“Geoengineering” can mean a number of things, but it usually refers to the attempt to offset the rising global temperatures that result from the greenhouse effect by introducing particles in a systematic and sustained way into the earth’s atmosphere so that it better reflects the sun’s rays. Although the idea sounds futuristic, the basic concept has been around for a long time. In 1965, a group of scientific advisers to U.S. President Lyndon Johnson suggested that some kind of tinkering with the planet’s mechanics might be necessary. “The climatic changes that may be produced by the increased [carbon dioxide] content could be deleterious from the point of view of human beings,” they noted. “The possibilities of deliberately bringing about countervailing climatic changes therefore need to be thoroughly explored.”

They weren’t. Over the years, interest in geoengineering has periodically surged. But it has never attracted as much official attention or private investment as other methods of preventing climate change, mitigating its worst effects, or adapting to it. Now, however, as the pace and destructiveness of extreme weather events seem to be quickening beyond even some of the most pessimistic forecasts, geoengineering might finally have its moment.

Scientists are confident that geoengineering would have the desired effect because periodic volcanic eruptions, which spew all kinds of particles into the air, have cooled the earth in the past. But human intervention in the earth’s natural systems raises questions about the potentially dangerous impacts it could have on the weather and the oceans. There are also concerns about the moral hazard created by encouraging continued or even greater use of carbon-dioxide-emitting fossil fuels by suggesting the harm they do can be avoided. This potential consequence, in particular, explains the strong opposition to geoengineering from climate change activists and governments intent on addressing climate change by reducing fossil fuel emissions.

For decades, such concerns could remain merely theoretical. But the time has come for governments and the private sector to address them and to more seriously commit to applying geoengineering techniques while greatly increasing research to monitor the risks they pose.


For many across the globe, recent months brought the summer from hell. Places such as China, Pakistan, and Europe saw record heat, drought, wildfires, and flash floods. In the United States, the sudden intensity of Hurricane Ian, which caused devastation across southwestern Florida, made it abundantly clear that the effects of climate change have arrived sooner and with greater ferocity than even many climate change activists had been expecting. As Steven Bowen, the former head of catastrophic insight at Aon, a leading property and casualty insurer, recently acknowledged, “The modeled climate impacts we assumed were 25 to 50 years away are in some cases already occurring today.”

Fortunately, in the United States, this summer also brought legislative progress on climate change. The Inflation Reduction Act, signed into law in August, included record-setting green technology subsidies. But no one should rely on such policy measures to avert future shocks from severe weather driven by climate change. Reducing the rate of growth of emissions will certainly be helpful over the long run, but it will not help the world avert extreme weather crises any time soon for several reasons.

For one thing, the United States accounts for only about 15 percent of the world’s annual carbon dioxide emissions, and emission reductions there are likely to be easily overtaken by increases in emissions from the rest of the world—especially developing countries, as they use fossil fuels to power their economic growth in future decades. For example, the public policy professor Jack Goldstone has calculated that if per person carbon dioxide emissions in Africa reach India’s level by midcentury, Africa’s annual emissions will equal all of the United States’ annual emissions today. This calculation doesn’t count the huge growth in emissions expected in India, too.

The United States accounts for only about 15 percent of the world’s annual carbon dioxide emissions.

More fundamentally, the earth’s atmosphere has already absorbed enormous amounts greenhouse gases, especially carbon dioxide, which trap heat and warm the planet. These gases have accumulated over the course of human history but especially over the past several decades of fossil-fuel-driven economic growth. As a result, continued extreme weather is already baked in, regardless of the world’s efforts between now and 2050 to reduce the growth of new emissions.

Natural and technological methods for sucking carbon dioxide out of the atmosphere will not work in time to rescue the world from more decades of severe weather. Growing huge quantities of trees, which remove carbon dioxide naturally through photosynthesis, would help, but it would require acreage as large as the United States and Canada combined to make a material dent in existing carbon dioxide atmospheric concentrations.

Carbon dioxide can be sucked out of the air with technology, either directly, known as “direct air capture,” or indirectly, by taking it out of ocean water, giving the oceans the capacity to absorb more of it. Both technologies are very expensive, however, and are years away from being implemented at the scale required to make a difference in global temperatures, even with the generous subsidies for carbon capture technologies provided in the Inflation Reduction Act. Writing for the Environmental Defense Fund earlier this year, the journalist Joanna Foster noted that the United States alone may need to vacuum up as much as 1,850 million tons of carbon dioxide annually to hit its zero-emission target. But there are only a small number of direct air capture plants operating in the United States and Europe, and even the most advanced ones, such as the recently opened Orca plant in Iceland, can remove just 4,000 tons per year.

To be clear, all the above measures are necessary in the long run to tackle climate change, but they will not work fast enough to avert continued severe weather. The time has come for a more radical solution.


