Temperatures around the tip of the Antarctic Peninsula started rising around 600 years ago, long before human activity would have had any influence on the region, scientists have discovered.
But they say the rate at which it’s warmed over the last 100 years is more unusual and out of line with natural variation, although it’s not necessarily unprecedented.
Centuries of continual warming meant that, by the time warming began to accelerate, the Antarctic Peninsula’s ice shelves were already poised for the dramatic break-ups seen since the 1990s. The Wilkins and Larsen A and B ice shelves are notable examples.
The region is now warming faster than almost anywhere else in the world. Average temperatures from James Ross Island have risen by nearly 2°C in the past 50 years.
“Continued warming to temperatures that now exceed the stable conditions of most of the Holocene is likely to cause ice-shelf instability to encroach farther southward along the Antarctic Peninsula,” wrote the authors in their report, published in Nature.
Researchers from Britain, Australia and France collected a 364-metre-long ice core from James Ross Island on the northeastern tip of the Antarctic Peninsula. They wanted to find out how much of the recently observed warming around the Earth is down to natural variations in the climate and how much can be blamed on human activity since the Industrial Revolution.
It might seem obvious to link the break-up of ice shelves with increased warming in the region. But researchers have been reluctant to make this link, because the record of temperature measurements in the area is short compared with the length of the natural variability.
The ice in Antarctica and parts of the Arctic is made of multiple layers of snow which have become compressed eventually turning into ice under the pressure. As the snow falls it traps bubbles of air, which contain a unique record of what the climate was like thousands of years ago.
This latest ice core – the longest yet from the Antarctic Peninsula – goes back some 50,000 years and reveals that, around 11,000 years ago, the peninsula was about 1.3°C warmer than today’s average temperatures. Dr. Robert Mulvaney from the British Antarctic Survey, is lead author of the study. He said:
What we see in the ice core temperature record is that the Antarctic Peninsula warmed by about 6°C as it emerged from the last Ice Age. By 11,000 years ago the temperature had risen to about 1.3°C warmer than today’s average and other research indicated that the Antarctic Peninsula ice sheet was shrinking at this time and some of the surrounding ice shelves retreated.
The warming demonstrated by Mulvaney and his colleagues suggests that loss of ice shelves is at least partially down to changes in the climate driven by man’s activities. Mulvaney said:
What we are seeing is consistent with a human-induced warming on top of a natural one.