About a quarter of CO2 emissions are absorbed into the ocean, and there's growing evidence that a rapid increase in these emissions is beginning to change the chemistry of sea water.
It's a relatively new area of science that has only recently been confirmed with evidence of changes to marine organisms in the Southern Ocean and along the Great Barrier Reef.
Presenter: Peter McCutcheon
Speaker: Professor Will Howard, Antarctic Climate and Ecosystems Cooperative Research Centre; Katharina Fabricius and Dr Janice Lough, Marine researchers from the Australian Institute of Marine Science; Sophie Dove and Alicia Crawley, Marine Researchers from University Of Queensland
PETER MCCUTCHEON: Scientists are becoming increasingly alarmed about ocean acidification, a process that involves massive amounts of human produced carbon dioxide being absorbed into the ocean.
WILL HOWARD: Carbon dioxide unlike other gases actually forms a weak acid in sea water. As it goes into the ocean it lowers the PH and shifts the chemistry of the ocean.
PETER MCCUTCHEON: And that means it's a lot tougher for coral and shellfish to grow.
WILL HOWARD: This is a consequence of our carbon emissions that's independent of climate change.
PETER MCCUTCHEON: Last year the 7.30 Report travelled with a group of scientists who were mapping the chemistry of sea water off north-eastern Australia.
MATT (over the radio): At 150 metres, ready to fire.
SCIENTIST (on boat): Thanks, Matt.
PETER MCCUTCHEON: At the time evidence of ocean acidification was limited to laboratory experiments, with little evidence from nature. But that's no longer the case. Marine researchers Katharina Fabricius and Janice Lough have evidence that coral growth is slowing down.
KATHARINA FABRICIUS: We are pretty certain that what we are seeing here is a widespread phenomenon that affected the whole Great Barrier Reef.
PETER MCCUTCHEON: The researchers from the Australian Institute of Marine Science took hundreds of core samples from a common, robust type of coral that is often up to 400 years old. This coral has growth rings similar to that of trees and the researchers were able to calculate the growth rate had dropped 14 per cent since 1990.
JANICE LOUGH: I think we have maybe reached some sort of tipping point where the combined effects of thermal stress and ocean acidification have really kicked in and the corals are noticing it. Something definitely in their environment has changed and they are responding and they are telling us that story.
PETER MCCUTCHEON: A world away from Australia's tropical reefs, scientists recently discovered another important piece of evidence that ocean acidification is beginning to affect the marine environment. This time the organism under scrutiny is not coral but a minute shellfish found in the Southern Ocean.
Professor Will Howard from the Antarctic Climate and Ecosystems Cooperative Research Centre compared shellfish to a fossil record going back some 50,000 years.
WILL HOWARD: These organisms have already lowered their calcification by something like 30 to 35 per cent. So they're making lighter, thinner shells in response to the amount of fossil fuel CO2 that has been taken up by the Southern Ocean.
PETER MCCUTCHEON (to Will Howard): Does it really matter that some microscopic marine organisms have slightly thinner shells?
WILL HOWARD: Well it may not matter in some ways but what it implies is that the ecosystems will shift in response to this.
PETER MCCUTCHEON: Unfortunately the news gets worse. Scientists Sophie Dove and Alicia Crawley have shown acidification has the potential to not only affect shell and coral growth but also to affect vital biological processes. They discovered that increased acidity destroyed an important defence mechanism for a common coral algae.
ALICIA CRAWLEY, MARINE RESEARCHER, UNIVERSITY OF QUEENSLAND: They have to protect themselves from the excess light and so we found that this mechanism that they used declined in the higher CO2 scenarios.
PETER MCCUTCHEON: And this algae known as zooxanthellae provides vital nutrients to coral. (To Sophie Dove) In effect you've found that ocean acidification could lead to corals starving.
SOPHIE DOVE: Yes and so starvation means not being able to grow any more, which is something corals have to do to support our reefs all the time, they have to be growing all the time. Or it could mean actually literally dying back.
PETER MCCUTCHEON: Ocean acidification is an emerging and disturbing area of science. Seventy academies of science from around the world, including Australia, released a statement warning of an impending underwater catastrophe. The only way to stop this process is to pump less carbon dioxide into the atmosphere.
WILL HOWARD: This is something that many scientists have felt needs to be brought to the attention of policymakers, that they need to take this into account as they think about how to approach the problem of controlling future carbon emissions.
KATHARINA FABRICIUS: If you are losing coral cover as we do at present the reefs will basically not look the same in 50 years as they are looking now.