IT IS nothing to boast about, but our greenhouse gas emissions may be acidifying the oceans faster than at any time in the last 300 million years. The sheer speed means we do not know how severe the consequences will be.
As well as warming the planet, carbon dioxide seeps into the oceans and makes the water more acidic. The pH is now dropping by about 0.1 per century, harming shelled organisms like corals and disrupting animal behaviour.
Bärbel Hönisch of Columbia University in Palisades, New York, and colleagues used the chemical record preserved in rocks to gauge previous acidification events. The best match for today was the Palaeocene-Eocene thermal maximum of 55 million years ago, when a huge greenhouse gas release caused rapid global warming, ocean acidification and mass extinctions (Science, DOI: 10.1126/science.1208277).
But even then, it took 3000 years for ocean pH to drop by 0.5. "That is an order of magnitude slower than today," Hönisch says.
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