Ancient Glacial Melting Shows that Small Amount of Subsurface Warming Can Trigger Rapid Collapse of Ice Shelves
"Ancient Glacial Melting Shows that Small Amount of Subsurface Warming Can Trigger Rapid Collapse of Ice Shelves"
An analysis of prehistoric “Heinrich events” that happened many thousands of years ago, creating mass discharges of icebergs into the North Atlantic Ocean, make it clear that very small amounts of subsurface warming of water can trigger a rapid collapse of ice shelves….
If water were to warm by about 2 degrees under the ice shelves that are found along the edges of much of the West Antarctic Ice Sheet … it might greatly increase the rate of melting to more than 30 feet a year.
Greenland Ice Sheet Icebergs spilling out of Jakobshavn Fiord from the Greenland Ice Sheet, seen on the horizon. (Photo Credit: Oregon State University)
We knew that one West Antarctic Glacier is disintegrating much faster than almost anybody imagined — see “Nothing in the natural world is lost at an accelerating exponential rate like this glacier” (8/09). And we knew deep ocean heat is rapidly melting Antarctic ice (12/10), which noted: “Global warming is sneaky. For more than a century it has been hiding large amounts of excess heat in the world’s deep seas. Now that heat is coming to the surface again in one of the worst possible places: Antarctica.”
Now this new Proceedings of the National Academy of Sciences study, “Ice-shelf collapse from subsurface warming as a trigger for Heinrich events” (subs. req’d) provides paleoclimate evidence that very small temperature increases of the subsurface water at the poles can trigger rapid collapse of ice shelves. The study concludes that a subsurface warming of only 2°C ( 3.6°F) “increases basal melt rate under an ice shelf … by a factor of approximately 6.” And remember, we are headed for very large temperature increases at the poles on our current emissions path — see M.I.T. doubles its 2095 warming projection to 10°F — with 866 ppm and Arctic warming of 20°F.
Here’s more from the news release:
The results are important, researchers say, due to concerns that warmer water could cause a comparatively fast collapse of ice shelves in Antarctica or Greenland, increasing the flow of ice into the ocean and raising sea levels. One of the most vulnerable areas, the West Antarctic Ice Sheet, would raise global sea level by about 11 feet if it were all to melt.
“We don’t know whether or not water will warm enough to cause this type of phenomenon,” said Shaun Marcott, a postdoctoral researcher at Oregon State University and lead author of the report. “But it would be a serious concern if it did, and this demonstrates that melting of this type has occurred before.”
If water were to warm by about 2 degrees under the ice shelves that are found along the edges of much of the West Antarctic Ice Sheet, Marcott said, it might greatly increase the rate of melting to more than 30 feet a year. This could cause many of the ice shelves to melt in less than a century, he said, and is probably the most likely mechanism that could create such rapid changes of the ice sheet….
A present-day concern, Marcott said, is that ocean currents could shift and change direction even before overall ocean water had warmed a significant amount. If currents shifted and warmer water was directed toward ice shelves, more rapid melting might begin, he said.
Actually that appears to be happening already. In fact, just in June we learned the details of how ocean currents were carving out ice caves in Antarctic ice, as “seawater appear[s] to boil on the surface like a kettle on the stove”
Remember, in 2001, the IPCC “consensus” said neither Greenland nor Antarctica would lose significant mass by 2100. They both already are. As Penn State climatologist Richard Alley said in March 2006, the ice sheets appear to be shrinking “100 years ahead of schedule.” And the ice loss is accelerating (see “JPL bombshell: Polar ice sheet mass loss is speeding up, on pace for 1 foot sea level rise by 2050“).
Not only is the West Antarctic ice sheet (WAIS melting from underneath, it is, as I wrote in the “high water” part of my book, inherently less stable:
Perhaps the most important, and worrisome, fact about the WAIS is that it is fundamentally far less stable than the Greenland ice sheet because most of it is grounded far below sea level. The WAIS rests on bedrock as deep as two kilometers underwater. One 2004 NASA-led study found that most of the glaciers they were studying “flow into floating ice shelves over bedrock up to hundreds of meters deeper than previous estimates, providing exit routes for ice from further inland if ice-sheet collapse is under way.” A 2002 study in Science examined the underwater grounding lines-the points where the ice starts floating. Using satellites, the researchers determined that “bottom melt rates experienced by large outlet glaciers near their grounding lines are far higher than generally assumed.” And that melt rate is positively correlated with ocean temperature.
The warmer it gets, the more unstable WAIS outlet glaciers will become. Since so much of the ice sheet is grounded underwater, rising sea levels may have the effect of lifting the sheets, allowing more-and increasingly warmer-water underneath it, leading to further bottom melting, more ice shelf disintegration, accelerated glacial flow, and further sea level rise, and so on and on, another vicious cycle. The combination of global warming and accelerating sea level rise from Greenland could be the trigger for catastrophic collapse in the WAIS (see, for instance, here).
Buckle your seatbelts. It’s going to be a bumpy ride
- Science: CO2 levels haven’t been this high for 15 million years, when it was 5° to 10°F warmer and seas were 75 to 120 feet higher — “We have shown that this dramatic rise in sea level is associated with an increase in CO2 levels of about 100 ppm.”
- Science stunner: On our current emissions path, CO2 levels in 2100 will hit levels last seen when the Earth was 29°F (16°C) hotter
- Satellite data stunner: “Our data suggest that EAST Antarctica is losing mass” — Antarctica may soon be contributing significantly more to global sea-level rise.”
