Climate change will have numerous effects on the condition of the Baltic Sea, 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 when 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 in 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, may also have unpredictable effects on the sea.
Increased rainfall and water flow from land will reduce the salinity of the Baltic Sea. Currently salinity is maintained by infrequent salt water 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 stratification of the sea water, as well as affect the habitants of the sea. Marine species would suffer, 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 ecosystem and foodwebs of the Baltic Sea are somewhat 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, and it would greatly weaken the sea’s biodiversity. Losses in biodiversity would make the Baltic Sea’s ecosystems increasingly vulnerable to the effects of climate change.
Changes in species will not be limited to organisms living in the Baltic Sea. The shores and archipelago could attract birds that have formerly not nested there. Their predation might in turn change the species composition in the foodwebs of the sea. Changes in plant species in 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.