Differences between Arctic Interannual and Decadal Variability across Climate States

Abstract

Long-term climate variations have the potential to amplify or dampen (human-induced) trends in temperature. Understanding natural climate variability is therefore of vital importance, especially since the 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 five quasi-equilibrium climate simulations of a state-of-the-art global climate model with 0.25, 0.5, 1, 2, and 4 times present-day atmospheric CO2 forcing. The natural fluctuations in Arctic temperature, including their dependence on the state of the climate, are linked to anomalous atmospheric and oceanic heat transports toward the Arctic. Model results suggest that atmospheric heat transport leads (and also controls) Arctic temperature variations on interannual time scales, whereas oceanic transport is found to govern the fluctuations on decadal time scales. This time-scale 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 surface air temperature on any time scale. In cold climates (with full Arctic sea ice cover), interaction between ocean and atmosphere is limited, leaving poleward atmospheric heat transport to be the primary driver on all time scales (interannual and decadal).

Climate State Dependence of Arctic Precipitation Variability

“…The Nucleus for European Modeling of the Ocean (NEMO) model for the ocean uses a horizontal grid configuration with a resolution of approximately 1.1° and a vertical resolution of 42 levels. The performance of the EC‐Earth model in the Arctic in terms of the mean and variability (e.g., AO) can be found in Koenigk et al (2013) and Reusen et al (2019), respectively. The Arctic's oceanic components are evaluated by Koenigk and Brodeau (2014) and Sterl et al (2012).…”

“…The Arctic's oceanic components are evaluated by Koenigk and Brodeau (2014) and Sterl et al (2012). The EC‐Earth model realistically simulates various aspects of the global climate (Hazeleger et al, 2012), the atmospheric dynamics that govern poleward energy transport (sensible and latent heat) (Reusen et al, 2019) and surface evaporation (Koenigk et al, 2013).…”

“…Temporal variability on shorter (interannual) time scales is linked to other mechanisms than those that govern longer‐term (decadal) variabilities. Interannual variations are generally associated with atmospheric processes, whereas decadal variations are often dominated by ocean interactions due to the ocean's comparatively high inertia and heat capacity (Reusen et al, 2019). To assess such differences, the time series were subdivided into high and low frequencies following Reusen et al (2019).…”

“…In the Arctic region, the Arctic Oscillation (AO) is the dominant mode of variability and in terms of circulation regimes strongly linked to precipitation variability (Boer et al, 2001; Groves & Francis, 2002; Oshima & Yamazaki, 2004). The relation between atmospheric circulation regimes and temperature variability will alter toward warmer climates because of the diminishing role of sea ice due to melting (Reusen et al, 2019; Van der Linden et al, 2017).…”

“…Additionally, precipitation variability is locally affected by the availability of open water. In warmer conditions, interannual sea ice variability will decrease (Reusen et al, 2019), which is expected to affect variability in the amount of atmospheric moisture in the Arctic through surface evaporation. How such changes will combine to affect precipitation variability is, however, not yet understood.…”