Oceans already acidic from absorbed carbon dioxide... Oceans are already experiencing large-scale changes at a warming of 1°C, due to increased water temperatures and higher carbon dioxide concentrations. At a warming of 1.5°C coral reefs are projected to decline by a further 70-90%. At 2°C, virtually all coral reefs will be lost, affecting not only wildlife; around half a billion people rely on fish from coral reefs as their main source of protein.