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Arctic warming upsets ocean currents

Spells of Arctic warming have always come in fits and starts, but the current winter’s record-breaking extremes are puzzling scientists.

LONDON, 30 March, 2018 –There are indications from the present Arctic warming – tentative, inconclusive, but enough to arouse intense scientific interest – to suggest that the planet may now be close to one of the significant climate tipping points that could usher in drastic change.

At worst, some scientists now believe, the North Atlantic current, the northern part of the Gulf Stream, appears to be slowing. The current transports enough heat from tropical waters to the Arctic to keep north-west Europe’s temperature several degrees warmer than it would otherwise be.

If the North Atlantic current changes significantly, parts of Europe would cool and sea levels would rise. Parts of West Africa could experience more drought, and the Asian monsoon might also be affected. Reports that the current may change are not new, but recent evidence from the Arctic itself has given them new urgency.

In the high Arctic it is still deep winter, with temperatures dropping to –30°C.
But across large parts of the Arctic the temperature has been above freezing, even at the North Pole itself.

One Arctic weather station, at Cape Morris Jesup, in northern Greenland, has regularly recorded temperatures above zero, and this winter it has so far experienced 61 hours above freezing. The previous record, in 1980, was 16 hours to the end of April.

“Until now, models have predicted that fresh water will threaten convection in the future. It is already affecting convection to a greater extent than we thought”

Scientists call these episodes – which are not unknown – warm intrusions, as they bring in moist, mild air. The present one is the largest on record.

The intrusions are linked to a decline in Arctic winter sea ice, which has undergone unusual melting and thinning, making it vulnerable to winter storms. The southern Arctic winds have blown this broken ice far to the north, to end in the central Arctic.

The result has been large gaps of open water in the ice pack, which in turn have released large amounts of heat into the atmosphere, melting more ice.

Scientists believe the abnormal warming of the last five Arctic winters is linked to this melting. Normally the cold winter surface water sinks towards the sea bed as it heads south out of the Arctic and is replaced by warm water which flows up from the tropics, a process called convection. But this is now being disrupted, with the warmer and less saline tropical water staying near the surface.

At the same time large quantities of fresh meltwater are pouring off the Greenland landmass, with the run-off thought to be diluting the salt water already in the sea.

Smallest extent

On 19 March NOAA reported that February’s average Arctic sea ice extent was the smallest in the 39-year record at 521,000 square miles (8.8%) below the 1981-2010 average, according to an analysis by the National Snow and Ice Data Center, using data from NOAA and NASA. The monthly extent was 62,000 sq m smaller than the previous record set just last year.

Scientists work by developing theories which, in their judgment, provide the best available explanation of the facts they observe. But observations improve, evidence from the physical world changes, and so they constantly refine and revise their theories – and sometimes replace them altogether.

That constant renewal of the current research is vigorously going ahead now in the Arctic, which is no stranger to weather and climate anomalies. There is evidence of similar interruptions to Arctic Ocean circulation in the past, but they did not persist, the journal New Scientist reports.

If newer research bears out the scientists’ findings so far, confirming that the present Arctic warming is growing stronger and happening more often, and that the interplay of wind, ice and meltwater is contributing to changes in convection, we may expect serious impacts on agriculture, weather and human wellbeing over a large part of the globe.

Marilena Oltmanns of the GEOMAR Helmholtz Centre for Ocean Research in Kiel, Germany, told the New Scientist: “Until now, models have predicted that fresh water will threaten convection in the future. It is already affecting convection to a greater extent than we thought.” – Climate News Network