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Researchers say it would be cheap and doable to dim the sun to curb global warming

Carbon dioxide emissions are causing a greenhouse effect that is warming the earth. Reducing such emissions has been a focus. But some say it’s worth looking at ways to reflect the sun’s energy back into space. Sean Gallup/Getty Images

It would be doable, but would it be wise?

Researchers say they’ve looked into how hard it would be to spray chemicals into the atmosphere to block the sun and curb global warming — and it would be neither technically difficult nor too expensive.

The researchers, in a new study, did not make any judgments about whether it should be done, but they did “show that a hypothetical deployment program starting 15 years from now, while both highly uncertain and ambitious, would be technically possible strictly from an engineering perspective,” said Gernot Wagner, research associate at Harvard’s School of Engineering and Applied Sciences and codirector of Harvard’s Solar Geoengineering Research Program.


The project would also be “remarkably inexpensive, at an average of around $2 [billion] to 2.5 billion per year over the first 15 years,” Wagner, one of the paper’s two authors, said in a statement. The research was published recently in the journal Environmental Research Letters.

Wagner’s coauthor was Wake Smith, former chief executive and president of Pemco World Air Services, a leading global aircraft modification company. Smith is a lecturer at Yale.

One solution that has been floated for solving global warming is the introduction of aerosols (small reflecting particles) into the stratosphere, increasing the amount of sunlight that is reflected back to space. The idea has been taken seriously enough to be considered by the National Research Council in a 2015 report.

But the NRC said the “more speculative approach” would come with a “currently unknown environmental price.”

“The committee is concerned that understanding of the ethical, political, and environmental consequences of [efforts to increase reflection of the sun into space] is relatively less advanced than the technical capacity to execute it,” the NRC report also said.

“There is no substitute for dramatic reductions in the emissions of CO2 and other greenhouse gases,” the report said. Still, it said, it might be “prudent” to look at a “broader portfolio of climate response.”


The new study by Wagner and Smith, who worked with a number of aerospace companies, found that existing aircraft are unlikely to be useful for such a project, but developing a new tanker with the ability to carry a large payload of sulfates for dispersal into the air would be feasible.

The researchers envisioned a fleet of just under 100 tankers flying just over 60,000 missions a year by the 15th year of the project.

Not everyone thinks such “solar geoengineering” is a good idea.

David Archer of the Department of Geophysical Science at the University of Chicago told CNN, “The problem with engineering climate in this way is that it’s only a temporary Band-Aid covering a problem that will persist essentially forever, actually hundreds of thousands of years for fossil fuel CO2 to finally go away naturally.”

Phil Williamson at the University of East Anglia in England told Reuters, “Such scenarios are fraught with problems — and international agreement to go ahead with such action would seem near-impossible to achieve.”

Wagner himself in a February 2018 essay in the Wall Street Journal coauthored with a Harvard economics professor said, “Seriously addressing climate change means cutting carbon emissions and, ultimately, reducing the carbon already in the atmosphere. There’s no way around it.”


He said solar geoengineering is “not a permanent solution to climate change, and it carries worrisome environmental and political risks of its own.” But he also said, “It’s an idea worth exploring.”

Jeremiah Manion of the Globe staff contributed to this report.