Scientists have just documented an unexpected process occurring in the air over the Antarctic ice sheet: The wind is causing snowflakes to vaporize — literally — before they hit the ground.
This means less snow may be accumulating on the continent's surface than scientists thought. And that could change researchers' understanding of the way climate change affects the ice sheet, including their estimates of future sea-level rise.
“If there is warming over Antarctica, which is likely to happen, then the classical view is to say, well, warmer air, you can have more moisture in the air, so we should expect an increase in precipitation,” said Alexis Berne, a researcher at the Swiss Federal Institute of Technology and senior author of the new study, which was published yesterday in Proceedings of the National Academy of Sciences.
That's because snow that builds up on the ground tends to turn to ice over time, adding more mass to the ice sheet.
But now, the researchers believe that future climate change could also produce an increase in the kinds of wind conditions that are causing snowflakes to vaporize — meaning the two effects could cancel each other out.
What this means for the future of the ice sheet is unknown, Berne cautioned. But, he added, “Our point is we should be careful in evaluating the evolution of the ice mass balance, taking into account these processes.”
The news comes at a time when concern over the Antarctic ice sheet is at an all-time high. Over the weekend, the Pine Island Glacier in west Antarctica — one of the region's largest — made headlines by calving an iceberg with a total area of more than 100 square miles.
The event has renewed concerns about the increasingly unstable glaciers in west Antarctica, which could raise global sea levels by several feet if they all collapsed.
But while scientists have been closely monitoring ice loss from glaciers by satellite, ice gains via snowfall remain much less understood.
“Precipitation in Antarctica is a big unknown because it's very remote, there are very few people, so not much is known about what's going on there,” Berne told E&E News. “And so we thought it would be a good idea to bring kind of state-of-the-art remote sensing instruments to study precipitation in this environment.”
The team set up weather radar and precipitation gauge systems in Antarctica's Adélie Land region in 2015 and 2016 to observe precipitation patterns. Researchers found that significant amounts of snow were disappearing before reaching the ground.
The cause, they believe, is a particular type of wind pattern known as katabatic winds — cold, dry air currents that flow down from high elevations toward the coast. These dry winds can cause snowflakes to turn from a solid state to a gas — a process known as sublimation — while they're still drifting through the air. This means less snow accumulates on the ground and less mass is added to the ice sheet over time.
The researchers used models to expand the observations they collected in Adélie Land. Overall, they estimate that katabatic winds in Antarctica could lead to a 17 percent reduction in snowfall across the continent. The effect is even more pronounced around the margins of east Antarctica, potentially causing reductions of up to 35 percent in some areas.
Because satellite observations don't capture the sublimation process, which occurs too close to the continent's surface to be detected from space, many current estimates of snow accumulation in Antarctica may be too low, the researchers note.
These estimates are important in helping scientists predict the future of the ice sheet, including how much ice is being lost every time an iceberg calves and how much ice is being replaced by new snowfall over time. As Berne noted, many scientists suggest that Antarctica's warming climate could lead to more precipitation. But the new study indicates that sublimation could partially cancel out some of those gains.
For now, the science is too new for the researchers to say definitively what it all means for the future. But they do believe the findings will play an important role in predicting Antarctic ice sheet loss. That could be true in Greenland, too, where many of the same processes also remain poorly understood.
“The ice cap is smaller, it's not the same as Antarctica, but there are some katabatic winds there,” Berne said of Greenland. “So if you have precipitation coming in, you may have the same sublimation process.”
Reprinted from Climatewire with permission from E&E News. E&E provides daily coverage of essential energy and environmental news at www.eenews.net.