A model study of natural variability in the Arctic climate

Abstract

The arctic climate response to natural perturbations in the atmosphere is simulated with two numerical models. The first is a single-column, energy balance model of the atmosphere, sea ice, and upper-ocean system which I use to investigate how the variability in atmospheric energy transport is partitioned in the climate system between storage in the sea ice and net radiation to space. The processes of sea ice ablation/accretion and heat conduction through the sea ice, integrate stochastic variability forcing from the atmosphere. I find that significant, natural, low frequency variability in the arctic sea ice results solely from thermodynamic processes associated with the arctic climate system and the nature of the atmospheric energy transport into the Arctic.The second model is a sea ice and upper ocean model that is designed to explore variability in the sea ice due to thermodynamics and dynamic processes in a laterally inhomogeneous system. Ice dynamics in this model (including ridging and advection) forced by winds with the proper synoptic scale variability increase the sensitivity of the ice to air temperature anomalies. The air temperature anomalies primarily influence interannual variability in the central region: without realistic air temperature anomalies, the low-frequency variance of the ice volume is seriously underestimated.The results provide an estimate for the magnitude and time scales of the natural variability in the arctic climate system. The implications of the low-frequency, natural variability in sea ice volume for detecting a climate change are discussed. Finally, calculations suggest that the variability in the thermodynamic forcing of the polar cap could lead to a freshening in the North Atlantic that is comparable to the freshening associated with the Great Salinity Anomaly.