Ice shelf collapse tied to global warming

Scientists on Oct. 16 reported the first direct evidence linking the 2002 collapse of an Antarctic ice shelf to global warming. The researchers found that stronger westerly winds in the northern Antarctic Peninsula, fueled primarily by human-induced climate change, were responsible for the dramatic summer warming that led to the retreat and collapse of the Larsen B ice shelf. "This is the first time that anyone has been able to demonstrate a physical process directly linking the break-up of the Larsen Ice Shelf to human activity," said lead author Gareth Marshall from the British Antarctic Survey (BAS). The study, by BAS scientists as well as researchers at the University College London's Center for Polar Observation and Modeling and the Katholieke Universiteit Leuven in Belgium, was published in the "Journal of Climate." The 1,255-square mile ice shelf collapsed into the Weddell Sea over a 35-day period in early 2002. Scientists believe the 720 ft. thick shelf had been in place for some 5,000-12,000 years. Its disintegration was the third recent, sudden collapse of an Antarctic ice shelf, following the collapses of the 618-square mile Larsen A Ice Shelf in 1995 and the 425-square mile Wilkins Ice Shelf in 1998. The collapses did not affect sea levels–ice shelves are thick plates of ice, fed by glaciers, that float on the ocean around much of Antarctica. But scientists warn that the loss of ice shelves in the region could predicate sea level rise. Ice shelves act to hold back glaciers from the sea and keep warmer marine air at a distance from the glaciers. A study released in 2004 revealed that this concern has started to materialize. It found Antarctic glaciers melting and moving more quickly toward the sea in the wake of the collapse of the Larsen B ice shelf, with several of the glaciers moving at up to five times their previous speed. In this latest study, Marshall and his colleagues report that global warming–and manmade holes in the ozone layer–has changed Antarctic weather patterns. Scientists worldwide are convinced that human emissions of heat-trapping gases released by the burning of fossil fuels are largely responsible for temperature increases over the past century. The western Antarctic Peninsula has shown the biggest increase in temperatures observed anywhere on Earth over the past half-century. Stronger westerly winds are forcing warm air eastward and over the natural barrier created by the Antarctic Peninsula's 6,600 ft.-high mountain chain. During the past 40 years the average summer temperatures in this region of the north-east peninsula has been 36º Fahrenheit, but on days when warm winds top the mountains of the peninsula, temperatures rise by 9 to 18º Fahrenheit, the researchers said. This warming created the conditions that allowed the drainage of melt-water into crevasses on the Larsen Ice Shelf, a key process that led to its break-up in 2002. "Climate change does not impact our planet evenly–it changes weather patterns in a complex way that takes detailed research and computer modeling techniques to unravel," Marshall said. "What we've observed at one of the planet's more remote regions is a regional amplifying mechanism that led to the dramatic climate change we see over the Antarctic Peninsula."