We're seeing lots of headlines about heavy snowfalls and cold temperatures gripping Eastern and Southern Europe. Not surprisingly some activist scientists are blaming manmade global warming.
Expected snow depths by January 15. Chart: WXCharts.EU.
Junk theory: Global warming causing more snow extremes
Yet global warming logically isn't supposed to be directly causing massive snow and bitter cold, and so there has to be some explanation for the unexpected cold and snowy weather. So to explain its all, a gaggle of activist scientists have concocted a theory that claims "unprecedented" Arctic sea ice loss over the past two decades has led to an increase in blocking over North America and Europe [e.g., Liu et al., 2012; Francis and Vavrus, 2012] and so is indirectly causing lots of snow and cold.
These desparate scientists then hope that the public and media will be gullible enough to buy into it.
Blocking is strongly tied to weather extremes in the midlatitudes (e.g., cold snaps, heat waves) and can persist for days to weeks [e.g., Black et al., 2004; Dole et al., 2011], so more blocking could mean more weather extremes as Arctic sea ice continues to decline (Note: Arctic sea ice in fact hasn't declined in more than 10 years).
Analyses: no data to support the theory
However, a recent paper authored by Elisabeth A. Barnes, Department of Atmospheric Science, Colorado State University, says the data to support this just aren't there.
The paper's abstract:
Observed blocking trends are diagnosed to test the hypothesis that recent Arctic warming and sea ice loss has increased the likelihood of blocking over the Northern Hemisphere. To ensure robust results, we diagnose blocking using three unique blocking identification methods from the literature, each applied to four different reanalyses. No clear hemispheric increase in blocking is found for any blocking index, and while seasonal increases and decreases are found for specific isolated regions and time periods, there is no instance where all three methods agree on a robust trend. Blocking is shown to exhibit large interannual and decadal variability, highlighting the difficulty in separating any potentially forced response from natural variability."
The results of the analyses are summed up in the following charts of the paper's Figure 3:
Time series of blocking frequencies for the three indices and four reanalyses for (a, c, and e) Asia in DJF and (b, d, and f) the North Atlantic in JJA. Trends significantly different from zero at 95% confidence are denoted by asterisks in the legend of each panel for Asia (1990–2012) and the North Atlantic (1980–2012). Filled circles (stars) denote the seasons following the 5 highest (lowest) years of September Arctic sea ice extent over the trend period. Blocking frequencies are averaged between 40° and 80°N for the 2‐D indices. Chart: Barnes et al (2014)
Not supported by observations
The findings reiterate those of Barnes [2013], The 2014 paper concludes that "the link between recent Arctic warming and increased Northern Hemisphere blocking is currently not supported by observations."
Blocking events well within historical observed range
The paper adds:
While Arctic sea ice experienced unprecedented losses in recent years, blocking frequencies in these years do not appear exceptional, falling well within their historically observed range."
In other words, the theory that global warming is causing more extremes due to melting Arctic sea ice is just plain crap. There's no data to support it.
Correspondence to: Elisabeth A. Barnes:
eabarnes@atmos.colostate.edu
Search for more papers by this author
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