Jakobshavn Glacier, Greenland
Greenland's Jakobshavn Isbræ glacier has retreated dramatically in recent years, adding freshwater to the ocean and contributing to global sea-level rise. Lines superimposed on this 2009 satellite image show how the glacier has retreated rightward from the mid-1800s to 2009. In this image, the white under the lines is ocean with ice floating on it.1
Located on the west coast of Greenland, Jakobshavn Isbræ is one of the most rapidly shrinking glaciers in the world. Melting of Greenland's glaciers contributes to sea-level rise,2,3,4 and is expected to fuel global warming.15,16
Greenland's Jakobshavn Isbræ glacier became known around the world in 2002, when its accelerated shrinking and massive breakup into the ocean helped raise awareness of the faster-than-expected pace of impacts from global warming. Like Jakobshavn Isbræ, many of Greenland's glaciers have broken up at the ocean end (terminus),2 and many have doubled in speed.2,4
Outlet glaciers such as Jakobshavn Isbræ are intimately connected to changes in the Greenland ice sheet. They grow when the ice sheet gains mass through snowfall. If they melt or calve (break up), however, this discharges water and icebergs into the ocean, contributing to global sea-level rise.2,3,4
The volume of Jakobshavn Isbræ glacier remained fairly steady from 1950 to 1996, because winter snow accumulation and summer ice loss remained roughly equal. However, Greenland's annual average temperature has risen steadily since 1995, and snowfall has not compensated for the increase in summer ice loss. The result was that Jakobshavn Isbræ's rate of retreat doubled from 1996 to 2005.4,5
Jakobshavn Isbræ began to disintegrate into the ocean in 2002. By 2003, this glacier—already among the world's fastest-moving—reached speeds of more than 7.8 miles (12.6 kilometers) per year.2 In just one day—between July 6 and 7, 2010—satellite images showed that Jakobshavn Isbrae lost approximately 2.7 square miles (7 square kilometers) of ice area.6
The accelerated retreat of glaciers on Greenland has surprised scientists, many of whom expected the ice sheets to have a slower response time to climate change.7 Instead, glaciers flowing from ice sheets seem to react rapidly to changes in both seasonal and annual regional temperatures
The Global Context
The impact of the melting of the great ice sheets of Greenland and Antarctica is the biggest unknown in projections of future sea-level rise. However, the accelerated retreat of glaciers, combined with greater melting of these ice sheets, suggest that earlier projections of sea-level rise over the next century—such as in the 2007 report of the Intergovernmental Panel on Climate Change—are conservative.8,9
For example, the melting of the Greenland ice sheet broke previous records in 2002, 2005, and 2007, and seasonal melting from 1996 to 2007 was above average compared with the 1973-2007 period.10,11 The melting of the Greenland ice sheet contributed around 0.02 inch (0.6 millimeter) to global sea-level rise in 2005—more than double the 1996 contribution.4 From 1993 to 2003 the average rate of sea-level rise increased to about 0.12 inches (3.1 millimeters) per year.12 That means that in 2005 Greenland could have contributed 19 percent of the average annual global sea level rise rate.
The Greenland ice sheet is almost the size of Mexico. If it melted completely, it would raise global sea level by about 23 feet (7 meters).13 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 (See Greenland ice sheet hotspot for more information.)
The melting of glaciers such as Jakobshavn Isbræ has also begun to expose rock, soil, and ocean waters, which in turn causes further melting, because darker surfaces absorb more heat. This is known as positive feedback, or amplification.
Albedo is a measure of how much sunlight an object or surface reflects. Bright surfaces such as ice and snow have a high albedo, as they reflect much of the solar radiation they receive. Dark surfaces such as soils, dark rock, and ocean have a low albedo, absorbing light in the form of heat.
Given the rising pace at which ice and snow in Greenland, Siberia, Alaska, and other Arctic regions are disappearing, the resulting changes in albedo may worsen global warming and its consequences.15,16
Rapid melting of Greenland's glaciers has even produced a special category of earthquake known as a glacialquake.7,17 Jakobshavn Isbræ glacier triggered 11 recorded glacialquakes in Greenland from January 1993 to October 2005.17 (See Kangerdlugssuaq glacier hotspot for more information on glacialquakes.)