It is now well known that the world’s large-scale emissions of greenhouse gases are leading to climate change and global warming. However, there is less awareness of what has been called “the other carbon dioxide problem” – ocean acidification.

In the 1980s, acidification of soil, watercourses and lakes was one of the environmental problems attracting most attention. Emissions of sulphur and nitrogen oxides from combustion processes (e.g. in motor vehicles and power and heating plants) was giving rise to precipitation of sulphuric and nitric acids. This was popularly called “acid rain” and had major effects on lake and forest ecosystems. However, in the 1980s and 1990s, a combination of greatly improved emission control and the liming of lakes and waterways resulted in decreased acidification in the Baltic Sea area.

In its stead, another type of acidification has attracted attention in recent years – global ocean acidification. This is caused by massive emissions of carbon dioxide and cannot be solved by liming. Up until now, the changes have not been large in the Baltic Sea. However, in the long run, this acidification will have effects here too and, eventually, threaten the sea’s ecosystems.


  • To minimise the consequences of ocean acidification, work towards implementing more stringent carbon dioxide emission goals (as per Sustainable Development Goal 14.3).
  • Expand the acidification measurement programmes to include both open sea and coastal waters. High-quality and cohesively longer time series for all parts of the year and in all parts of the Baltic Sea will give a more comprehensive basis for deciding on measures.
  • Accelerate measures against problems such as eutrophication, overfishing and emissions of hazardous substances. Many species can tolerate water that is more acidic. However, their resistance and resilience to stress is diminishing.
  • Coordinate controls and measures against the above-mentioned problems. To strengthen the Baltic Sea’s resistance to future acidification, a marine environment perspective needs to be integrated into land management measures.
  • To promote the development of low-sulphur fuels, investigate a prohibition on emitting scrubber system water from vessels.
  • Widen the support for research into how acidification is affecting ecosystems in the Baltic Sea.


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Download the full policy brief (pdf) Emerging ocean acidification threatens Baltic Sea ecosystems (1187 Kb)



Erik Gustafsson
Oceanographer, Baltic Sea Centre


Monika Winder
Marin ecologogist, Department of Ecology, Environment and Plant Sciences