Could Global Warming Disintegrate The West Antarctic Ice Sheet, Gradually Inundating Coastal Regions?
An article published in the scientific journal Nature, finds a substantial risk that warming from projected emissions of greenhouse gases during the next 100 years will cause the gradual disintegration of the West Antarctic Ice Sheet (WAIS), which would remake coastlines everywhere. In the most likely scenario the loss of land-based ice into the ocean would occur over the next five to seven centuries, but could become inevitable in as little as 100 years. In recent years, the global average sea level has been rising 0.25 to 0.5 centimeters, or 1 to 2 inches, a year.
The complete collapse of WAIS would cause sea level to rise rapidly, at ten times the rate of the recent past. Eventually, all of South Florida and more than a quarter of Louisiana would be permanently submerged, as would significant portions of all coastal cities including 15% of Washington DC. In Florida, Louisiana, South Carolina, Virginia, New York, and New Jersey, areas where about ten percent or more of the current population live would be permanently lost, according to a previous report of the National Academy of Sciences.
In low-lying countries like Bangladesh land loss would be much higher. "The good news is that collapse of WAIS is not imminent, but the bad news is that warming gases emitted during the next century could make collapse of WAIS inevitable thereafter. Society simply cannot afford to ignore long term consequences and take such a high-risk roll of the dice", said Dr. Michael Oppenheimer, author of the peer-reviewed article and an atmospheric physicist with the Environmental Defense Fund (EDF). "Once the ice sheet begins to disintegrate, there will be no turning back".
WAIS is composed of ice streams, vast rivers of land-based ice that end at floating ice shelves. Opinions vary on the degree to which the ice shelves impede the movement of WAIS toward the ocean. Ocean warming of only a few degrees, which is expected to occur in the next hundred years, could cause one or more of the floating ice shelves surrounding West Antarctica to thin and eventually disintegrate. Since ice shelves float, their disintegration does not increase sea level. But if the flow of WAIS into the ocean increased as a result, global sea level would rise. Rapid collapse of smaller ice shelves along the Antarctic Peninsula in recent years raises the possibility that WAIS’ ice shelves may be quick to disintegrate once they have been thinned by warming.
The Nature article examines other plausible, but less likely scenarios including: 1) the continued melting of some of the floating ice shelves accompanied by an increase of the land-based ice due to additional precipitation; 2) the very fast collapse of WAIS with a duration of as little as 250 years. The article largely rules out a catastrophic collapse within less than a century.
Several other recent findings add to concerns regarding the stability of WAIS: WAIS, as well as the entire Antarctic Ice Sheet, may already be losing ice and could be a contributing factor to the four to ten inches of sea-level rise that has occurred in the last hundred years.
WAIS may be inherently unstable and primed for collapse by climate changes of the distant past, according to a recent model of the ice sheet. Global warming could accelerate this process. It has been suggested that WAIS disappeared entirely at least once during a previous epoch when Earth was a few degrees warmer than today.
Considerable melting is already occurring on the undersides of some of WAIS’ ice shelves due to contact with the ocean, as indicated by recent measurements. An ocean warming of only a few degrees could cause these ice shelves to thin significantly. In contrast, some earlier studies suggested WAIS’ large ice shelves would remain intact until an atmospheric warming of 15 degrees Fahrenheit had occurred.
Significant warming of the deep ocean around Antarctica is likely to occur during the next century if Earth warms about 4 degrees Fahrenheit, rather than taking several centuries as some have thought. Warmer waters in the deep ocean around Antarctica would lead to increased melting under some of the floating ice, particularly in the vicinity of Pine Island Bay in the southeast Pacific sector of WAIS.
At other locations, unpredictable changes in ocean circulation may increase or decrease melting. "Reductions of greenhouse gases must begin now to insure our planet’s future. The potential for unprecedented loss of coastal regions should move policy makers to take swift and responsible action against global warming", said Dr. Oppenheimer. "In addition, it is imperative that governments increase support for research to reduce uncertainty over the response of WAIS to global warming".
NOTE: Dark dust particles from burning of coal have been falling in polar regions. Solar heating of the dark particles accelerates melting of the ice caps. Scientists recently discovered that the polar regions are warming faster than other regions.
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