Solar Geoengineering 'Only Option' to Cool Planet Within Years, UN Says

The UN is calling for a large effort to study solar geoengineering, but warns it's too dangerous to implement immediately.
Solar Geoengineering Is 'Only Option' to Cool Planet Within Years, UN Says
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Research into sun and heat-deflecting technologies to tackle climate change are proceeding at a rapid pace around the globe, prompting the United Nations Environment Programme (UNEP) to investigate their potentials and dangers while stating that these controversial interventions are humanity's "only option" to quickly cool the planet within years.  

In a report published by UNEP in February, an independent panel describes what’s currently known about so-called solar radiation modification, also called solar geoengineering, and concludes that, despite its great potential, it's not viable or even safe right now. Nonetheless, amid growing calls from governments to find an emergency brake for climate change—and ongoing, independent efforts to develop solar geoengineering technology—the UNEP is calling for a full-scale global review of the tech and eventual multinational framework for how it should be governed. 


The recommendations have some opponents fearing that this amounts to endorsement of adopting the technology–a move that could create an even worse environmental crisis by messing with intertwined natural climate systems or pulling the focus away from mitigation measures, as well as further widening the inequalities that already exist as a result of climate change.

Solar radiation modification describes a range of technologies that aim to cool our overheated planet by reflecting incoming sunlight back out into space, or making it easier for heat coming off the earth to escape. Blocking out just two percent of sunlight could, according to some estimates, totally offset the warming that comes from doubling the amount of CO2 in the atmosphere from pre-industrial levels. 

It’s a tantalizing prospect, but comes with a raft of issues. 

For one, as the report notes, the best large-scale evidence we have that it could even work is from volcanic eruptions, where the smog cooled the globe for a couple of years afterwards. Most of the actual research has involved climate modeling, theoretical analyses or cost estimates. Some groups have conducted small-scale indoor experiments of how the tech might work. No one’s taken the trials outdoors yet. Even if we knew more, it’s not a be-all-end-all climate solution, said UNEP’s chief scientist, Andrea Hinwood. 


“Solar geoengineering is getting mainstream in a way that’s almost inevitable that we’re going to do it”

“SRM technologies, should they be considered at some point in the future, do not solve the climate crisis because they do not reduce greenhouse gas emissions nor reverse the impacts of climate change. The world must be crystal clear on this point,” she said in a UN media release.

What solar geoengineering might do though, is buy the planet some time. The UNEP report highlights that even if we fully halted CO2 emissions right now, it could take at least until the end of the century to see a drop in temperature. 

“Make no mistake: there are no quick fixes to the climate crisis,” wrote UNEP executive director Inger Andersen in the report. “Increased and urgent action to slash greenhouse gas emissions and invest in adapting to the impacts of climate change is immutable. Yet current efforts remain insufficient.”

If we could suddenly flip a switch on global temperature rise, however, there’s no shortage of potential unintentional consequences. For one, some areas of the planet, like the tropics, might overcompensate and cool down too much while other areas, like the polar regions, would cling on to warmth. 


Messing with the atmosphere could also mess with natural climate systems like El Nino Southern Oscillation or the polar vortex. It might even change more local events like rainfall, meaning how many crops particular regions produce dwindle. As Andersen noted in the report, "we only have one atmosphere," and so humanity can't afford to rush ahead with interventions that could have disastrous consequences.

A diagram of basic solar geoengineering mechanisms.

Image: UNEP

The biggest argument against solar geoengineering is that pursuing it draws attention and funding away from the effort to reduce greenhouse gas emissions. 

“Solar geoengineering is getting mainstream in a way that’s almost inevitable that we’re going to do it,” said Jennie Stephens, a sustainability and policy scientist at Northeastern University. 

“It’s disappointing to see the UN getting on the bandwagon of mainstreaming this as a legitimate approach. It’s such a distraction from what we need to be focussing on,” she told Motherboard, saying that instead we should be quashing our fossil fuel reliance—a measure the report also notes is still the priority.

“Our best bet for a prosperous and equitable future remains putting in the unavoidable hard work to achieve climate stability by reducing greenhouse gas emissions, to create a pollution-free planet and societies that live in harmony with nature,” Andersen wrote in the report.


Stephens is one of the signatories on an open letter calling for a total non-use of solar geoengineering. 

Political and environmental scientist Kevin Surprise, who also signed the letter, told Motherboard that pursuing solar geoengineering plays into the hands of fossil fuel companies. 

“Where is a discussion of the political and economic interests that will actively work to use solar geoengineering to expand fossil fuels and maintain other polluting activities that enrich the wealthy and corporations?” Surprise, a lecturer at Mount Holyoke College lecturer, said in an email.

“Solar geoengineering is about modifying the climate for everyone”

Stephens is also skeptical that it’s even possible to coordinate an international effort to first study then keep geoengineering in check, she said, when that hasn’t been possible for other climate change efforts. 

Both Surprise and Stephens said the UNEP report neglects the voices of social scientists, indigenous communities, feminists and other groups, focussing instead only on the views of physical scientists. They fear the resulting global review would do the same. “[The report is] almost misleading in that it presents a very pro-solar geoengineering perspective. We’re trying to get our voices heard and are really struggling,” said Stephens.

Others are more optimistic that future reviews will include more diverse viewpoints. 

“It’s significant to have the UN recommending a globally inclusive conversation on it,” says Philip Boyd, a professor of marine biogeochemistry at the University of Tasmania. “It ensures these discussions don’t take place in a technical or scientific vacuum, which has largely been the case so far.”

“When the UN says something is important, people pay attention,” adds Ben Kravitz, an earth and atmospheric scientist at Indiana University. “I particularly like that they are calling for an inclusive conversation. Solar geoengineering is about modifying the climate for everyone, and we need to think about how as many people as possible can have some kind of voice in what that might look like. This hopefully moves that process along.”

Despite firm opposition from some, the message from the UNEP report seems to be to proceed with caution. “While UNEP is concerned, it is naive to think research will cease and the issues will disappear. We cannot afford to bury our heads in the sand,” said chief scientist Hinwood.