March 5, 2010

European Storms

The winter of 2009-2010 has produced its fair share of winter storms in the Northern Hemisphere – recall that President Obama arrived back in Washington from his appearance at the Copenhagen climate conference only to find the White House grounds buried under near-record amounts of snow. Europe and Asia have seen their share of large winter storms as well during the 2009-2010 winter. Hardly a large storm goes by without someone, somewhere suggesting that whatever we are seeing, it is related to “climate change”. If one looked no further than the Technical Summary of the IPCC, they would discover that the IPCC is rather quiet on this subject with no claims whatsoever that winter storms will increase in frequency, magnitude, duration, or intensity due to the ongoing changes in atmospheric composition.

Two new articles are out that further confirm that global warming has not and will not be causing mid-latitude winter storms to become some new destructive result of the greenhouse effect.

The first is by two scientists from Sweden and Poland, the article appears in the International Journal of Climatology, and the work was funded by the European Community. The title lets us know the authors are dealing with Scandinavian storminess back to 1780; one line in the abstract caught our attention as it says “We find pronounced interdecadal variability in cyclonic activity but no significant overall consistent long-term trend.”

Bärring and Fortuniak begin their piece noting that “Long-term variability in extra-tropical cyclone frequency and strength is at the centre of international attention, both because of scientific theoretical analysis of climate change and because of socio-economic consequences of potential changes in storminess activity.” They state that these storms cause severe damage to property and forests and that storm surges associated with intense storms are damaging as well. They quite correctly remind us that “The question is whether changes to such storminess characteristics are a result of changes in frequency and intensity of deep cyclones in exposed regions. The essential problem is thus if any changes to cyclone activity are within natural variability or not, that is, the classical problem of climate change detection. As intense cyclones and severe windstorms are comparatively rare events, long-term records are required to capture the natural variability.”

We completely agree with their assessment – long-term records provide a necessary dimension of historical perspective and can often make any recent trends look very different. Bärring and Fortuniak note that “Several studies using reanalysis data covering the second half of the 20th century suggest increasing storm intensity in the northeastern Atlantic and European sector.” So to extend the record back in time, they examined the thrice-daily sea level atmospheric pressure measurements taken in Stockholm and Lund. Their statistical methodology was complicated, but they showed that their method could clearly identify large storms in the past.

The authors present many graphs of storm activity, but the one below is probably the best one for capturing
temporal variations in storm activity. The graph shows principal component scores taken from the Lund and Stockholm datasets; the values are standardized with a mean of zero and a standard deviation of one; higher positive values are associated with periods with large storms and large negative values show periods of low storm activity. Imagine if the dataset began in 1950 … the upward trend would lack the necessary context and perspective and might seem unusual–which, as the longer perspective shows, it is not.


Figure 1. Time evolution of principal component scores from the Lund and Stockholm datasets (from Bärring and Fortuniak, 2009)

Bärring and Fortuniak do not waste any words with their conclusions (the Dalton minimum occurred between 1790 and 1830, and was a time of low sunspot activity). They state “(1) There is no significant overall long-term trend common to all indices in cyclone activity in the North Atlantic and European region since the Dalton minimum. (2) The marked positive trend beginning around 1960 ended in the mid-1990s and has since then reversed. This positive trend was more an effect of a 20th century minimum in cyclone activity around 1960, rather than extraordinary high values in 1990s. Both the 1960s minimum and the 1990s maximum were within the long-term variability. (3) Because the period between the 1960s minima and the 1990s maxima spans a substantial part of the period covered by most reanalysis datasets, any analysis relying solely on such data is likely to find trends in cyclone activity and related measures.”

Our next article on the subject was published recently in Quaternary International by scientists with the UK’s University of Nottingham and Loughborough University. Their interest lies with western European coastlines and storms over a variety of timescales. Clarke and Rendell begin stating “There is growing evidence that periods of sand drift and dune development provide proxy records of the impacts of storms in coastal areas”. Furthermore, “An understanding of the patterns of past storminess is particularly important in the context of future anthropogenically driven climate change, with predictions of increased storm frequency and sea level rise by the end of the current century”. Once again, someone is out there suggesting an increase in storms frequency thanks to global warming.

They examine many other studies in their review article, and conclude (LIA is the Little Ice Age) “The analysis of documentary records, discontinuous instrumental data and proxy records indicate that the period of the LIA (AD 1570–1900) included periods of enhanced storminess relative to present. This increased storminess coincided with numerous episodes of sand drift and dune building along the western European coast, as demonstrated by both documentary records and independent dating of sand movement.” Furthermore, Clarke and Rendell found “The Holocene record of sand drift in western Europe includes episodes of movement corresponding to periods of Northern Hemisphere cooling, particularly 8.2 ka, and provides the additional evidence that these periods, like the LIA, were also stormy.”

In other words, these articles suggest that it is the cooler periods in Europe that were stormier, not the warmer ones.

References:

Bärring, L. and K. Fortuniak. 2009. Multi-indices analysis of southern Scandinavian storminess 1780–2005 and links to interdecadal variations in the NW Europe–North Sea region. International Journal of Climatology, 29, 373-384.

Clarke, M.L. and H.M. Rendell. 2009. The impact of North Atlantic storminess on western European coasts: A review. Quaternary International, 195, 31-41.




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