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Arctic is warmer than in 40,000 years

October 24, 2013 in Arctic, Climate, Permafrost, Polar ice, Science, Warming

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Gifford MIller collecting the now-exposed tundra plants on Baffin Island, Canada. These climate clocks suggest unprecented warmth in the Arctic Image: Gifford Miller via AGU

The now-exposed tundra plants on Baffin Island, Canada suggest exceptional warmth in the Arctic
Image: Gifford Miller via AGU

By Tim Radford

Average summer temperatures in the Canadian Arctic are now at the highest they’ve been for approaching 50,000 years, new evidence suggests.

LONDON, 24 October - Good news for Arctic mosses, if not for any other Arctic creatures: little tundra plants that have been buried under the Canadian ice can feel the sunlight for the first time in at least 44,000 years.

The implication is that the Arctic is now, and has been for the last 100 years, warmer than at any time in the last 44,000 years and perhaps for the last 120,000 years.

This also means that the Arctic is warmer now than it was in what geologists call the early Holocene, the end of the last Ice Age – when the peak summer sunlight was roughly nine per cent greater than it is today, according to Gifford Miller of the University of Colorado Boulder, in the US.

The mosses studied by Dr Miller, of course, could feel nothing: they were dead. But they could tell a story, all the same.

The Arctic ice cap has been in constant retreat for the last century, and glaciers almost everywhere have been melting: there are fears that the process has begun to accelerate as greenhouse gases concentrate in the atmosphere.

But as the ice recedes, it exposes evidence of the past, preserved over the millennia in the natural deep freeze.

Creating a timeline of climate change

The researchers used a technique called radiocarbon dating to establish that the mosses had been screened from the elements for at least 44,000 to 51,000 years. Since radiocarbon dating is only accurate for about 50,000 years, the mosses could have been buried for perhaps 120,000 years, since the last “interglacial” when the polar regions experienced a natural thaw.

Miller and colleagues report in Geophysical Research Letters that they did their fieldwork on Baffin Island in the Arctic Circle, and measured the radiocarbon ages of the dead mosses in at least four different locations.

They were careful to pick their 145 samples within one metre of the receding ice cap. Since the ice is receding at two or three metres a year, they could be sure the plant tissues had just been exposed that season.

Since the plants could only have taken root in sunlight, they were evidence that the exposed terrain was once free of ice. They became silent witnesses, telling researchers about the changes through time in the frozen North.

“The key piece here is just how unprecedented the warming of Arctic Canada is. This study really says the warming we are seeing is outside any kind of known natural variability, and it has to be due to increased greenhouse gases in the atmosphere,” said Miller.

Recent decades critical

Since radiocarbon clocks can only tick for so long, the Colorado team used ice cores to provide clues to the climate history of Baffin Island: each winter’s snowfall and summer melt is preserved in the icepack and like the growth rings in a tree provides a calendar of annual change.

The last time temperatures on Baffin Island were as high as today was about 120,000 years ago. About 5,000 years ago, after a mellow period in the early Holocene, the Arctic began to cool again, and stayed cool until the beginning of the last century.

“Although the Arctic has been warming since about 1900, the most significant warming in the region didn’t really start until the 1970s,” said Dr Miller.

“And it really is in the last 20 years that the warming signal from that region has been just stunning. All of Baffin Island is melting, and we expect all of the ice caps to disappear, even if there is no additional warming.” - Climate News Network

Thawing tundra threat to frozen carbon

February 11, 2013 in Science

 

Svalbard tundra - how fast it thaws is crucial     Image: Billy Lindblom

Svalbard tundra – how fast it thaws is crucial            Image: Billy Lindblom

By Tim Radford

The melting of Arctic ice frozen for many thousands or even millions of years is speeding up, a potential route for carbon frozen deep below ground level to seep into the atmosphere.

LONDON, 12 February – The first kiss of sunlight on the frozen soils of the Arctic could spell increasing trouble as the world warms.

The return of the spring sun melts domes and lakes of frozen water called thermokarsts – karst is a word usually linked to limestone country, but it has been pressed into service as a label for the hard surfaces caused by ice.

Within this ice is dissolved organic carbon. Once the ice melts, microbes get to work releasing carbon dioxide into the air. The soil thaws, the surface collapses, lakes form, water flows, land surfaces erode which in turn releases more carbon dioxide to create more warming, to make the tundra even more vulnerable to spring thaw, and of course to accelerated warming.

This is not a scare story. It is happening now, according to Rose Cory of the University of North Carolina and colleagues who report in the Proceedings of the National Academy of Sciences.

They analysed water from 27 undisturbed sites in Alaska, and seven unique thermokarst failures – a polite word for landslides – near Toolik Lake in Alaska. The places they examined had been frozen for at least 10,000 years, and in some places two million years.

Speed the key factor

 

The team found dissolved organic carbon in all of them, and they found that newly-exposed muddy water was liable to surrender 40% more CO2 to the atmosphere.

This has of course been going on at the fringe of the Arctic permafrost for at least 10,000 years. The hazard is not in the process itself, but in its potential acceleration: nobody knows how much carbon is stored in the Arctic tundra as a greenhouse gas source, and nobody can guess what proportion of this will be released as the world warms. Thermokarsts are also found on a smaller scale in the Himalayas and the Swiss Alps.

But, as the soils warm, and the microbes get a chance to draw breath and get to work, say the authors, “the ultimate fate of deep, frozen soil carbon will be affected by coupled photobiological processing, by the available light field in streams that receive thermokarst drainage, and eventually by the landscape configuration of lakes and streams.”- Climate News Network