Roughly 25% of the Baltic Sea’s nitrogen load originates from airborne sources (Chapter 2.3). Climate change may present a further challenge because precipitation is projected to increase, especially in the northern part of the Baltic Sea catchment area, which may, in combination with increasing winter temperatures, lead to increased winter runoff and leaching of nutrients. Furthermore, an increase in water temperatures will make benthic communities more vulnerable to eutrophication and hypoxia (Box 2.4). Policy responses to climate change, however, may limit the impacts of climate change. Thus, the net effect of climate change and climate policy for the Baltic Sea are not easily judged, especially as the relative abatement costs across different countries are also likely to change under these circumstances. There are no internationally common policy instruments designed with the particular purpose to reduce eutrophication in the Baltic Sea (Elofsson, 2010).