Ice sheet melting in Greenland and Antarctica is accelerating, increasing much faster than predicted by the IPCC, according to NASA scientists. They calculate sea level will rise 1 foot by 2050. Ice sheet melting will be the largest contributor to global sea level rise in this century. One foot may not seem like much but combined with storms, king tides, seasonal effects on sea level, and multidecadal weather pattern oscillations, it could prove very destructive to barrier islands and port facilities in many parts of the world including the United States. Moreover, water tables would rise across the coastal plain running from Maryland to Texas, damaging farmland and structures up river. Even Washington DC would be affected.
The NASA study may be the most accurate and precise measurement of ice loss to date because it reconciled 20 years of results from two independent methods. NASA scientists compared a method that subtracted observed ice mass loss from snow accumulation with the GRACE satellite method that used changes in gravity to measure ice mass loss (gain). The independent methods agreed well.
This video made by glaciologist Mark Tedesco of the City University of New York shows astounding amounts of meltwater on top of Greenland's ice sheet seen in summer 2010. Record warmth over Greenland in 2010 combined with the heating effects of soot, caused record melting of the Greenland ice sheet in 2010.
The length of Greenland's melt season has been growing noisily, but steadily, since 1978, contributing to an acceleration of the amount of melting of the ice sheet.
Movie and images by Mark Tedesco, CUNY.
Photo by Eric Rignot, NASA JPL
The NASA researchers calculated a 1 foot rise in sea level by 2050 by assuming that the acceleration of ice sheet loss will remain constant and that an IPCC average would affect glacial melting and ocean thermal expansion. Because the west Antarctic ice sheet is grounded below sea level, the ice sheet is unstable. The assumption of a constant acceleration may be optimistic.
If the acceleration in ice sheet loss of 36.3 ± 2 Gt/yr2 continues for the next decades, the cumulative ice sheet loss would raise global sea level by 15 ± 2 cm in year 2050 compared to 2009/2010. The GIC would contribute a sea level rise of 8 ± 4 cm, and thermal expansion of the ocean would add another 9 ± 3 cm based on the average of scenarios A1B, A2 and B1 [Meehl et al., 2007], for a total rise of 32 ± 5 cm.
"That ice sheets will dominate future sea level rise is not surprising -- they hold a lot more ice mass than mountain glaciers," said lead author Eric Rignot, jointly of NASA's Jet Propulsion Laboratory, Pasadena, Calif., and the University of California, Irvine. "What is surprising is this increased contribution by the ice sheets is already happening. If present trends continue, sea level is likely to be significantly higher than levels projected by the IPCC in 2007."
Total ice sheet mass balance between 1992 and 2009, as measured for Greenland (top), Antarctica (middle) and the cumulative sum of both ice sheets (bottom), in gigatonnes per year, as measured by the two different methods used by the researchers: the mass budget method (solid black circles) and time-variable gravity measurements from the NASA/German Aerospace Center’s Gravity Recovery and Climate Experiment (Grace) satellites (solid red triangles). Image credit: NASA/JPL-UC Irvine-Utrecht University-National Center for Atmospheric Research