Accidental Blogger

So apparently there’s some other CO2 problem that doesn’t get talked about as much as rising temperatures.

CO₂ forms carbonic acid when it dissolves in water, and the oceans are soaking up more and more of it. Recent studies show that the seas have absorbed about a third of all the fossil-fuel carbon released into the atmosphere since the beginning of the industrial revolution, and they will soak up far more over the next century. Yet until quite recently many people dismissed the idea that humanity could alter the acidity of the oceans, which cover 71 per cent of the planet’s surface to an average depth of about 4 kilometres. The ocean’s natural buffering capacity was assumed to be capable of preventing any changes in acidity even with a massive increase in CO₂ levels.

And it is – but only if the increase happens slowly, over hundreds of thousands of years. Over this timescale, the release of carbonates from rocks on land and from ocean sediments can neutralise the dissolved CO₂, just like dropping chalk in an acid. Levels of CO₂ are now rising so fast that they are overwhelming the ocean’s buffering capacity.

In 2003 Ken Caldeira of the Carnegie Institution in Stanford, and Michael Wickett at the Lawrence Livermore National Laboratory, both in California, calculated that the absorption of fossil CO₂ could make the oceans more acid over the next few centuries than they have been for 300 million years, with the possible exception of rare catastrophic events. It was in their Nature paper that the phrase "ocean acidification" appeared in the scientific literature for the first time.

The potential seriousness of the effect was underlined in 2005 by the work of James Zachos of the University of California at Santa Cruz and his colleagues, who studied one of these rare catastrophic events. They showed that the mass extinction of huge numbers of deep-sea creatures around 55 million years ago was caused by ocean acidification after the release of around 4500 gigatonnes of carbon (New Scientist, 18 June 2005, p 19). It took over 100,000 years for the oceans to return to their normal alkalinity.

Around the same time as the Zachos paper, the UK’s Royal Society published the first comprehensive report on ocean acidification. It makes grim reading, concluding that ocean acidification is inevitable without drastic cuts in emissions. Marine ecosystems, especially coral reefs, are likely be badly affected, with fishing and tourist industries based around reefs losing billions of dollars each year. Yet the report also stressed that there is huge uncertainty about the effects on marine life.

"On the one hand the chemistry of ocean acidification is very certain," says James Orr of the Laboratory of Sciences of the Climate and Environment (CEA-CNRS) in France. "On the other hand the biological and ecological impacts are very complex. The consequences for ocean life are far harder to predict."

So what progress has been made since the report came out? How serious an issue is acidification given all the other threats to the oceans, from overfishing and pollution to warming waters and changes in currents?

The sea creatures most likely to be affected are those that make their shells or skeletons from calcium carbonate, including tiny plankton and massive corals. Their shells and skeletons do not dissolve only because the upper layers of the oceans are supersaturated with calcium carbonate

Acidification reduces carbonate ion concentrations, making it harder for organisms to build their shells or skeletons. When the water drops below the saturation point, these structures will start to dissolve.

Now, I’m no scientist. But I feel like the world’s oceans being turned into giant vats of carbonic acid might have problematic side effects for human beings–even for those non-"tree huggers" who don’t care about things like plankton and coral for their own sake.