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Tuesday, May 13, 2014

Joe Romm: New Studies Suggest Many Coastal Cities Eventually To Be Abandoned With Antarctic Ice Collapse

by Joe Romm, Climate Progress, May 13, 2014

Thwaites glacier
West Antarctica’s Thwaites glacier, one of a cluster that appear to have started irreversible collapse, threatening devastating sea level rise. Via NASA.
New studies in Science and Geophysical Research Letters (GRL) find that glaciers in the Amundsen Sea region of the great Antarctic ice sheet have begun the process of irreversible collapse. That by itself would raise sea levels 4 feet in the coming centuries.
antarctica_amundsen_sea_sector-1But more importantly these glaciers act “as a linchpin on the rest of the [West Antarctic] ice sheet, which contains enough ice to cause” a total of 12 to 15 feet of global sea level rise, as the University of Washington news release for the Science study explains.
What most of the media has failed to emphasize is that (1) this is not a worst-case scenario and (2) failure to curb carbon pollution ASAP will result in vastly higher levels of sea level rise that devastate the world’s coastlines.
NASA’s Eric Rignot, lead author of the GRL study, explains the basic scientific findings in this video:
The New York Times story on the studies warns:
[Climatologist Richard Alley] added that while a large rise of the sea may now be inevitable from West Antarctica, continued release of greenhouse gases will almost certainly make the situation worse. The heat-trapping gases could destabilize other parts of Antarctica as well as the Greenland ice sheet, potentially causing enough sea-level rise that many of the world’s coastal cities would eventually have to be abandoned.
“If we have indeed lit the fuse on West Antarctica, it’s very hard to imagine putting the fuse out,” Dr. Alley said. “But there’s a bunch more fuses, and there’s a bunch more matches, and we have a decision now: Do we light those?
But for some reason the New York Times buries these bombshells at the very end of a long piece. Even more inexplicably, the Times changed its online headline for the story from
NYT 5-12-2014
to an indefensibly lamer one:
NYT Revised
That new headline cuts out the heart of the news. It could have been used in stories about literally dozens of studies in the past quarter century. Heck, the New York Times headline in 1981 (!) for a NASA study led by James Hansen was … wait for it … “STUDY FINDS WARMING TREND THAT COULD RAISE SEA LEVELS.”
Apparently somebody associated with the Times thought the headline and lede were too strong, that “collapse” is somehow an inappropriate word that needed to be excised.
But it wasn’t. The headline of the news release from NASA and UC-Irvine (for the GRL study) was:
NASA-UCI Study Indicates Loss of West Antarctic Glaciers Appears Unstoppable
The Science study is titled, “Marine Ice Sheet Collapse Potentially Under Way for the Thwaites Glacier Basin, West Antarctica.” The headline from the news release is:
West Antarctic Ice Sheet collapse is under way
So the original NY Times story was accurate: the revised version, less so.
I asked Rignot for his thoughts on whether his study (along with the other) means we should revise the upper estimate for sea level rise this century (and beyond) if we stay on our current emissions path, which will take us to 4 °C (7 °F) warming or more by 2100. He replied:
I think that the minimum will be the upper end of the IPCC projections (90 cm) by 2100 and the maximum is hard to figure out but will likely exceed 1.2–1.4 meters.
The systems we are looking at do not respond to climate forcing in a smooth way, they start slow and then they proceed faster and faster. I am not convinced the numerical models are there yet, they are still conservative and do not include all the feedbacks, they are getting better than IPCC-class models but still trailing reality quite a bit.
After 2100, it will be several meters from the ice sheets, there is no red button to stop that. I surely hope that by then humanity will have reacted and slowed down the warming. I do not think we want to experience how fast Antarctica could fall apart if we push it hard … as we do now.
So the upper end of sea level rise will likely exceed 48 to 56 inches! That would not leave “southeastern Florida having many people at the end of this century,” to quote Hal Wanless, chair of the geological sciences department at University of Miami, from a 2013 interview.
