Key Facts

The Greenland ice sheet is melting at an accelerating rate, with both the extent of melting and the length of the melt season growing. Melting in Greenland has implications for sea life, fisheries, and coastal communities worldwide, by contributing to global sea-level rise and adding freshwater to ocean ecosystems.

• The melt area set a new record in 2007: it was 60 percent larger than the previous record in 1998, and extended farther inland.^7,8
• By 2007 the melt season at elevations above 6,500 feet (2,000 meters) lasted a month longer than the average from 1988 to 2006.⁹
• Shrinkage of the ice sheet has continued to accelerate since 2007.¹⁰
• If it melted completely, the Greenland ice sheet—nearly the size of Mexico—would raise global sea level by around 23 feet (seven meters).^3,11 While the ice sheet is unlikely to disappear in our children's lifetimes, the pace of shrinking largely depends on what we do to limit future warming.¹⁴

Details

Glaciers can be found on every continent on Earth, but only three massive ice sheets exist in the world today: the Greenland ice sheet, the West Antarctic ice sheet, and the East Antarctic ice sheet. Like glaciers, ice sheets are large masses of slow-moving ice formed from layers of compacted snow. But unlike glaciers, ice sheets are thick enough to cover most of the terrain beneath them, including mountains.

The Greenland ice sheet is shrinking.^2,3,4,5 Ice sheets grow through snowfall, and shrink through surface melting, water runoff, breakup into the ocean (calving), and direct transformation into water vapor (sublimation).

The Greenland ice sheet accumulates snow in its northernmost area and in the central region at high elevations. The ice sheet loses most of its mass on the perimeter, through a dozen relatively fast-moving glaciers that have recently become thinner, significantly increased their rates of retreat, and broken up at the ocean end (the terminus). (See Helheim and Jakobshavn Isbræ hotspots for more information on Greenland''s rapidly retreating glaciers.)

Over the past quarter-century, both the extent of melting and the length of the melt season on the Greenland ice sheet have been growing, as local temperatures have risen.⁶ Satellites measure the extent of melting by differentiating between areas of the ice mass that are fully frozen and those with surface meltwater. Melting reaches its maximum in late summer.

In 2005 the Greenland ice sheet lost around 53 cubic miles (220 cubic kilometers) of mass—more than two times the amount it lost in 1996 (22 cubic miles, or 90 cubic kilometers).⁵ The melt area set a new record in 2007: it was about 60 percent larger than the previous record in 1998, and extended farther inland.^7,8 By 2007 the melt season at elevations above 6,500 feet (2,000 meters) was a month longer than the average from 1988 to 2006.⁹

Evidence of accelerating shrinkage of the Greenland ice sheet continues to increase. Satellite images—comparing average ice loss from 2003 to 2007 with the 2003-2009 average—show rapid loss around the perimeter of the ice sheet, reflecting the melting of outlet glaciers.¹⁰

The Global Context

The shrinking of the Greenland ice sheet is a global issue: it is affected by and contributes to climate change, and helps shape fisheries, other sea life, and coastal communities around the world.

The Greenland ice sheet is nearly the size of Mexico. The amount of water it contains could raise global sea level by around 23 feet (seven meters).^3,11 If warming continues, scientists project that melting from the perimeter of the Greenland ice sheet and the West Antarctic ice sheet are likely to contribute to global sea-level rise long before the Greenland ice sheet finally melts away.^3,12

The melting of the Greenland ice sheet is also adding freshwater to the North Atlantic, altering ecosystems and changing ocean circulation and regional weather patterns.¹³

The Greenland ice sheet is unlikely to disappear in our children's lifetimes. However, the pace of shrinking largely depends on what we do to limit future warming.¹⁴

Credits

Endnotes

1. Image: Abdalati, W., and C. Starr. Scientific Visualization Studio, NASA/Goddard Space Flight Center. Greenbelt, MD. Online at http://svs.gsfc.nasa.gov/ vis/ a000000/ a003400/ a003475/ index.html. Accessed March 19, 2010. ↑
2. Joughin, I., W. Abdalati, and M. Fahnestock. 2004. Large fluctuations in speed on Greenland''s Jakobshavn Isbrae glacier. Nature 432:608-610 ↑
3. Alley, R.B, P.U. Clark, P. Huybrechts, and I. Joughin. 2005. Ice-sheet and sea-level changes. Science 310:456-460. ↑
4. Hanna, E., P. Huybrechts, I. Janssens, J. Cappelen, K. Steffen, and A. Stephens. 2005. Runoff and mass balance of the Greenland ice sheet, 1958-2003. Journal of Geophysical Research 110:D13108, doi:10.1029/2004JD005641. ↑
5. Rignot, E., and P. Kanagaratnam. 2006. Changes in the velocity structure of the Greenland ice sheet. Science 311:986-990. ↑
6. Box, J.E., L. Yang, D.H. Bromwich, and L.S. Bai. 2009. Greenland ice sheet surface air temperature variability, 1840-2007. Journal of Climate 22:4029-4049. ↑
7. Mote, T.L. 2007. Greenland surface melt trends, 1973-2007: Evidence of a large increase in 2007. Geophysical Research Letters 34: L22507, doi:10.1029/2007GL031976. ↑
8. Mernild, S.H., G.E. Liston, C.A. Hiemstra, and K. Steffen. 2009. Record 2007 Greenland ice sheet surface melt extent and runoff. EOS American Geophysical Union 90:13-14. ↑
9. Tedesco, M. 2007. A new record in 2007 for melting in Greenland. EOS American Geophysical Union 88:383. ↑
10. Kahn, S.A., J. Wahr, M. Bevis, I. Velicogna, and E. Kendrick. 2010. Spread of ice mass loss into northwest Greenland observed by GRACE and GPS. Geophysical Research Letters 37, doi:10.1029/2010GL042460 ↑
11. Dowdeswell, J.A. 2006. The Greenland ice sheet and global sea-level rise. Science 311:963-964. ↑
12. Overpeck, J.T., B.L. Otto-Bliesner, G.H. Miller, D.R. Muhs, R.B. Alley, and J.T. Kiehl. 2006. Paleoclimatic evidence for future ice-sheet instability and rapid sea-level rise. Science 311:1747-1750. ↑
13. Arctic Climate Impact Assessment. 2004. Impacts of a warming Arctic: Arctic climate impacts assessment. Cambridge University Press. Online at http://www.acia.uaf.edu. Accessed April 21, 2010. ↑
14. Gregory, J.M., P. Huybrechts, and S.C.B. Raper. 2004. Threatened loss of the Greenland ice sheet. Nature 428:616. ↑