Robust Changes in Temperature Variability under Greenhouse Gas Forcing and the Relationship with Thermal Advection

Recent temperature extremes have highlighted the importance of assessing projected changes in the variability of temperature as well as the mean. A large fraction of present day temperature variance is
associated with thermal advection, as anomalous winds blow across the land-sea temperature contrast for instance. Models project robust heterogeneity in the warming pattern under greenhouse gas forcing, resulting in land-sea temperature contrasts increasing in summer and decreasing in winter, and the pole-to-equator temperature gradient weakening in winter. In this study, monthly and daily variability changes in the 17 member ensemble ESSENCE are assessed. In winter, variability in midlatitudes decreases while in very high latitudes and the tropics it increases. In summer, variability increases over most land areas and in the tropics, with decreasing variability in high latitude oceans. Multiple regression analysis is then used to determine the contributions to monthly variability changes from changing temperature gradients and circulation patterns. Thermal advection is found to be of particular importance in the northern hemisphere winter midlatitudes, where the change in mean state temperature gradients alone is sufficient to produce changing variability of the same magnitude as that projected by ESSENCE. In the summer, thermal advection changes are also found to be important in Europe and coastal areas. Comparison with CMIP5 data shows that the midlatitude changes in monthly variability are robust across large regions, particularly high northern latitudes in winter and mid northern latitudes in summer.