Some experts are heralding the news as a silver lining: Scientists have found snowfall recently escalated in East Antarctica, which could lessen the high amounts of melt seen in West Antarctica that are contributing to rising seas. That prospect is comforting because the vast frozen desert at the underbelly of our world contains about 200 feet of potential sea level rise. But other scientists argue the story line is not so simple.
Scientists have long maintained rising temperatures would cause an increase in the amount of vapor the air can hold. And they have suspected this could lead to more snowfall in Antarctica, but observations were few and far apart. So Brooke Medley, a NASA research scientist, and her colleagues, analyzed a 500-foot-deep ice core extracted from the thick ice sheet in Queen Maud Land, an area in East Antarctica due south of Africa’s southern tip.
Such a lengthy ice core contains a snowfall record dating back 2,000 years, allowing the team to discover the flaky downfall is 25 percent higher today than it was in the preindustrial era. What is more, when the team compared the observations with global climate models, they found the snowfall accumulation was outpacing the model predictions—a result that could mean the sea levels would not rise as much as previously thought. “It’s not all doom and gloom,” Medley says. The team published results earlier this month in Geophysical Research Letters.
But why would more snow mean less ocean rise? The answer has to do with Antarctica’s delicate mass balance—the difference between the amount of ice gained through snowfall and that lost via melting. In a world with a constant climate, that difference would be zero; parts of the enormous ice sheet would gain mass whereas other parts would lose it. “There is this kind of balancing act, or a tug of war between the two processes,” Medley says. Even if more vigorous melting removes a greater and greater amount of ice, that added water can evaporate into the cold air surrounding the continent and fall back onto the ice sheet as snow. The continent might shape-shift a little, perhaps with a lower ice sheet in the melting west and a higher one in the snowy east, but the mass would stay the same, not raising seas.
An imbalance, however—which occurs when one of those processes gains the upper hand—would either cause the ice sheet to grow, lowering the height of the oceans, or shrink, raising the height. This appears to be the case for Antarctica today. The prevailing view has been the subtracted melt—caused by glaciers that surge toward the sea, icebergs that shatter into the ocean and meltwater that pools across the surface—far outweighs the added snowfall. There is no doubt the continent would shrink and the oceans rise. The big question is how much that rise might be.
Unfortunately, the answer is not as simple as adding and subtracting ice in a basic algebra equation. “On the one hand, if we just look at the snowfall, it will mitigate the mass loss,” says Indrani Das, a geophysicist at Columbia University’s Lamont–Doherty Earth Observatory. “But increased snowfall comes at a cost.”
That cost is a variety of side effects that would continue to force sea levels to rise instead of drop. Over time ice sheets flow downhill from land to sea, seemingly in slow motion, and extend out onto the water as ice shelves. Adding more snowfall can send more ice into the ocean, according to Anders Levermann, a climate scientist at the Potsdam Institute for Climate Impact Research in Germany who was not involved in the new study. That is because the snow falls partially on land, where it increases the surface elevation, and partially onto the floating ice shelf, where it actually pushes the shelf down into the water. The result is a steeper slope, which causes a faster flow. And the effect is not small—in 2012 Levermann co-published a study that demonstrated 30 to 65 percent of the ice from additional snowfall would slide back into the ocean.
Winds are another factor. Alexis Berne, a radar meteorologist at the Swiss Federal Institute of Technology, and his colleagues published a study last year that argued snowflakes vanish—yes, vanish—before they hit the ground. The cause is cold, dry air currents, known as katabatic winds, that flow from the high ice plateau down toward the coast. When snow falls near the coast it hits that air and turns into water vapor. “It’s just like a magician,” says Marco Tedesco, a geophysicist at Lamont–Doherty. “You have snow there and then—boom—it’s in the atmosphere.”
Berne’s study estimated katabatic winds could lead to a 35 percent reduction in snowfall around the margins of East Antarctica. And although his team has not yet crunched the numbers, he suspects a warming world would only make this effect more extreme. Even though Medley’s study found an increase in snowfall, Berne suspects this effect might not last. Tedesco even argues those winds might have pushed the snow toward Medley’s testing site.
It is easy to see why scientists like Jonathan Bamber, a glaciologist at the University of Bristol in England, are nervous about extrapolating Medley’s results into the future. “It’s an interesting story, but I think how you tell it really does depend on where you are on that temperature curve,” he says. Evidence comes from Greenland, which is warming much faster than Antarctica. There, an uptick in temperature is causing snow crystals to merge together into larger grains than before. According to a 2016 study by Tedesco and colleagues, that reduces their reflectivity, allowing them to absorb more sunlight than before and therefore melt faster. In other words: An increase in snowfall might—once again—lead to an increase in melt.
Luckily, Antarctica is nowhere near as warm as Greenland, and its frigidity is protected by intense polar winds. But should those temperatures rise drastically, both Tedesco and Bamber argue the same processes seen in Greenland today would likely occur in Antarctica.
At the end of the day, many scientists argue it is not clear whether snowfall would truly mitigate sea level rise or not. Scientists, however, agree on the overall story. Theodore Scambos, a senior research scientist at the National Snow and Ice Data Center, points out that in a warmer climate, Antarctica would shrink. And Tedesco says the graveness of the situation is clear. “Antarctica is a sleeping giant, and it’s waking up very quickly.”