August 29, 2013
East Antarctic Ice Sheet May Be More Vulnerable Than Previously Believed
April Flowers for redOrbit.com - Your Universe Online
A team of researchers used declassified spy satellite imagery from 1963 to 2012 to create the first long-term record of changes in the terminus of outlet glaciers – where they meet the sea – along 3,355 miles of the East Antarctic Ice Sheet's coastline.
The team used measurements from 175 glaciers to show the rapid and synchronized periods of advance and retreat the glaciers underwent coincided with cooling and warming. This suggests large sections of the ice sheet, which reaches thicknesses of more than 2.5 miles, could be more susceptible to changes in air temperature and sea-ice than scientists originally believed.
According to current scientific theories, the glaciers in East Antarctica are at less risk from climate change than areas such as Greenland or West Antarctica. This is due to the region’s extremely cold temperatures which can fall below minus 30°C at the coast, and much colder further inland. The Durham researchers say there is now an urgent need, however, to understand how vulnerable the East Antarctic Ice Sheet is becoming, as it holds the vast majority of the world's ice and enough to raise global sea levels by over 164 feet.
Dr Chris Stokes, in Durham's Department of Geography, said, "We know that these large glaciers undergo cycles of advance and retreat that are triggered by large icebergs breaking off at the terminus, but this can happen independently from climate change.” The findings of the new study were published in Nature.
"It was a big surprise therefore to see rapid and synchronous changes in advance and retreat, but it made perfect sense when we looked at the climate and sea-ice data. When it was warm and the sea-ice decreased, most glaciers retreated, but when it was cooler and the sea ice increased, the glaciers advanced.”
"In many ways, these measurements of terminus change are like canaries in a mine – they don't give us all the information we would like, but they are worth taking notice of,” said Stokes.
Despite large fluctuations in terminus positions between glaciers – linked to their size – the research team found three significant patterns emerged:
• Temperatures rose and most glaciers retreated in the 1970s and 80s.
• Most glaciers advanced and temperatures fell during the 1990s.
• During the 2000s, a mix of retreat and advance was recorded as a result of temperature increases and decreases.
Along the East Antarctic Ice Sheet's warmer Pacific Coast, trends in temperature and glacier change were statistically significant. The team found no significant changes along the much cooler Ross Sea Coast, which might be expected if climate is driving the changes.
The cause of the recent trends in air temperature and sea ice were difficult to unravel, according to Dr. Stokes, but were likely to reflect a combination of both natural variability and human impacts. Stokes added the changes observed in glaciers in East Antarctica need to be investigated further against the backdrop of likely increases in both atmospheric and ocean temperatures caused by climate change.
Dr Stokes notes, "If the climate is going to warm in the future, our study shows that large parts of the margins of the East Antarctic Ice Sheet are vulnerable to the kinds of changes that are worrying us in Greenland and West Antarctica – acceleration, thinning and retreat.
"When temperatures warm in the air or ocean, glaciers respond by retreating and this can have knock-on effects further inland, where more and more ice is drawn-down towards the coast. We need to monitor their behavior more closely and maybe reassess our rather conservative predictions of future ice sheet dynamics in East Antarctica."