Australian and British scientists have uncovered startling evidence of rapid ice melt in Antarctica, posing concerns about rising sea levels and other serious impacts of climate change.
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The Australian National University's Nerilie Abram recently returned from an expedition with the British Antarctic Survey during which an extremely rare reconstruction of past ice melt was undertaken.
The international science team drilled a 364-metre long ice core from James Ross Island, near the northern tip of the Antarctic Peninsula, to measure past temperatures in the area.
What they discovered was that summer ice melting has escalated dramatically over the past 50 years.
Today there is a ten-fold increase in the annual melt from what occurred hundreds of years previously.
The core drill samples provided information that helped the scientists determine ice melt levels for the past thousand years.
''We found that the coolest conditions on the Antarctic Peninsula and the lowest amount of summer melt occurred around 600 years ago,'' Dr Abram said.
''At that time temperatures were around 1.6°C lower than those recorded in the late 20th century and the amount of annual snowfall that melted and refroze was about 0.5 per cent.
''Today, we see almost 10 times as much of the annual snowfall melting each year. Whilst temperatures at this site increased gradually in phases over many hundreds of years, most of the intensification of melting has happened since the mid-20th century.''
Dr Abram said the Antarctic Peninsula had warmed faster than anywhere in the Southern Hemisphere over the last half century, and scientific assessments attribute this partly to human causes.
The melting was starting to cause ice shelves to collapse and mountain glaciers to lose ice into the ocean.
The amount of melting and the areas where that melting is happening will respond very sensitively to any further warming of the climate in the area, she said.
Only one other Antarctic ice-melt reconstruction has been done, making records of past ice melt incredibly rare. ''This is because the ice cores that are used to reconstruct past climate and environmental changes in Antarctica are usually collected high on the main Antarctic ice sheets where summer temperatures are still well below freezing,'' Dr Abram said.
''In this case, we were working on an ice core from one of the most northerly and relatively warm parts of Antarctica, and in a place where climate has been warming very rapidly. When we went out to drill the ice core we hadn't anticipated that we would get such a valuable record showing what the history of ice melt had been at the site. It was an unexpected, but as it turns out really important, bit of science.''
The expedition was led by Robert Mulvaney from the British Antarctic Survey, who has co-authored a research paper with Dr Abram that is being published in the latest edition of Nature Geoscience journal.
''Having a record of previous melt intensity for the peninsula is particularly important because of the glacier retreat and ice-shelf loss we are now seeing in the area,'' Dr Mulvaney said.
''Summer ice melt is a key process that is thought to have weakened ice shelves along the Antarctic Peninsula leading to a succession of dramatic collapses, as well as speeding up glacier ice loss across the region over the last 50 years.''
Understanding how ice melt responds to a warming climate is particularly important for predicting how quickly sea levels might change in the future.
Summer melting is a process that weakens ice shelves and causes them to collapse all together. It also causes glaciers to lose ice more quickly.
