New satellite images reveal that large Antarctic ice sheets are "just a fewdegrees" away from a potentially catastrophic meltdown. If the ice melts,billions of gallons of water will rush into the oceans, raising sea levelsmuch more rapidly than has been predicted.
Polar ice has been melting for the past 14,000 years, and sea levels havebeen steadily rising. The EPA has been predicting a rise of a foot eachcentury. But if Antarctic ice sheets melt, the world's oceans could suddenlyrise 3 feet by the year 2100, which would wipe out large, low-lying areas ofcontinents as well as entire island nations. Hundreds of millions of peoplecould have their homes permanently disappear.
Melting polar ice hasn't been considered to be a significant factor inrising sea levels in the past, but new evidence, published in the Journal ofGlaciology, shows how floating sheets of ice are at major risk of breakingoff during short periods of warm weather. When air temperatures rise, moreice melts, forming deep pools of water. The water forces its way into cracksin the ice shelf, setting up a catastrophic chain reaction. Cracks in theice widen, breaking off massive chunks of the ice sheet. Just a few degreesof global warming could trigger these ice chunks to break off.
Christina Hulbe, of NASA's Goddard Space Flight Center, says, "The weight ofthe water essentially forces the cracks open, so a relatively small amountof climate warming can destroy a large, centuries-old ice shelf."
Scientists previously thought ice shelves stayed too cold to be vulnerableto this type of break-up, but new analysis shows that right now they areclose to their critical limit. Huge sheets of ice act as dams that hold backrivers of ice that extend far inland. If one of these breaks off, a hugegush of ice that had been on solid ground could flow rapidly into the sea,says Ted Scambos of the National Snow and Ice Data Center at the Universityof Colorado. "The Antarctic has been up to now a relatively minor player insea-level rise, but it is the 600 pound gorilla in a way."
The Larsen Ice Shelf in Antarctica broke up several years ago. Scambos saysthat the new study shows that the Ross Ice Shelf, which is much larger thanthe Larsen Shelf (about the size of France), is at a critical juncture andcould break up within the next 20 to 50 years. However, it would still be atleast 100 years-perhaps several hundred-before the break-up fed asignificant amount of water into the oceans. A 1999 study by Britain'sMeteorological Office concluded that there could be a six foot rise in sealevels during the next few centuries.
Melting ice means that less sunlight is reflected, accelerating globalwarming. Since water and earth are darker than ice, they absorb moresunlight and warm up the whole planet.
While scientists and politicians argue over whether global warming reallyexits, the ocean is steadily gaining ground, and this doesn't just effectplaces that are far away. The Mississippi River Delta gave up about 16square miles of land to the Gulf of Mexico every year between 1930 and 1990.But the rate has increased to about 25 square miles a year, according to astudy released by coastal geologist Shea Penland, of the University of NewOrleans. "We've living on the verge of a coastal collapse," she warns.
New Orleans may be the first U.S. casualty. The city is 8 feet below sealevel and is protected by manufactured and natural barriers. But many ofthese tiny islands are expected to disappear by 2050, and the city itself issinking at a rate of 3 feet per century.
The director of the U.S. Geological Survey, Chip Groat, warns, "With theprojected rate of subsidence, wetland loss and sea-level rise, New Orleanswill likely be on the verge of extinction by this time next century."
The new U.S. administration plans to curtail studies of this type.
For the MSNBC story, click here.
For the New Scientist story, click here.
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