Giant floating ice shelf off the Antarctic Peninsula marks the end of a great flow of ice. The flow begins with snowfall in the continental interior, which compacts into ice and slowly makes its way to the edge of the continent and into the ocean. As climate change accelerates the breakup of ice shelves, it can speed the movement of the upstream ice across the land and into the sea.
Image: Sebastian Copeland
In Brief
- The land-based ice sheets of Greenland and Antarctica hold enough water to raise global sea level by more than 200 feet.
- A complex “plumbing system” of rivers, lakes and meltwater lies under the ice sheets. That water “greases” the flow of vast streams of ice toward the ocean.
- For millennia, the outgoing discharge of ice has been balanced by incoming snowfall. But when warming air or surface meltwater further greases the flow or removes its natural impediments, huge quantities of ice lurch seaward.
- Models of potential sea-level rise from climate change have ignored the effects of subglacial water and the vast streams of ice on the flow of ice entering the sea.
As our P-3 flying research laboratory skimmed above the icy surface of the Weddell Sea, I was glued to the floor. Lying flat on my stomach, I peered through the hatch on the bottom of the plane as seals, penguins and icebergs zoomed in and out of view. From 500 feet up everything appeared in miniature except the giant ice shelves—seemingly endless expanses of ice, as thick as the length of several football fields, that float in the Southern Ocean, fringing the ice sheets that virtually cover the Antarctic landmass. In the mid-1980s all our flights were survey flights: we had 12 hours in the air once we left our base in southern Chile, so we had plenty of time to chat with the pilots about making a forced landing on the ice shelves. It was no idle chatter. More than once we had lost one of our four engines, and in 1987 a giant crack became persistently visible along the edge of the Larsen B ice shelf, off the Antarctic Peninsula—making it abundantly clear that an emergency landing would be no gentle touchdown.
The crack also made us wonder: Could the ocean underlying these massive pieces of ice be warming enough to make them break up, even though they had been stable for more than 10,000 years?
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9 Comments
Add CommentAs I read Robin E. Bell's article, I realized that just as the popllation is in the middle of relocating above 200 feet, the pressure distribution change in the sea towards the equater is sure to produce an increase in the volume of magma venting in the ring of fire. So along with all the disruption in our geography, we also would seem to have a much poorer air supply to breath. Tell me I'm wrong someone...please!
Reply | Report Abuse | Link to thisI have a question about the estimate for global sea-level rise where Greenland is concerned. I read that if the Greenland Ice Sheet were to melt, global sea level would rise by about 7m. I also read that much of the landmass in Greenland is as much as 300m below sea level due to the downward pressure exerted by the ice mass. Ice cores of up to 3200 meters indicate that perhaps 10% or more of the ice sheet is below sea level.
Reply | Report Abuse | Link to thisSince liquid water has about 2/3 the density of ice, If the Greenland Ice Sheet is resting on land, some portion (possibly as much as 450m, or about 14%) of that ice displaces ocean water that would replace it.
My question is: Has this displacement been factored into the estimates for sea level change already? Has this displacement also been applied for Antarctica? Is the number really 200m or is it more like 180m after seawater displacement is factored in?
I recognize that there are other factors involved in sea-level rise, such as thermal expansion, etc.
these are inconvenient questions!
Reply | Report Abuse | Link to thisgreenland has been colder than average so far this winter, and just about all of asia is experiencing the coldest winter in 100 years!
vast parts of north america are also experiencing a record cold winter.
the winter of 2007 was the coldest in 20 years in the southern hemisphere (pay no attention to the melting ice sheets on the antarctic peninsula as it was caused by a change in oceanic currents, which brought an influx of warmer water from the north--unrelated to atmospheric temperatures in general).
its going to be quite a trick for the models to recover their trend predictions...let's see how they engineer it to keep the hoax alive, while the vast majority of those dying across asia are learning a thing or two about global warming.
the extreme pressure and temperature gradients being produced between high and low pressure systems at mid latitudes world wide is an indicator of colder northern and southern polar regions, not warmer.
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Edited by hallucinogenic toreador at 02/06/2008 10:15 AM
it's La Ninya, 'stupid'.
Reply | Report Abuse | Link to thistemperature trends averaged over a full el nino/la nina cycle or more are consistently up.
here is a nice easy little essay that might explain the basic math to you;
Uncertainty, noise and the art of model-data comparison
http://www.realclimate.org/index.php/archives/2008/01/uncertainty-noise-and-the-art-of-model-data-comparison/
how much ice needs to melt before you believe the evidence of your own eyes?
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Edited by u.k.gerda at 02/08/2008 12:38 PM
If Greenland is so much warmer than it has been in thousands of years, how did Eric the Red form a colony on Greenland in the 900's. (His son, Leif Erikson you will remember built a settlement in Newfoundland, Canada- L'Anse aux Meadows in 1001. ) The Greenland Colony expanded to have as many as 2-3000 people in the 1100's. It then gradually declined due to increasingly cold weather.
Reply | Report Abuse | Link to thisBefore the 1300's, active trading and communications were kept between the colony and Iceland and Norway--and especially the Church which maintained a bishop there and has records to this day regarding some of the ways of life and even dates of events such as marriages.
No, the colonists did not live like Eskimos (native Inuits) but primarily off of dairy farming and sheep with hundreds of acres in cultivated valleys supplying hay for the long winters. Sure it was cold -- but it is difficult to believe Greenland was not considerably warmer then than it is now. Take a look at those settlement locations now if you think not.
Ramifications of Weather Modification
Reply | Report Abuse | Link to thisIn the News.Global Warming, truth or consequences. Please pass
Reply | Report Abuse | Link to thison to your friends. Thanks
http://www.quazen.com/News/Opinions/Al-Gores-Decree-on-Global-Warming-is-Not-Our-Only-Crisis.51904
Al Gore's Decree on Global Warming is Not Our Only Crisis
http://www.quazen.com/Science/Environment/Our-Energy-Conservation-Dilemma.32660
Our Energy Conservation Dilemma
A little known fact is that ice needs 80 calories per gram to melt. While the calories go in it stays solid but when the last one goes in it suddenly melts. Our ice caps are under going this calory transference right now, melt waters are passing surface calories down into the Ice caps, when they have enough calories, huge areas of Ice will suddenly vanish. Another little known fact is Isostatic uplift. When enough ice disappears from a continental land mass, (which float on the magma below), they uplift usually suddenly due to friction, so we can expect earthquakes, tidal waves and increased volcanic activity as well as increased sea levels, regards, Peter
Reply | Report Abuse | Link to thisIs anyone aware of the folklore regarding "The Grinding of the Mills"... every 10,000 years (estimated) the shifting of the poles. I am not a scientist , just a science buff. Wouldn't such explain the current state of true north and or south? My quest for knowledge on this subject is an innate part of my being... so feed back would be greatly appreciated.
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