The other carbon dioxide problem

The home to 80% of the Earth’s organisms is currently under attack from global warming’s ‘evil twin’: ocean acidification.The gases in the atmosphere and dissolved in the ocean are in equilibrium, meaning that as the carbon dioxide concentrations in the atmosphere increase, those in the ocean do too. Approximately 27% of the carbon dioxide released from burning fossil fuels and deforestation since the industrial revolution has been taken up by seawater.

Initially this was thought to be a good thing, as removing some of the anthropogenic carbon dioxide from the atmosphere limits its ability to warm up the planet. But about 15 years ago scientists realised that this excess carbon dioxode is changing the carbonate chemistry of the ocean. ‘When you add carbon dioxide to water it forms carbonic acid,’ explains Carol Turley, a senior scientist at Plymouth Marine Laboratory, UK, who coordinates the UK Ocean Acidification Research Programme. ‘Then it goes through a series of other chemical reactions which result in a release of hydrogen ions making the pH decrease,’ she adds.

‘The pH has decreased by 0.1 of a unit [from 8.2 to 8.1] since the industrial revolution,’ says Turley. ‘It’s a logarithmic scale, meaning an approximately 30% increase in acidity.’

The term ocean acidification is also used to cover the other impacts that increasing carbon dioxide concentrations are having on the ocean and marine organisms. This includes an increase in bicarbonate ion (HCO₃^–) concentrations and a decrease in that of carbonate ions (CO₃^2–) that happen in seawater as a result of the cascade of reactions that occur when excess carbon dioxide dissolves in it. The reduction of carbonate ions, required to build the calcite and aragonite polymorphs of calcium carbonate, is of particular concern as many marine organisms require them to keep shells and skeletons intact. Damage to some calcium carbonate based marine organisms, such as coral reefs, oyster larvae and sea snails, in carbon dioxide enriched water is already being seen in some parts of the world.

Nina Notman investigates the other carbon dioxide problem. This article provides a link to the article by Chemistry World.