17 October, 2003
South American Glaciers' Big Melt
A dramatic image looking down the Calvo Glacier in Chile The Patagonia glaciers of Chile and Argentina are melting so fast they are making a significant contribution to sea-level rise, say scientists.
They report ice was lost at a rate sufficient to push up ocean waters by 0.04 millimetres per year during the period from 1975 through to 2000.
This is equal, the researchers say, to 9% of the total annual global sea-level rise from all mountain glaciers.
The American research team reports its findings in the journal Science.
The team combined data from a space shuttle mission in 2000 and survey data gathered on the ground to study the 63 largest Patagonia ice fields.
They compared ice loss rates between 1968 and 1975, and from 1975 to 2000. As well as the general increase in melting, the team also found accelerated ice-mass loss between 1995 and 2000.
This period saw melting sufficient to push up sea-levels by 0.1 millimetres per year.
In comparison, the team says, Alaska's glaciers, which cover an area five times larger, account for about 30% of the total annual global sea-level rise from mountain glaciers.
The researchers, led by Eric Rignot, from the US space agency's Jet Propulsion Laboratory, believe climate change has led to the region experiencing a rise in air temperatures and decreased precipitation.
Still, those factors alone are not sufficient to explain the rapid thinning.
Lucia Glacier: Like many others its leading edge calves into a lake The rest of the story appears to lie primarily in the unique dynamic response of the region's glaciers to climate change, the researchers believe.
"The Patagonia ice fields are dominated by so-called 'calving' glaciers," Rignot said.
"Such glaciers spawn icebergs into the ocean or lakes and have different dynamics from glaciers that end on land and melt at their front ends.
"Calving glaciers are more sensitive to climate change once pushed out of equilibrium, and make this region the fastest area of glacial retreat on Earth," he said.