The United Nations last month laid bare how badly the world is doing on its climate targets. Today the US National Academy of Sciences (NAS) says such slow progress means the US should launch a $100-$200 million research programme on solar geoengineering, a controversial set of techniques to reflect sunlight back to space in order to cool the Earth.
However, the group that it isn鈥檛 calling for听deployment of such solar geoengineering technologies and warns that doing more research is no excuse for 鈥済iving up on decarbonisation鈥�.
The report reviews geoengineering methods such as 鈥渟olar shields鈥�, which rely on injecting aerosols into the stratosphere. A group led by Harvard University is researching this approach with an experiment releasing a few hundred grams of mineral dust from a high-altitude balloon above Sweden later this year. It will be the first time that particles have been intentionally injected into the stratosphere in an attempt at geoengineering.
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That project, called , will only go ahead if an initial test balloon flight at Esrange Space Center in Kiruna, Sweden, goes well. It also hinges on a green light from an independent advisory committee, which has giving a verdict, initially due on 15 February.
鈥淲e really need to do the research because I鈥檓 really worried where we鈥檙e going with climate change, as action is just not fast enough,鈥� says Frank Keutsch at Harvard University, who is leading SCoPEx . Modelling how particles behave that high up, and how much sunlight they reflect, or extrapolating from what happens during a volcanic eruption only goes so far, says Keutsch 鈥� at some point observational data is needed.
The NAS backs the idea of real world experiments like Keutsch鈥檚, provided they are subject to good oversight. 鈥淟imited outdoor experimentation could help advance the study of certain atmospheric processes that are critical for understanding solar geoengineering,鈥� the report says.
Shaun Fitzgerald at the University of Cambridge says more research and funding is welcome so that governments are informed if they have to deploy such radical measures one day. 鈥淭here is a responsibility that when decisions are made on deployment, they are not made in the absence of knowledge. That would be a dereliction of duty,鈥� he says. The research could conclude that deployment must be ruled out entirely, he adds.
Evidence to date suggests that solar geoengineering could lower Earth鈥檚 surface temperature, but also indicates that there could be unintended negative consequences. Those include weakening resolve to cut carbon emissions and creating 鈥渦nfavourable鈥� changes in rainfall and extreme temperatures in some countries, says the report.
Still, critics fear that crossing the Rubicon of moving from indoor to outdoor tests would ultimately lead to deployment. Without limits imposed by the SCoPEx advisory committee on what the team can do after initial tests, 鈥渢here is a real risk of inducing a slippery slope where one experiment will lead to another鈥�, says Ina M枚ller at Wageningen University and Research in the Netherlands.
The NAS report calls for the US government to adopt a $100-200 million research effort over five years. It could explore which solar geoengineering approaches are 鈥渕ost fruitful鈥�, fund chemistry and microphysics research on the properties of particles used for reflecting sunlight, and gain a better understanding of what the public thinks about the technology.
鈥淚t isn鈥檛 saying solar geoengineering鈥檚 time has come,鈥� says Emily Shuckburgh at the University of Cambridge. 鈥淚t is very specifically saying only that the time has come for an international transdisciplinary solar geoengineering research programme focused on understanding the options and risks, and explicitly not on a path to deployment.鈥�
However, Clive Hamilton of Charles Sturt University, Australia, says even without deployment, a big research effort would be a significant moment.听 鈥淭he call for a solar geoengineering research programme is an indicator of the rising panic among climate scientists about approaching tipping points. Taking the solar geoengineering path, even a major US research programme, would be a political tipping point,鈥� he says.
Fitzgerald questions whether the three technologies covered by the NAS report 鈥� which also include cloud brightening and cloud thinning 鈥� are necessarily the right ones to focus efforts on. He says more localised approaches, such as trying to preserve Arctic ice to reflect light back to space, may be worth considering too, partly because they would be less controversial.
If the US did adopt a major research programme, it might go part way towards allaying one of the biggest concerns of opponents of solar geoengineering: the lack of any international body controlling what experiments and deployment could take place. The NAS says the research effort 鈥渟hould support the development of international governance mechanisms鈥�.
David Santillo at the University of Exeter, UK, says bodies such as SCoPEx鈥檚 advisory committee aren鈥檛 sufficient because they won鈥檛 consider all the social and ethical issues. He thinks the role could go to an existing United Nations body, such as one overseeing , or a new one could be created.
Such global governance is a long way off, though. In the short term, the NAS report is a boost for Keutsch鈥檚 experiments, and any that might follow. Keutsch is aware that the success or failure of his project could determine whether future experiments happen. He is also clear the world stands at an important milestone. 鈥淚t doesn鈥檛 get much more symbolic than some balloon you鈥檙e launching up there, it symbolises 鈥榦h, where has humanity got itself to鈥�,鈥� he says.
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