By mid-century, more Antarctic snowfall may help offset sea-level rise

When Antarctica's air temperature rises, moisture in the atmosphere increases. That should mean more snowfall on the frozen continent. So why hasn't that trend become evident in Antarctica's surface mass balance as climate models predict?

In a new study, scientists used historical records and climate simulations to examine that question. They found that the effect of rising temperatures on snowfall has so far been overshadowed by Antarctica's large natural climate variability, which comes from random, chaotic variations in the polar weather. By mid-century, however, as temperatures continue to rise, the study shows how the effect of human-induced warming on Antarctica's net snow accumulation should emerge above the noise.

The expectation of more snowfall is something of a silver lining as temperatures rise. Global warming is already increasing sea level through melting ice and thermal expansion. The increase in snowfall over Antarctica could help reduce the amount of global sea level rise by 51 to 79 millimeters, or about 2 to 3 inches, by the year 2100, according to the study. That would be a small but important benefit: the Intergovernmental Panel on Climate Change estimates global sea level rise will be at least 10 times that by 2100 under the same high-emissions scenario used in the new study.

"Increased snowfall over Antarctica is the sole process connected to global warming that is thought to have a significant mitigating effect on global sea level rise," said lead author Michael Previdi, a professor at Columbia University's Lamont-Doherty Earth Observatory. "While the magnitude of this effect is uncertain, it is likely that the balance of different processes determining Antarctica's net contribution to global sea level rise will be decidedly different in the future than it has been in the recent past."

On a continental scale, surface mass balance is the difference between the amount of snowfall that accumulates and the amount of snow lost to sublimation. It affects global sea level because the amount of water on earth is essentially constant, so when more water is stored as snow or ice on land, less water is available to contribute to rising seas.