- Nature: “Dynamic thinning of Greenland and Antarctic ice-sheet ocean margins is more sensitive, pervasive, enduring and important than previously realized.”
- Sea levels may rise 3 times faster than IPCC estimated, could hit 6 feet by 2100
- Antarctica has warmed significantly over past 50 years
- West Antarctic ice sheet collapse even more catastrophic for U.S. coasts
Below are old comments from the earlier Facebook commenting system:
- Barry Saxifrage · Top Commenter
Not to worry. I just heard the GOP have all signed a pledge to cut funding for any ice sheet that tries to pull any global warming lefty hijinks.
Plus the Ice Tea Party will thrash-talk the the laws of physics on talk radio until they knuckle under and promise to stop their Co2mmunistic plot to capture black body radiation.
Obama says those who are wealthy and live on higher ground will not be totally disappointed in his followship on this issue.
I like that one. :-)
Paul Magnus · Top Commenter
Warm moist air swirling into the Arctic….
Just the icing on the cake this week:
US government department criticised for failing to collect oil revenues.
A US government department that has spent six months investigating potential fraud in polar bear studies has failed to collect tens of billions of dollars in royalties from oil companies, it has emerged. ( http://www.guardian.co.uk/business/2011/aug/02/us-polar-bear-science-oil-row ).
Paul Magnus · Top Commenter
The rebound effect as the ice gets thiner may also contribute to the break up of the ice sheets.
It will surely be uneven, not just causing fracturing of the ice, but triggering ice-quakes which will drive the process even faster. Who knows there may even be an increase in volcanic activity in these areas.
janumakonda (signed in using AOL)
Excellent article on collapse of ice shelves because of surface warming. Surface Warming is a Warning for ice shelves.
Dr.A.Jagadeesh Nellore(AP), India.
We could see 100k decline in extent today ice in the arctic- weather conditions very conducive to melting.
flatcatcanyon (signed in using Yahoo)
Current conditions in St. Louis (12:45AM CST).
From wunderground.com (hopefully a misprint/goof on the web-site).
Feels Like 137 °F.
brademey (signed in using Yahoo)
“And remember, we are headed for very large temperature increases at the polls…”
Joseph Romm · Top Commenter · Center for American Progress
Voice dictation software….
Paul Magnus · Top Commenter
“… it would be a serious concern if it did,”.
A very serious concern, indeed…. more like biblical…
Paul Magnus · Top Commenter
So are we taking lovelock and mercer seriously now… 1978 this was…
West Antarctic ice sheet and CO2 greenhouse effect: a threat of disaster
Ice is something that would enjoy today in St. Louis today. Currently 110 degrees.
Paul Magnus · Top Commenter
I sweat for you Pete…
Not in St. Louis- in beautiful Connecticut, currently 78 degrees- low humidity. Those suffering people in the Midwest and great plains, I wonder when they will begin to realize they are in deep trouble with the climate?
15 days this summer 90 or above at Windsor Locks, the official record station for Connecticut. Last year 35 days 90 or better. The ‘new average’ is 19 days, we should beat easily in 2011.
Take a yacht to Siberia. Perhaps someone could start a business taking people to watch the amazing bubbling sea. On second thought, forget it. Asphyxiation and detonation might ruin the boat trip.
But then there are the flaming lakes of Siberia and Alaska which would make a great tourist attraction. This would be a wonderful opportunity to educate the public on the joys of Methane exhalation.
Some prominent scientist, Richard Alley, I think, summed up the situation in Congressional testimony by saying, “It gets warm… ice melts.” I don’t think the science can get any simpler or clearer than that. Yet the deniers will still keep claiming that Wiley Coyote hasn’t run off the edge of the cliff and his feet aren’t spinning in mid-air. Cartoon physics is fun on a Saturday morning, but in the real world, not so much. At least we can count on those True Patriots, the Tea Partiers, to lead us in the right direction.
The “it’s worse than we thought” news has been particularly gruesome of late. WAIS, aerosols appearing to be even better at counteracting GHG warming (meaning we’re in for a bigger than expected whiplash effect as we continue to add sulfur scrubbers to coal plants), and so on. Some mornings, it truly isn’t worth the effort of chewing through the leather straps…
John McCormick · Top Commenter
Joe, your “Hell and High Water” excerpt:
“Since so much of the ice sheet is grounded underwater, rising sea levels may have the effect of lifting the sheets, allowing more-and increasingly warmer-water underneath it, leading to further bottom melting, more ice shelf disintegration, accelerated glacial flow, and further sea level rise,” says it all.
There is no uncertainty about sea levels rising and with that, WAIS rising as well. This cannot be reversed. “Houston, you have a problem.”
Joe, your first para states “…it might increase the melt rate to more than 30 feet (10metres) a year;” Something wrong there – perhaps you mean, per century? (which is quite frightening enough!).
Average over the entire ice shelf is less; ice shelves tend to melt fastest at the grounding line. But there are places where modern ice melt is 100’s of meters per year; grounding line of Pine Island glacier, west Antarctica, and various Greenland glaciers.
Jeffrey Davis · Top Commenter
More than ice melt, the item to keep track of is the amount of CO2 and CH4 emerging from sub-Arctic soils. If the curve is exponential — and I don’t know if it is — well, it’s time, like Kent Brockman said, to crack each other’s heads open and feast on the goo inside.
And with the cutbacks to science we wont even see it coming.
Is it me, or are the first two paragraphs bi-polar?