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Category — Arctic Sea Ice

Dark shadow falls on melting icecap

Tim Radford

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Signs of melting can be seen as darkness descends on the Greenland icecap. Image: Matthew Hoffmann/NASA ICE via Wikimedia Commons

Dust blowing in from warming areas of the Arctic is causing the Greenland icecap to melt faster by reducing the whiteness that reflects light and keeps it cool 

French scientists have identified a new mechanism that could cause the Greenland icecap to melt even faster – because dust is making its surface darker.

Marie Dumont, of the French national meteorological service, Météo-France, reports with colleagues in Nature Geoscience that, since 2009, the snows of the Arctic region’s biggest single permanent white space have been steadily darkened by “light-absorbing impurities” − known to the rest of the world simply as dust.

The Arctic has always been cold and white, simply because it is not just cold but is also white. The phenomenon is called albedo. Regions with a high albedo reflect light and stay cooler, so ice is a form of self-insulation.

Conversely, things that absorb light become warmer − and satellite data analysed by Dr Dumont and her fellow researchers shows that the Greenland ice is getting darker in the springtime.

They think the dust is blowing in from areas of the Arctic that are losing snow cover much earlier in the season as the climate warms. And, they calculate, this steady darkening alone has led to “significant” melting of the icecap.

This finding is ominous. What the researchers have identified is yet another case of what engineers call positive feedback. In the last 30 years, the Arctic sea ice has been in retreat, and researchers expect that, later in the century, the Arctic ocean will be entirely free of ice most summers. [Read more →]

June 13, 2014   No Comments

No way back for West Antarctic glaciers

Tim Radford

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Birth of an iceberg: a massive crack in West Antarctica’s Pine Island glacier. Image: Nasa Earth Observatory via Wikimedia Commons

Satellite data analysis reveals the ominous news that the melting glaciers of West Antarctica have passed the ‘point of no return’ as the southern hemisphere gets warmer

The glaciers of the West Antarctic may be in irreversible retreat, according to the evidence of satellite data analysed by scientists at the US space agency Nasa.

The study of 19 years of data, due to be reported in the journal Geophysical Research Letters, confirms the ominous news that the southern hemisphere is not just warming − it is that it is warming in a way that speeds up the melting of the West Antarctic glaciers.

Long ago, glaciologists began to wonder whether the West Antarctic ice sheet was inherently unstable. The water locked in the ice sheet in the Amundsen Sea region – the area the Nasa researchers examined − is enough to raise global sea levels by more than a metre. If the whole West Antarctic ice sheet turned to water, sea levels would rise by at least five metres. [Read more →]

May 26, 2014   No Comments

Greenland ice may melt even faster

 Tim Radford

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Melting away: an aerial view of the margin of Greenland’s threatened ice sheet. Image: Hannes Grobe/Alfred Wegener Institute via Wikimedia Commons

Research scientists discover that the vulnerability of Greenland’s glaciers to global warming is much greater than feared, increasing the threat of rising sea levels around the globe 

Just days after US researchers identified geophysical reasons why West Antarctica’s glaciers are increasingly vulnerable to global warming, a partner team has pinpointed a related cause for alarm in Greenland.

Many of the bedrock crevices and canyons down which the island’s glaciers flow have basements that are below sea level. This means that as warm Atlantic waters hit the glacier fronts, the glaciers themselves become more vulnerable to global warming and increasingly likely to melt at a faster rate.

Researchers have been worried for years about rates of melting in Greenland, which is why scientific attention to the vast, ancient ice cap has been stepped up. But the latest finding suggests that what had seemed bad news could turn out to be much, much worse.

If accelerated melting does happen – and all such predictions will be tested initially by yet more research, and then ultimately by time itself – it will be the consequence of an unholy mix of man-made global warming and entirely accidental geomorphology.

The presumption is that terrestrial landforms are routinely above the sea’s highest tides. But Mathieu Morlighem, of the University of California, Irvine, and colleagues – one of whom is Eric Rignot, who authored the research on West Antarctic glaciers, reported in Nature Geoscience − found that this is not always the case. [Read more →]

May 26, 2014   No Comments

Greenland’s icecap loses stability

Tim Radford

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The calving front of the Jakobshaven Glacier in western Greenland in April 2012. Image: NASA ICE via Wikimedia Commons

Greenland is losing ice from part of its territory at an accelerating rate, suggesting that the edges of the entire ice cap may be unstable.

Greenland – the largest terrestrial mass of ice in the northern hemisphere – may be melting a little faster than anyone had guessed.

A region of the Greenland ice sheet that had been thought to be stable is undergoing what glaciologists call “dynamic thinning”. That is because the meltwater from the ice sheet is getting into the sea, according to a study in Nature Climate Change.

In short, Greenland’s contribution to sea level rise has been under-estimated, and oceanographers may need to think again about their projections.

Shfaqat Khan from the Technical University of Denmark and colleagues used more than 30 years of surface elevation measurements of the entire ice sheet to discover that overall loss is accelerating. Previous studies had identified melting of glaciers in the island’s south-east and north-west, but the assumption had been that the ice sheet to the north-east was stable. [Read more →]

April 15, 2014   No Comments

Whale dumps temper Antarctic warmth

Alex Kirby

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Whales play a key part in recycling iron and carbon in the Antarctic. Image: US National Oceanic & Atmospheric Administration

By enriching the seas with iron expelled from their digestive systems, sperm whales are helping to slow the warming of the Antarctic, scientists say.

