Trapped interior a prolonged glass tube in a ground-ground lab at Harvard University is a tiny reproduction of the stratosphere.

After I visited Frank Keutsch in the autumn of 2019, he walked me all of the contrivance down to the lab, the set the tube, wrapped in grey insulation, ran the length of a bench in the again corner. By filling it with the upright mixture of gases, at impart temperatures and pressures, Keutsch and his colleagues had simulated the stipulations some 20 kilometers above Earth’s surface.

In making an strive out how diversified chemicals react on this rarefied air, the team hoped to habits a shameful take a look at of a controversial diagram is called solar geoengineering, which goals to counter climate substitute by spraying diminutive particles into the stratosphere to repeat extra of the solar’s warmth again into location.

Nevertheless is what’s in that tube “undoubtedly what the stratosphere is admire?” asks Keutsch, a professor of engineering, chemistry, and atmospheric science, as he gestured toward it. “That’s the search data from. We strive to possess all the pieces, however I would argue you by no manner somewhat know.”

That’s why he and fellow researchers, including Harvard climate scientist David Keith, are making an strive to transfer their experiments out of their toy stratosphere and up into the exact one. They hope to habits a series of scientific balloon flights, the foremost of which can perchance well initiate from the Esrange Home Center in Kiruna, Sweden, as soon as this summer season.

I seriously hope we’ll by no manner gain in a command the set this if reality be told needs to be done, because I composed possess that is a actually provoking conception and one thing will recede erroneous.

Frank Keutsch, main investigator of SCoPEx

The preliminary flight will merely have faith in whether the plane’s equipment and instrument work properly in the stratosphere, the set temperatures can fall beneath 50 ˚C and the stress ranges from one tenth to one thousandth the amount at sea stage. Nevertheless in subsequent launches, the researchers hope to liberate diminutive amounts of the categories of particles that will perchance well scatter sunlight.

In a international that’s cutting carbon dioxide emissions too slowly to forestall catastrophic climate substitute, solar geoengineering would possibly per chance per chance well snatch a whereas. Nevertheless doing it on a gigantic scale would possibly per chance per chance well indicate messing with planet-huge weather patterns. The outcomes are unpredictable; in some areas, they would possibly per chance perchance perchance well even be disastrous.

Within the approaching weeks, as a result of this reality, an neutral advisory committee that is reviewing the suitable, moral, and environmental considerations surrounding the mission is predicted to resolve whether the overview crew need to composed proceed with the foremost flight. The committee will additionally need to rule before any flights that if reality be told liberate materials, and resolve what steps the overview team need to composed or must take to get rid of with the final public and regulators.

If those launches are permitted—and that’s composed a worthy if—they’ll be the foremost geoengineering experiments in the stratosphere. Nevertheless before the balloons occupy even left the bottom, they’re already drawing criticism.

Too unhealthy to use

The premise of cooling the planet by dispersing particles in the ambiance, dimming sunlight and offsetting just among the warming pushed by greenhouse-fuel emissions, has a precedent: nature already does it.

Major volcanic eruptions equivalent to Mount Pinatubo in 1991 occupy spewed hundreds and hundreds of loads of sulfur dioxide into the air, depressing international temperatures in the years that adopted. The sulfur dioxide emitted from coal vegetation and ships produces measurable cooling outcomes to boot.

To some critics, doing this deliberately as a measure towards climate substitute is reckless even to ponder, let alone experiment with. A limited overview occupy found out that solar geoengineering would possibly per chance per chance well considerably alter rainfall patterns and decrease some chop yields in determined areas. On the opposite hand, other papers occupy concluded that the environmental aspect outcomes shall be diminutive as prolonged as geoengineering is completed in a moderate contrivance.

Nevertheless the full overview done to this point, with just a few diminutive-scale exceptions, has been conducted in computer models or lab experiments. So Keutsch and his colleagues argue that their balloon trials are a important subsequent step.

The wanted conception for their so-called SCoPEx experiments, first proposed again in 2014, is to initiate a balloon, equipped with propellers and sensors, that will perchance well liberate up to 2 kilograms of sub-micrometer-dimension particles in a roughly kilometer-prolonged plume. A business airliner pumps out identical amounts of topic matter every minute, Keith notes.

