Ice sheets in Greenland and Antarctica are losing little if any ice mass, thus having very little impact on global sea level, results from several recent studies show.
Andrew Shepherd of the University of Edinburgh and Duncan Wingham of University College London examined data from 14 satellite-based estimates of Greenland and Antarctic ice sheet volume taken since 1998. According to the scientists, who published their findings in the March 16 issue of Science magazine, the ice sheets are affecting sea level somewhere between a rise of 1.0 millimeters per year and a fall of 0.15 millimeters per year.
Examining the data for Greenland and Antarctica, the two scientists concluded, “Our best estimate of their combined imbalance is about 125 gigatons per year of ice, enough to raise sea level by 0.35 millimeters per year. This is only a modest contribution to the present rate of sea-level rise of 3.0 millimeters per year.”
The Shepherd and Wingham estimates mean less than an inch-and-a-half of sea level rise due to polar ice melt over the entire next century. “Yet even this unimpressive [estimate of] sea level increase may be far too large,” said Craig Idso, founder and former president of the Center for the Study of Carbon Dioxide and Global Change.
“For although two of Greenland’s largest outlet glaciers doubled their rates of mass loss in less than a year back in 2004, causing many climate alarmists to claim that the Greenland Ice Sheet was responding much more rapidly to global warming than anyone had ever expected, Howat et al. report–in the very same issue of Science as Shepherd and Wingham–that the two glaciers’ rates of mass loss ‘decreased in 2006 to near the previous rates’,” Idso continued.
“And these observations, in their words, ‘suggest that special care must be taken in how mass-balance estimates are evaluated, particularly when extrapolating into the future, because short-term spikes could yield erroneous long-term trends,'” Idso said.
Ice Sheet Stabilized
In the March 30 issue of Science, still more evidence indicated there is no reason to fear rising sea levels resulting from polar ice melt. Four scientists from Pennsylvania State University and the University of Texas studied a sedimentary wedge (also known as a “till delta” of rocks and sediment) deposited by West Antarctica’s Whillans Ice Stream.
The scientists determined the sedimentary wedge will prevent the West Antarctic ice sheet from sliding into the Antarctic Ocean any time in the foreseeable future.
The sedimentary wedge, the scientists explain, “serves to thicken the ice and stabilize the position of the grounding line,” such that “the ice just up-glacier of the grounding line is substantially thicker than that needed to allow floatation, owing to the restraint from friction with the wedge.” As a result, the scientists conclude, “the grounding-line will tend to remain in the same location despite changes in sea level (until sea level rises enough to overcome the excess thickness that is due to the wedge).”
The four scientists then conclude that a substantial rise of sea level would be required to budge the sedimentary line and destabilize the ice sheet. “Sea-level changes of a few meters are unlikely to substantially affect ice-sheet behavior,” the scientists report.
In a separate article in the same issue of Science, John B. Anderson, a scientist at Rice University, concluded, “at the current rate of sea-level rise, it would take several thousand years to float the ice sheet off [its] bed.”
Additionally, a study by five scientists also published in the March 30 issue of Science reports the ice thickness caused by the sedimentation line will tend to stabilize it against “any other environmental perturbation.”
The scientists report, “Large sea-level rise, such as the ~100-meter rise at the end of the last ice age, may overwhelm the stabilizing feedback from sedimentation, but smaller sea-level changes are unlikely to have synchronized the behavior of ice sheets in the past.”
“Cumulatively and individually, these studies show once again that global warming alarmism and scientific reality are in serious conflict,” said Competitive Enterprise Institute Senior Fellow Iain Murray. “In an effort to scare the American public into reducing their emissions, Al Gore and his fellow alarmists talk about 20 feet of sea level rise, while science shows that is pure fantasy.”
James M. Taylor ([email protected]) is managing editor of Environment & Climate News.