There is plenty yet to learn about the causes and effects of climate change, and here is one fact you may perhaps not have known until now: defecating sperm whales are helping to slow the warming of the Southern Ocean.

A team of Australian scientists and colleagues based at Flinders University in Adelaide reported inProceedings of the Royal Society B (in 2010) that the whales help to increase levels of iron in Antarctic waters (which are iron-deficient).

Iron is important for marine life, and the polar oceans are important for helping to regulate atmospheric CO2 levels. So the whales’ personal hygiene is helping vastly smaller lifeforms to thrive, which in turn keeps the ocean ecosystem in balance and able to recycle carbon safely to the seabed.

Scientists had believed that the whales’ breathing decreased the efficiency of the Southern Ocean’s biological pump by returning carbon from the depths to the surface and thence to the atmosphere, where it would add to the greenhouse gases already there.

But the Flinders team says that by consuming prey in deep water (the whales search for squid  at 1,200 metres or even further down) and then releasing iron-rich liquid faeces into the sunlit zone near the surface, the whales instead stimulate new primary production and return the carbon to deep water. [Read more →]

March 28, 2014   No Comments

Arctic ‘is set to reach 13°C by 2100′

Alex Kirby

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Iceberg in Rødefjord (Scoresby Sund), Greenland: Arctic sea ice volume has shrunk by 75% since the 1980s. Image: Hannes Grobe 20:05, 16 December 2007 (UTC) via Wikimedia Commons

There is wide political agreement that global average temperatures should not rise more than 2°C above their level several centuries ago. The rise some scientists expect in the Arctic by 2100 is more than six times as great.

US scientists say that by the end of this century temperatures in the Arctic may for part of each year reach 13°C above pre-industrial levels. Global average temperatures have already risen by about 0.8°C over the level they were at in around 1750.

The Intergovernmental Panel on Climate Change said in its 2013 Fifth Assessment Report that it thought the probable global temperature rise by 2100 would be between 1.5 and 4°C under most scenarios. Most of the world’s governments have agreed the global rise should not be allowed to exceed a “safety level” of 2°C.

But James Overland, of the US National Oceanic and Atmospheric Administration, and colleagues, writing in the American Geophysical Union’s journal Earth’s Future, say average temperature projections show an Arctic-wide end of century increase of 13°C in the late autumn and 5°C in late spring for a business-as-usual emission scenario.

By contrast, a scenario based on climate mitigation would reduce these figures to 7°C and 3°C respectively. The team say they consider their estimates “realistic”, and they have used a large number of models in reaching them. [Read more →]

February 23, 2014   No Comments

Atlantic changes are warming Antarctic

Tim Radford

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Ice covering the Bellingshausen Sea in Antarctica – and feeling the impact of changes in the Atlantic. Image: NASA/Michael Studinger via Wikimedia Commons

More evidence has emerged that changing climate in one region can have unpredictable effects many thousands of miles away.

The Antarctic Peninsula is now the strongest-warming region on the planet. Blame that on changes in the faraway North and tropical Atlantic Ocean.

Xichen Li of New York University in the US and colleagues matched sea surface temperature variations in the northern Atlantic over a three-decade period against long-term changes in the Antarctic. They found a clear correlation, they report in Nature.

They also observed that warming Atlantic waters were followed by changes in sea level pressure in the Antarctic’s Amundsen Sea, and these changes also preceded changes in sea ice between the Ross and Amundsen-Bellinghausen-Weddell Sea. Both stretches of water lie many thousands of miles south of the Atlantic.

Correlations are not causes, so the authors then followed up their observational data by experiments with computer models of the global atmosphere. When they simulated a warming of the North Atlantic, the model “changed” the climate in Antarctica.

That Pacific Ocean temperatures can affect Antarctica is no surprise: such things have been linked to the El Niño cycle, a periodic natural pulse of heat in the equatorial Pacific. [Read more →]

January 31, 2014   No Comments

Arctic melting ‘affects temperate zones’

Tim Radford

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Bear on the ice near Svalbard: Arctic warming appears to be having effects far to the south. Image: Hannes Grobe via Wikimedia Commons

Weather extremes in temperate countries may be the consequence of the melting of Arctic snow and ice, according to Chinese and American scientists.

The shrinking Arctic sea ice – a loss of 8% per decade during the last 30 years – isn’t just bad news for polar bears. It could be bad news for citizens of Europe and the United States who like to think they live in a temperate zone.

Qiuhong Tang of the Chinese Academy of Sciences and colleagues from Beijing and the US report in Nature Climate Change that they have identified a link between declining snow and ice in the polar north, and catastrophic heat waves, droughts and floods in the mid-latitudes.

Recent years have been marked by devastating extremes of heat in Russia, Europe and the US, and by unprecedented floods in the UK and in East Asia. Over the same period, snow cover and sea ice in the Arctic have been in retreat.

The link, the scientists say, could be changes in atmospheric circulation triggered by the loss of snow cover.

There are perfectly good reasons to expect some impact on weather systems from a retreat of the snow line. In the first place, snow and ice are white – that is, they reflect sunlight, and its warmth – while ocean and forest and tundra are dark, and absorb heat. [Read more →]

December 18, 2013   No Comments