AbstractKnowledge about current and future climate change in the Baltic Sea region is scattered in various scientific publications which are mostly not usable for non-scientists. Nevertheless, trustworthy scientific information on the effects of regional climate change is necessary for decision makers. In the BACC assessments (BALTEX Assessment of Climate Change for the Baltic Sea basin), more than 100 experts from the entire Baltic Sea region summarize the currently available published knowledge of climate change and its impacts in the Baltic Sea region. Observed changes are described, scenarios of possible future changes are pre-sented and observed and estimated impacts on the environment are discussed. The assessments encompass the knowledge about what scientists agree on but also identify cases of disagreement or knowledge gaps. The assessments are evaluated by independ-ent scientific reviewers. The BACC assessments of 2008 (BACC I) and 2013/14 (BACC II) are used by HELCOM, the intergovern-mental Baltic Marine Environment Protection Commission, as a basis for future deliberations on regional climate change.
According to BACC I, a warming is going on in the Baltic Sea region presently, and is expected to continue throughout the 21st century. So far, and in the next few decades, the signal is limited to temperature and directly related variables, such as ice condi-tions. Later, changes in the water cycle are expected to become obvious. This regional warming will have a variety of effects on terrestrial and marine ecosystems – some predictable such as the changes in the phenology others so far hardly predictable. BACC II confirms BACC I results. Some aspects are treated in more detail in the new assessment, or are completely new. The issue of multiple drivers on ecosystems and socio-economy is recognized, but more efforts are needed. In many cases, the relative im-portance of different drivers next to climate change needs to be evaluated.