Posts Tagged ‘Ice Sheet’

Greenland Melting 2012

31 August 2012 1 comment

Extent of surface melt over Greenland’s ice sheet on July 8 (left) and July 12 (right). By July 12, nearly 97% of Greenland was experiencing surface thaw. Image Credit: Nicolo E. DiGirolamo, SSAI/NASA GSFC, and Jesse Allen, NASA Earth Observatory

The mighty Greenland Ice Sheet retains enough water to raise global sea level by 7 meters. Luckily, the bulk of the ice sheet resides at altitudes greater that 1000m meaning most of it rarely is exposed to melt; that is until now. Summer heat records were broken around the world this summer with the Continental US recording its hottest June ever. This heat also found its way to Greenland where melt was recorded at higher elevations on the ice sheet than ever before. Generally, the portion of the ice sheet exposed to melt during a season looks like the map on the left, with melt occurring along the lower elevation periphery while the high elevation dome remains untouched. This year however, melt reached nearly all of the surface (97%).

Ice sheets are controlled by a complex set of mechanisms and physics that result in a dome shaped pile of ice. Simply put, when they’re cold, they flow slow; when they’re warm they flow faster. They’re affected by air temperature and sea temperature, but also by melt water formed on the surface of the glacier. Water, which is denser than the ice, has the potential to flow down beneath the glacier which lubricates the bed and allows for faster flow. Normally, melt is constrained to the lower portions of the glacier and the upper elevations flow very slowly until they reach the melt zone. This year however, melt reached far higher elevations than usual. This is cause for concern because melt at higher elevations has the potential to lubricate and accelerate a larger area of the ice sheet. This is further complicated by a feedback measure by where faster ice, by laws of conservation, becomes thinner ice. Thinner ice sheets lower in elevation, thus exposing more of the ice sheet to to melt, thus completing the feedback mechanism.

While a single year of anomalously high reaching melt in itself will not have much impact on the ice sheet, this, in conjunction with gigantic icebergs breaking off of Petermann Glacier and record breaking velocities of the Jakobshavn Glacier presents a strong argument for an ice sheet, and a climate, in change.

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