The behavior of a glacier follows a pretty simple budget- a balance of “ins” and “outs”. If snowfall is greater than losses due to melting and calving, a glacier grows. If melting wins out, it shrinks. Because climate models project snowfall to increase over eastern Antarctica as the atmosphere (and ocean) warms, it’s been expected that the East Antarctic Ice Sheet would help counteract a bit of the expected sea level rise. Growing an ice sheet is like stealing ocean water and putting it in continental storage, so glaciers have a lot of influence on sea level trends.
A recent paper in Nature shows that it might not be that simple in eastern Antarctica, and the future behavior of the ice sheet might not be as helpful as we’d hoped.
Glaciers and ice sheets are not static blocks of ice- they constantly flow and spread like the world’s thickest pancake batter. The rate of flow determines how quickly ice moves toward the melting edges where, for marine-terminating glaciers, calving occurs. Researchers from Potsdam University used a computer model of the East Antarctic Ice Sheet to see how the flow would respond to the additional snowfall over the next several centuries.
To tease apart the contribution from increased snowfall, they ran a second set of simulations where snowfall was held constant (but temperatures increased). The difference between the two showed what was caused by increased snowfall versus warming. The thickening ice on land due to increased snowfall led to a greater flow rate toward the sea, which means more melting and calving. They found that this cut the growth in ice volume by 30 to 65%. That means a smaller offset against sea level rise than expected.
Fortunately, this isn’t much of a factor for the immediate future. In the simulations, it added an additional 0.1 to 1.25 meters of sea level rise by 2500, with most of that coming after 2200. If we eventually get anthropogenic greenhouse emissions under control, we’ll stay on the lower side of that range. Still, these kinds of details are important for getting future sea level rise projections right.
Nature, 2012. “Increased future ice discharge from Antarctica owing to higher snowfall” DOI:10.1038/nature11616