Friday, July 01, 2005

Climate Change: The Impact of CO2 on Oceans

A lot has been written about the impact of global warming on land but this is the first story I've seen about the impact of CO2 emissions on the world's oceans.

The oceans are naturally alkaline but, since the industrial revolution, the sea surfaces have been turning ever more acidic. The report says that if CO2 emissions continue at current rates then by 2100 the pH of the sea will fall by as much as 0.5 units from its current level of pH 8.2. The pH scale runs from 1 (acidic) to 14 (alkaline), with 7 being neutral. And in the case of the oceans, the change would be effectively irreversible.
“The only way to minimise the long-term consequences is to decrease CO2 emissions,” Raven says.

The sea life expected to be worst hit include organisms that produce calcium carbonate shells, as these are harder to form in acidic waters. That means that corals, crustaceans, molluscs and certain plankton species will be at risk.

“It would not kill penguins, orca and other big animals directly, but it would affect the food chain with potentially damaging effects on larger animals,” Raven explains.

Coral reefs face a three-pronged attack, the report says. There is global warming and coastal pollution, and now acidification. Raven says we can expect to see degradation of coral reefs in the tropics.

And it get's worse:

And it does not stop there. There is an important group of photosynthetic plankton called coccolithophores that grow calcium carbonate shells and form giant “blooms” in spring and summer before sinking to the bottom of the ocean.

But the increasing acidification will hinder their ability to grow, meaning they remove less carbon from the atmosphere. This in turn will result in more carbonic acid being formed at the seas’ surface.

“Calcium carbonate helps organisms to sink and enhances the biological pump,” says Andrew Watson, an environmental biologist at the University of East Anglia, UK. The sea has absorbed about half of the CO2 produced by humans in the last 200 years and currently takes up one tonne of the gas each year for every person on the planet. But if the water becomes too acidic, the pump will not work and the ability of the oceans to mop up CO2 will fall, he says.