Ice on the coast of the Wadden (Photo: Peter Elzinga)
This pattern was caused by a well-know climate mode of variability: the Arctic Oscillation (AO), also referred to as the Northern Annular Mode. The Arctic Oscillation had its largest negative excursion sinc the beginning of observations in 1900. The net effect on the global mean temperature was close to zero: the cold air brought south to Siberia, Europe and the eastern US was compensated by warm air going north into other regions. The global mean temperature was in fact near record high, pushed up by the combination of the slow trend and the effects of the 2009/2010 El Niño.

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