Latest research findings show that failure to check mankind's emissions of carbon dioxide will have severe consequences for the world's oceans. The marine environment is doubly affected: continuing warming and ongoing acidification both pose threats. In combination with over-fishing, these two threats are further jeopardizing already weakened fish stocks. Sea-level rise is exposing coastal regions to mounting flood and hurricane risks. To keep the adverse effects on human society and ecosystems within manageable limits, it will be essential to adopt new coastal protection approaches, designate marine protected areas and agree on ways to deal with refugees from endangered coastal areas. All such measures, however, can only succeed if global warming and ocean acidification are combated vigorously. Ambitious climate protection is therefore a key precondition to successful marine conservation and coastal protection.