We are, slowly at first, turning over 70 per cent of the earth's surface and 97 per cent of its water into an acid graveyard. You might well ask: who is this 'we', mammal? Let's admit that this 'we' tends to suppress social antagonism and dilute blame for this state of affairs in a way that evades remedy. This is true. But since that is not the immediate focus of this article, and since 'we' are all implicated one way or another, I'm sticking with the traditional usage.
So we are acidifying the oceans. That, too, is old news. Ocean acidification has been established in study after study, with serious and wide-ranging consequences. Here, for the perplexed, or anyone who would simply wants to begin their seasonal depression a little early this year, is what is happening.
We release about 38.2 billion tonnes of carbon dioxide into the atmosphere each year. A quarter of that is dissolved into the oceans, thus dampening capitalogenic climate change. But the chemical reactions that produces are lethal for marine life. This life, as it happens, produces most of the oxygen that we breathe. It was oceanic cells that oxidised the atmosphere in the first place. And it is responsible for at least half of all 'primary production' on the planet -- that is, the synthesis of organic compounds using energy from the sun.
The reason increasing carbon dioxide in the oceans is so deadly is because of the increase in concentration of hydrogen ions in the sea. An ion is a particle which doesn't have a net neutral electrical charge. It may, for example, have been separated from one of its electrons or protons in a chemical reaction, thus is charged either negatively (anions) or positively (cations).
Carbon dioxide has a net neutral electrical charge. But when it dissolves into seawater, it is converted into three substances: carbonic acid (H2CO3), carbonate ion (HCO−3) and bicarbonate ion (CO2−3). A molecule of carbonic acid is capable of 'donating' two positively charged hydrogen ions to react with other chemicals in the environment. These are extremely reactive and usually bond with (hydrogenate) another chemical rapidly. This is what makes it acidic. The more hydrogen ions per litre in any solution, the higher its acidity.
The more carbon dioxide is dissolved into the oceans, the more hydrogen ions are released, the more acidic it becomes. Nearer the surface of the water, this is partially counteracted by the existence of marine life which uses carbon dioxide for photosynthesis, thus removing hydrogen ions and keeping the pH balance slightly alkaline. However, light penetrates to only a couple of hundred metres, and far less if there is a lot of marine life absorbing light near the surface.
Marine organisms such as corals, oysters and echinoderms have evolved to survive in slightly alkaline seas, by developing skeletons or skeletal elements articulated with the skin, which they produce by combining seawater calcium with carbonate ions, to make calcium carbonate. The more hydrogen ions are in the sea, the more likely they will combine with carbonate ions and thus reduce the materials available to make these skeletons. And of course, the more acidic the ocean turns, the more it dissolves exoskeletons and mesoskeletons made of calcium carbonate.
Corals are particularly important here. It is a cliche to refer to coral reefs as "the rainforests of the sea" because of the complex ecosystems they support. They live near the surface, in shallower coastal waters, because they depend on solar energy. And though they only occupy a fraction of a percent of total surface area, they are inhabited by a quarter of all marine life. This is made possible through the calcium carbonate skeletons they produce, around which complex ecosystems develop.
But rates of calcification are slowing down dramatically. About a fifth of the coral reefs are gone already, partly due to acidification and partly due to increased ocean temperatures causing 'coral bleaching'. Interestingly, a great deal of the 'save the reefs' campaigning foregrounds the estimated economic value of the structures: hundreds of billions of dollars. This sort of figure, based on arbitrary assumptions and guesswork, is beside the point. Our complex planetary dependencies are usually not expressible in economic terms, least of all a magic monetary figure, because the screen of capital tends to screen out anything that isn't susceptible to the production of surplus value.
What can we possibly say about what will happen if, as is predicted, the coral reefs go extinct? Not only will the quarter of marine life which depends on them die off, but so will the species which depend on them, such as dolphins. Fisheries are already heavily exploited, and many would tip over into depleted or dying. The primary production of organic materials by phytoplankton would drop substantially, as would the amount of oxygen in the atmosphere. The air would become less breathable, compounding a tendency that would already be underway as other parts of the food chain break down. For example, dropping insect biomass and the disappearance of bees means far less pollination, which means less plant life, and less oxygen.
If they're headed for extinction, so are we.