New research suggests that Antarctica’s contribution to sea level rise over the next few decades has been underestimated
By Bob Berwyn
When it comes to the question of how much sea levels will rise in the global warming era, Antarctica is the big, frozen, enchilada.
Just a partial meltdown of the ice shelves along the western fringe of the continent could raise sea level two to three feet in a few hundred years, and more extensive melting of inland ice sheets would send seas surging upward higher and faster than most coastal communities could adapt for.
Until recently, Antarctica’s inland ice fields were deemed as relatively stable, and recent NASA research even suggested that global warming will increase snowfall over Antarctica and build more ice mass—a process that could slow melting and offset sea level rise.
But after taking a close look at new ice core samples that indicate temperatures and snowfall rates going back several thousand years, researchers with the University of Washington said they’re not sure of the linkage between a warming climate and precipitation.
“Depending on what part of the record you look at, you can draw different conclusions,” said T.J. Fudge, a UW postdoctoral researcher in Earth and space sciences. “We show that warmer temperatures and snowfall sometimes go together, but often they don’t. During some of the more abrupt climate changes, from when we had ice sheets to our current climate state, there’s actually no relationship between temperature and snowfall,” Fudge said, describing the findings published the journal Geophysical Research Letters.
The new findings add to concerns about how much of Antarctica’s ice will melt in coming decades and how much sea level will rise as a result. Last week, a widely reported study in Nature Climate Change suggested that one of East Antarctica’s large glaciers collapsed during recent warm geological epochs, raising sea level by several meters.
And last month, University of Amherst Massachusetts Professor Rob DeConto said new modeling, reported in the journal Nature in late March, shows that some of Antarctica’s coastal ice shelves could be much more susceptible to collapse because of surface melting. The study focused on the prospects of temperatures going above freezing in Antarctica.
“It will make meltwater on the surface of the ice sheets which can get into cracks and crevasses, which can break up the floating extensions of the ice sheets that help control the flow of ice sheets out into the ocean,” DeConto said during a presentation at the European Geophysical Union conference in mid-April.
DeConto’s research showed there’s a potential up to a meter of potential sea level rise by 2100 from Antarctica under a business as usual climate scenario, with few cuts in greenhouse gas emissions. But if the goal of limiting the global temperature increase to under 2 degrees Celsius is achieved, many Antarctic ice sheets would stay intact.
DeConto’s findings represent a significant update to assumptions made as recently as the last big climate report from the IPCC in 2013.
“At that time the general consensus was that Antarctica might not contribute much to sea level rise on that 2100 time frame,” he said. “Now we’re talking about the potential for a meter that would need to be added on to the previous estimates, that puts the potential for sea level rise nearly off the charts,” he said.
Looking at the results of the study in the context of the Paris climate deal, DeConto said the temperature goals are important because there is a significant threshold somewhere between the 2 degree Celsius increase eyed as the upper limit of allowable warming and the 2.7 degree rise that the world is headed for right now.
“At the 2 degree limit we get very little response from the antarctic ice sheet. The problem is the, 2.7, where things stand now, we get a very big response … 80 centimeters or so of sea level rise,” he said.
The Antarctic Ice Sheet covers about 14 million square miles, as big as the U.S. and Mexico combined, and 7.2 million cubic miles of ice, which, if it all melted, would raise sea level by about 200 feet.
Specifically, the new University of Washington study looked at evidence from the West Antarctic Ice Sheet Divide ice core to get a first clear look at how the continent’s snowfall has varied over 31,000 years. The 2.1-mile deep ice core preserves climate history in enough detail to show individual snow years. It shows that, when Earth was coming out of its last ice age about 8,000 years ago, air temperature went up by several degrees without any boost in the amount of snowfall.
“Our results make it clear that we cannot have confidence in projections of future snowfall over Antarctica under global warming,” said co-author Eric Steig, a UW professor of Earth and space sciences.
Overall, shifts in regional weather patterns may be a bigger factor in Antarctic snowfall than a few degrees warming, especially on the timescale that matter in terms sea level rise in the next few centuries.
“For sea-level rise, we’re not really interested in what happens over thousands of years,” Fudge said. “We’re interested in what happens over the next few hundred years. At that shorter timescale, the variability in how the storms reach the continent matters much more than a few degrees of warming.”
The detailed record of snowfall may help researchers gain a better understanding of regional weather pattern changes and how atmospheric connections with the tropics influence the amount of relatively warm ocean water that laps at the frozen continent’s edge.
“By getting models to better capture the variability in our snowfall record, we actually will get a better idea of how the warm ocean is going to interact with the ice sheets at the edge, and those will have an even bigger impact on sea level, eventually,” Fudge said.