Oceans turn acidic faster than any time in 300m years

The world’s oceans are turning acidic at what could be the fastest pace of any time in the past 300m years, even more rapidly than during a monster emission of planet-warming carbon 56m years ago, scientists said.

Looking back at this bygone warm period in Earth’s history could offer help in forecasting the impact of human-spurred climate change, researchers said.

Quickly acidifying seawater eats away at coral reefs, which provide habitat for other animals and plants, and makes it harder for mussels and oysters to form protective shells. It can also interfere with small organisms that feed commercial fish like salmon.

The phenomenon has been a top concern of Jane Lubchenco, the head of the US National Oceanic and Atmospheric Administration, who has conducted demonstrations about acidification during hearings in the US Congress.

Oceans get more acidic when more carbon gets into the atmosphere. In pre-industrial times, this occurred periodically in natural pulses of carbon that also pushed up global temperatures, the scientists wrote in the journal Science.

Human activities, including burning fossil fuels, have increased the level of atmospheric carbon from about 280 parts per million at the start of the industrial revolution to 392 parts per million now.

Carbon dioxide is one of several heat-trapping gases that contribute to global warming.

The researchers viewed the 5,000-year hot spell 56m years ago, likely due to factors like massive volcanism, as the closest parallel to current conditions at any time in the 300m years.

During that span, the amount of carbon in the atmosphere doubled and average temperatures rose 6C, the researchers said. The oceans became more acidic by about 0.4 unit on the 14-point pH scale over that 5,000-year period, the researchers said.

That is a fast warm-up and a quick acidification, but it is small compared with what has happened on Earth since the start of the industrial revolution about 150 years ago, according to study author Baerbel Hoenisch.

During the warming period 56m years ago, which occurred about 9m years after the extinction of the dinosaurs, acidification for each century was about .008 unit on the pH scale, Hoenisch said.

The UN Intergovernmental Panel on Climate Change has projected that world temperatures could rise by 1.8C to 4C this century.