But even these new studies may be conservative. Recent global CO2 emissions have been outstripping so-called business-as-usual emissions scenarios, which assume that no country adopts climate-specific limits on emissions.
From a human perspective, ocean acidification is relative; no one is talking about dissolving surf boards. On the pH scale – which runs from strong acids such as battery acid to strong bases such as laundry bleach – the oceans fall on the base side of the spectrum. The oceans have a pH of 8. Distilled water is considered neutral, with a pH of 7. Battery acid has a pH of 1.
Typically, seawater is heavily saturated with dissolved calcium carbonate from eroded limestone. This neutralizes any acid that forms from CO2 and leaves plenty of carbonate for marine creatures to use for shell- and reef-building. But as oceans absorb increasing amounts of CO2 from fossil fuels, their stores of calcium carbonate dip. Over time, this reduces carbonate available for marine creatures. Shell and coral formation slows.
Once seawater is too deficient in carbonate, these creatures find it hard to form shells or corals at all. In fact, existing shells start to dissolve, notes Ben McNeil, a researcher at the University of New South Wales in Australia.
In a recent study, he and a colleague looked at trends in the Southern Ocean. Oceans at the top and bottom of the world might be expected to lead in acidification because cold water soaks up more CO2 than warm water. But the duo also found large seasonal swings in carbonate levels. They traced increases in the water’s relative acidity to strong wintertime winds off Antarctica that bring to the surface cold water from the deep, which has low levels of carbonate.