Climate variations for the last millennium

Variability and long-term climate change in the Baltic Sea region have been investigated in a 1000-year long climate model simulation.

For the first time long-term climate variations over the region have been simulated with a regional climate model. Solar variability, changes in orbital parameters and changes in greenhouse gases over the last millennium are used to force the models.

The results show 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. This is in broad agreement with climate reconstructions based on proxy data 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, says Erik Kjellström, climate researcher.

Strongest response for winter

Time series and spatial patterns of temperature, sea level pressure, precipitation, cloud cover, wind speed and gustiness for annual and seasonal means are investigated. Most parameters show the strongest 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.

The report “A regional climate model simulation over the Baltic Sea region for the last Millennium” is financed by the research projects INFLOW and ECOSUPPORT within the BONUS programme, and project Landclim.

The temperature difference between the warm medieval period and the later, colder period. The left map show the difference during winter season and the right map the difference during summer season.