[O]cean 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.

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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.

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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.