Until now, concern about rising levels of carbon dioxide in the atmosphere has been focused on global warming. But scientists have discovered a second reason to worry: About half of the greenhouse gases added to the atmosphere from burning fossil fuels -- an amount weighing about the same as 140 billion Volkswagen Beetles -- has ultimately ended up in the world's oceans.
While this has the beneficial effect of slowing down the rate at which the planet's atmosphere is heating up, ocean researchers have found that the huge influx of carbon dioxide since 1800 is making oceans more acidic than they have been for millions of years. If not reversed, this trend could destabilize -- or even threaten --much of the world's marine life, particularly animals that can't adapt to living in a more corrosive environment.
So far, the ocean's pH (the commonly used scale of whether something is acidic or alkaline) has become about 30 per cent more acidic over the past 200 years because humans have added so much carbon dioxide to the atmosphere. Scientists say this change has never occurred in the recent history of the planet -- either in such a massive way, or so quickly.
"The pH changes that are occurring in the ocean today are truly extraordinary," says Joan Kleypas, a scientist at the U.S. National Centre for Atmospheric Research in Boulder, Colo., and the lead author of a report issued this month that rang alarm bells about the trend. "Unfortunately, this is not an environmental problem that we've had to deal with in the past, and so we really don't have a very good grasp of what this means for ocean biology."
Although experts don't yet have a thorough understanding of all the implications of a more acidic ocean, they do know it has scary potential for all creatures that secrete calcium carbonate to build shells or skeletons, including corals, starfish, snails and many microscopic varieties of plankton. Should nothing be done to stop global warming, scientists predict that oceans could become acidic enough that the shells or skeletons of the most vulnerable marine animals may start to dissolve, possibly as early as 2050.
This is a particular worry for coral reefs, which are viewed as the ocean's rain forests because of their amazing biological diversity. "What we're finding is that [acidification] decreases their ability to build their skeletons," says Chris Langdon, a coral-reef expert at the University of Miami. "We think this is important because one of the sure outcomes of this is going to be the loss of coral-reef framework around the world."
About 25 per cent of all ocean species spend at least part of their life cycle on reefs. But in a more acidic ocean, corals will grow more slowly and become less dense -- a process like osteoporosis in humans -- and won't be able to grow fast enough to offset erosion from wave action. Corals are also under threat of bleaching from rising water temperatures.
The reason that oceans are becoming acidic is that carbon dioxide is water-soluble and easily passes from the air into the sea. Most of the carbon in the ocean is in the form of bicarbonate, a familiar ingredient in household baking soda.
What is happening in the oceans is the reverse of the common high-school experiment in which vinegar, an acid, is poured on baking soda to produce a fizzy mass of carbon dioxide air bubbles. In this case, the ocean is holding the "baking soda," which is reacting with the influx of carbon dioxide to produce an acid.
Although there is intense debate about the impact that global warming will have on land, scientists say there is absolutely none about the alteration in ocean chemistry under way. And the impacts from a more acidic ocean will not reverse quickly, either. Even if all carbon dioxide emissions from human sources cease, experts believe it will take hundreds of thousands of years for ocean pH to return to normal levels.
Oceans at high latitudes, such as the Antarctic, Arctic and the Northern Pacific off of British Columbia, are more vulnerable to the trend than tropical oceans, and the Pacific Ocean is more vulnerable than the Atlantic. This is because the Pacific has what is considered older water, or water that has been submerged longer in deep currents. This allows it to absorb more carbon dioxide from the decay of organic matter. New concerns over ocean acidification will be flagged in the report expected next year from the Intergovernmental Panel on Climate Change, the United Nations body amassing all scientific knowledge on global warming.
Martin Mittelstaedt is The Globe and Mail's environment reporter.
