Naval war cooled Europe in WWII.
The evidence is a three year cold package.
By Arnd Bernaerts, May 2011 

Fig.1
The relevance of naval war on the weather had been handed in to science in a neatly tied parcel since long. A number of scientist realized the content fairly quickly, and expressed astonishment:

·        The present century has been marked by such a widespread tendency towards mild winters that the ‘old-fashioned winters’, of which one had heard so much, seemed to have gone for ever. (Drummond, 1943)

Rodewald (1948), was not less explicit and emphasized that the winter 1939/40 came so suddenly, and in contrast to the principle of conversion of the circulation and temperature deviation. Rodewald points to the air pressure aspects in the Atlantic during the months preceding the winters (1939-42) as follows:

Figure 2: Is an extract from Fig. 8 (below) and indicates the cold-pool during the three war winters, namely the Baltic Sea. Note the low temperature over the UK, and that the south-west to north-east  extension(UK to northern Ural) is due to flow of the west-wind .

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•  “From October to November a huge area of low depression covers most of Europe. The centre with –11mb (from mean value) is stationed between Norway and Shetland, which is usually south of Iceland…..December shows an inverse picture. Europe is dominated by a pressure increase of +12mb (from mean value) with the centre west of the Hebrides.”

 Fig.3     What observation does weather science need to get active? Over the last 100 years every weather expert familiar with Europe would have told you that three cold winter in a row is highly unlikely. The Russian campaign of the German Army in winter 1941/42 was severely punished by General Frost. It was the fault of the forecaster, because they had been absolute convinced that after the two cold winter 1939/40 and 1941/42, a third cold winter was impossible. But that went completely wrong. The first three war winters did not only ended a long period of an increasing trend of milder winters since the mid of the 19^th Century very suddenly, but even beat the conditions of the Little Ice Age, by coming up with three winter in succession that match the lowest  winter condition during the Little Ice Age (LIA). If there are strong indication that the war in question came along with the lowest temperature over a period of 300 years from about 1550 to 1850, it seems time to ask tough question. 

 It is worth noting that only Europe experienced the three arctic winters during 1939-42. North America and Asia did not go through the same experience.  

It got warmer & warmer – The situation prior WWII
See Figure: 1, 4,  6 and 7

Fig.4     The last decade before WWII was the warmest period since meteorology had started recording in the 18th century. To this extent, the temperature had been gaining strength since the Little Ice Age. As already mentioned Rodewald (1948) summarized it as follows: “a ‘secular heat wave’ made itself felt over most of the Earth, we noticed this especially in the increasing mildness of the winters,  which became more and more striking between 1900 and 1939.”  Even the eruption of the Krakatoa volcano in Indonesia on August 27, 1883, whose dust clouds spread around the globe and blocked solar radiation by up to 20% for three years, had no significant effect on the weather and the climate. At least, no extraordinary weather conditions had been reported from anywhere.

Unprecedented was the increased warming of the Northern Hemisphere since winter 1918/19, which started in the region where the North Atlantic and the Artic Ocean meet (Fig. 4). The rise was steeper and at the pick around 1938/39 eventually roughly as high as the temperature trend from 1980 to about 2005 (Fig. 4). It should be noted that the previous warming stopped in the USA already around 1933 (Fig.3), while the European record moved higher and higher until WWII started.

Figures 5 (winter T°C) & 6 (annual & season) ; Norway South (Oslo)

Actually , northern Europe was more affected, and the North Cap more than the south of Scandinavia. In Scandinavia the last very cold year was 1867, which had had a polar character by a mean of –2,7°C, in contrast to that are the 4.3°C of the year 1938 (Groissmayer, 1948:13). The warming, which was most marked in winter, was associated with a reduction in atmospheric pressure in northern Europe and an increased frequency of westerly winds (Lamp; 1988:392). This had primarily to do with the warming at high latitude since 1919 (Fig.4). Whether it is the only reason for the different trend  between the USA and Europe since 1933, is not to be answered here. But whoever is interested in this  aspect, should put an eye on the permanent increase ship traffic in the North and Baltic Sea between 1919 and 1939. What ever the cause, it had been getting warmer and warmer in Europe for 20 years until winter 1939/40.

 The global situation is well demonstrated by Figure 7 (Nasa/Giss), showing the winter temperature anomalies (DJF) during the winters 1935-1939. The North America was colder, Europe warmer than the mean from 1900-1939.

 The rising trend was stopped abruptly in winter 1939/40.  From one day to the other the ocean use scenario changed dramatically, and with it the winter weather. The change was from warm to extreme cold.  Not only once, or twice, but three winter in a row. The contrast is impressive illustrated if one compares the winter season (DJF) of 1935-1939 (Fig.7) with the corresponding winter period for the first three war years 1939/40 to 1941/42 (Fig.8). That is quite a contrast.

 The winter scenario in Europe is shown in Figure 2 (above & below again (Fig.9) is an extract from Fig.8. Interesting detail become clearly visible. The Baltic Sea region had been hit by General Frost most severely. Not less interesting is that Great Britain is covered by colder conditions than parts of the North Sea. 

Fig. 9 (same as  Fig.2)