The fact that these models do not include all the feedbacks and are conservative is a key point missed by much of the media. The Science article’s abstract concludes, “Less certain is the time scale, with the onset of rapid (>1 mm per year of sea-level rise) collapse in the different simulations within the range of 200 to 900 years.”
The article itself points out:
An important feature of our numerical simulations is that they reveal a strong sensitivity to mechanical and/or rheological weakening of the margins, which can accelerate the rate of collapse by decades to centuries. Thus, future models will require careful treatment of shear margins to accurately project sea-level rise. Our simulations also assume that there is no retreat of the ice-shelf front. Full or partial ice-shelf collapse should produce more rapid retreat than we have simulated. In addition, we have not modeled ocean-driven melt that extends immediately upstream of the grounding line, which could also accelerate retreat.
Of course we know from a 2012 Nature study that Antarctica is melting from below, which “may already have triggered a period of unstable glacier retreat.”
The new Science study (Joughin et al.) also notes:
Our simulations are not coupled to a global climate model to provide forcing nor do they include an ice-shelf cavity-circulation model to derive melt rates…. As such, our simulations do not constitute a projection of future sea level in response to projected climate forcing.
Again, things could go faster and be much worse than this study suggests — as shown by Nature’s bombshell study on observations pointing to 10 °F warming by 2100.
Also, the West Antarctic Ice Sheet (WAIS) is only one contributor to sea level rise. We know Greenland’s ice melt is up nearly 5-fold since the mid-1990s, as we reported in late 2012. And parts of the East Antarctic Ice Sheet are not stable either — and have points of no return, as we reported earlier this month.
That was a point Dr. Alley made to me:
Joughin et al. didn’t run a worst-case scenario, as they state. So, it is possible that a worst-case version would shift the time of rapid retreat forward into this century. I don’t think we know yet, and I think that there is plenty of science to do, incorporating the new Rignot et al. data, and other measurements and ideas that many groups including Penn State have been working on.
And, maybe most important, if we have committed to 3 m or so of globally averaged sea-level rise from West Antarctica, even if delayed by many centuries, the costs are sobering, but are not as high as the costs of also committing to loss of Greenland’s ice and parts of East Antarctica’s ice as well. And, while some additional shrinkage of Greenland probably is already committed, major loss in Greenland and East Antarctica is not guaranteed yet. Too much warming is expected to cause major loss, with Greenland not too many degrees away and East Antarctica more uncertain. But, even with such a sobering possibility on the table, the costs are likely to rise faster than the temperature, so that each degree of warming costs more than the previous degree, and adding Greenland’s ice or parts of East Antarctica’s ice to the marine parts of West Antarctica would raise the costs a lot more.
In short, the fact that we may be stuck with 10 feet of sea level rise from WAIS over the next 200 to 900 years or so doesn’t mean we should stay on a CO2 emissions path that would (1) make it far more likely WAIS collapses sooner rather than later and (2) guarantees accelerated melting and/or collapse of large parts of Greenland and EAIS, too, leading to many tens of feet of sea level rise, and ultimately loss of virtually all land-based ice — raising seas over 200 feet.
The fact that such an unimaginable catastrophe would probably take many, many centuries to occur does not make it any less immoral for us — if we are the ones who make that outcome unstoppable.
I’ll end with the comments sent to me by sea-level-rise expert Stefan Rahmstorf, Co-Chair of Earth Systems Analysis, Potsdam Institute for Climate Impact Research:
What climate scientists have feared for decades is now beginning to come true: We are pushing the climate system across dangerous tipping points. Beyond such points, things like ice sheet collapse become self-sustaining and unstoppable, committing our children and children’s children to massive problems. The new studies strongly suggest the first of these tipping points has already been crossed. More tipping points lie ahead of us. I think we should try hard to avoid crossing them.

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