Then the balloon would tack around and slowly zigzag via the plume from the reverse course. Its sensors would strive to measure how widely the particles disperse, how they have interaction with other compounds, and the contrivance noteworthy sunlight they replicate.


Whatever they found out shall be fed again into computer models, refining our thought of what spraying loads of of hundreds to hundreds and hundreds of plenty of topic matter would possibly per chance per chance well additionally operate.

At this point, the team hopes to habits a series of flights over a different of years. Within the originate, they intend to liberate a lovely mud of calcium carbonate—the main ingredient of chalk—however finally the researchers are making an strive to take a look at other materials, seemingly including sulfuric acid (which is a derivative of the sulfur dioxide launched from volcanoes).

Nevertheless some alarm that even these restricted experiments are a step too a long way.

Wil Burns, co-director of the Institute for Carbon Removal Law & Protection at American University, believes there need to be an strive to reach some invent of international consensus about whether society need to composed ever use this kind of instrument before out of doors experiments recede ahead.

Nevertheless for him, the solution is no longer any: The environmental impacts are unknown. The challenges of governing this kind of instrument are gigantic—a single nation would possibly per chance per chance well operate solar geoengineering by itself, however all international locations would be affected. And future generations shall be forced to location up the outcomes for loads of of years. He adds that we can’t know what this would possibly per chance perchance perchance well undoubtedly operate at a planetary scale till it’s absolutely deployed—and at point, we’ll be stuck with any droughts or other dangers till the outcomes subside.

Some environmental groups and geoengineering critics are calling on authorities officers in Sweden, the set the foremost SCoPEx flight would initiate, and the heads of the Swedish Home Corporation, which can perchance well location up them, to oppose the experiments. They argue no longer that the overview itself offers environmental dangers however that it creates a “slippery slope toward normalization and deployment” of a perilous and strong instrument.

Solar geoengineering “is a abilities with the aptitude for vulgar penalties, and stands out as unhealthy, unpredictable, and unmanageable,” reads a letter issued by Greenpeace Sweden, Biofuelwatch, and other groups. “There is no longer this kind of thing as a justification for making an strive out and experimenting with abilities that appears to be like to be too unhealthy to ever be worn.”

The reluctant researcher

Keutsch says it’s a “very right” alarm that geoengineering experiments would possibly per chance per chance well make eventual use of the abilities extra seemingly. As he urged me all via an interview in his office, he himself thinks geoengineering is the erroneous approach to take care of climate substitute. He compared it to opiates that ease acute wretchedness however lead to other considerations admire dependancy. The a long way safer, extra effective solution would be to posthaste gash greenhouse-fuel emissions.

Nevertheless, he fears, climate substitute is to this point along and so seemingly to became so disruptive that some determined nation would possibly per chance per chance well additionally transfer ahead with geoengineering anyway. An earlier Harvard study found out that the fee of increasing and flying a fast of specialised planes to retain out the job would fee as limited as $2 billion a year, placing it all via the business reach of many international locations.

Because it’s the top possible instrument that will perchance well make any exact disagreement to international temperatures all via the duration of a political term, it would possibly per chance per chance well became an extremely seductive likelihood in countries struggling via lethal warmth waves, droughts, famines, fires, or floods. Utilizing it with out ample overview would be “very unhealthy,” Keutsch says.

Harvard professor Frank Keutsch, main investigator of SCoPEx.


“Folks possess that because I’m doing geoengineering overview I kind of are making an strive to retain out geoengineering,” he says. “My leer is if reality be told very strongly that I seriously hope we’ll by no manner gain in a command the set this if reality be told needs to be done, because I composed possess that is a actually provoking conception and one thing will recede erroneous.”

“Nevertheless on the same time, I possess better thought what the dangers would possibly per chance per chance well additionally very well be is terribly necessary,” he adds. “And I possess for the declare overview I’m most attracted to, if there is believed to be one of those topic matter that will perchance well considerably decrease dangers, I operate possess we should always composed know about this.”


The team in the originate hoped to originate up balloon flights as early as 2018 in Tucson, Arizona, and therefore explored plans in Fresh Mexico. They opted to transfer the foremost effort to Sweden thanks to “COVID-19 and other logistical and scheduling challenges,” per the mission web order.

