We were told that the mild winters we experienced in Europe were due to global warming. Now, suddenly, we are getting hit with yet another nasty cold winter.
Why? Guest writer Juraj Vanovcan presents his observations and interesting evidence that it has nothing to do with CO2. He presents what I think is an astonishing finding near the end.
Predicting The European Climate From The CET Record – Lesson Learned
By guest writer Juraj Vanovcan
This post was inspired by the article Negative AO bringing cold winters back to Europe.
Recalling the summers and winters of the early 1980s, it becomes obvious to me that it is the prevalence of air circulation that determines if a season is warm or cold. The very mild winter of 2006/2007 in Central Europe was characterized by a sustained flow of warm Atlantic air over the European continent, while the cold and snowy 2005/2006 winter received a lot of Arctic air entering the mid-latitudes from the North.
Air circulation is governed by pressure differences and basically this is what North Atlantic Oscillation is all about.
Fig 1 Example of positive NAO (Source: JISAO webpage).
I compared the NAO index with the European long-term climate record. Checking the Central European Record (CET) shown, one sees there is an obvious correlation between NAO and winter temperatures. The dark blue line is CET, orange/light blue is NAO.
Fig 2 North Atlantic Oscillation index compared with CET winter record, 1860-2010 (CET graph source: http://climate4you.com/ ).
As observed above, the NAO oscillates in an 80-year long sine wave cycle. The first period with mild winters happened in the 1920s, which of course we do not remember. The second positive phase began in 70s and mild winters in Central Europe become frequent since late 80s. It also seems that the current period with prevalent NAO-positive years has ended; the recent string of cold winters in North-Western Europe suggests this as well.
On the other hand, CET summers do not show correlation with NAO in the early part of 20th century. Comparing the CET summer anomalies with AMO index (detrended North Atlantic SST) however gives reasonable correlation again. Summers in the period 1930-1950 were often as warm as the recent ones, and the extremely hot and dry summer of 1946 in Central Europe with its catastrophic impact on crops has since never been repeated. However, warm summers in this period were combined with cold winters, like those of 1939/40/41.
It is worth noting that while the NAO peaked circa 20 years before the warm AMO phase centered on 1940, their warm phases were much closer to each the other in the later part of the century. It means that while Europe experienced cold summers and mild winters in 1920s and warm summers and cold winters in the 1940s, the last 20 years saw both warm summers as mild winters. This is also probably the reason why 2000-2010 decade is slightly warmer than 1940-1950.
Based on the observed SST and OHC record for North Atlantic, it seems however that AMO had peaked around 2005 and it is now heading down. This time, both NAO and AMO being in their negative phases will mean miserable summers and cold winters. Such shift in temperature trend is already being observed in the whole northern extratropics record.
Fig 4 Northern hemisphere north of 30N, HadCRUT3 data
IPCC attributed the post-1975 warming phase almost solely to anthropogenic reasons, namely to increased “greenhouse effect” caused by increase of CO2 molecules from 3.5 to 4 per other 10,000 molecules in the atmosphere.
We can conclude, however, that at least for Europe, observed warming is fully explainable by natural variations, two of which – AMO and NAO – had their positive phases overlaid during the last 20 years. Neither CO2, aerosols nor greenhouse effect theory are needed.
For those still seeking the anthropogenic signature in recent warming, here is a comparison of 1890-1920 warming trend compared against 1980-2010 warming trend in the winter CET record. The running 10-year mean is strikingly similar, following even minor dips and upticks.
Extrapolations into the future may be tricky, especially when pulling some 20-year trend into year 2100, which seems to be a favorite practice in modern climatology. Observing the European climate record of the early part of 20th century and understanding its causes gives us much more predictive skill when forecasting climate for the next decades. All climate indicators today point to cooling, and not only in the European region.
Juraj Vanovcan (firstname.lastname@example.org)
26 November 2010