Differences between Arctic interannual and decadal variability across climate states

Abstract

Understanding natural climate fluctuations is of vital importance in a globally warming world. These climate variations may amplify or dampen (human-induced) trends in temperature, even more so since variability itself may change with a changing climate. Here, we quantify the magnitude and other characteristics of interannual to decadal variability in Arctic temperature and their dependence on the climate state. Moreover, we identify the processes responsible for the state-dependency of the variations, using a state-of-the-art global climate model with which five quasi-equilibrium climate states with one-fourth, halved, present-day, doubled and quadrupled atmospheric CO2 forcing have been simulated. The main reasons behind the natural fluctuations in Arctic temperature including their dependence on the state of the climate are linked to anomalous atmospheric and oceanic heat transport towards the Arctic. Correlations of Arctic surface air temperature with poleward atmospheric and oceanic transports are strongly dependent on the time scale of the variations. Model results suggest that atmospheric heat transport leads (and also controls) Arctic temperature variations on interannual timescales, whereas oceanic transport is found to govern the fluctuations on decadal timescales. This timescale transition of atmospheric to oceanic dominance for Arctic temperature variations is most obvious when there is interannual to decadal variability in Arctic sea ice cover. In warm climates (without Arctic sea ice cover), there is no correlation between oceanic transport and temperature on any timescale. In cold climates (with full Arctic sea ice cover), interaction between ocean and atmosphere is limited, suggesting that poleward atmosperic heat transport is the primary driver on all timescales (interannual and decadal).