Geoengineering is the idea of controlling the weather and climate by the large-scale engineering of the environment. The idea has come to prominence in recent years as concerns about man-made global warming have increased and governments have faltered on negotiations to restrict carbon-dioxide emissions. But many people are concerned about geoengineering: its environmental impact; how the presence of a “plan B” that may prove unreliable could affect efforts to cut carbon emissions; and who on the global stage should regulate use of the technology, particularly when it may reduce rainfall in some areas.

One high-profile geophysicist who has reservations about geoengineering is Ken Caldeira of the Carnegie Institution for Science in the US. Caldeira believes that geoengineering efforts should focus on existing areas of science and technology research. This includes the removal of carbon dioxide from smokestacks in power plants, no-till agriculture and other soil amendments, and stratospheric particle and chemistry research based on volcanoes and the ozone layer. Activities such as whitening clouds over the ocean, meanwhile, could be carried out by those who are already studying marine clouds.

Caldeira is in favour of environmental-science studies into the option of sunlight reflection by distributing reflective particles into the atmosphere. But he is against work that strays into the engineering development of implementation techniques.

While geoengineering is not yet on most people’s agendas, future events could cause a radical shift in public opinion in the US, says Caldeira. In turn, this would put pressure on politicians to implement the technology. But Caldeira is aware that what is best from a political point of view is not necessarily best for the environment, given the variations in timescales between political and environmental cycles.

As well as altering the environment, geoengineering will affect human systems such as agriculture. This gives poor people in tropical countries perhaps the biggest incentive of all to implement geoengineering, says Caldeira, as crop yields in the tropics are more likely to be badly affected by heat stress than those in northern climes, where yields may even improve.

But are countries likely to go it alone when it comes to geoengineering, without complying with any international agreements that may be set up? On this point, at least, Caldeira is sure that when citizens and environmental resources are under threat, politicians will not refrain from acting in their national interests.