Following on from last week’s Graph of the Day showing the downward spiral in Arctic sea ice, comes disturbing findings from the Australian National University and the British Antarctic Survey: summer ice melting in the Antarctic Peninsula has intensified almost ten-fold in the last 600 years, with the most rapid melting occurring in the last 50.
The research, published in the latest edition of the journal Nature Geoscience, will help make more accurate projections about the direct and indirect contribution of Antarctica’s ice shelves and glaciers to global sea level rise, and follows the drilling of a 364-metre long ice core from James Ross Island, near the northern tip of the Antarctic Peninsula.
That ice core was designed to measure past temperatures in the area, but it was soon found that it could give a unique and unexpected insight into ice melt in the region.
From the ANU press release:
“Summer melting at the ice core site is now at a level that is higher than at any other time over the last 1,000 years,” says lead author, Dr Nerilie Abram of the ANU Research School of Earth Sciences and British Antarctic Survey.
Visible layers in the ice core indicated periods when summer snow on the ice cap thawed and then refroze. By measuring the thickness of these melt layers, the scientists were able to examine how the history of melting compared with changes in temperature at the ice core site over the last 1,000 years.
“We found that the coolest conditions on the Antarctic Peninsula and the lowest amount of summer melt occurred around 600 years ago,” said Dr Abram.
“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%. Today, we see almost ten 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.”
This is only the second reconstruction of past ice melt on the Antarctic continent, and the first time it has been demonstrated that past levels of ice melt responded in a non-linear way to climate warming.
“What that means is that the Antarctic Peninsula has warmed to a level where even small increases in temperature can now lead to a big increase in summer ice melt. This has important implications for ice instability and sea level rise in a warming climate,” said Dr Abram.
Dr Robert Mulvaney from the British Antarctic Survey led the ice core drilling expedition and co-authored the paper.
“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,” he 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.”
Dr Abram adds: “The Antarctic Peninsula has warmed faster than any other place in the Southern Hemisphere over the last 50 years, and scientific assessments attribute this, at least partly, to human causes. In other parts of Antarctica, such as the West Antarctic Ice Sheet, the picture is more complex and it is not yet certain whether the levels of recent ice melt and glacier loss are exceptional or caused by human-driven climate changes.”
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