Scientists, White House say ocean acidification is well under way

The oceans aren’t vast enough to absorb growing amounts of carbon dioxide without ill effects to marine life and to the 1 billion people who make their living on the seas. Longer heat waves, drought, rising sea levels, more intense storms—these are some of the better-known impacts of climate change. Less familiar is the acidification of the oceans, which is well under way and will continue as the amount of atmospheric carbon dioxide rises.

The oceans absorb about one-quarter of the CO2 emitted from fossil-fuel combustion, about the same proportion taken up by land. The rest remains in the atmosphere, where its concentration steadily increases. The rate at which the oceans are acidifying, through chemical reactions with the CO2, is faster than has occurred in at least 65 million years and possibly 300 million years, according to Ove Hoegh-Guldberg of the University of Queensland. Marine organisms that require carbonate ions to build their shells likely won’t have sufficient time to adapt to the changing pH. “We’re taking life outside the conditions that it actually evolved for,” Hoegh-Guldberg said at the Our Ocean Conference, sponsored by the US Department of State and held 16–17 June in Washington, DC.

A much slower acidification event that occurred 55 million years ago (the Paleocene–Eocene Thermal Maximum) caused a mass extinction of deep-sea plankton and a collapse of coral reefs, according to research published in May’s Paleoceanography.

Since the Industrial Revolution, the acidity of the oceans has jumped 25%, from a pH of 8.2 to 8.1, according to the US Global Change Research Program’s 2014 National Climate Assessment. If current trends in CO2 emissions continue unchecked, acidity will increase by 100–150% from preindustrial levels by the end of the century, said Carol Turley of the Plymouth Marine Laboratory in the UK. “It is happening now, it’s happening rapidly, and it’s happening at a speed we haven’t seen for millions of years,” said Turley at the State Department conference.

The physical chemistry of ocean acidification caused by increased atmospheric CO2 is straightforward: Some of the dissolved gas reacts with water to form carbonic acid, H2CO3. However, “it gets much more complicated in coastal waters, around a coral reef or shellfish beds and estuaries, because there’s other processes besides invasion of fossil-fuel CO2,” says Scott Doney of the Woods Hole Oceanographic Institution (WHOI). “Coastal waters can be affected by a variety of biological processes, by chemicals, and by materials from the land,” he says. “In some places, fossil-fuel carbon may not even be the biggest contributor.”

Kramer D., 2014. Scientists, White House say ocean acidification is well under way. Physics Today 67 (8): 20-21. Article.



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