Climate change will have numerous effects on the Baltic Sea’s condition, as well as on its habitants. Some species might benefit from climate change but mostly its effects are predicted to be negative. This is why combating climate change is an essential part in ensuring the future well-being of the Baltic Sea. Some climate change effects are already observable.
During springtime, massive amounts of fresh water flow into the sea, as snow melts on the catchment area. However, the amount of snow will decrease as a result of global warming, while precipitation increases. Subsequently, fresh water runs from land to the sea continuously throughout the year, instead of one big spring flood. This runoff might bring nutrients to the sea, since warm winters prevent the ground from freezing. An unfrozen ground is not able to retain nutrients efficiently.
Sea-surface water temperature has already risen. Higher temperatures together with excess nutrients from land can increase eutrophication. Changes in ice conditions, such as shorter ice seasons due to higher temperatures, can also have unpredictable effects on the sea.
Increased rainfall and water flow from land will reduce the Baltic Sea’s salinity. Currently salinity is maintained by infrequent saltwater inflows from the Danish straits. Climate change can affect the occurence of these inflows in unexpected ways, possibly making them even less frequent. Reduced salinity would change the sea water’s stratification, as well as affect the sea’s habitants. Marine species would be at disatvantage, while species adapted to fresher water would thrive.
As climate change progresses, some species’ range extends to the north. The Baltic Sea has already had its share of non-indigenous species, i.e. species that are not part of the sea’s original ecosystem. The Baltic Sea’s ecosystem and foodwebs are simple, which makes it easier for the non-indigenous species to override the original ones – especially if the sea’s native, marine species are already suffering from the water’s reduced salinity. The loss of marine key species, such as bladder wrack, would have dramatic effects on the sea’s fauna.
Changes in species will not be limited to organisms living in the Baltic Sea. The sea’s shores and archipelago could attract birds that have formerly not nested there. Their predation might in turn change the species composition in the sea’s foodwebs. Changes in plant species on the catchment-area would also have consequences for the Baltic Sea. In Finland, boreal forest is expected to move towards the northern parts of Finland. Different forest types have distinctive effects on water evaporation and on flow of water in soil, i.e. hydrological processes.