THE chemistry of the oceans is changing faster than it has in many thousands of years because of the carbon dioxide being absorbed from the atmosphere.
The finding comes in a report from the US National Research Council.
Carbon dioxide and other industrial gases in the air raise global temperatures in the greenhouse effect.
One factor easing that warmth has been the amount of CO2 taken up by the oceans, but that makes the water more acidic, which can affect sea life.
Since the Industrial Revolution in the 18th century, the pH of ocean water has declined from 8.2 to 8.1 and a further decline of 0.2 to 0.3 units is expected by the end of this century, according to the council, an arm of the National Academy of Science.
The current rate of change ''exceeds any known change in ocean chemistry for at least 800,000 years'', the report said.
The pH level is a measure of how alkaline or acidic something is. A pH of 7 is neutral, while higher numbers are more alkaline and lower numbers more acidic.
As the ocean becomes more acidic scientists have raised concern about dissolving coral reefs and potential effects on fish and other sea life.
The US government has developed the National Ocean Acidification Program, which has called for a 10-year strategic plan and states have been asked to consider options.