Ocean acidification, a side-effect of global warming, occurs when excess carbon dioxide dissolves in the ocean and becomes carbolic acid -- making it harder for corals and plankton with chalky skeletons to calcify.

Scientists who have researched the problem say the acidification is potentially devastating for the marine environment, particularly affecting such coral areas as Australia's Great Barrier Reef along with crustaceans and plankton.

Presenting their findings at a scientific forum in Canberra Thursday, Prof. Malcolm McCulloch of the Australian National University, said "it appears this acidification is now taking place over decades, rather than centuries as originally predicted."

He said research indicated oceans have become "about one-third of a pH unit more acid in the past 50 years."

"It is happening even faster in the cooler waters of the Southern Ocean than in the tropics," he said. "It is starting to look like a very serious issue."