Arctic Decline Doubles Severe Winters In Eurasia
26.10.2014 18:00 Age: 32 days
Declining Arctic sea ice has doubled the probability of severe winters in Europe and Asia, according to research published in Nature Geoscience.
Click to enlarge. Fig a (caption below).
Click to enlarge. Fig b (caption below)
Click to enlarge. Fig c (caption below).
Click to enlarge. Fig d (above). Caption for all figures: Observed and simulated change in winter SAT and atmospheric circulation associated with sea-ice retreat in the Barents–Kara region. a,b, Differences of composite fields between the low- and high-ice years (that is, the former minus the latter) for SAT (colour) and SLP (contours) in DJF, taken from ERA-Interim (a) and the 100-member ensembles of the LICE and HICE experiments (b). Contour interval is 0.8 hPa in a and 0.2 hPa in b, with negative contours dashed. Stippling indicates regions of significant difference exceeding 95% statistical confidence. c,d, Differences of composite fields between the low- and high-ice years (that is, the former minus the latter) for Z500 in DJF, taken from ERA-Interim (c) and the 100-member ensembles of the LICE and HICE experiments (d). Stippling indicates regions of significant difference exceeding 95% statistical confidence. Courtesy: authors and Nature Geoscience.
Severe winters across Europe and Asia are twice as likely as a result of the decline in Arctic sea ice, according to new research.
Computer simulations have linked the observed decline in sea ice in the Arctic since 2004 with an increased probability of the occurrence of persistent atmospheric circulation patterns, known as blocking patterns, suggests a study published online in Nature Geoscience.
These blocking situations favour the transport of cold air to Eurasia, and hence create conditions for severe winters in the region, the researchers write in their paper, entitled “Robust Arctic sea-ice influence on the frequent Eurasian cold winters in past decades”.
The researchers, led by Masato Mori of the Atmosphere and Ocean Research Institute, the University of Tokyo, ran multiple simulations to arrive at their conclusion. They performed 200 slightly different computer simulations of the global atmospheric circulation using a computer model based on two distinct settings for Arctic sea-ice concentrations. These settings were derived from observations in years with high and low ice cover, respectively.
They discovered that atmospheric blocking patterns, leading to cold air transport and severe winter conditions occurred twice as often in the low sea ice scenario model runs. This approach showed that as a result of sea ice reduction in the Arctic, Barents and Kara seas, the probability of severe winters has more than doubled across Eurasia.
Analysing existing climate model projections for twenty-first century climate they found that this phenomenon is likely to be temporary because continued global warming is expected to outweigh the impact of sea ice decline towards the end of the twenty-first century; although they caveat this with a reference to uncertainties about the future evolution of Arctic and mid-latitude climates.
This new study agrees with previous work that the decline in sea ice cover in the Barents-Kara Sea area in early winter has led in recent years to unusually cold winters throughout Eurasia, including the UK, according to Colin Summerhayes, Emeritus Associate of the Scott Polar Research Institute in the UK.
Summerhayes explains that the warming of the atmosphere associated with the absence of sea ice weakens the high level winds of the polar vortex. That in turn leads to meandering of the jet stream, with the meanders becoming stuck which is what meteorologists call ‘blocking’. This pull cold air south out of the Arctic, and because the system is stuck in position, the cold air supply can last quite a while.
Summerhayes points out that other factors also influence the polar vortex that controls the jet stream and so more research is needed to see how the interaction of all the controlling factors may affect the pattern of blocking in a warming world.
Over the past decade, severe winters occurred frequently in mid-latitude Eurasia, despite increasing global- and annual-mean surface air temperatures. Observations suggest that these cold Eurasian winters could have been instigated by Arctic sea-ice decline, through excitation of circulation anomalies similar to the Arctic Oscillation. In climate simulations, however, a robust atmospheric response to sea-ice decline has not been found, perhaps owing to energetic internal fluctuations in the atmospheric circulation. Here we use a 100-member ensemble of simulations with an atmospheric general circulation model driven by observation-based sea-ice concentration anomalies to show that as a result of sea-ice reduction in the Barents–Kara Sea, the probability of severe winters has more than doubled in central Eurasia. In our simulations, the atmospheric response to sea-ice decline is approximately independent of the Arctic Oscillation. Both reanalysis data and our simulations suggest that sea-ice decline leads to more frequent Eurasian blocking situations, which in turn favour cold-air advection to Eurasia and hence severe winters. Based on a further analysis of simulations from 22 climate models we conclude that the sea-ice-driven cold winters are unlikely to dominate in a warming future climate, although uncertainty remains, due in part to an insufficient ensemble size.
Robust Arctic sea-ice influence on the frequent Eurasian cold winters in past decades by Masato Mori, MasahiroWatanabe, Hideo Shiogama, Jun Inoue and Masahide Kimoto published in Nature Geoscience, online: 26 October 2014, DOI: 10.1038/NGEO2277
Read the abstract and get the paper here.