If people can warm the Earth, they can probably cool it too. That is the idea behind geo-engineering, which holds that besides cutting the rate at which it is turning fossil fuels into climate-changing carbon dioxide, humanity should also consider planet-wide engineering projects intended to reduce the side-effects of this combustion. All sorts of ideas have been proposed, from filling the stratosphere with reflective particles to giant space-borne parasols designed to shade the Earth from the sun. The idea of such a technological last chance, even if it sounds implausible, is a secret comfort to many of those frustrated by the lack of progress around the world in cutting emissions of greenhouse gases. Two papers published this week suggest, though, that those hopes may be misplaced.
The first, by a group of researchers from Britain’s National Oceanography Centre, led by Raymond Pollard, looked at the idea of dumping iron in the oceans to promote huge blooms of phytoplankton—tiny algae that consume carbon dioxide as they grow. This approach has received a lot of interest. Though much of the carbon thus absorbed returns to the atmosphere when the plankton die, around 8-9% ends up locked away beneath the waves for decades or more. Dr Pollard’s paper, which appeared in Nature, outlined the results of an experiment that looked at the effects of iron on the growth of phytoplankton near the Crozet Islands in the Southern Ocean.