A panel of academics, engineers, and environmentalists, chaired by former U.S. Geological Survey Director Marcia McNutt, did say that albedo modification—the technical term for atmospheric engineering—could potentially "rapidly offset" some of the consequences of global warming. It's theoretically possible, although unproven, that within a few years of spraying, the Earth could be cooled.
But, the report found, the idea carries "environmental, ethical, social, political, economic, and legal risks associated with intended and unintended consequences."
The unpredictably of climate change and a lack of knowledge means that albedo modification could upend precipitation or atmospheric patterns, the report stated. The social impacts of blocking out the sun are unknown, but they could carry serious political consequences depending on what countries possess the technology to control the atmosphere.
The technology could even be used in a military fashion, the NRC report warns (the 1998 Avengers movie features Sean Connery as the villainous Sir August De Wynter, who produces a weather-controlling machine to blackmail world leaders).
More to the point, blocking out the sun does nothing to fix the problem of greenhouse gases, whose effects will be felt for centuries. Spraying the atmosphere is nothing more than a short-term fix.
"That scientists are even considering technological interventions should be a wake-up call that we need to do more now to reduce emissions, which is the most effective, least risky way to combat climate change," said McNutt, now the editor-in-chief of the journal Science.
A second study also focused on more proven carbon dioxide removal and sequestration techniques, saying they would do more to take carbon out of the economy and limit the direct emissions that are contributing to climate change.
McNutt said the committee decided to separate carbon dioxide removal from atmospheric modification to avoid conflating the two. The former concept is more proven, even if its still in its early technological stages, but is likely to be deployed. As the report lays out, the lingering concerns with carbon dioxide removal are about cost, rather than the risk-based concerns about albedo modification.
National Academy of Sciences President Ralph Cicerone made it clear that mitigating emissions is the best course of action, but he said that "every year of inaction on the emissions reduction does increase the likelihood" that more drastic intervention will be necessary. Thus, he said, "the scientific community needs to have answers and a much better understanding" of geoengineering.
Rafe Pomerance, a former State Department climate official who was not involved in the NRC report, said in an interview that with extreme storms and sea-level rise showing the growing risk of climate change, the time is ripe to put every option on the table.
"How can we not think about this?," he asked. "If you think there are catastrophic outcomes in the future, why wouldn't you think about responses to avoid it? If you don't intervene, and we keep going on this trajectory, then we may want these options. In the end, it's just going to be a comparison of risks."