Photo: Brian MacKenzie

Baltic Sea a model for the consequences of climate change

Wednesday 13 Jun 18


Brian MacKenzie
DTU Aqua
+45 35 88 34 45


Reusch, T. H. B. et al. 2018:
The Baltic Sea as a time machine for the future coastal ocean
Sci. Adv. 2018; 4.
The Baltic Sea is one of the world’s most affected and most intensely studied marine areas and can therefore be used as an example of what’s in store elsewhere in the world.

Warming, acidification, nutrient load, and lack of oxygen—these are some of the major challenges that are already seen or can be expected in coastal waters worldwide. In the Baltic Sea, change takes place at a much higher pace than in other regions, but at the same time the Baltic Sea region has extensive experience of how these challenges can be met.

A team of international researchers, headed by GEOMAR Helmholtz Centre for Ocean Research Kiel with participation from DTU Aqua, now proposes in the journal Science Advances that the rest of the world use the Baltic Sea as a model for what—for better or worse—can be expected in other coastal waters, and for how to respond to the challenges.

Special conditions in the Baltic Sea
The changes in the Baltic Sea are happening at a faster pace than elsewhere because the Baltic Sea has a relatively small water volume and a fairly limited exchange of water to and from the open sea. It makes the many processes happen at a high pace.

For example, over the past 30 years, the temperature in the world’s oceans has increased by an average of 0.5°C, while the temperature in the Baltic Sea has increased by approximately 1.5°C. Similarly, the areas lacking oxygen have increased by a factor of ten in the Baltic Sea in the past century, and the pH value, which is an expression of acidification of the sea, in the Baltic Sea is regularly down to levels that are not expected in other marine areas before the coming century.

The negative change in the Baltic Sea is reinforced by the intensive impact from humans. The nine countries bordering the Baltic Sea are all highly industrialised and have densely populated coastal areas. In addition, the agricultural sector contributes to emissions of nutrients, and fishing affects marine food chains.

One of the most studied areas of the world
There are also positive things to learn from the Baltic Sea which is one of the most extensively studied marine areas on Earth. Scientific research and monitoring of physical and biological processes began around 1900, and there is a strong tradition of scientific cooperation on the Baltic Sea. These long and numerous data series provide a strong scientific basis for the management of the Baltic Sea, and the cooperation between the countries has produced results.

Among the success stories is the fact that the nutrient emissions have been significantly reduced since the 1980s, and that overfishing has been limited.

“One of the good stories from the Baltic Sea is that the cooperation between the countries on research and management has meant that fish stocks have generally improved. But this is now challenged by increasing temperatures, lack of oxygen, and changes in food chains, and these are problems that other areas will probably also experience in the future,” says Professor Brian MacKenzie, DTU Aqua, who co-authored the article in Science Advances.

The Science Advances article is based on knowledge from researchers who have participated in a large number of projects under the EU BONUS programme, which has supported research and development for the purpose of protecting the Baltic Sea. DTU Aqua has held leading roles in two of these projects (BIO-C3 and INSPIRE).