Abstract
Abstract. An ensemble of simulations of the climate of the past millennium conducted with a three-dimensional climate model of intermediate complexity are constrained to follow temperature histories obtained from a recent compilation of well-calibrated surface temperature proxies using a simple data assimilation technique. Those simulations provide a reconstruction of the climate of the Arctic that is compatible with the model physics, the forcing applied and the proxy records. Available observational data, proxy-based reconstructions and our model results suggest that the Arctic climate is characterized by substantial variations in surface temperature over the past millennium. Though the most recent decades are likely to be the warmest of the past millennium, we find evidence for substantial past warming episodes in the Arctic. In particular, our model reconstructions show a prominent warm event during the period 1470–1520. This warm period is likely related to the internal variability of the climate system, that is the variability present in the absence of any change in external forcing. We examine the roles of competing mechanisms that could potentially produce this anomaly. This study leads us to conclude that changes in atmospheric circulation, through enhanced southwesterly winds towards northern Europe, Siberia and Canada, are likely the main cause of the late 15th/early 16th century Arctic warming.
Highlights
Studies of the Arctic climate indicate a considerable warming in this region in recent decades
An ensemble of simulations of the climate of the past millennium conducted with a three-dimensional climate model of intermediate complexity are constrained to follow temperature histories obtained from a recent compilation of well-calibrated surface temperature proxies using a simple data assimilation technique
While instrumental temperature data are relatively sparse during the first half of the last century, the early 20th century Arctic warm period appears to have been characterized by a large-scale spatial pattern different from the current warm period
Summary
Studies of the Arctic climate indicate a considerable warming in this region in recent decades. At the hemispheric or global scale, these temperature changes are largely consistent with the response of the climate system to external changes over the past millennium in natural (and after the 19th century, anthropogenic) radiative forcing The evolution of the model was constrained by selecting, among all available realizations, the realization of the internal variability that most closely matches the information from the proxies Those estimates of past climate changes based on model simulations using data assimilation will be referred to as “reconstructions”, even though the methodology used in this framework differs from the more traditional, statistically-based approach to reconstructing climate over the past millennium. Using the model data assimilation experiments, we analyze the role of various physical and dynamical processes that appear responsible for the pattern of the observed Arctic warmth, and demonstrate that this pattern likely arises from dynamical variability
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