The Baltic Sea not only provides us with food and recreation, but can also counteract climate change by absorbing the greenhouse gas carbon dioxide. But when the sea is overfished and marine life is weakened, the situation may become the opposite – the sea releases greenhouse gases instead, fuelling ongoing climate change. We have taken a deep dive into the Baltic Sea in a changing climate, what policy makers are doing – and should be doing.
A thriving sea provides us with many services
A thriving sea provides us with food, recreation, swimming and nature experiences. More than one million Swedes are estimated to be active recreational fishermen and both the value added and the employment rate linked to recreational fishing are increasing. In 2022, recreational fishing is estimated to have added around SEK 5.7 billion to society. Tourism around the Baltic Sea is likely to increase in importance in connection with the new trend of ‘coolcation’, whereby tourists from southern Europe seek northern latitudes to avoid the hot summers around the Mediterranean.
The ocean provides another important service that has received increasing attention in recent years: carbon sequestration. The ocean has a climate regulating function, with the coastal zone considered to play a particularly important role. Research shows that the potential for the ocean to sequester carbon is enhanced when the coastal zone harbours a diversity of plants and animals and viable fish stocks. However, as the coastal zone environment deteriorates and wildlife is wiped out, the ocean risks becoming a source of carbon emissions instead, fuelling ongoing climate change.
A changing climate – how will it affect the Baltic Sea?
Warmer water
The Baltic Sea has warmed the fastest of all the world’s oceans and marine heatwaves have increased in both frequency and duration. The surface waters warm particularly quickly as they absorb heat from the atmosphere, but after a while the temperature also increases in deeper waters. However, some deep parts of the western Baltic Sea are warming even faster than the sea surface. According to one study, the exceptional warming can be explained by an increase in warm saltwater inflows from the North Sea. Warming has ecological consequences, as oxygen is consumed faster in warm water, and large areas of the deep Baltic Sea are already oxygen deficient. A warmer climate may also lead to oxygen deficiency in coastal waters as a result of more extensive algal blooms in summer.
The salinity of the upper water layer of the Baltic Sea, from the surface down to 40-50 metres, has decreased in recent decades. The depletion of surface waters is expected to continue, but to what extent is uncertain. Average annual precipitation has increased in the northern Baltic Sea and is expected to increase further in the future, but for the central and southern Baltic Sea it is difficult to predict how precipitation patterns will change.
The waters of the Baltic Sea are stratified as a result of both temperature and salinity. The stratification of the water is expected to increase due to warming. Climate change is also affecting sea ice, which has shrunk by 30 per cent over the last century and the ice season has become shorter.
An altered ecosystem
Changes in the waters of the Baltic Sea affect the whole ecosystem in different ways – both directly and indirectly. Warmer waters may favour some species – but when some species are favoured and others are disfavoured or wiped out, the interaction between plant and animal species changes. It is difficult to predict these changes, but research shows climate-related effects across the entire ecosystem, from bacteria to phytoplankton, zooplankton and fish.
Changes in temperature, salinity and species interactions can affect cod, herring and sprat stocks – although fishing remains the dominant factor. For many coastal fish species, eutrophication remains a key driver. The impacts on Baltic fish populations will be the result of climate-related factors interacting with other drivers such as fisheries, habitat degradation and eutrophication.
Higher water temperature can have a direct effect on fish spawning and egg survival. For example, large female perch produce offspring that are more resistant to a wide range of temperatures. This shows the importance of maintaining the size distribution of our fish populations in a warmer climate and that management advice needs to include regulations on size-selective fishing.
In the case of Baltic herring, research shows that warmer waters negatively affect their reproductive success. Changes in salinity and oxygen levels also affect cod reproductive success as a certain level of salinity and oxygen is required for the survival of fertilised eggs.
The fish of the Baltic Sea originate from both salt and fresh water – therefore, depletion of the water may favour fish species of freshwater origin but disadvantage those of marine origin. Along the Swedish coast, where a number of saltwater species already live at the edge of their range (e.g. herring and cod), such changes may be particularly noticeable. In addition to the direct effects of temperature, salinity and oxygen levels, food availability is also an important factor affecting fish growth and survival – which may also shift in a changing climate.
