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Researchers: Seas Could Rise Dramatically in Rapid Ice Melt; 'What We are Doing is Irreversible'

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PRINCETON, New Jersey -- Something is missing from the estimates of future sea level rise in the recent report by the Intergovernmental Panel on Climate Change: the potentially catastrophic impact of a rapid melt of the Greenland and Antarctic ice sheets.

The IPCC asserts that melting by dynamic processes is too poorly understood to be included in scientific simulations, but many scientists disagree and believe that the report underestimates the threat that global warming will pose to coastal cities over the next century. Dynamic melting begins at the base of an ice sheet, where it meets the ground. As ice turns to water, the whole sheet can move as if part of a stream. Sea level could rise rapidly if dynamic melting pushes ice from land to ocean.

“The IPCC does not include dynamic processes where the ice flows rather than melts,” said Michael Oppenheimer, a geoscientist at Princeton University. “The bottom line is that the ice sheets are a big threat.” Oppenheimer estimates that the volume of water trapped in the Greenland ice sheet is equivalent to over twenty feet in sea level rise, and the western Antarctic ice sheet is equivalent to about fifteen feet.

The IPCC report estimates that sea level will increase between seven inches and two feet by the year 2100. Ice sheet flow was omitted from the report despite recent observations of the thinning of ice shelves and streams because some scientists are concerned that these are “transient effects,” not necessarily due to global warming, according to Jonathan Gregory. Gregory, a meteorologist at the University of Reading in England, is an author of the report who thinks sea level changes will be slow. “Sea level is more of a long-term issue,” he said. “The time scale for ice sheets to melt is centuries.”

Aside from dynamic melting, global warming largely raises sea level through two other processes: the gradual melting of ice sheets and the thermal expansion of the oceans because of increased temperature. Imagine the ocean as a big fishbowl- the volume of water would increase by both adding melt from ice initially stored outside the bowl and by heating the fishbowl itself.

According to Dean Roemmich, an expert on ocean currents at the Scripps Institute of Oceanography in California, one quarter of the inch-per-decade sea level rise over most of the 20th century is from thermal expansion and the remainder is due to gradual melting of ice. This combination of melting and expansion caused sea level to rise between an estimated six and nine inches over the course of the last century.

“When we talk about global warming, we are talking mostly of the oceans because the atmosphere has little capacity to hold heat,” explains Roemmich. He and other scientists estimate the oceans have absorbed more than eighty percent of the heat produced by human emissions.

One problem in projecting oceanic change is that no one is sure exactly how and where warmer temperatures will influence thermal expansion in the oceans. “Heat is not stored uniformly throughout the ocean,” explained University of Reading’s Gregory; the current models just aren’t good enough yet. An international group chaired by Roemmich has deployed about 3,000 flotation devices to collect data on the oceans, which Gregory said should help refine future models of sea level change.

But the ice sheets are “already frittering away at the edges, adding to sea level rise,” emphasized Princeton’s Oppenheimer. Glaciers are shrinking and ice shelves such as the Larsen B, a shelf about the size of Yosemite National Park, are falling into the seas, he says.

Ice movement was incorporated into the models of a study published this January in the journal Science by Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research in Germany. His team projects a sea level rise between twenty inches and four and a half feet by the end of the 21st century. This is faster than the current IPCC predictions. Furthermore, a recent review by Rahmstorf and colleagues demonstrates that sea level rise has been following the upper limits of previous predictions – such as those from the 2001 IPCC report.

“What we are doing is irreversible,” warned Oppenheimer. “The last time the earth was as warm as it will get this century, the sea level was four to six meters [or 12 to 18 feet] higher.” That was 125,000 years ago. At that point in earth’s history, of course, there weren’t billions of human beings living on the earth’s coasts. Today, for example, an 18-foot increase in sea level would swamp the barrier islands south of Long Island and flood JFK International Airport.

Useful links for a visual look at sea level rise:,-72.8974&z=4&m=0

Views expressed in this article do not necessarily reflect those of, its staff or its advertisers.

Reader Comments

2 people have commented so far. cloud add your comment

What am I missing here? If, at 125,000 years ago, the "earth was as warm as it will get this century", where were all of the people leaving their carbon footprint, causing the global warming? Where was General Motors, and all of the power companies generating all of the pollutants that "unequivocally" are causing global warming? What kind of incandescent light bulbs were they using at that time? Didn't they yet have the new bulbs that only cost $10 apiece? Those people must have been idiots!
   comment# 1   - Dean Streblow · Duluth, MN USA · Apr 7, 2007 @ 12:22pm

Climate The expansion of the Germanic tribes 750 BC AD 1 (after the Penguin Atlas of World History 1988): Settlements before 750BC New settlements until 500BC New settlements until 250BC New settlements until AD 1The Nordic Bronze Age was characterized by a warm climate that began with a climate change circa 2700 BC (comparable to that of present-day Mediterranean). The warm climate permitted a relatively dense population and good farming, for example grapes were grown in Scandinavia at this time. However a small change in climate between 850 BC and 760 BC and a more radical one circa 650 BC brought in a deteriorating, wetter and colder climate (sometimes believed to have given rise to the legend of the Fimbulwinter). It seems likely that the climate pushed the Germanic tribes southwards into continental Europe. During this time there was Scandinavian influence in Eastern Europe (and a thousand years later, the numerous East Germanic tribes that claimed Scandinavian origins (e.g. Langobards, Burgundians, Goths and Heruls) rendered Scandinavia (Scandza) the name womb of nations in Jordanes' Getica). In fact, the Scandinavian influence on Pomerania and northern Poland from period III onwards was so considerable that this region is sometimes included in the Nordic Bronze Age culture (Dabrowski 1989:73). Due to the climate change and the loss of population, the Nordic countries are generally described as going through a cult
   comment# 2   - Hmmm · Sweden · Jan 15, 2008 @ 1:13pm
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