European land temperatures according to combined climatic datasets of Met Office Hadley Centre, NOAA and NASA. (Click for comparison to world land temperature graph according to the BEST study.)
European winters are strongly influenced by the North Atlantic Oscillation (NAO), which index can act as a switch to turn off the usually dominant mild westerlies coming from the Atlantic Ocean – allowing for cold continental or Arctic air to spread out, and bring sometimes long-lasting freezes.
This means the variation in European winter temperatures is much larger than that of the summer temperatures.
When analysing recent climatic development this high natural winter variation easily leads (due to a wrong focus on overly short climatic timescales – for instance 10-20 years) to wrong assumptions, as the one that in Europe average winter temperatures are not increasing as fast as the average temperatures of the other seasons.
‘Wrong’ because when zooming out to a larger timescale it becomes clearly visible that the warming trend of annual average temperatures is very similar in magnitude to that of European summer and winter warming – as shown in the above graph, which was published in the new European Environmental Agency report Climate Change, Impacts and Vulnerability 2012 (PDF).
That study does note there are seasonal differences in European climate warming on the shorter timescales (between 1990-2011) – and also regional differences. Recent winter warming it states has been strongest over Scandinavia, whereas summer warming has been relatively strong over the Iberian Peninsula.
© Rolf Schuttenhelm | www.bitsofscience.org