GSA Annual Meeting Presentation: Could Estimates of the Rate of Future Sea-Level Rise Be Too Low?
Boulder, Colorado, USA – Sea levels are rising faster than expected from global warming, and University of Colorado geologist Bill Hay has a good idea why. The last official IPCC report in 2007 projected a global sea level rise between 0.2 and 0.5 meters by the year 2100. But current sea-level rise measurements meet or exceed the high end of that range and suggest a rise of one meter or more by the end of the century.
“What’s missing from the models used to forecast sea-level rise are critical feedbacks that speed everything up,” says Hay. He will be presenting some of these feedbacks in a talk on Sunday, 4 Nov., at the meeting of The Geological Society of America in Charlotte, North Carolina, USA.
One of those feedbacks involves Arctic sea ice, another the Greenland ice cap, and another soil moisture and groundwater mining.
“There is an Arctic sea ice connection,” says Hay, despite the fact that melting sea ice — which is already in the ocean — does not itself raise sea level. Instead, it plays a role in the overall warming of the Arctic, which leads to ice losses in nearby Greenland and northern Canada. When sea ice melts, Hay explains, there is an oceanographic effect of releasing more fresh water from the Arctic, which is then replaced by inflows of brinier, warmer water from the south.
“So it’s a big heat pump that brings heat to the Arctic,” says Hay. “That’s not in any of the models.” That warmer water pushes the Arctic toward more ice-free waters, which absorb sunlight rather than reflect it back into space like sea ice does. The more open water there is, the more heat is trapped in the Arctic waters, and the warmer things can get.
Then there are those gigantic stores of ice in Greenland and Antarctica. During the last interglacial period, sea level rose 10 meters due to the melting of all that ice — without any help from humans. New data suggests that the sea-level rise in the oceans took place over a few centuries, according to Hay.
“You can lose most of the Greenland ice cap in a few hundred years, not thousands, just under natural conditions,” says Hay. “There’s no telling how fast it can go with this spike of carbon dioxide we are adding to the atmosphere.”
This possibility was brought home this last summer as Greenland underwent a stunning, record-setting melt. The ice streams, lubricated by water at their base, are speeding up.
Hay notes, “Ten years ago we didn’t know much about water under the Antarctic ice cap.” But it is there, and it allows the ice to move — in some places even uphill due to the weight of the ice above it.
“It’s being squeezed like toothpaste out of a tube,” explains Hay. The one thing that’s holding all that ice back from emptying into the sea is the grounded ice shelves acting like plugs on bottles at the ends of the coastal glaciers. “Nobody has any idea how fast that ice will flow into the oceans once the ice shelves are gone.”
Another missing feedback is the groundwater being mined all over the world to mitigate droughts. That water is ultimately added to the oceans (a recent visualization of this effect in the U.S. was posted by NASA’s Earth Observatory: http://earthobservatory.nasa.gov/IOTD/view.php?id=79228).
All of these are positive feedbacks speeding up the changes in climate and sea-level rise.
“You would expect negative feedbacks to creep in at some point,” says Hay. “But in climate change, every feedback seems to go positive.” The reason is that Earth’s climate seems to have certain stable states. Between those states things are unstable and can change quickly. “Under human prodding, the system wants to go into a new climate state.”
WHAT: Could Estimates of the Rate of Future Sea-Level Rise Be Too Low?
WHEN: Sunday, 4-November, 9:15–9:30 a.m.
WHERE: Charlotte Convention Center, Room 219AB
ABSTRACT: https://gsa.confex.com/gsa/2012AM/finalprogram/abstract_209198.htm
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Dr. Hay may find this upcoming NASA JPL project problematic with his claims:
Finally: JPL intends to get a GRASP on accurate sea level and ice measurements
They must have been holding this “study” for just the right time to spring it on the public in order to maximize effect on the political front.
How is sea level rise separated from crustal motion in order to determine actual sea level rise vs land subsidence? Do all the tide gauges have a valid terrestrial reference point?
Lars P. says:
November 3, 2012 at 6:11 am
Reading now the post of Bill Hay I get a better understanding of the attitude at the U of C. I fear it looks like some theorists far away from the sea working too much with models and too little with real data.
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That reminded me of this:
Aristotle maintained that women have fewer teeth than men; although he was twice married, it never occurred to him to verify this statement by examining his wives’ mouths.
Bertrand Russell, Impact of Science on Society (1952) ch. 1
British author, mathematician, & philosopher (1872 – 1970)
PS Not that I’m saying Aristotle worked with models ….
“Nobody has any idea how fast that ice will flow into the oceans once the ice shelves are gone.”
And nobody will get any idea for a very long time, because the ice shelves will be here for at least a couple of thousands of years.
But yeah, CO2GlobalWarmingClimateChange is gonna get you big time!!!!!!
(And a nice one, omitting how much energy open water radiates compared to an sea ice cover.)
Gunga Din says:
November 3, 2012 at 9:05 am
“That reminded me of this:
Aristotle maintained that women have fewer teeth than men; although he was twice married, it never occurred to him to verify this statement by examining his wives’ mouths.
Bertrand Russell, Impact of Science on Society (1952) ch. 1
British author, mathematician, & philosopher (1872 – 1970)”
How did Russell know that Aristotle’s wives didn’t have fewer teeth? How did Russell know that Aristotle never looked into his wives’ mouths to count their teeth? Maybe the wisdom teeth of his wives hadn’t come out? Russell is being disingenious to deceptive here, assuming he didn’t give more context.
The buildup of cool water in the East equatorial Pacific as recorded by BOM:
http://www.bom.gov.au/climate/enso/sub_surf_mon.gif
is such that another La Nina looks increasingly likely. Those arguing that the recent slowing of SLR is due to La Nina linked precipitation stored on land and “just wait for that water to come back” will have to wait a little longer. More “Waiting for el Ninot”.
tonyb says:
November 3, 2012 at 5:06 am
Thanks Tony, that was fascinating. I’ve saved a pdf copy of the document so I can read through it a few times and understand it properly.
Why is it that sea levels always are on the rise but never where you’re at by the sea shore at the moment?
cross-posted from earlier JPL thread:
James Houston of the US Army Corps of Engineers has been doing some interesting work on GIA, subsidence, and GPS in relation to measuring sea level. Fortunately his recent paper is open access at http://www.jcronline.org/doi/abs/10.2112/JCOASTRES-D-11-00227.1 .
NASA says ITRF accuracy needs to improve by a factor of 10 to 20 in order to support sea level studies. http://science.gsfc.nasa.gov/sed/content/uploadFiles/highlight_files/sgp_poster_120723.pdf
If this is so, how do present sea level determinations derive their millimeter accuracy?
Was anyone able to attend and provide feedback?