CHANGE IN SEA-CHEMISTRY A HUGE THREAT

ScienceDaily reports a dire warning about the changing chemistry of the oceans due to the amount of carbon-dioxide they have been forced to absorb through human activity.

They have absorbed about 40% of the CO2 that we have emitted over the past two centuries. That has slowed global warming but at a serious cost: the extra carbon dioxide has caused the ocean's average surface pH (a measure of water's acidity) to shift by about 0.1 unit from pre-industrial levels. Depending on the rate and magnitude of future emissions, their pH could drop as much as 0.35 units by the middle of this century.

That acidification can damage marine organisms. Experiments have shown that changes of as little as 0.2-0.3 units can hamper the ability of key marine organisms such as corals and some plankton to calcify their skeletons, which are built from pH-sensitive carbonate minerals. Large areas of the ocean are in danger of exceeding those changes in pH by the middle of the century, including reef habitats such as Australia's Great Barrier Reef.

Most marine organisms live in the sunlit surface waters, which are also those most vulnerable to CO2-induced acidification. To stop their pH from declining more than 0.2 units, which is the current limit set by the U.S. Environmental Protection Agency in 1976, CO2 emissions would have to be reduced immediately.