Ice influence will prevent some cold spells
Dr James Screen has just produced mathematical evidence to show that extreme cold periods are less likely as the Arctic warms up at a faster rate. Both Europe and North America have experienced severe cold spells recently, during winter. Previously, it had been supposed that last winter's very cold conditions over much of the continental US was related to "Arctic amplification." Now we can state that this effect is likely to reduce the number of such events.
Arctic near-surface air temperature has risen twice as fast as average global warming over the last 2 decades. The cause of this Arctic amplification is still poorly understood. The warming effect is strongest at the surface for most of the time. The loss of sea ice has affected the temperature amplification but other factors seem to be involved, as the loss has been much more than any model has suggested. For example, factors such as pole-ward heat transport have slowed since the 1980s and Arctic storm behaviour could have caused extra warming.
New techniques in modelling have revealed that, from mainly non-direct satellite radiance observations of temperature, it is possible to show the Arctic amplification is at its maximum at the surface of the ocean. Only in summer does the warming increase above the surface of the water. Decrease in sea ice and snow cover are the prime causes, energy being used to melt ice and warm the ocean surface waters. Even though the sea ice declines slowly, the majority of winter warming is due to that loss. The ocean loses the heat stored from the summer into the atmosphere during winter. This will be helped nowadays by the thinner sea ice and there was the possibility of reduced cloud cover effects. In the spring clouds have a warming influence, so their loss would be expected to cool the surface. This seems to be incorrect.
Based on the last 20 years, the reduction in sea ice cover and its thickness have enhanced the warming of the Arctic throughout the year. The amplification is due to the diminishing ice cover for the most part, being strongest in the lower atmosphere where heat exchanges with the ocean take place. This now leaves us with the likelihood of a rapid Arctic warming and consequent loss of sea ice. James Screen sees the effect on Europe and North America is to reduce their terrible cold spells because, "Cold days tend to occur when the wind is blowing from the north, bringing Arctic air south into the mid-latitudes. Because the Arctic air is warming so rapidly these cold days are now less cold than they were in the past."
James A. Screen & Ian Simmonds of the Universities of Melbourne and Exeter publish their results in Nature-Climate Change as - The central role of diminishing sea ice in recent Arctic temperature amplification.
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