Shifts of means are not a proxy for changes in extreme winter temperatures in climate projections

Changes in severity of extreme weather events under influence of the enhanced greenhouse effect could have disproportional large effects,
compared to changes in the mean climate. In this paper, the meteorological circumstances of extremes and changes therein are explored using two
49-member climate model ensembles, for present-day (1961-1990) and scenario (2051-2080) greenhouse-gas concentrations. We have focused on daily-mean
surface-air temperatures in winter over the Northern Hemisphere. Over large parts of the continents, changes in the one-in-10-year temperature events are influenced at least as much by changes in the shape of the Probability Distribution Functions (PDFs) as by shifts in the mean. In coastal areas this is largely attributable to changes in the large-scale circulation, for those types of extremes linked to infrequent wind directions. In other areas, the inhomogeneous mean warming, increasing inland and polewards, affects the tails of the local temperature PDFs. Temperature extremes in widely different regions are linked by a large-scale circulation anomaly
pattern, which resembles the Northern Hemisphere Annular Mode. In the projected ensemble, this anomaly pattern favours its positive phase,
leading to enhanced probabilities of westerly winds in a belt around the Northern Hemisphere.