Part of the extend used to be as a result of the Keutsch team’s technique to location up an neutral committee to have faith in the moral and appropriate impacts of their proposed experiments. They didn’t need to occupy one, for the explanation that overview effort has no federal funding. (Certainly, when the mission started, there used to be no US federal funding for geoengineering overview. The mission runs on interior Harvard money and donations from folks and groups including Bill Gates, the William and Plants Hewlett Foundation, the Alfred P. Sloan Foundation, and others.)

Nevertheless Jane Long, a frail accomplice director at Lawrence Livermore Nationwide Laboratory, strongly advised that an exterior evaluation committee be created. (She additionally helped snatch its chairperson.) “It used to be necessary for the contrivance ahead for this abilities that they’re no longer seen as hideous scientists working off to retain out some experiment with out any evaluation,” she says.

Long stresses that the experiments, as first proposed, are very diminutive scale and no longer going to unique well being or environmental dangers. Nevertheless the board, she says, forces the researchers to assert what the work is for and to take care of public concerns.

The committee has already issued a memoir offering suggestions on how the overview team need to composed check with the final public before any flights that liberate particles. Among other things, it implys increasing a briefing guide to tell the considerations and sharp those who dwell shut to the balloons’ flight path to “take part in deliberative dialogue about the experiment itself as well to governance of solar geoengineering overview.”

Silent, Burns and others argue that the committee is missing some obligatory voices, including critics of geoengineering overview and representatives from poorer international locations. And he believes these blind spots are evident in the committee’s preliminary memoir. “It assumes, and invent of evinces a bias, that we’re top possible doing the final public engagement to identify guidelines on how to gain to the subsequent stage via topic experiments—and that appears to be like to be increasing thought to be one of those foregone conclusion via what is going to happen and what need to composed happen,” he says.

What they would possibly per chance perchance perchance well study

Keutsch’s team has already elope computer simulations exploring how the particles launched from their equipment will dissipate into the air. If and when they starting making an strive out this for exact, they’ve so that you can measure extra precisely how specks of calcium carbonate or sulfuric acid unfolded or clump collectively—a necessary take a look at of how well these materials would possibly per chance per chance well work for geoengineering. If the particles are too worthy, they’ll sink too rapidly out of the stratosphere, requiring extra materials to scatter the same quantity of sunlight.

Every other obligatory search data from is how the particles will react with other chemicals in the stratosphere—notably the calcium carbonate, because it doesn’t happen up there naturally.


The team selected calcium carbonate somewhat than sulfates for two reasons, Keutsch says: sulfates eat away on the protective ozone layer, and whereas they’ve a cooling gain on the Earth’s surface, they warm the stratosphere. That can perchance well fire up weather patterns in ways in which shall be laborious to foresee. “You is in all likelihood attempting to coast the Earth machine in ways in which I don’t possess our models are neutral appropriate at predicting,” he says.

Calcium carbonate comes with its occupy unknowns, on the other hand. These experiments in the glass tube found out that it is a long way no longer always notably reactive with the compounds this would possibly per chance perchance perchance well hit upon in the stratosphere. Nevertheless the contrivance it interacts with other chemicals in the exact one would possibly per chance per chance well occupy an affect on how noteworthy ultraviolet radiation is absorbed and the contrivance noteworthy sunlight is scattered.

The observations from the flights would possibly per chance per chance well again refine our thought of how noteworthy of those materials would possibly per chance per chance well additionally very well be desired to diminish international temperatures, what dangers releasing them would possibly per chance per chance well pose—or whether this would possibly per chance perchance perchance well work the least bit.

Nevertheless there will composed be exact limits on what the researchers can study from diminutive balloon experiments. They won’t be in a position to detect the longer-term destiny of particles launched into the stratosphere, because they’ll rapidly became too dilute to detect. Furthermore, Keutsch acknowledges, there are merely some things that will perchance well’t be known till any individual deploys solar geoengineering at pudgy scale.

“The Earth machine is so complex,” he says. “I don’t possess we can predict fully. We can’t ever be undoubtedly obvious of what’s going to happen when you happen to operate this.”

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