Atmospheric carbon dioxide is being soaked up by the oceans causing the pH to drop and placing marine life at risk.
According to a report from John Raven of the University of Dundee, CO2 from the air is dissolving into the sea producing carbonic acid, which makes the water more acidic, and is causing the pH to drop.
He claims that carbonic acid levels have risen at a rate 100 times faster than the world has seen for millions of years.
In a report covering the study, Nature says that the pH level could drop 0.5 units by 2100, causing the pH to plummet from the usual 8.2 to 7.7 - a decline which could have drastic consequences for all marine life - from plankton to fish.
CO2 outputs need to be cut back to levels way below those set by the Kyoto Treaty if the reaction is to be stopped.
"It will take many thousands of years for natural processes to return the oceans to their pre-industrial state," Raven told New Scientist.
"The only way to minimise the long-term consequences is to decrease CO2 emissions.
"It would not kill penguins, orca and other big animals directly, but it would affect the food chain with potentially damaging effects on larger animals."