Ice Shelf Collapse Triggers Debate
In February and March, an ice shelf known as the Larsen B ice shelf in the Antarctic Peninsula collapsed, leading many to raise once again the specter of global warming.
“The disintegration of the ice shelf—1,260 square miles in area and 650 feet thick—was most alarming to some because of the extraordinary rapidity of the collapse,” wrote the Washington Post on March 20. “The shelf is believed to have existed for as long as 12,000 years before regional temperatures began to rise, yet it disintegrated literally before scientists’ eyes over a 35-day period that began Jan. 31.”
Extremists sound alarm
Although there is no evidence to link the event to global warming, the New York Times could not help raising the issue in its March 20 edition. “While it is too soon to say whether the changes there are related to a buildup of the ‘greenhouse’ gas emissions that scientists believe are warming the planet, many experts said it was getting harder to find any other explanation.”
Though some scientists quoted were hesitant to link global warming to the collapse, they certainly didn’t dispel the notion. Ted Scambos, a glaciologist at the University of Colorado’s National Snow and Ice Center, told the San Francisco Chronicle on March 20, “We can’t say that CO2 or the other greenhouse gases have been dive bombing Antarctica, but we have our suspicions.”
Michael Oppenheimer, who recently joined the Princeton University faculty after serving at Environmental Defense, where he was chief scientist and held the Barbra Streisand Chair in Environmental Studies, told the Washington Post, “Ascribing a temperature trend in a small region like that to the broader global trend is difficult. Nevertheless, the collapse of the ice shelf in my opinion can be partially ascribed to human-induced climate change.”
Warming or cooling?
To its credit, the Washington Post noted Nature recently published a study that found the Antarctic has actually been cooling since 1966. Another study in Science recently found the West Antarctic Ice Sheet has been thickening rather than thinning. (See “New studies throw cold water on warming theory,” Environment & Climate News, March 2002.)
Although the Antarctic Peninsula has warmed over the past 50 years, it is a tiny part of the whole Antarctic continent. Unless one is willing to believe the peninsula is responding to global warming while ignoring regional cooling, it becomes very difficult to link the ice shelf collapse to global warming.
The study in Nature found the Antarctic has been cooling for some time now, contradicting the findings of the climate models upon which the case for global warming is built. Those models predict the Earth’s poles will warm more rapidly than the rest of the Earth.
According to the study, “Climate models generally predict amplified warming in the polar regions, as observed in Antarctica’s peninsula region over the second half of the 20th century.” The study finds, “Our spatial analysis of Antarctic meteorological data demonstrates a net cooling on the Antarctic continent between 1966 and 2000, particularly during summer and autumn.” The McMurdo Dry Valleys, for example, have cooled about 0.7 degrees Celsius per decade during this period of time.
The authors conclude, “Continental Antarctic cooling, especially the seasonality of cooling, poses challenges to models of climate, and ecosystem change.”
The research into the continent’s temperature record was motivated by the unexpected coldness of the summers, according to lead author Peter Doran with the Department of Earth and Environmental Sciences at the University of Illinois. “Two or three years ago when we were waiting for the big summers, we noticed that they didn’t come,” Doran told the Washington Post on January 14. “We were thinking that warm summers were the norm, and we were saying, ‘It’s going to get back to normal,’ but it never did.”
Michael Oppenheimer, chief scientist for Environmental Defense, isn’t buying it, however. “I’d be very careful with this,” he told the Washington Post. “My general view has been that there’s simply not enough data to make a broad statement about all of Antarctica.”
Of course, lack of data has never stopped Oppenheimer from making “broad” statements about the whole Earth. In a November 2000 Environmental Defense press release he stated, for instance, “The 1990s, likely the hottest decade of the past thousand years, capped decades of shrinking glaciers, thinning Arctic ice, intensifying rainstorms, and rising seas.” According to Oppenheimer, that means “The world must end its dependence on fossil fuels that are too dirty and too expensive. Governments must take action now.”
Antarctic ice sheet thickening
The study in the January 18 issue of Science concluded that the West Antarctic Ice Sheet (WAIS) is thickening, rather than thinning as was previously thought. Earlier studies found that in the Ross Sea Sector, “The grounding line (the point where the ice sheet loses contact with its bed and begins to float) has retreated nearly 1300 km along the western side of the Ross Embayment,” since the last glacial maximum.
This led researchers to predict that the entire WAIS would collapse in 4,000 years, implying a sea-level rise of 12.5 to 15 centimeters per century. This was based on a measurement of a loss of ice mass of -20.9 +/- 13.7 gigatons per year.
The authors of the Science study, Ian Joughin and Slawek Tulaczyk, with the Jet Propulsion Laboratory at the California Institute of Technology, note, “The ice-discharge estimates of earlier studies relied on relatively sparse in situ measurements of ice-flow velocity. For some ice streams the ... estimates were based on only one or two velocity measurements.”
The study used satellite remote sensing to get better measurements. Contrary to earlier studies, the authors found “strong evidence for ice-sheet growth (26.8 +/- 14.9 gigatons per year).” They conclude, “The overall positive mass balance may signal an end to the Holocene retreat of these ice streams.”
The Nature and Science research provide further evidence the climate models are poor tools for predicting climate change. They cannot properly simulate the current climate. They predict greater and more rapid warming in the atmosphere than at the surface, yet the opposite is happening. Moreover, they predict amplified warming at the poles, which are cooling instead.
What, then, is the most likely explanation for the break-up of the ice sheet? As John Daly says in the commentary elsewhere on this page, “The Larsen break-up has been coming for years, and its demise has long been expected. ... It's dramatic, happens on a grand scale, but also very, very, natural.”