The unprecedented rate of ocean acidification is one of the most alarming phenomena generated by climate change and the only way to mitigate the dangers it represents consists in reducing CO2 emissions significantly. This is the conclusion of the summary of the Third Symposium on the Ocean in a High CO2 World (Monterey, USA, September 2012) which were presented at the Conference on Climate Change taking place in Warsaw (Poland) from November 11 to 22. The document represents the conclusions of 540 experts from 37 countries reflecting the latest research on the subject.