November 19, 2007

Changes in European Storminess?

Filed under: Climate Changes

One of the popular tenets of the greenhouse scare is that storms will become more fierce and more common in the future due to global warming. Whether we are looking at tropical storms (hurricanes) or extra-tropical storms, anything and everything should be blamed on the ongoing build-up of greenhouse gases. Given that the global weather system produces tropical and extra-tropical storms every single day, there is no end of fresh material needed to keep the greenhouse story alive and well.

However, a recent article will soon appear in Climate Dynamics, and we suspect it will not be carried by any news service. The international team of scientists is from the Climate Research Division of Environment Canada, the Central Institute for Meteorology and Geodynamics in Austria, the Swedish Meteorological and Hydrological Institute, and the Institute for Coastal Research in Germany. The Matulla et al. group begin by noting “Severe storms can do widespread damage to ecosystems, property and society. Inland areas are affected by wind-throw uprooting trees, soil erosion and damage to construction. Coastal regions are not only exposed to the wind force but to storm surges and wind waves in the wake of storms as well. Due to its impact on socioeconomic structures storm-climate naturally attracts public attention. In the North–East Atlantic and the North Sea a roughening storminess was perceived and public concern was raised in the early 1990s.” Of course, the early 1990s was also the time when the global warming scare was launched and thrown into high gear, and we suspect that Europeans made the link between global warming and their perceived increase in storminess.

Matulla et al. note that others have investigated trends in storminess in Europe over the timescale of 100 years, and based on daily wind data, they have detected no trend. However, long-term wind data “are characterized by spatial sparseness and inhomogeneities, caused by instrumentation changes, site moves and environmental changes.” They state that this fact “highlights the importance of employing data that reach far back in time before any judgment about storminess can be made.” Fair enough – we at World Climate Report applaud any effort to collect actual data and test any suggestion made by the greenhouse advocates.

The scientists argue that “High wind speeds across Europe are generally associated with extratropical cyclones, which occur in North or North-Western Europe all year but in Central Europe almost entirely from November to February.” Therefore, if we had evidence of the strength of the cyclones, we would have a way to detect if they have become more or less fierce in recent decades. Well, people have been observing weather in Europe for a long time, and some of the longest records of weather come from European locations. Along with temperature and rainfall records, many European stations have barometric pressure measurements that would be perfect for estimating the strength of storms. Mattula et al. write “In Central Europe we have pressure readings at four stations. These are Kremsmuünster (1874–2005) and Vienna (Hohe Warte, 1872–2005) in Austria, and Klementinum (1874–2001) plus Karlov (1921–2005) in Prague, Czech Republic.” Along with these records for central Europe, they also gathered similar long-term records for stations in northwestern Europe.

If you haven’t taken a course in atmospheric science recently, you might have forgotten how to calculate the wind speed from pressure data? It is actually quite simple and involves nothing more than the barometric pressure gradient between two points. The resulting “geostrophic wind” achieves a balance between the pressure gradient and the Coriolis Effect; the basic dynamic principles work today, they worked 100 years ago, and they will work tomorrow.

Their calculations resulted in a geostrophic wind speed estimate for every day, and for each year, the authors determined the value of the highest five percent and the highest one percent of the wind speeds. They standardized the resulting time series and then smoothed the values using a 21-year running filter.

Figure 1 below shows the results, and don’t look now, but the values have generally decreased over the past century. They find:

North-Western European storminess starts at rather high levels in the 1880s, decreases below average conditions around 1930 and remains declining till the1960s. From then until the mid 1990s a pronounced rise occurs and values similar to those of the early century are reached. Since the mid 1990s storminess is around average or below. This picture—a decline that lasts several decades followed by an increase from the 1960s to the 1990s and a return to calm conditions recently, is to be found for the North European triangle as well. The increase, however, is far less pronounced. Central Europe features high-level storminess peaking around the turn from the nineteenth to the twentieth century which is followed by a rapid decrease. Since then a gradual increase prevails until the 1990s and most recent values show a return to average or calm conditions.

In their own words, they conclude that their work is in agreement with other studies in Europe showing “that storminess has not significantly changed over the past 200 years.”

Enough said!


Figure 1. Gaussian low-pass filtered (21 years) curves for the 95th (left) and 99th (right) percentiles of the geostrophic wind throughout Europe. The heavy curve is made up by Kremsmünster, Vienna and
Prague–Klementinum while the heavy dashed curve by Kremsmünster, Vienna and Prague–Karlov (note that tails are based on less data than the rest)(from Matulla et al., 2007)

Reference:

Matulla, C., W. Schöner, H. Alexandersson, H. von Storch, and X. L. Wang. 2007. European storminess: late nineteenth century to present. Climate Dynamics, DOI 10.1007/s00382-007-0333-y.




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