How unusual was autumn 2006 in Europe?
KNMI, De Bilt, The Netherlands
Abstract. The temperatures in large parts of Europe have been record high during the meteorological autumn of 2006. Compared to the 1961–1990 normals it was more than three degrees Celsius warmer from the North side of the Alps to southern Norway. This made it by far the warmest autumn on record in the United Kingdom, Belgium, the Netherlands, Denmark, Germany and Switzerland, with the records in Central England going back to 1659, in the Netherlands to 1706 and in Denmark to 1768. Also in most of Austria, southern Sweden, southern Norway and parts of Ireland the autumn was the warmest on record.
Under the obviously false assumption that the climate does not change, the observed temperatures for 2006 would occur with a probability of less than once every 10 000 years in a large part of Europe, given the distribution defined by the temperatures in the autumn 1901–2005. However, even taking global warming linearly into account the event was still very unusual, with return times of 200 years or more in most of this region using the most conservative extrapolation.
Global warming and a southerly circulation were found to give the largest contributions to the anomalous temperature, with minor contributions of more sunshine and SST anomalies in the North Sea. Climate models that simulate the current circulation well do not simulate an increasing probability of warm events in autumn under global warming, implying that it either was a very rare coincidence or some non-linear physics is missing from these models.