Read: What happens if we start solar geo-engineering—and then suddenly stop?

“That’s stunning. If it’s really true, it’s a huge deal,” says David Keith, an author of the paper and a professor of applied physics at Harvard. The study, which relies on a relatively rosy and moderate geo-engineering scenario, was co-authored by several widely recognized climate scientists who had never published on the topic before: Kerry Emanuel, an MIT professor who specializes in tropical cyclones, and Gabriel Vecchi, a geoscience professor at Princeton.

Keith believes that these optimistic early results should justify the establishment of a new international research program on solar geo-engineering.

Yet the paper, published in Nature Climate Change, has already been criticized by those who worry that geo-engineering researchers are moving too fast and overselling the still-notional technology. They also fret that optimistic talk of geo-engineering could discourage the public from embracing emissions cuts.

“They are desperately trying to conjure demand for their research topic, but I think they’re hamstringing themselves over the long term by overclaiming,” said Jane Flegal, a climate-policy researcher and an adjunct faculty member at Arizona State University, in a message. She worried that the study’s cheerful conclusion downplays the chance that geo-engineering will require economic or political trade-offs.

“I don’t think it is correct to imply that geo-engineering is a good or safe idea,” said Alan Robock, a professor of environmental sciences at Rutgers, in an email. He questioned how the study used computer climate models—that is, its authors did not simulate solar geo-engineering by modeling volcanic aerosols in the high atmosphere. Instead, they told the computer model to reduce the strength of the sun’s rays, a sort of brute-force proxy for geo-engineering. “And there is no way to do what they modeled, as we cannot turn down the sun,” Robock said.

Keith and his colleagues acknowledge some of these criticisms in the paper. Simulating geo-engineering by turning down the sun in models is “a very widely used technique,” he told me. It allows easier comparison between different computer models that may use varying processes to simulate high-atmospheric aerosols.

The new paper does not investigate whether solar geo-engineering could restore the climate to pre-global-warming levels. (Right now, the only way to avoid climate change altogether is to cut emissions.) The new paper asks instead whether geo-engineering could essentially cut the dangers of climate change in half. It uses high-resolution climate models, including one developed by the National Oceanic and Atmospheric Administration, to compare two different scenarios: one where atmospheric carbon levels have doubled above preindustrial levels and geo-engineering is not used, and another where they have doubled, but geo-engineering is used.