Take note: the back-up plan for saving the world is no joke. A major scientific institution has published a comprehensive review of possible ways to engineer the climate to reverse global warming.
The UK Royal Society's review of geoengineering will make it difficult for governments to ignore the issue. It says that while reducing emissions of greenhouse gases "absolutely" must remain a priority, there is a serious chance that this will not be enough to stave off global warming of 2 °C.
"My guess would be that there is a 50-50 chance that we can achieve something with emissions reductions," says John Shepherd of the University of Southampton in the UK, chair of the Royal Society group behind the report.
If humanity wants to avoid the worst effects of climate change, it must be ready to safely deploy geoengineering methods as and when necessary, the report says. "We are already staring 1.6 °C in the face," says Shepherd.
He believes we should know some time in the next two decades whether or not efforts to curb emissions will be enough to avoid 2 °C of warming. If not, his personal view is that we should be prepared for a two-step plan B.
Step one: deploy some sort of sun shield to deflect solar energy away from Earth. Reflective technologies could cool the planet within a year, and according to the Royal Society's findings the most promising method in terms of cost and effectiveness would be to pump sulphate particles into the stratosphere (see illustration). However, this will not curb ocean acidification and other side effects of greenhouse emissions, and could disrupt weather patterns, so another method is required.
Step two: enact a means of sucking carbon dioxide out of the atmosphere. Several methods are already being investigated, which fall broadly into two categories: "tech-heavy" solutions, such as artificial trees that filter air and extract CO2 for storage, and "biological" methods, such as planting trees, using biofuels and fertilising the oceans.
According to Shepherd, tech-heavy methods are preferable because they are less likely to interfere with complex ecosystems. "Most of the things that have gone wrong in the past have happened when we've tampered with biological systems," he says.
Geoengineering methods have so far been on the fringe of climate discussions and research. Few, if any, could be developed tomorrow or even tested on a large scale. The Royal Society report calls on the UK government to invest £10 million a year towards an international research effort into geoengineering. This amounts to roughly 10 per cent of the UK climate research budget.
Such an international effort is conceivable. There are signs that the field is increasingly being taken seriously at national and international levels. Earlier this month the US National Academies tweaked the remit of its climate panelsuch that it will now assess geoengineering proposals. The Intergovernmental Panel on Climate Change will decide next month whether or not to do the same.
"It is clear that a lot of people are arguing that the IPCC should include an assessment of geoengineering in its next report," says Ottmar Edenhofer of the Potsdam Institute for Climate Impact Research in Germany and co-chair of one of the IPCC's three working groups. More worryingly, perhaps, military and naval representatives have also taken to attending research and policy workshops on the topic.
The Royal Society gave some reassurance that discussions of geoengineering will not deflate the public will to cut emissions. Results from focus groups suggested that the fact that scientists are giving geoengineering serious thought could be enough to spur people into acting on climate change. Whether this will hold true for politicians remains to be seen.