Scientists Find Melting of Antarctic Ice Sheet Accelerating
by Bill Chameides | May 14th, 2014
posted by Erica Rowell (Editor)
The Thwaites glacier in West Antarctica is rapidly retreating, but when scientists say “rapid,” they mean it in the context of the life of a glacier. (NASA)
Two new papers point to eventual complete loss of glaciers, but it will take centuries or more to occur.
Many news outlets have covered the two new papers on the melting of the Antarctic ice sheet: see for example here, here, here, here and here. I think the papers will prove to be important, but a good deal of the media coverage leaves something to be desired.
Destabilization of the Ice Sheet in West Antarctica
The two papers both provide evidence of the environmental costs — in this case in the form of melting glaciers — wrought by the slow rise in global temperatures over the past century. The two papers are:
1) “Widespread, rapid grounding line retreat of Pine Island, Thwaites, Smith and Kohler glaciers, West Antarctica from 1992 to 2011” by Eric Rignot of the University of California, Irvine, and colleague to be published in the journal Geophysical Research Letters.
2) “Marine Ice Sheet Collapse Potentially Underway for the Thwaites Glacier Basin, West Antarctica” by Ian Joughin of the University of Washington and colleagues in the journal Science.
Here’s what they say.
Accelerating Ice Retreat Passes ‘Point of No Return’
First a related finding. In a paper published earlier this year, Jeremie Mouginot of the University of California, Irvine, and Rignot and their co-authors found that the rate of ice flow through the Amundsen Sea Embayment (one of the primary paths for Antarctic ice to glow into the sea) had increased by 77 percent since 1973.
In the more recent paper, Rignot et al. report on data from six outlet glaciers that flow into the Amundsen Sea Embayment.
The data shows that because of the melting that has already occurred, there is little in the way of topography or physical barriers to slow the glaciers’ accelerating flow into the sea. For example, for five out of the six glaciers studied, once they retreat beyond the ridge they are currently grounded to (including the important Thwaites glacier), the authors found “no major bed obstacle that would prevent the glaciers from further retreat and draw down the entire basin.” Excuse the scientific jargon — Rignot et al. are saying that there is little to nothing physically to slow the glaciers’ retreat.
Joughin et al., working independently from Rignot et al., came to a similar conclusion from their work on the Thwaites glacier. Already retreating at a fair clip, they estimate that once the glacier retreats another 60-80 kilometers inland, melting would become “rapid.” Why? As explained in Science Daily:
“the glacier beds slope deeper below sea level as they extend farther inland. As the glaciers retreat, they cannot escape the reach of the ocean, and the warm water will keep melting them even more rapidly.”
These findings suggest that the glaciers have, in the words of Rignot, “passed the point of no return,” that the slow melt and march of these glaciers to the sea cannot be stopped. A march that will eventually mean a devastating four-foot rise in sea level — a rise that will change coastal maps around the globe and threaten the life and character of some of the world’s greatest cities like New York, London and Shanghai.
Moreover, the loss of these glaciers could destabilize the entire ice sheet, ultimately leading to a sea level rise of about 11 feet.
This is serious business. Estimates of how much sea level rise we will see by the end of the century (currently set at one to three feet [pdf]) will most likely have to be revised upward.
Planners and coastal communities must begin, if they have not already, to rethink and revise coastal development plans and zoning laws — hey, North Carolina Legislature, are you listening?
People living in developing economies along coastal plains and in small island nations are already threatened by sea level rise and the addition of meltwater from Antarctica to the world’s oceans will exacerbate their already perilous lives. And these findings should give pause to anyone who believes we can ignore climate change and continue with our fossil-fuelish lives.
Not So Fast — No Need to Panic on This One
But, it is important to note that the melting glaciers and concomitant sea level rise occur very, very slowly by human standards; we’re talking time scales of centuries or even millennia. Joughin et al. estimate that it will be between 200 and 900 years before the onset of rapid melting (greater than one millimeter a year) initiates the collapse of the West Antarctic Ice Sheet. If the past 200 years are any measure, a lot can happen and change in 200 years. So yes, this is serious business, but business that we have plenty of time to plan for and adapt to.
So, folks, let’s resist the temptation to couch this in alarmist terms for your denier or even fence-sitting friends. A lot of the media coverage of these two new papers seems to err on the alarmist side with too many attention-cadging headlines touting details like the “unstoppable,” cataclysmic glacial “collapse.” We’ve seen this done to undercut climate science by using scientific terms taken out of their scientific context — think the word “trick,” which in science refers to an “elegant mathematical algorithm,” one of several terms that were taken out of context by deniers in the so-called Climategate episode.
Similarly, using words like “unstoppable” and “collapse” are misleading when divorced from their glacial context. These terms are accurate, but their appearance in a headline intended for the lay public without a prominent time-scale caveat may simply alarm much of the public at first and then alienate them when they find out the “collapse” is hundreds of years away. I personally prefer the coverage from the New York Times (and blogger Andy Revkin) and the Wall Street Journal — less alarming headlines and statements on the centuries time scale right in the opening paragraph.
Media Critique on Climate Coverage
Many in the scientific community, myself included, have found fault with the media’s coverage of climate change because of their penchant for presenting the climate deniers’ view on an issue related to climate change, giving the impression that a vigorous debate remains on climate change when in truth there is not. John Oliver’s humorous but spot-on critique of this very same issue went viral this week.
It does not help to err in the other direction, sensationalizing climate change issues with headlines and ledes that tend to alarm. It may sell newspapers and get eyeballs on computer screens, but it does not help people understand, cope with and engage in solving the problem.
There is undoubtedly a lot of stuff, even scary stuff headed our way in the coming decades, and a lot of that from climate change. Melting ice caps and rising sea level is one that we at least have plenty of time to think through and plan for. Wouldn’t it be a great testament to our species’ intelligence and forethought if history wrote centuries from now that in this instance at least we were able to come together and meet the challenge?filed under: Antarctica, climate change, faculty, global warming, science, science literacy
and: glaciers, ice, media, sea level rise, Thwaites glacier, West Antarctica ice sheet