The future of the oceans: Acid test

The world’s seas are becoming more acidic. How much that matters is not yet clear. But it might matter a lot.

HUMANS, being a terrestrial species, are pleased to call their home “Earth”. A more honest name might be “Sea”, as more than seven-tenths of the planet’s surface is covered with salt water. Moreover, this water houses algae, bacteria (known as cyanobacteria) and plants that generate about half the oxygen in the atmosphere. And it also provides seafood—at least 15% of the protein eaten by 60% of the planet’s human population, an industry worth $218 billion a year. Its well-being is therefore of direct concern even to landlubbers.

That well-being, some fear, is under threat from the increasing amount of carbon dioxide in the atmosphere, a consequence of industrialisation. This concern is separate from anything caused by the role of CO₂ as a climate-changing greenhouse gas. It is a result of the fact that CO₂, when dissolved in water, creates an acid.

That matters, because many creatures which live in the ocean have shells or skeletons made of stuff that dissolves in acid. The more acidic the sea, the harder they have to work to keep their shells and skeletons intact. On the other hand, oceanic plants, cyanobacteria and algae, which use CO₂ for photosynthesis, might rather like a world where more of that gas is dissolved in the water they live in—a gain, rather than a loss, to ocean productivity.

Two reports attempting to summarise the world’s rather patchy knowledge about what is going on have recently been published. Both are the products of meetings held last year (the wheels grind slowly in environmental bureaucracy). One, in Monterey, California, looked at the science. The other, in Monaco, looked at possible economic consequences. Together, the documents suggest this is an issue that needs to be taken seriously, though worryingly little is known about it.

Omega point

Regular, direct measures of the amount of CO₂ in the air date to the 1950s. Those of the oceans’ acidity began only in the late 1980s (see chart). Since it started, that acidity has risen from pH 8.11 to pH 8.06 (on the pH scale, lower numbers mean more acid). This may not sound much, but pH is a logarithmic scale. A fall of one pH point is thus a tenfold rise in acidity, and this fall of 0.05 points in just over three decades is a rise in acidity of 12%.

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