It may seem contradictory to say that global warming will lead to colder winters but a new study has found a link between the progressive shrinking of Arctic sea ice and the possibility of colder, snowier winters in the UK and other areas of Europe, North America and China. Writing in Proceedings of the National Academy of Sciences (PNAS), a US/China-based team show this affects the jet stream and brings cold, snowy weather. The team working on the research were from Georgia Institute of Technology in Atlanta USA, and the Institute of Atmospheric Physics in Beijing. The research suggests that on average, winters in the UK will be colder in years to come than they have been in recent decades.
As global temperatures continue to rise, the area of Arctic Ocean covered by ice in summer and autumn has been falling. A marked deterioration in ice cover was recorded between the summers of 2006 and 2007, which still holds the record for the lowest extent on record; and it has not recovered since. Various computer simulations have generated a range of dates by which the Arctic might be completely ice-free in summer and autumn, ranging from 2016 to about 2060.
It is well established that the dramatic loss of winter sea ice in the Arctic has caused it to feel global warming more sharply than the rest of the planet. Less ice means more exposed water, which – being darker than ice – absorbs more solar energy. To compound things, with less ice to insulate the warmer ocean from the air above, more of that energy is released back into the atmosphere as heat. The net result is that Arctic air is significantly warmer than before. Some years, winter temperatures have reached 4 °C above average. The reduction in the temperature difference between the Arctic and the Atlantic Ocean further south reduces the strength of the polar jet stream, which usually brings wet, windy and milder weather to Europe from the west. This allows areas of high pressure that bring "blocking" cold air leading to wintry weather across parts of Europe including the UK. The researchers also found that the extra evaporation from the Arctic Ocean makes the air more humid, with some of the additional water content falling out as snow.
The study is not the first to propose a causal relationship between low Arctic ice in autumn and Europe's winter weather, but it has gone further than others in assessing the strength of the link. Other studies have shown that changes in solar activity and natural variability such as El Niño have an impact on European winters. Dr Adam Scaife, head of monthly to decadal prediction at the UK Met Office was involved with one of these studies published last year and he emphasised that the declining Arctic ice cover was just one of several factors that could increase blocking. Dr Scaife told the BBC "This is no bigger than the solar effect or the El Nino effect. But they vary, whereas Arctic ice is on a pretty consistent downward trend. The study adds weight to growing belief that Arctic sea ice is driving an increase of cold winters."