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A210  The El Niño didn’t do it.
Rev: 05 May 2011

• Brünnimann, Stefan (2005); “The global climate anomaly 1940-1942”, Weather, Vol. 60, Issue 12, p.336 –342.

Stefan Brünnimann claims that a prolonged El Niño lead to the three extreme war winter in Europe. An event in the Pacific may have contributed remotely. Any claim beyond is mere speculation.  

An extract from the cited paper reads:

Although data from the past 50 years show that not all El Niño events lead to such extreme periods, the agreement between the 1940–1942 period and strong El Niño events in a coupled climate model simulation is striking. The global climate anomaly in 1940–1942 was unprecedented in strength, yet exemplary in character, providing a unique opportunity to study large scale climate variability. (Brünnimann, 2005)

 The study of the large scale climate variability during the years 1940-1942 should have started and focused on the war activities in Europe. According S. Brünnimann there had been more in the air, e.g. an “unusual high values of total ozone over several European sites”, including at sites in China, North America, and the Arctic (p.339), “that can not be explained by chemical processes , but points to anomalous ozone transport and hence an anomalous stratospheric circulation”, and the author does not even consider the role the war on land, in the air, and at sea. He does not consider, whether the anomalous circulation observed in the Northern Hemisphere might have affected the circulation prevailing during El Niño events, and not the other way around.  

 Figure 1: El Niño/Southern Oscillation (ENSO) is the most important coupled ocean-atmosphere phenomenon to cause global climate variability on interannual time scales

The problem with Brünnimann’s thesis is that he works with a number of very superficial assumptions. His reasoning offers little more as the timely correlation between the cold war winters in Europe in the early 1940s, which is indeed stunning, but that does not prove any major contribution to the three arctic war winters in a row. 

Particularly to question is the reliability of the claim of a prolonged El Niño event. Already the temperature data taken during the war period, including in the Pacific are very questionable, as investigated in a paper in 1997 (Bernaerts, 1997). Even is one is willing to trust the most known data in this respect, NASA/Giss, the Figure 1 shows for winter 1939/40 only a remote increase of temperature in the equatorial Pacific. For comparison the values for the strong El Niño 1997/98 is shown as well (Fig. 1). For the three years period see Figure 2, below. 

Particularly more attention should be given to the usual physical condition of such an event, which speaks strongly against El Niño conditions that are lasting for 30 months. Every El Niño is based on a warm water pool originating at the Indonesian Archipelagos, moving along the equator to the American Continent, where it over a short period of time overlap the cold water from the Antarctic, than mix, and usually disappear within a couple of months. 

Over a time span of 120 years there have been about 25 El Niño events, of which none seem to match the war situation from 1939-1942. The winter which presumably came closest to the first war winter 1939/40 is the winter 2009/10, with a strong ENSO and the coldest winter in Europe for 30 years. However, the winter 1939/40 was considerable colder, and came along with much stronger sea ice condition in the Baltic, and was followed by another two extreme winter. Due to naval war activities? In contrast the winter 2010/11 was exceptional cold in December 2010, but mild for the rest of the winter.

Even though there are considerable reservation concerning the relevance of the El Niño thesis on the war winters 1939-1942, the idea is interesting, but has at most a peripheral connection with the three war winters. It does not affect the naval war thesis. This investigation is about war and weather. Particularly naval activities in the marine environment is in focus. 

 Fig. 2; the winter temperature anomaly 1939/40, 1940/41 & 1941/42 (Dec/Jan/Feb) vs 1900-1939