In 2009 and again in 2013, a team of climate and foreign policy specialists led by the energy expert David Victor noted in Foreign Affairs that geoengineering research was not where it should be. They argued that it was time to substantially boost scientific research about geoengineering to combat climate change. Since then, the physicist David Keith has considerably fleshed out and tested one particular technique that has been studied most: introducing sulfur particles into the atmosphere so that it better reflects sunlight and thereby cools the planet.

According to Keith, the rewards of this technique, which he calls “Stratospheric Sulfate Injection” (SSI), outweigh the risks. In The New York Times in October 2021, Keith wrote: “While limited, the science so far suggests that the harms that would result from shaving a degree off global temperatures would be small compared with the benefits. Air pollution deaths from the added sulfur in the air would be more than offset by declines in the number of deaths from extreme heat, which would be 10 to 100 times larger.”

According to Keith, this method of geoengineering is “cheap and acts fast.” Gernot Wagner, an economist who specializes in climate change, and Wake Smith, a climate intervention lecturer, estimate that SSI would cost the world about $2 billion to $2.5 billion annually for 15 years, an amount the United States alone could easily afford even if no other countries shared the cost.

Recognizing the benefits of this technology does not mean dismissing the risks it could pose. SSI would likely increase oceanic acidification, which could harm coral reefs and sea life as the sulfites being sprayed fall back to the earth. It could also alter weather patterns in unknown ways. That is why SSI deployment must be accompanied by continuous monitoring of its effects and substantially more research into the possible use of other, more benign particles. Scientists should also study ways to offset oceanic acidification by, for example, introducing base elements into ocean water.

National security imperatives should offset moral hazard concerns about geoengineering.

Fortunately, Keith has calculated that the efforts required to deploy SSI are manageable: “Less than two million tons of sulfur per year injected into the stratosphere from a fleet of about a hundred high-flying aircraft would reflect away sunlight and cool the planet by a degree.” And importantly, SSI can be dialed down by reducing sulfur injections or stopping them altogether if the risks look too great or other means of cooling the planet or removing carbon from the atmosphere prove more cost effective. One of those alternatives might eventually be a less risky form of geoengineering: cloud brightening (spraying saltwater into clouds to make them more reflective of sunlight) or cloud thinning (inserting ice into clouds to shorten their lifespan and thus allow more heat to escape from the earth). At this point, however, both of those alternatives are in the experimental stage and 15 to 20 years away from deployment.

Meanwhile, recent world events are mitigating the concerns about moral hazard that, up to now, have discouraged even research into geoengineering. Russia’s war in Ukraine and the Saudi-led OPEC+ reduction in oil production, which is expected to drive up energy prices, are stark reminders of the national security dangers of relying on other countries for fossil fuels. For years, national security arguments in the United States have been used to promote domestic oil and gas drilling so that the country won’t be so dependent on potentially unreliable Middle Eastern energy sources. But with the Russian economy’s reliance on fossil fuels, and with the U.S. economy and even the U.S. political system continuing to be subject to the whims of OPEC, the more the United States and other countries move away from fossil fuels, the less exposed all economies will be to future fossil fuel supply interruptions and oil price hikes. Indeed, the Biden administration’s recently released National Security Strategy makes the transition away from fossil fuels an integral part of the U.S. national security agenda.

In short, current national security imperatives should considerably, if not entirely, offset moral hazard concerns about geoengineering. The United States and its allies and partners have more reasons than ever before to avoid increasing their carbon emissions through more fossil fuel consumption.


In an ideal world, the United States would not begin geoengineering without an international agreement and a global system of governance to supervise the effort. But our world is not ideal, and it is unimaginable that global consensus on geoengineering could be reached any time soon.

Accordingly, the United States should begin by cooperating more narrowly with like-minded countries on implementing geoengineering. Europe and much of the developed world, which this summer experienced firsthand the ravages of climate change, should cheer on this effort and maybe even join in. Although China may not cooperate or share the modest costs of implementing SSI, it, too, suffered this summer from climate-change-induced drought and flooding, and Chinese leaders would likely look the other way while other countries attempt to cool the planet. The only dissenting major power would probably be Russia, which is counting on more climate change to thaw Siberia, expanding arable land for agriculture, and to further melt the Arctic, allowing more opportunities for oil exploration. But in a scenario in which China is on the sidelines and the rest of the world is supporting geoengineering, Russia, already a global pariah, would just have to stew.

Almost everything in life involves tradeoffs. Responding to climate change is no exception. The world can continue to suffer through decades of tragic natural disasters and extreme weather events, or it can take the measured risk of changing course, given the changed circumstances. As the saying goes, “When the facts change, I change my mind. What do you do?”

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  • ROBERT LITAN is Nonresident Senior Fellow in the Economic Studies Program at the Brookings Institution.
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