A regional climate model simulation over the Baltic Sea region for the last Millennium

Typ: Rapport
Serie: Oceanography 111
Författare: Semjon Schimanke, Erik Kjellström, Gustav Strandberg, H.E. Markus Meier


Variability and long-term climate change in Fennoscandia is investi-gated in a 1000-year long climate model simulation. We use the Rossby Centre Regional Climate model (RCA3) with boundary conditions from a General Circulation Model (GCM). Solar variability, changes in orbital parameters and changes in greenhouse gases over the last millennium are used to force the climate models. It is shown that RCA3 generates a warm period corresponding to the Medieval Climate Anomaly (MCA) being the warmest period within the millennium apart from the 20th century. Moreover, an analogy for the Little Ice Age (LIA) was shown to be the coldest period. The simulated periods are 1100-1299 A.D. for the MCA and 1600-1799 A.D. for the LIA, respectively. This is in agreement with recon-structions and mostly related to changes in the solar irradiance. We found that multi decadal variability has an important impact on the appearance of the MCA and LIA. Moreover, multi decadal variability may help to explain sometimes contradicting reconstructions if these are representative for relatively short non-overlapping periods. In addition to time series, we investigate spatial patterns of temperature, sea level pressure, precipitation, cloud cover, wind speed and gustiness for annual and seasonal means. Most parameters show the clearest response for the winter season. For instance, winter during the MCA are 1-2.5 K warmer than during the LIA for multi decadal averages.