Helheim Glacier, Greenland
Rapid melting and retreat of glaciers such as Helheim, in Greenland, contribute to rising sea levels and growing amounts of freshwater in oceans worldwide. Satellite images of the terminus—or ocean end—of Helheim (smoother striped surface) in May 2001 (top) and June 2005 (bottom) relative to reference points A and B clearly show that it has retreated leftward.1
Greenland's Helheim glacier has been rapidly retreating—that is, shrinking as ice breaks up and melts—since 2001. Accelerated retreat of glaciers can exert effects worldwide, from causing sea-level rise2,3,5 to adding freshwater to oceans, both of which can affect weather and ocean cycles in the North Atlantic.7
Helheim glacier in southeast Greenland is one of the world's fastest-moving glaciers. Helheim is also one of the best-known and most-studied glaciers in Greenland, and one of several whose rate of retreat has increased dramatically in recent years.
These glaciers are fed by the massive Greenland ice sheet, which is shrinking despite recent increases in local snowfall. Losses from surface melting, water runoff, the breakup of glaciers into the ocean (calving), and the transformation of solid ice into water vapor (sublimation) exceed any gains through snowfall.2,3,4,5 The Greenland ice sheet loses most of its mass on the perimeter, through a dozen fast-moving glaciers, including Helheim.5,6
Scientists have recently observed major changes in these glaciers: several have broken up at the ocean end (the terminus), and many have doubled the speed at which they are retreating.2,5 This has meant a major increase in the amount of ice and water they discharge into the ocean, contributing to sea-level rise, which threatens low-lying populations.2,3,5 Accelerated melting also adds freshwater to the oceans, altering ecosystems and changing ocean circulation and regional weather patterns.7 (See Greenland ice sheet hotspot for more information.)
Part of a Larger Pattern
Glaciers follow an annual cycle, melting in summer and growing in winter owing to seasonal changes in temperature and precipitation. Greenland has seen both warming and cooling trends in the past century.8 However, the warming since 1995 has led to greater changes than any measured since 1950.8,9
As with many other glaciers, changes in Helheim glacier have correlated with changes in local temperatures. For example, the Helheim terminus remained relatively stable from the 1950s to 20009—roughly when summer temperatures in Greenland were cooler than average (late 1960s to mid-1990s).8 Beginning around 1995, local summer temperatures began to rise, and in 2001 the Helheim glacier terminus began a rapid retreat that totaled nearly five miles (more than 7.5 kilometers) by 2005.10,11
The accelerated retreat of glaciers such as Helheim has surprised scientists, many of whom expected the ice sheets to have a slower response time to climate change.8 Instead, glaciers flowing from ice sheets seem to react almost immediately to changes in both seasonal and annual regional temperatures. The warmer summers of 2002, 2005, and 2007 each broke the previous record for melting of the Greenland ice sheet.12
All this melting has begun to expose rock and soils (and ocean in areas where sea ice has melted), 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, reflecting much of the solar radiation they receive, whereas 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.13,14
Rapid melting of Greenland's glaciers has also produced a special category of earthquake known as a glacialquake.15,8 Helheim glacier triggered nearly 20 percent of the 136 glacialquakes recorded from January 1993 to October 2005 in Greenland—second only to the nearby Kangerdlugssuaq glacier.15 (See Kangerdlugssuaq hotspot for more information about glacialquakes.)