop when old accumulations of snow in mountains transform to ice. The ice builds up layer after layer, year after year, and flow into valleys. As glaciers age, the size of their crystals increase, some growing to be bigger than a baseball. There are also flat, glacial ice sheets more than 50,000 square kilometers in size that previously covered approximately 30% of the ocean and 30% of all land. Today, only two such dome-shaped "ice caps" remain in Greenland and Antarctica.

Scientists and decision makers study glaciers and ice sheets because they are important sources of water and aquatic nutrients, are greatly affected by and influence weather, shape land, can pose a hazard to communities, and contribute to sea level rise and the health of ocean environments. Researchers can rely on NASA’s glacier and ice sheet data to accurately measure their size and determine how these massive ice giants affect our world. 

How Are Glaciers/Ice Sheets Measured?

Since 2002, the twin Gravity Recovery and Climate Experiment (GRACE) satellites have made a complete map of Earth’s gravitational field every 30 days. Gravity is determined by mass. While most of the planet’s mass — its land and core — doesn’t move much in 30 days, its water and ice do, causing Earth’s gravity to shift. By tracking these changes, GRACE and GRACE-FO can identify how much ice sheets and glaciers are shrinking.

GRACE data are used extensively to determine mass changes of the world’s land ice (ice sheets, icefields, ice caps, and mountain glaciers). Land ice continually adds mass through precipitation and loses mass via meltwater runoff and calving of solid ice into the ocean. If losses are greater than gains, land ice loses mass, causing sea level to rise. Over the last decade or so, losses from land ice have been implicated in causing two-thirds of the observed rise in sea level.