A time may come when mankind will need to consider geoengineering the climate to counteract climatic effects of greenhouse gases. If that time comes, we need to have a good understanding of whether such efforts will work and, just as importantly, whether they will have any negative side effects. Those who oppose such exploratory research on the grounds that we do not know what its effects may be (Want to mimic a volcano to combat global warming? Launch a Wembley-size balloon, 1 September) are missing a fundamental point of research, which is to allow us to potentially rule out any technology that would have negative effects that outweigh the positive.
The article was incorrect in stating that the Royal Society backs the Stratospheric Particle Injection for Climate Engineering (Spice) project, the subject of the article. The Society's comprehensive review of possible geoengineering technologies, published in 2009, did identify stratospheric aerosols, which the Spice project is investigating, as one of the more plausible ideas that required further research. However, the Society's current work is focused on the Solar Radiation Management Governance Initiative (SRMGI), a project to develop guidelines to ensure that geoengineering research is conducted in a manner that is transparent, responsible and environmentally sound.
Geoengineering research can be considered analogous to pharmaceutical research. One would not take a medicine that had not been rigorously tested to make sure that it worked and was safe. But, if there was a risk of disease, one would research possible treatments and, once the effects were established, one would take the medicine if needed and appropriate. Similarly we need controlled testing of any technologies that might be used in the future. Hopefully we will never need geoengineering but, if we do, to fail to assess its usefulness and safety in advance would be a risk no one, least of all those most concerned with the environment, would thank us for.
Paul Nurse
President of the Royal Society
Pumping water and particulates 20km into the air to reduce solar warming seems more like plan D. Particulates that mimic volcanic dust might stay in the atmosphere for years and would reduce the efficiency of photovoltaics, one of the primary green energy sources available. Also, pumping a 20km head of water would require considerable energy in itself. A greener solution would be to build a set of windmills on pontoons in equatorial seas that are anchored in large circular formations. Most of the time they could be faced into the prevailing winds and generate electricity. But when the seas are warm, they would be faced along the circle and consume that energy to fan a mini hurricane. This would draw moisture from the warm seas into the atmosphere and create shorter-lived normal clouds. This has the added benefit of cooling the seas and so reducing the numbers of destructive hurricanes.
Dr Shaun Hughes
Cambridge
