Bad news from the Southern Hemisphere: the West Antarctic ice sheet is shedding ice at an accelerating rate, with six large glaciers in this region discharging nearly the same amount of ice as the entire Greenland ice sheet, according to a new study.
The study is the first to combine observations from satellites, radar data, and other remote sensing methods to construct a long-term record of ice movement trends for six of the fastest-flowing glaciers in Antarctica.
Published this week in the journal Geophysical Research Letters, the study examines glaciers in the Amundsen Sea Embayment of West Antarctica. The glaciers in this region include the Pine Island Glacier, which made headlines in recent years by discharging massive icebergs into the ocean.
This region also encompasses the Thwaites, Haynes, Smith, Pope and Kohler glaciers, each of which are behemoths in their own right.
A research team from the University of California at Irvine and NASA found that the total amount of ice coming off these glaciers has increased by 77 percent since 1973, with much of that increase coming since 2000. Together, these glaciers drain one-third of the West Antarctic Ice Sheet, or about 158 million square miles of ice, the study said.
We need to know how quickly and extensively parts of Antarctica as well as the Greenland ice sheet are melting in order to accurately project how high global sea levels are likely to rise during the next several decades. It’s melting land-based ice, not the melting North Pole sea ice, that contributes to rising seas.
According to a 2013 report from the U.N. Intergovernmental Panel on Climate Change (IPCC), average global sea level rise will likely be in the range of 10.2 to 32 inches by the end of the century, depending on the amounts of greenhouse gas emissions between now and then.
If emissions continue on a business as usual path, which has been the trend in recent years, the IPCC said global average sea level rise could be closer to 40 inches — which would doom some low-lying coastal cities and nations, from Bangkok to Miami and Bangladesh.
Illustrating the high stakes involved in the fate of West Antarctica, the study found that these six glaciers contributed about 10% of all the global average sea level rise that occurred between 2005 and 2010. If all six glaciers were to melt completely (which is not expected to happen during this century), global average sea level would rise by a catastrophic 3.9 feet, the study said.
The new study also found, for the first time, that West Antarctic glaciers are not only flowing faster at the point where their base meets the ocean, which is known as the grounding line. Instead, areas as far inland as nearly 160 miles are also speeding up their march to the sea.
Until this study, it was not known that sections of glaciers deep into the interior are also speeding up their movement. This is a troubling sign because of what it implies for sea level rise in the future, according to the study’s lead author, Jeremie Mouginot of the University of California at Irvine.
“Increased ice discharge will have an impact on how [much] the sea level is going to rise,” Mouginot told Mashable.
Mouginot says most of the action is taking place at the grounding line, then having ripple effects inland.
In the same way that plaque slowly rots a tooth until it falls out, mild ocean temperatures are thought to be causing ice to thin and retreat where these glaciers meet the sea. This is likely setting in motion a chain of events that results in a far more unstable glacier.
The grounding line positions of these glaciers have been retreating at a rate of 0.6 miles per year, the study found, which is among the fastest rates of glacier retreat in the world.
According to Mouginot, all six of the glaciers in this study come into contact with the same body of water, which indicates that higher sea surface temperatures are likely playing a role in speeding up melting. Other studies have found evidence for this in other parts of the globe, including Greenland, and in other parts of Antarctica.
“I think there is more warm ocean going beneath the ice shelf,” Mouginot says.
It’s not absolutely clear exactly what is causing ocean temperatures to increase in that area — but global warming from the increased amount of greenhouse gases in the atmosphere, is almost certainly playing a role.
“What I can say is, if you look at Greenland, it is changing, and West Antarctica is changing a lot,” Mouginot says. “And they are really far apart from each other. I don’t think it’s a regional change occurring. I think it’s more global.”
The IPCC is scheduled to release another major climate report on Sunday evening eastern time, which is expected to detail some of the likely impacts of global sea level rise during the next several decades, among other findings.