Northern Europe may be facing more severe cold weather spells this year with even more disruption to travel and further deaths while a climate scientist has warned that the current freezing winter may not be a one-off and could be more common in future years.
by Leon Clifford, reportingclimatescience.com, December 6, 2010
Further cold weather this winter is possible if the current Atlantic high pressure system that is trapping sub-tropical air and preventing it from reaching Europe stays put or goes away and returns. While the severity could be exacerbated if current arctic sea ice levels continue to remain low, according to one climate scientist.
Britain's Meteorological Office forecasts that the cold snap affecting northern Europe will continue for the next week or so, according to a Met Office spokesman. "Much of December looks like being on the cold side," commented Met Office chief forecaster Ewen McCallum.
These conditions are due to the action of a high pressure weather system over the Azores, linked to the so called North Atlantic Oscillation (NAO), in trapping warm sub-tropical air and preventing it from reaching Europe, according to climate scientist Mark Maslin of University College London (UCL). "It is acting like an open gate and letting cold air in from northern Russia," Maslin explained.
"As a climate scientist I do not predict the future. We have no idea when the blocking high across the Atlantic will start to shift and whether we could be back to 10C by Christmas Day," Maslin told Reporting Climate Science .Com. He explained that the nature of the weather pattern meant that it would take on the order of a week to unwind and that this was why the UK Met Office could be confident in its current forecast.
Maslin commented that the temperatures themselves were not unusual but that the timing of them is: "It is interesting how early it has occurred and this is what is anomalous," he said.
"The timing is a significant anomaly," agreed the Met Office's McCallum. "This is something that will be remembered as a significant event." He added that the atmospheric pressure over the North Sea is lower than is usually seen with such blasts of cold air from the north east and this is what has led to the exceptionally heavy snow falls in the east of the UK, as the cold moist air over the North Sea is able to rise much higher.
But there is "no evidence to suggest" that a slow-down in the Gulf Stream is to blame for the early cold weather as has been reported in the press, according to UCL's Maslin. "This is an atmospheric effect and is not due to a slow down of ocean circulation," he explained. The view is echoed by the Met Office which has just released a report saying that the Atlantic Conveyor, or Gulf Stream, is not slowing down by as much as had been feared.
Furthermore, recent research indicates that such cold weather conditions over northern Europe can be favored by low levels of sea ice in the Barents-Kara Sea, north of Norway and Russia which has the effect of making the weather even colder.
Sea ice levels in mid/late November were nearly as low as they had been during the same period in the harsh winter of 2005 and 2006, according to Vladimir Petoukhov, a climate scientist at the Potsdam Institute for Climate Impact Research in Germany. These conditions were reinforcing the NAO weather system at work during the current cold spell, according to Petouhkov.
This sea ice situation could, if it persists, result in a continental-scale winter cooling reaching on average, 1.5 °C colder than it would otherwise have been. This is an average so minimum temperatures may in reality dip by much more than 1.5 °C. By the end of December we will have a much clearer idea as to the contribution of the Barents-Kara effect, according to Petoukhov. If it persists then extreme cold conditions could return across northern Europe throughout the coming winter months just as it did across the continent through the winter of 2005 and 2006.
It is possible that such conditions may become more common in future years. Recent research by Petoukhov and colleague Vladimir Semenov published last month found a link between low levels of sea ice in the Barents-Kara Sea, and an increased probability of harsh winters across Europe. These sea ice declines associated with warmer oceans could triple the probability of cold winter extremes in Europe and northern Asia, they reported. So cold winter weather such as the mid/late November conditions across northern Europe could be much more common in future years than they have been in the past if the levels of winter sea ice in the Barents-Kara Sea would remain low.
Petoukhov believes that we may already be seeing evidence of an increase in the frequency of cold winters compared with the more random, or stochastic, distribution of cold winters in previous decades that were associated with the NAO. “We have already had two chilly winters in Europe in the last decade, and this November situation, as it developed, also forces us to be on the alert. This makes it questionable that only a purely stochastic mechanism of the European cold winter extremes is at work, and this deserves an exhaustive investigation,” he commented.
The possibility suggested by Petoukhov that the Barents-Kara Sea effect could triple the probability of cold winter extremes in Europe,will almost certainly be of interest to policy makers and planners in north European states such as the UK where there is an ongoing debate about the level of investment required to deal with “occasional” cold weather events.
Computer models suggest that a reduction in sea ice in the eastern Arctic leads to a loss of ocean heat and a consequent warming of the lower atmosphere which can trigger atmospheric circulation anomalies that can in turn lead to an overall cooling of northern continents, according to the research which was published in the Journal of Geophysical Research.
And while the research does not make a direct link with global warming or climate change it is clear that the reduced levels of Barents-Kara sea ice are due to warmer ocean temperatures and related to colder winter conditions in northern Europe. So regardless of whether or not global warming is causing the reduction of sea ice, the fact is that the low levels of Eastern Arctic sea ice are probably contributing to colder weather than Europe would otherwise experience.
Similarly, there is no evidence of a direct link between climate change and the position of the NAO high pressure system but the fact of the high pressure system leads to a trapping of warm air and to a consequent cooling in Europe. And if there is a subtle link to global warming then such events could be expected to become more common if global temperatures rise.
Citation
Petoukhov, V., & Semenov, V. A. (2010). A link between reduced Barents-Kara sea ice and cold winter extremes over northern continents, Journal of Geophysical Research 115, D21111; doi: 10.1029/2009JD013568Link: http://www.reportingclimatescience.com/news-stories/article/europe-faces-even-more-cold-weather-this-winter-and-in-future-years-thanks-in-part-to-global-warming.html
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