Changes in atmospheric variability in a glacial climate and the impacts on proxy data: a model intercomparison

Abstract

Abstract. We investigate sea level pressure variability in the extratropical North Atlantic in the preindustrial climate (1750 A.D.) and at the Last Glacial Maximum (LGM, 21 kyr before present) using four climate models. In general, the models exhibit a significant reduction in interannual variance of sea level pressure during the LGM compared to pre-industrial simulations and this reduction is concentrated in winter. For the preindustrial climate, all the models feature a similar leading mode (EOF) of sea level pressure variability that is also similar to the leading mode of variability in the instrumental record: the North Atlantic Oscillation (NAO). In contrast, the leading mode of sea level pressure variability during the LGM is model dependent, but in each model different from that in the preindustrial climate. In each model, the leading (NAO-like) mode of variability explains a smaller fraction of the variance and also less absolute variance in the LGM than in the preindustrial. The leading (NAO-like) mode of sea level pressure variability is shifted southward in the LGM simulations relative to the preindustrial simulations. Finally, we correlate the leading mode of sea level pressure variability with surface temperature and precipitation within each model and for the two time periods. In the preindustrial climate, the leading mode of sea level pressure variability is similar from model to model and the temperature and precipitation correlation patterns are also similar. In contrast, since the models find different dominant modes of sea level pressure variability for the LGM climate, they also disagree on the associated patterns of temperature and precipitation variability. Assuming stationarity of the relationship between surface climate and the leading mode of sea level pressure variability could lead to a misinterpretation of signals recorded in proxy data.