Arctic Ice

Sea Ice

Sea ice is formed from frozen ocean water in polar regions. In 2008, Arctic sea ice extent dropped to its second-lowest level, and likely its lowest volume ever, due to warming waters and the melt off of the more robust multi-year sea ice in previous years, which left ice thinner and more vulnerable, according to the NSIDC. Scientists are troubled that 2008 sea ice extent levels approached the 2007 record even though melt conditions were not ideal as they were in 2007. It is unlikely sea ice extent levels can rebound to previous levels without 5-10 colder years to rebuild the multi-year ice, which is very unlikely at this point. In 2007, ice receded to record breaking levels to the point that the long-awaited Northwest Passage was opened briefly. Since 1979, enhanced Arctic warming has reduced summer sea ice by more than 40%, with many climate models predicting its disappearance by 2030 if not much sooner. To put this in perspective one study noted that the amount of ice lost in 2007 would have covered about half of the continental United States. As thicker sea ice is lost, it is replaced with thinner, seasonal ice which requires less energy to melt. NSIDC scientists predict that because sea ice is thinning, once a tipping point is reached, a rapid melt-off of remaining summer sea ice could occur in a 10-year period. View a presentation by Dr. Serreze of NSIDC and CIRES on Arctic sea ice melt given at the American Meteorological Society's Environmental Science Seminar Series. 

Sheldon Drobot, Applied Climatologist with the Colorado Center for Astrodynamics Research at the University of Colorado, talks to us about his research on sea ice. View his graphics that show how the average age of the Arctic sea ice is diminishing.

Dr. Walt Meier, of the National Snow and Ice Data Center (NSIDC) answers important questions about sea ice.

View NOAA's Arctic Annual Report Card for Sea Ice Cover

The Albedo Effect

A positive feedback mechanism is the albedo effect. The Arctic's highly reflective snow and ice cover reflects the sun's energy back into space, keeping the Arctic cold and balancing Earth's regional temperatures. As the white Arctic snow and ice melts it is replaced by darker water and land surfaces, which absorb more energy from the sun, further warming the surface of the region and accelerating Arctic and global warming. This self-reinforcing loop is called the albedo affect and it is one of many positive feedback mechanisms. As dark ocean water absorbs heat, it expands. This thermal expansion, along with freshwater runoff from melting ice sheets and glaciers into the ocean, will cause sea levels to rise.

Glaciers and Ice Sheets

Ice sheets are masses of glaciers covering land and are found in Greenland and Antarctica.  The rate at which Greenland's ice sheets are melting, moving and disintegrating into the ocean is central to how fast the global climate system approaches thresholds, and is the subject of recent scientific debate. Scientists at CIRES estimate that if the entire Greenland ice sheet, which contains 8% of the planet's fresh water, were to melt, sea levels would rise by 7 meters.

Presently, there is no ice sheet model capable of predicting the effects of faster flowing ice and the other ice sheet dynamics recently observed. This is in large part because various ice sheet dynamics are just beginning to be understood including meltwater lubrication of the ice sheet bed and increased ice stream flow after the removal of buttressing ice shelves.

Ice Shelves

Ice shelves are large formations of ice that extend out beyond the ice sheet of the coastline over the ocean in the Arctic and the Antarctic. The warmer climate is causing ice shelves to disintegrate. When ice shelves disintegrate, they no longer buttress the ice sheet on top of land causing the acceleration of glacier flow into the ocean.

The Greenland Ice Sheet

The edges of the Greenland ice sheet are melting and thinning at an accelerated pace.  This fresh meltwater contributes to global sea-level rise as well as affecting ocean circulation by diluting the ocean saltwater.  Dr. H. Jay Zwally of NASA and Dr. Konrad Steffen of CIRES have found that increased melt water at the bottom of the ice sheets is causing faster ice sheet flow during the summer. Various forces, including meltwater lakes on top of the ice sheets channeling water to the bottom of the ice through shafts called moulins, are increasing this lubrication

Scott Luthcke of NASA reports that Greenland’s ice sheet lost 101 ± 16 gigaton/year from 2003-2005. In the 1990s mass loss and gain were nearly balanced. View Dr. H. Jay Zwally's presentation on polar ice sheets, Dr. Konrad Steffen's presentation on Greenland's ice sheet, Scott Luthcke’s presentation on space ice mass observation from American Meteorological Society's Environmental Science Seminar Series and NASA's article on Greenland's ice sheet slide.

Sources: ACIA, 2004; CIRES, 2005; Serreze, 2007; Rahmstorf 2007, IPCC, AR4 WG1.

Learn more: NOAA's Arctic Annual Report Card for Greenland,NASA's Cryosheric Sciences Program, Arctic Climate Impact Assessment (ACIA), NOAA's Essays on the Arctic, National Snow and Ice Data Center, sea ice ARCUS's Sea Ice Outlook for May

Sea Level Rise

Global sea level is rising primarily because of thermal expansion of the oceans and the meltwater from land-based ice runingoff off into the ocean.  Land-based ice contributing to this melting includes mountain glaciers and small ice caps as well as the Greenland and Antarctic Ice Sheets. Ice sheet disintegration and the acceleration of glacier flow accelerates sea level rise. Many experts believe that sea level is responding more quickly to global warming than climate models indicate. (S Rahmstorf, A Cazenave, JA Church, JE Hansen, Science, 2007).

The melting of the Greenland ice sheet is contributing proportionately more to sea level rise each year. Scott Luthcke of NASA reports that most recent Gravity Recovery and Climate Experiment (GRACE) data show that Greenland’s contribution to Cryospheric sea level rise has risen to 30% from 20% in 2006. View his presentation given at the American Meteorological Society's Environmental Science Seminar Series.

Dr. Stefan Rahmstorf of Potsdam Institute for Climate Impact Research reports that the complete melting of the ice sheets of both Greenland and Antarctica would raise sea level by 70 meters. The Greenland ice sheet alone contains 8% of the planet’s fresh water.  If it were to melt it is estimated that sea level would rise by 7 meters. (CIRES) If the West Antarctic ice sheet were to melt, sea level would rise by 5 meters. (Shepherd, A. and D. Wingham (2007).

Learn more: NSIDC, UNEP/GRID-ARENDAL, IPCC AR4G1, Presentation of Dr. Konrad Steffen of CIRES given at the American Meteorological Society's Environmental Science Seminar Series, NASA