The Coast to Come Ice Loss

Rapid Melt Arctic sea ice is melting much faster than scientists projected even five years ago. And ice sheets, or continent-sized slabs of ice resting on land in Greenland and Antarctica, are accelerating their flow and runoff into the sea as a result of structural changes wrought by the enhanced melting on the surface and underneath the floating ice.

Rapid Melt (cont’d) This graph shows the Arctic sea ice extent from 1979 through 2009 using data from September of each year, which is when the minimum extent typically occurs.

Rapid Melt (cont’d) White Arctic sea ice reflects much more radiation in summer than dark ocean, so the less ice, the more warming. Amplified warming is already occurring in the Arctic, and at the current melt rate, the Arctic may be ice-free in summer within two decades, as opposed to the originally predict 50- 100 years.

Rapid Melt (cont’d) Rapid ice loss not only leads to a warmer ocean, but likely accelerates warming on land. In 2010, Arctic sea ice extent was 22% below the average minimum of the past 30 years.

Mechanics of Meltwater Another cause for concern is water loss from ice sheets. Central Greenland's ice sheet is currently frozen to the bedrock, with very little horizontal motion. But thawing the base could double its pace. On its own, extra heat would take on the order of 10,000 years to reach the base. But drawn down quickly by meltwater, the same heat can reach the base easily in minutes, rather than millennia.

Mechanics of Meltwater (cont’d) Scientists have already identified new and larger meltwater lakes at the surface of ice sheets near Greenland's edges. These lakes may soon occur in central Greenland, which could accelerate the percolation of meltwater to the center of the glacier.

Mechanics of Meltwater (cont’d) As these processes increase, ice sheets' flow toward the ocean will be accelerated, and as a result, scientists project continued ice loss. In a few decades, we might reach the level of warming that would commit us to catastrophic sea level rise from this melting ice over coming centuries.

Projections Together, the world's glaciers and ice sheets cover more than 10% of Earth's land, and hold 66 m (220 ft) of potential sea level rise. That amount is very unlikely to melt anytime soon, but even one half of a meter of sea level rise – less than 1% of the total potential - could greatly affect the coasts.

Projections (cont’d) Scientists are working hard to gauge how quickly this could happen, but they still don't have high confidence in their understandin g of ice sheet dynamics. Current climate models don't yet incorporate ice sheets, though researchers are working to make that happen.

Projections (cont’d) While some scientists have suggested that increases in falling snow from greater evaporation and precipitation might offset ice loss in ice sheets, most evidence indicates that the increased snowfall won't be enough to offset much of the loss. Still, though we may be committed to a path of eventual ice sheet loss within decades, it would probably take centuries or more for an entire ice sheet to disappear.

Projections (cont’d) Scientists also project that frozen polar soils – called permafrost, will thaw to greater depths in summer. Less permafrost in northerly climes could cause coasts to erode faster, endanger homes, roads, and buildings constructed on it, and reduce water supplies.