Ever thought about tackling climate change by spraying aerosols into the upper atmosphere to act as a giant sunblock? Or how about placing trillions of tiny parasols in space to divert solar radiation? Or perhaps fertilizing the oceans with iron to promote artificial blooms of phytoplankton that can soak up carbon dioxide? The problem with these and other proposed “geoengineering” techniques is that they sound so crazy, expensive and dangerous that many mainstream climate scientists have refused to take such solutions seriously. Indeed, some fear that even discussing geoengineering is enough to scupper climate negotiations, such as those that are due to take place in Copenhagen in December, by implying that we do not need to bother cutting greenhouse-gas emissions.

Thankfully, however, geoengineering has slowly been entering the mainstream in recent years. This month marks a watershed in that process with the publication by the Royal Society of a study – the first by a major scientific academy – into whether planetary-scale geoengineering schemes could help to prevent the worst aspects of climate change. Although Physics World was not able to obtain an advance copy of the report before going to press, the main issues are described in a feature elsewhere in this issue by physicist Peter Cox from the University of Exeter – one of the report’s co-authors – and Hazel Jeffery from the UK’s Natural Environment Research Council (“Engineering the climate”).

Geoengineering techniques basically fall into two main camps: removing carbon dioxide directly from the air or reflecting more sunlight back into space. The former is a pricey, long-term but relatively low-risk solution, while the latter could be implemented quickly and cheaply but does nothing to stop the rising acidity of the world’s oceans. The technique that appears to bring the biggest benefit for the least cost involves using a fleet of ships to suck up seawater and spray it into the atmosphere. The sea salt would provide extra cloud-condensation nuclei that would brighten lower-altitude stratocumulus clouds lying over oceans and coastal regions, and so reflect more short-wave solar radiation back into space.

Indeed, a report published last month by the Copenhagen Consensus Center – a Danish think tank led by Bjørn Lomborg, author of the controversial book The Skeptical Environmentalist – suggests that the current century’s global warming could be avoided by spending just $9bn on a fleet of unmanned cloud-brightening ships. However, no less a figure than Steven Koonin – former chief scientist at energy giant BP and now under-secretary of science at the US Department of Energy – has co-authored a new report for the California-based Novim think tank suggesting that our best approach would instead be to pump sulphates into the upper atmosphere to mimic the effects of volcanic eruptions.

The problem with geoengineering is that it is laced with too many scientific, economic and political uncertainties. There are also ethical concerns about modifying the Earth’s climate: a technique that cools one region could actually raise temperatures, or slash rainfall, in another. If that is the case, who then would decide how we should act? Geoengineering may only ever be a plan B for dealing with climate change, but unless we do more research, we will never know for sure if it could work and, if so, what the best approach should be.