European Temperatures Winter 2005/2006

Andrew Masterman 21 May 2006

AVERAGED across Europe using the ten stations this website regularly uses to monitor European temperatures, winter 2005/2006 had temperatures 0.4 C below the 1961-90 average with December close to average and both January & February colder than average. Fifty-seven per cent of the 30 monthly anomalies were negative indicating a modest bias to below average temperatures. Northern Europe including northern UK had a mild winter while southern UK had an average winter and most of the rest of Europe had a colder than average winter. Negative monthly anomalies were not large with only Wroclaw in January (-3.3 C) exceeding 3 C.

FIGURE 1 below compares the average winter temperature anomaly of these ten  European stations with the winter North Atlantic Oscillation (NAO) from 1900 to 2006.   The ranking of winter 2006 is 26th coldest since 1900 putting this winter on the cold side but not remarkably so. The winter NAO had a ranking of 14th most negative since 1900 confirming the well-known relationship between winter temperatures and the NAO and this winter has continued the trend of recent years to lower NAO compared with the 1990s. This trend is even more obvious if you look at January to March data (graph here).

Figure 1 Relationship between mean European Temperature anomaly from 1961-90 average (defined in Table above) and the winter (Dec-Feb) NAO 1900-2006 (r = 0.651; P<0.001)

THE most notable feature of the winter was the persistent anticyclonic blocking across Eurasia which in January 2006 led to widespread cold in a band from western Europe eastwards all the way to Alaska and intense cold (negative anomalies of -5 C) across western Siberia & Alaska (Figure 2). In contrast, a mobile westerly flow across North America led to the warmest January on record in Canada with temperatures 5 C above average.  To some extent, the anomalous cold in Eurasia owed to the 'bathtub' effect in which the cold pool of arctic air sloshes around the arctic regions during each winter: in January 2006, the mobile westerly pattern across North America forced the cold pool over the Eurasian side of the pole. However, this is insufficient to explain such widespread cold across Eurasia and the persistent anticyclonic blocking during the winter allowing prolonged radiative cooling over the snow-covered land is the likely explanation.

Figure 2 January 2006 global temperature anomalies according to the NCDC

THIS theory is supported by the news stories reporting exceptional cold and in some cases record cold in the Baltic States and Moscow during January 2006 with night minima around -30 C. Such Siberian cold is unusual in these regions but the persistent anticyclonic blocking permitted widespread anomalous cold to develop across Eurasia (winter chart). This is in complete contrast to most winters in the 1989 to 2002 period when strong westerly winds off the Atlantic swept mild Atlantic air right across Europe and deep into Siberia resulting in anomalously mild winters (Figure 1). Such swings in temperature across Eurasia driven by changing weather patterns are sufficiently large to affect global temperature and explains why variations in the winter NAO are recognised as explaining much of the year to year and decade to decade variability in northern hemisphere temperatures. However, the IPCC with their claims that 'most global warming over the last 50 years owes to human activities' are underrating the role of weather patterns in climate change. There is no doubt that weather patterns dictate the day to day weather and year to year and decade to decade variations in climate of an individual region such as Europe and the same is true of the globe. The globe of course is simply a collective noun for the different regions of the world and global climate change is the sum of the effects of changing global weather patterns. It is very likely that the rise in winter NAO since the 1960s (Figure 1) leading to decreased radiative cooling over Eurasia in many winters has contributed to the rise in global temperatures since the 1960s.