Arctic climate over the past millennium: Annual and seasonal responses to external forcings

The annual and seasonal temperatures in the Arctic over the past 1150 years are analyzed in simulations performed with the three-dimensional Earth system model of intermediate complexity LOVECLIM forced by changes in solar irradiance, volcanic activity, land use, greenhouse gas concentrations and orbital parameters. The response of the system to individual forcings for each season is examined in order to evaluate the contribution of each forcing to the seasonal contrast. For summer, our results agree relatively well with the reconstruction of Kaufman et al. (2009). Our modelling results suggest that the temperature changes during this period were characterized by large seasonal differences. In particular, while annual mean temperatures display a decreasing trend during the pre-industrial period, spring temperatures appear to rise. The variations in the Earth's orbital parameters are the main cause for those seasonal differences. Larger climate variations are simulated in autumn compared with the other seasons in response to each forcing, particularly in response to changes in greenhouse gas concentration during the industrial period and in response to land use forcing, which surprisingly has a significant impact on Arctic temperature. These contrasting changes for the different seasons also underline the need for an adequate estimate of the season represented by a proxy.