This book offers an up-to-date overview of the latest scientific findings in regional climate research on the Baltic Sea Basin, including climate changes in the recent past, climate projections up until 2100 using the most sophisticated regional climate models available, and an assessment of climate change impacts on terrestrial, freshwater and marine ecosystems. The authors demonstrate that the regional climate has already started to change, and will continue to do so - projections show that the region will become considerably warmer and wetter in some parts, but dryer in others. Terrestrial and aquatic ecosystems have already shown adjustments to increased temperatures, and are expected to face further changes in the near future. The BACC Author Team consists of more than 80 scientists from 13 countries covering various disciplines related to climate research and related impacts. BACC is a project within the BALTEX (Baltic Sea Experiment) Programme and a contribution to the World Climate Research Programme. Lead authors of the team include Hans von Storch, Anders Omstedt, Raino Heino, Heikki Tuomenvirta, Valery Vuglinsky, Bo Gustafsson, L. Phil Graham, Benjamin Smith, Joachim W. Dippner and Ilppo Vuorinen.