Another year, another climate record broken. But don鈥檛 let this one wash over you. Arctic sea ice is usually at its most extensive in early March, which marks the end of the Arctic winter 鈥� but this year鈥檚 winter ice cap is the smallest recorded in almost 40 years of monitoring. The previous record low聽was set only last year. Around Antarctica, meanwhile, sea ice levels are the .
In February, Arctic sea ice covered about 13.9 million square kilometres. This is 1.74 million square kilometres below the seasonal average recorded between 1981 and 2010.
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Global warming is largely to blame for the ice loss. The Arctic has experienced its warmest winter on record, with . This has .
鈥淭he [Arctic] ice loss observed is generally faster than what many climate models predict,鈥� says Julienne Stroeve at University College London. Her research suggests this is not because of problems with computer models of sea ice but more to do with climate models .
If we continue to emit carbon dioxide at current levels, Stroeve predicts the Arctic might have ice-free summers in about 20 years.
Freak storms
As millions of people in Europe last week and the eastern United States right now are finding out, the effects are not confined to the Arctic. Warm weather in the polar region is thought to influence atmospheric air streams, forcing colder air further south where it can pass over densely populated regions. The unusually cold conditions experienced last week across Europe may be a direct consequence of the Arctic鈥檚 warmer winter.
The east coast of the United States聽has experienced聽. Winter Storm Quinn across the region聽last week. Some of the affected areas were still recovering from the effects of Winter Storm Riley, which blasted across the region聽the previous week.
Researchers used to think it was only the tropics that could drive extreme weather in temperate regions of the northern hemisphere. But after about 25 years of unusually fast Arctic warming, attitudes are shifting.
A team led by at Atmospheric and Environmental Research in Lexington, Massachusetts has the latest evidence. They looked at 66 years of data on Arctic air temperature and pressure, and compared it with records of severe winter weather collected at a dozen sites across the US.
Winds of winter
For all sites east of the Rockies, severe winter weather was more likely to occur in years of unusual Arctic warming. The correlation was strongest when Arctic warming occurred five days before the extreme winter weather hit the US. This implies warm Arctic conditions trigger the winter storms ().
Cohen thinks this discovery might go some way to convincing sceptics that the Arctic can drive extreme weather at mid-latitudes. What probably happens is that Arctic warming weakens a low-pressure atmospheric feature 鈥� the stratospheric polar vortex 鈥� and allows cold Arctic air to spill southwards.
This year鈥檚 extreme wintry weather across the US and Europe could help strengthen the case for a link, says Cohen. The east cost of the United States is still recovering from a winter storm last week that dumped heavy, wet snow across the region, leaving hundreds of thousands without power.
鈥淭his past winter, the extreme weather in both the US and Europe followed polar vortex disruptions,鈥� says Cohen.
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The situation is different around Antarctica. In recent decades there has actually been a slight average increase in the amount of sea ice forming around the frozen continent. Researchers are still working out why.
One contributing factor might be a strengthening of winds over Antarctica, perhaps caused in part by the hole in the ozone layer. The stronger winds drive cooler continental air further over the oceans and might encourage more sea ice to form. Another factor might be melting of Antarctic glaciers, which introduces freshwater into the ocean: fresher water freezes at higher temperatures.
However, things might now be changing. In March 2017, satellite images revealed that the area of sea blanketed by ice around Antarctica was . The Australian Antarctic Division has just revealed results of measurements taken this year 鈥� and again the , although not as low as last year.
Antarctic sea ice seems to have been tracking below the long-term average since August 2016. Finding out why is a high priority.