Politics, the sea and the climate
The government emphasises the link between the ocean and the climate – but pursues policies that increase greenhouse gas emissions. The government’s action plan emphasises that the ocean may change fundamentally as a result of climate change and that the ocean’s ability to support society and provide benefits such as fish and carbon sequestration may be lost. The Marine Environment Bill presented by the Government before the summer emphasises that the sea is both affected by and can contribute to solutions to climate change. At the same time, it recognises that a sick sea can become a source of emissions of the greenhouse gas methane, which in turn exacerbates climate change.
The government now wants to strengthen efforts to protect marine areas and introduce area protection of 30 per cent, of which 10 per cent will be strictly protected by 2030. This will strengthen biodiversity and contribute to the sequestration of carbon in the sea. Sweden’s county administrative boards have received SEK 49 million to work on increased protection of marine and aquatic environments in the Baltic Sea. It is positive that the Government is allocating funds to establish area protection and fulfil the commitments Sweden has already undertaken within the EU and the UN.
At the same time, the government has imposed a savings requirement of SEK 25 million on its own expert agency HaV in 2024, and the agency is now warning that up to 25 employees may be made redundant – something that does not signal higher ambitions for the marine environment. The government’s work to reduce Sweden’s greenhouse gas emissions has also been criticised by, among others, the Climate Policy Council, which notes that: ‘With the adopted policy, emissions are expected to increase during the term of office and the responsibility for achieving targets and EU commitments is postponed’. In the spring budget, the government also chose to direct billions in support to the aviation industry, and tax breaks for air travel are now on the table for the autumn budget. One of Sweden’s experts in the field says that ‘It is remarkable that a billion kronor is being given to a sector that has one of the greatest climate impacts’.
The government is thus emphasising the link between climate change and the marine environment, but with the policies pursued in other areas, there is a risk that greenhouse gas emissions will increase, which reduces the credibility of the government’s work on the marine environment.
What is important to do in the coming year?
Strong reductions in greenhouse gases are necessary to mitigate the long-term effects of climate change on the Baltic Sea. This is also a commitment we have made through European and international agreements. However, as we are not expected to be able to reverse climate change in the short term, it is of the utmost importance that we implement measures that strengthen the Baltic Sea ecosystem and increase its resilience to future changes.
For example, we need to counteract nutrient discharges at the coast with the aim of maintaining a good coastal environment. This will strengthen biodiversity and the coast’s ability to sequester carbon. Fisheries management needs to be reformed with the aim of resulting in viable stocks with a maintained size and age distribution. Another important effort is to create a system for systematic monitoring of greenhouse gas uptake and emissions from the Baltic Sea – to be compared with LULUCF (Net emissions and removals of greenhouse gases from land use).
It is positive that the government emphasises the connection between climate change and the marine environment – and that money is allocated for work on area protection. However, if climate emissions increase at the same time as a result of policies in other policy areas, the credibility of the government’s intentions is reduced. Instead, the government needs to ensure that laws, targets and guidelines are harmonised to reduce climate impact and contribute to a healthy Baltic Sea. A broad approach that spans several policy areas, party lines and national borders is a necessity if our inland sea is to continue to provide services such as fish, recreation and carbon sequestration – for current and future generations.
BalticWaters works systematically to strengthen ocean resilience
BalticWaters is carrying out major demonstration projects and funding research that will contribute to a healthy sea that is more resilient to climate change. The Thriving Bays project is about identifying environmentally and economically effective measures to restore eutrophic bays along the Svealand coast. Research shows that it is precisely in the coastal zone that carbon sequestration is greatest – provided that the ecosystems are healthy.
Within the ReCod project – release of small cod in the Baltic Sea, extensive releases of cod larvae have been carried out to test whether it is possible to strengthen the cod stock in this way. Viable predatory fish stocks have positive effects on the entire ecosystem and the health of the Baltic Sea. The research linked to the project also generates specific knowledge directly linked to climate change – for example, the effects of rising temperature and decreasing salinity on cod eggs.
