Slow-Motion Collapse of West Antarctic Glaciers is Unstoppable, 2 New Studies Say

Human-caused global warming has set in motion an unstoppable slow-motion collapse of the glaciers in West Antarctica of massive scale and power, said scientists at a NASA press conference and press release on Monday. The scientists, led by glaciologist Eric Rignot of NASA's Jet Propulsion Laboratory/the University of California, Irvine, analyzed 19 years of satellite data to show that the fast-melting glaciers that drain into West Antarctica's Amundsen Sea had passed a point of no return, since their bottoms are grounded below sea level. The glaciers had been lodged on "pinning points" on the bedrock--projections that snagged the glaciers from underneath and kept them from sliding toward the sea. Melting due to warmer ocean waters has been eating away the glaciers from beneath, freeing them from their pinning points, and setting in motion a slow-motion collapse that appears "unstoppable", Rignot said at the press conference. The glaciers contain enough ice to raise global sea level by 4 feet (1.2 meters) in a few hundred years at their current rate of melting, Rignot added. The research has been accepted for publication in the journal Geophysical Research Letters.


Figure 1. Thwaites Glacier, the West Antarctic glacier that is the most serious threat to bring large levels of sea level rise this century. Image credit: NASA.

Computer modeling study shows same result
A separate paper published on Monday in Science, Marine Ice Sheet Collapse Potentially Under Way for the Thwaites Glacier Basin, West Antarctica, came to a similar result, but using computer modeling instead of observations. The researchers, led by Ian Joughin of the University of Washington, found that West Antarctica's fast-moving Thwaites Glacier will likely disappear in a matter of centuries, raising sea level by nearly 2 feet. “All of our simulations show it will retreat at less than a millimeter of sea level rise per year for a couple of hundred years, and then, boom, it just starts to really go,” Joughin said. The Thwaites Glacier acts as a linchpin on the rest of the ice sheet, which contains enough ice to cause another 10 to 13 feet (3 to 4 meters) of global sea level rise. For comparison, 119,000 - 126,000 years ago, during the period before the most recent ice age, global sea levels were 16 - 33 feet (5 - 10 meters) higher than at present. Temperatures at that time were less than 2°C warmer than "pre-industrial" levels, and we are on track to warm the planet at least that much this century.


Figure 2. Historical global sea level rise from 1700 - 2012 as compiled by the 2013 IPCC report, along with predicted sea level rise from the IPCC and from a group of 26 ice sheet experts (Bamber and Asplinall, 2013). Sea level rose 7.5" (19 cm) between 1901 - 2012, with the rate of rise nearly doubling over the past 20 years. The low-end RCP 2.6 IPCC forecast corresponds to global warming of just 1°C between 1995 - 2100, which will be nearly impossible to achieve. Humanity is currently on pace to warm the planet more than IPCC's worst-case RCP 8.5 scenario (3.7°C between 1995 - 2100.) Before Monday's research results were announced, the IPCC sea level rise estimates were already viewed as quite conservative by the majority of sea level rise experts; see the write-up at real climate.org of the Bamber and Asplinall, 2013 study.

IPCC sea level rise estimates too low?
At the press conference, the scientists questioned the sea level rise estimates made by the Intergovernmental Panel on Climate Change (IPCC) in September 2013 as being too low. That report projected that sea level will rise by an extra 0.9 - 3.2' (26 to 98 cm) by 2100. The IPCC did not fully account for potential melting in Antarctica, and decided not to include estimates from at least five published studies that had higher numbers, including two studies with rises of 2 meters (6.6 feet.) This is in contradiction to NOAA's December 2012 U.S. National Climate Assessment Report, which has 6.6 feet (2.0 meters) as its worst-case sea level rise scenario for 2100.


Video 1. ScienceCasts: No Turning Back--West Antarctic Glaciers in Irreversible Decline

Jeff Masters