Antarctic Ice Melting at Fastest Rate in 1,000 Years

Photo courtesy: Public domain/Public Domain

Summer ice is melting at a faster rate in the Antarctic peninsula than at any time in the last 1,000 years, new research has shown.

The evidence comes from a 364-metre ice core containing a record of freezing and melting over the previous millennium.

Layers of ice in the core, drilled from James Ross Island near the northern tip of the peninsula, indicate periods when summer snow on the ice cap thawed and then refroze.

By measuring the thickness of these layers, scientists were able to match the history of melting with changes in temperature.

Lead researcher Dr Nerilie Abram, from the Australian National University and British Antarctic Survey (BAS), said: "We found that the coolest conditions on the Antarctic peninsula and the lowest amount of summer melt occurred around 600 years ago.

"At that time temperatures were around 1.6C 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 10 times as much (5%) of the annual snowfall melting each year.

"Summer melting at the ice core site today is now at a level that is higher than at any other time over the last 1,000 years. And while 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."

Levels of ice melt on the Antarctic peninsula were especially sensitive to rising temperature during the last century, he said.

"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 melt," Abram added.

Dr Robert Mulvaney, from the British Antarctic Survey, who led the ice core drilling expedition in 2008 and co-authored a paper on the findings published on Sunday in the journal Nature Geoscience.

He said: "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.

"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."

The ice core record suggested a link between accelerated melting and man-made global warming. But a different and more complex picture has emerged from another region of Antarctica.

A separate US study, published in the same journal, shows that thinning ice from the West Antarctic Ice Sheet Divide cannot confidently be blamed on greenhouse gas emissions.

An ice core record from this site indicates a strong influence from unusual conditions in the tropical Pacific during the 1990s.

In that decade, an El Niño event – a cyclical system of winds and ocean currents that can affect the world's weather – caused rapid thinning of glaciers in the west Antarctic.


Summer ice is melting at a faster rate in the Antarctic peninsula than at any time in the last 1,000 years, a new study has shown. Photo courtesy: Nasa/AFP/Getty Images

The spike in temperature was little different from others that occurred in the 1830s and 1940s, which also saw prominent El Niño events.

"If we could look back at this region of Antarctica in the 1940s and 1830s we would find that the regional climate would look a lot like it does today, and I think we also would find the glaciers retreating much as they are today," said lead author Prof Eric Steig, from the University of Washington.

He said the same was not true for the Antarctic peninsula, the part of the continent closer to South America. Here, more dramatic changes were "almost certainly" a result of human-induced global warming.

Here's a video of a city-sized glacier collapsing.

Antarctic Ice Sheet May Cover a Vast Reservoir of Methane

Half the West Antarctic ice sheet and a quarter of the East Antarctic sheet lie on pre-glacial sedimentary basins containing around 21,000bn tonnes of carbon, said the scientists. Photo courtesy: Nasa

A vast reservoir of the potent greenhouse gas methane may be locked beneath the Antarctic ice sheet, a study suggests.

Scientists say the gas could be released into the atmosphere if enough of the ice melts away, adding to global warming.

Research indicates that ancient deposits of organic matter may have been converted to methane by microbes living in low-oxygen conditions.

The organic material dates back to a period 35m years ago when the Antarctic was much warmer than it is today and teeming with life.

Study co-author Prof Slawek Tulaczyk, from the University of California at Santa Barbara, said: "Some of the organic material produced by this life became trapped in sediments, which then were cut off from the rest of the world when the ice sheet grew. Our modelling shows that over millions of years, microbes may have turned this old organic carbon into methane."

Half the West Antarctic ice sheet and a quarter of the East Antarctic sheet lie on pre-glacial sedimentary basins containing around 21,000bn tonnes of carbon, said the scientists, writing in the journal Nature.

British co-author Prof Jemma Wadham, from the University of Bristol, said: "This is an immense amount of organic carbon, more than 10 times the size of carbon stocks in northern permafrost regions.

"Our laboratory experiments tell us that these sub-ice environments are also biologically active, meaning that this organic carbon is probably being metabolised into carbon dioxide and methane gas by microbes."

The amount of frozen and free methane gas beneath the ice sheets could amount to 4bn tonnes, the researchers estimate.

Disappearing ice could free enough of the gas to have an impact on future global climate change, they believe.

"Our study highlights the need for continued scientific exploration of remote sub-ice environments in Antarctica because they may have far greater impact on Earth's climate system than we have appreciated in the past," said Prof Tulaczyk.

The Antarctic ice sheet covers the southern continent's land mass and not the sea around it. Methane hydrates - a combination of frozen water ice and methane - are also found at the bottom of the oceans where they form as a result of cold temperatures and high pressures.