ESSAR addresses how climate variability and change affects the marine ecosystems of the polar (Subarctic and Arctic) seas and their sustainability. To provide accurate projections on the impact of climate warming on these ecosystems requires improved knowledge of its components and their linkages. Because of the complexity of the interactions, accurate predictions of what will happen to individual species requires knowledge on key life-history traits and of what will happen to the ecosystem as a whole, as species do not function separately from their ecosystem. ESSAR, therefore, encompasses retrospective and field studies on physics, plankton, benthos, fish and shellfish, marine mammals, sea birds and humans. The field studies will be carried out in the Atlantic, Pacific and Arctic Oceans during 2007-2008. The data gathered will be used, together with bio-physical models, to make quantifiable predictions of the effects of both climate variability and long-term climate change on arctic polar marine ecosystems.