"Our study suggests that the future Baltic Sea ecosystem may unprecedentedly change," Markus Meier of the Swedish Meteorological and Hydrological Institute and Stockholm University told environmentalresearchweb. "Even in the case of the most optimistic nutrient-load reductions following the Baltic Sea Action Plan (BSAP), an environmental status of the Baltic Sea unaffected by human impact cannot be reacquired within the coming 100 years."

Adopted in 2007, the Baltic Sea Action Plan aims to improve water quality and prevent eutrophication and algal blooms. It gives each country that neighbours the Baltic a quota for reducing nutrient load. But these quotas did not account for climate change.

"Recent research indicates that...climate change may have considerable impacts on the marine ecosystem," said Meier. "Hence we studied, in a holistic approach, the combined impacts of changing climate and changing external nutrient loads. In addition, the impacts of other drivers like fisheries were investigated."

Meier and colleagues from Sweden, Germany, Denmark, Poland, Estonia and Finland modelled the marine biogeochemistry and food web of the Baltic Sea from 1850 to 2098. They used historical measurements alongside regionalized global general-circulation models and various greenhouse-gas and nutrient-load scenarios.

"Only a few modelling studies exist investigating the impact of changing climate on the marine ecosystem of the Baltic Sea or other shallow seas," said Meier. "In previous studies only the results of one regional, coupled climate-environmental ocean (Baltic Sea) model were analysed. Here, we employed two global General Circulation Models, one regional climate model, two hydrological models and three biogeochemical models for the Baltic Sea."

The team found that cod biomass was mainly controlled by the amount of fishing. But even if fishing pressure was reduced, climate change and eutrophication could still cause a decline of cod biomass during the latter part of the century.

"These effects need to be taken into consideration in management plans," said Meier. "Our results give a state-of-the-art, scientific basis for marine management and policy support. To reach HELCOM Baltic Sea Action Plan targets for a Baltic Sea unaffected by human impact, nutrient-load reductions and a sustainable fishery are even more important in the future than in the present climate."

Although the revision of the Baltic Sea Action Plan will "partly consider" the team's results, Meier said that climate change is still perceived as distant in space and time by coastal stakeholders. The researchers believe that more information is needed to raise public awareness of the possible impacts of climate change on marine ecosystems.

"Another new aspect of our approach was the estimation of uncertainties by using multi-model ensemble simulations," said Meier. "As models have considerable shortcomings, marine management should not rely on the results of only one model. Hence, at all levels of the dynamical downscaling approach, as many state-of-the-art models were employed as possible. Finally, the results were evaluated probabilistically."

The team feels that, despite considerable uncertainties, their approach is powerful enough to support marine management, as well as being unique. They plan to use the method, which they reported in Environmental Research Letters (ERL), in other regional seas with environmental problems similar to the Baltic.