London: Two glaciologists have determined that Antarctica isn’t melting as much as expected because it undergoes a seasonal pattern of warming.
During the continent’s summer this time last year, there was less melting than at any time in the 30 years that there have been reliable satellite measurements of the region.
According to a report in New Scientist, two glaciologists writing in Eos, the weekly newspaper of the American Geophysical Union, have said that the apparent contradiction is explained by the seasonal pattern of warming.
The continent’s winters and springs have warmed most, but it is still too cold in these seasons for anything to melt.
Melting in Antarctica happens almost entirely in the summers, which have warmed very little, according to Andrew Monaghan of the National Center for Atmospheric Research in Boulder, Colorado, and Marco Tedesco of the City College of New York.
“In 2005, we had summer melting occurring inland as well as over the coastal ice shelves, and over areas up to 2500 metres above sea level,” said Tedesco.
Even during the exceptionally low melt of last summer, ice on the Antarctic peninsula, which stretches out towards South America, continued to melt.
The Wilkins ice shelf, which is attached to the peninsula, has been collapsing rapidly since February 2008.
The continent’s huge ice sheets contain enough frozen water to raise sea levels globally by around 60 metres.
According to Tedesco and Monaghan, the main factor in how much they warm each summer is the strength of the winds that circle the continent.
Circumpolar winds act as a barrier to warm air.
They have become stronger over the past four decades, effectively sealing off most of the continent each summer from the effects of global warming.
The circumpolar winds appear to have strengthened because the ozone layer in the stratosphere has thinned.
This has made the lower stratosphere cooler and generated stronger winds beneath.
But Tedesco has warned that as the ozone hole heals in the coming decades, the winds will weaken, the continent will become much warmer in summer – and melting will increase.
ANI
