December 27, 2009

Winter Storms Update

Filed under: Extratropical Storms

If we happen to see an unusually large number of winter storms this year, we suspect some reporter or some scientist will insist we are witnessing the effects of global warming, or at least declare we are witnessing climate change before our very eyes. Oppositely, if this year’s winter storms are infrequent, we will expect to learn from someone that we have seen the effects of climate change. In fact, in a recent paper in the International Journal of Climatology, the authors begin their piece noting “One area of growing concern in climate science is the impact that global warming could have through modulations of the nature and characteristics of naturally occurring extreme events, such as severe mid-latitude storms.” In the very next sentence, the research team from the United Kingdom and Australia state “However, both observational and modelling studies of historical and future storminess patterns and scenarios are divided on the role that global warming has played, or could play, in changing patterns of mid-latitude storms”. Once again, we find any straightforward link between global warming and winter storms is a bit more dicey than originally thought … there is always more to the story.

The authors of the latest piece are Rob Allan, Simon Tett, and Lisa Alexander of the UK Met Office, the University of Edinburgh, and Monash University in Australia; funding for the research was provided by various sources including the UK Ministry of Defense … go figure? Anyway, Allan et al. made use of a newly digitized 3-hourly station surface pressure data for the United Kingdom and Ireland to extend previous analyses that used data beginning in the 1950s; the new dataset allowed analyses to extend back to 1920. They used the 3-hourly surface pressure data to identify severe winter storms, and their analyses suggested that no major severe winter storm would go undetected by their network of stations.

Allan et al. divided their work into two sub-periods including October – December (OND) and a second period including January – March (JFM). The first figure (Figure1) of special interest to us is below, and it immediately shows the importance of having the additional 30 years of data. The authors note “pronounced inter-annual variations in OND severe storminess across the British Isles are evident” “with most prominent activity in the 1920s and 1990s. There is evidence in the literature to support the 1920s period of a high frequency of severe storms in OND.”


Figure 1. History of OND decadal average severe storm frequency over the British Isles from 1920 (from Allan et al., 2009).

The authors also conducted the analyses for the JFM period, and when the results for OND are combined with the JFM period, the pattern below is established (Figure 2). Allan et al. conclude “The results from this study suggest that natural climate variability will play an important role in future changes in storminess, and thus could overwhelm any anthropogenic signal there might be.” We completely agree, and yet, the popular press continues to suggest that global warming is to blame for anything from few storms to big storms – it is all climate change!


Figure 2. History of October - March decadal average severe storm frequency over the British Isles from 1920 (from Allan et al., 2009).

A second article on storminess in Europe takes on a different perspective in terms of time period; Sorrel et al. were interested in reconstructing storm activity over the past 3,000 years. The research team is from impressive institutions in France, and effort was funded by the French state, the Haute Normandie Region and the other regions of the Paris Basin, the Agence de l’Eau Seine Normandie, and the industrial firms of the Haute-Normandie. Allan et al. collected sediment cores near the mouth of the Seine River in northwestern France and they used radiocarbon dating and paleomagnetic information to date the material in the core. The marine hydrodynamics are reflective of storm activity in the Seine River basin, and the sediment patterns within the core reveal periods of frequent large storms and periods with few or any storms.

Sorrel et al. found periods of intense storm activity around 2,700 BP and 1,250 BP, and they note both of these were unusually cool periods. They note that the Medieval Warm Period (around 900 AD to 1200 AD) was a time of few storms, while “In the subsequent 600 years after the MWP, corresponding to the so-called Little Ice Age (LIA), our proxy records mark the return towards more energetic conditions in the Seine estuary”. Basically, they showed over and over that storm activity increases in cold periods and diminishes in warm periods. Claiming that global warming will result in increased mid-latitude storm activity is simply not consistent with 1,000s of years of climate information collected in northwestern France.

Finally, President Obama returned home from Copenhagen recently only to find a massive snowfall covering much of the Northeast, including Washington DC. With climate change fresh on his mind, he might have wondered global warming impacted the massive winter storm. Fortunately, an article has just appeared in the Journal of Climate on trends in extreme snowfall seasons in the United States. To make a long story really short, Kunkel et al. conclude “The 1900–01 to 2006–07 trends in the annual percentage of high- and low-extreme snowfall years for the entire United States are not statistically significant.” Once again, there is no evidence of any trend upward or downward in extreme storm events in the winter season.

References:

Allan, R., S. Tett, and L. Alexander. 2009. Fluctuations in autumn–winter severe storms over the British Isles: 1920 to present. International Journal of Climatology, 29, 357-371.

Kunkel, K.E., M.A. Palecki, L. Ensor, D. Easterling, K.E. Hubbard, D. Robinson, and K. Redmond. 2009. Trends in twentieth-century U.S. extreme snowfall seasons. Journal of Climate, 22, 6204-6216.

Sorrel, P., B. Tessier, F. Demory, N. Delsinne, D. Mouaze. 2009. Evidence for millennial-scale climatic events in the sedimentary infilling of a macrotidal estuarine system, the Seine estuary (NW France). Quaternary Science Reviews, 28, 499-516.




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