Huh? What?

Ocean acidification is the carbon dioxide problem you haven't heard of. About 30 per cent of carbon dioxide emissions are absorbed by the world's oceans. Because of increased emissions of CO2 since the industrial revolution, the oceans are absorbing more CO2 than they can neutralise and are therefore becoming more acidic (or technically, less alkaline, as sea water has a pH of more than seven, so it is actually more alkaline than neutral water).

It is estimated that ocean pH has dropped by 0.75 units since the beginning of the industrial revolution, and will drop by a further 0.3 to 0.5 units by 2100.

How serious is it?

In February 2009 a group of 155 leading marine scientists released the Monaco Declaration  warning that the increasing acidification of the oceans could wipe out coral reefs and decimate global fishing stocks. Coral may be affected because acidification reduces the amount of calcite in the ocean. Many types of hard coral need calcite to build their skeletons or shell coverings - as do many other marine creatures with hard shells.

Scientists at the International Coral Reef Symposium in July 2008 declared ocean acidification the most significant threat to oceans - more serious than overfishing or marine pollution.

New research published in January 2009 shows coral on the Great Barrier Reef is growing more slowly than at any time in the past 400 years.

Why will it affect fish stocks?

Firstly, because coral reefs are vital nurseries for many fish species. Secondly, it is possible acidification may affect plankton, one of the building blocks of the marine food chain.

What are the consequences?

Apart from their intrinsic value and beauty, coral reefs support fish stocks and a large tourism industry. In many places they also provide a breakwater to protect coastlines from devastation by tropical storms.
A worldwide collapse in fish stocks would threaten food security for millions of people and wipe out the multi-billion dollar fishing industry on which millions of people depend for a living.

How can it be prevented?

By reducing the amount of carbon dioxide being emitted, probably to the levels found before the industrial revolution. Cutting down on pollution, overfishing and other threats to coral reefs and fish stocks would help manage the situation in the meantime.