One intuitively expects that if enough of Greenland melts to raise global sea levels by, say, three centimetres, that rise will occur everywhere more or less simultaneously. Detlaf Stammer, of Hamburg University, has suggested otherwise. His research on meltwater data since 1948 shows that meltwater forms a ‘slow wave’ of “rising sea levels that gradually works its way south from Greenland, down the American coast, reaching the tip of southern Africa after about a decade.”
Fifty years after any Greenland melting occurs, Stammer’s model suggests that sea level rise will be thirty times greater around Greenland and the east coast of North America than it will be in the Pacific ocean. If true, this will have a big effect on the kind of climate change adaptation planning that needs to take place. Everyone is exceptionally worried about Bangladesh right now, but perhaps they should be more immediately concerned about Florida and the Maritimes.
What makes the process of balancing out so slow?
I’m a bit confused about the possible rise in sea level that may be caused by global warming. I know that in general water expands when warmed, and that is one cause of sea level elevation with respect to global warming. The larger cause for alarm seems to be the melting or collapse of the polar ice caps. I recently read an article that warned that Antarctica, which stores 70 percent of the world’s fresh water, could lose the Ross Ice Shelf (a block of ice the size of France) suddenly and without warning and “that its collapse would make sea levels rise by at least 5 meters, with other estimates predicting a rise of up to 17 meters.” My question is how quickly would such a rise register?
Ice Age lesson predicts a faster rise in sea level
If the lessons being learned by scientists about the demise of the last great North American ice sheet are correct, estimates of global sea level rise from a melting Greenland ice sheet may be seriously underestimated. Writing this week (Aug. 31) in the journal Nature Geoscience, a team of researchers led by University of Wisconsin-Madison geologist Anders Carlson reports that sea level rise from greenhouse-induced warming of the Greenland ice sheet could be double or triple current estimates over the next century.
“We’re not talking about something catastrophic, but we could see a much bigger response in terms of sea level from the Greenland ice sheet over the next 100 years than what is currently predicted,” says Carlson, a UW-Madison professor of geology and geophysics. Carlson worked with an international team of researchers, including Allegra LeGrande from the NASA Center for Climate Systems at Columbia University, and colleagues at the Woods Hole Oceanographic Institution, the California Institute of Technology, University of British Columbia and University of New Hampshire.
Scientists have yet to agree on how much melting of the Greenland ice sheet — a terrestrial ice mass encompassing 1.7 million square kilometers — will contribute to changes in sea level. One reason, Carlson explains, is that in recorded history there is no precedent for the influence of climate change on a massive ice sheet.
Collapse of ice sheet would affect world’s coastlines differently
MARTIN MITTELSTAEDT
Globe and Mail Update
February 5, 2009 at 2:07 PM EST
“There is so much water locked away in the ice that if it were distributed evenly in the world’s oceans, it would raise sea levels by an average of five metres.
But a Canadian led research team has made an unusual discovery about what will happen if the ice melts: not all coastlines of the world will be affected equally.
Some lucky areas, most notably in Southern Chile and Argentina, will experience no sea level change at all along their coasts. But other places along the populous Atlantic and Pacific coasts of Canada and the U.S., will have seas rise by six to seven metres, inundating coastal cities such as Vancouver and New York with a much worse than expected increase.”
“One reason is that there is so much ice on West Antarctic that it exerts a huge gravitational pull on the surrounding ocean water, much like the moon is able to cause tides on earth.
If the ice were to melt, this attractive force would vanish and cause sea levels around the ice sheet in Antarctica to plunge, perhaps by as much as 20 metres to 30 metres, according to Dr. Mitrovica. But the water now attracted by gravity around the coast of southern continent will flow away if there is melting, causing additional sea level rise elsewhere in the world.
Another odd effect identified by the researchers is that the Antarctic bed rock on which the ice sheet currently rests will rise if there is melting. The ice is so thick it has caused the bedrock to be depressed by an estimated 500 metres to 1 kilometre. That means some land will rise, Atlantis-like, out of the ocean, if the ice melts.”
“The typical estimate of the sea-level change is five metres, a value arrived at by taking the total volume of the West Antarctic Ice Sheet, converting it to water and spreading it evenly across the oceans, says Mitrovica. “However, this estimate is far too simplified because it ignores three significant effects:
1. when an ice sheet melts, its gravitational pull on the ocean is reduced and water moves away from it. The net effect is that the sea level actually falls within 2,000 km of a melting ice sheet, and rises progressively further away from it. If the West Antarctic Ice Sheet collapses, sea level will fall close to the Antarctic and will rise much more than the expected estimate in the northern hemisphere because of this gravitational effect;
2. the depression in the Antarctic bedrock that currently sits under the weight of the ice sheet will become filled with water if the ice sheet collapses. However, the size of this hole will shrink as the region rebounds after the ice disappears, pushing some of the water out into the ocean, and this effect will further contribute to the sea-level rise;
3. the melting of the West Antarctic Ice Sheet will actually cause the Earth’s rotation axis to shift rather dramatically – approximately 500 metres from its present position if the entire ice sheet melts. This shift will move water from the southern Atlantic and Pacific oceans northward toward North America and into the southern Indian Ocean.
“The net effect of all of these processes is that if the West Antarctic Ice Sheet collapses, the rise in sea levels around many coastal regions will be as much as 25 per cent more than expected, for a total of between six and seven metres if the whole ice sheet melts,” says Mitrovica. “That’s a lot of additional water, particularly around such highly populated areas as Washington, D.C., New York City, and the California coastline.” Digital animation of what various sea-level rise scenarios might look like for up to six metres is at http://www.cresis.ku.edu/research/data/sea_level_rise.
I’d be very surprised if, even if we do solve global warming through the standard means, we don’t see in retrospect very scary alternative solutions such as increasing particulate content in the atmosphere to reduce solar radiation.
Geoengineering is certainly something that needs to be contemplated, if not actually investigated.
This Gristmill post argues that governments will inevitably choose to geoengineer, once things start to get bad.
Antarctic ice at risk if greenhouse gases rise even slightly
MICHAEL PERRY
Reuters News Service
March 18, 2009 at 9:45 PM EDT
SYDNEY — A large part of the ice covering West Antarctica could be lost if greenhouse gases in the atmosphere increase only slightly from today’s levels and ocean temperatures continue to rise, a study released on Thursday says.
Another related study said if the West Antarctic ice sheet collapsed and the East Antarctic ice sheet continued to melt at its marine margins, global sea level would rise seven metres from today’s level.