Copenhagen climate summit issues: oceans

The oceans are warming. That is clear.

The warming has penetrated to depths of more than a kilometre. In fact, such is the huge capacity of the oceans to absorb heat that 90 per cent of the extra warming so far caused by greenhouse warming of the atmosphere has ended up in the oceans.

One unambiguous consequence of the warming is rapid loss of ice across the Arctic Ocean, especially in summer. In the tropics there are concerns that more places may be vulnerable to hurricanes – which only form over oceans where the surface water is above 26 degrees Celsius. But there may be other factors involved, and the jury is still out on that.

Exactly how ocean life will respond to the warming is also hard to predict. Some species are migrating. Cod are moving north. Hence also, perhaps, those sharks spotted off south-west England. But how will things change overall?

Researchers predict the Arctic could bloom as waters warm and the disappearance of ice lets the sunlight through. But most sea life likes it cool, and away from the poles, warmer waters may already be reducing plankton growth. That could mean less food for fish. Also, the growth of plankton is the main mechanism by which the oceans absorb CO2 from the atmosphere. So if there is less plankton, more CO2 will stay in the air.

Some researchers think we should use the CO2-absorbing capacity of plankton to remove the gas from the air. In some waters, simply sprinkling iron filings on to the waves stimulates growth of plankton. In theory, the world could award carbon credits for “ocean seeding” – just as Copenhagen is expected to reward forest conservation. But nobody can yet provide good evidence whether the carbon absorbed in such experiments stays put or returns to the air later. That evidence may be hard to get, however, since another part of the UN system, the Convention on Biological Diversity, recently voted to ban further seeding of the oceans.

The oceans are also becoming measurably more acid – about 0.1 units on the pH scale, so far. By 2100, researchers expect a 0.5 unit change. It happens as excess CO2 is dissolved in the ocean waters, creating carbonic acid. Ocean life isn’t yet being eaten away by the acid. But the change will impede growth of coral, which is already under stress from warmer waters, and will make it harder for other organisms to form their shells and skeletons.

Fred Pearce,, 5 December 2009. Article.

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