Nature - Ocean Acidification May Provide Additional Warming Momentum As Plankton Die Off
The slow and inexorable increase in the oceans’ acidity as they soak up carbon dioxide from the atmosphere could itself have an effect on climate and amplify global warming, according to a new study. Acidification would lead certain marine organisms to emit less of the sulphur compounds that help to seed the formation of clouds and so keep the planet cool.
Atmospheric sulphur, most of which comes from the sea, is a check against global warming. Phytoplankton — photosynthetic microbes that drift in sunlit water — produces a compound called dimethylsulphide (DMS). Some of this enters the atmosphere and reacts to make sulphuric acid, which clumps into aerosols, or microscopic airborne particles. Aerosols seed the formation of clouds, which help cool the Earth by reflecting sunlight.
James Lovelock and colleagues proposed in the 1980s that DMS could provide a feedback mechanism limiting global warming1, as part of Lovelock’s ‘Gaia hypothesis’ of a self-regulating Earth. If warming increased plankton productivity, oceanic DMS emissions might rise and help cool the Earth.
More recently, thinking has shifted towards predicting a feedback in the opposite direction, because of acidification. As more CO2 enters the atmosphere, some dissolves in seawater, forming carbonic acid. This is decreasing the pH of the oceans, which is already down by 0.1 pH units on pre-industrial times, and could be down by another 0.5 in some places by 2100. And studies using 'mesocosms' — enclosed volumes of seawater — show that seawater with a lower pH produces less DMS2. On a global scale, a fall in DMS emissions due to acidification could have a major effect on climate, creating a positive-feedback loop and enhancing warming.
EDIT
http://www.nature.com/news/rising-ocean-acidity-will-exacerbate-global-warming-1.13602
= new reply since forum marked as read
