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As the planet warms faster, scientists study controversial ways to lower temperatures

The mushroom cloud from the 1991 Mount Pinatubo volcanic eruption temporarily cooled the atmosphere. Scientists theorize the controlled distribution of aerosols could help address climate change.ARLAN NAEG/AFP via Getty Images

As the planet continues to warm at an accelerating rate, scientists are looking into a potential insurance policy, a radical way of curbing climate change by altering the climate system itself.

A team at Harvard University this summer plans to conduct the first of a series of highly controversial tests of what’s known as solar geoengineering, a way to reduce global warming by spreading particles in the atmosphere to reflect sunlight back into space.

If an advisory board authorizes them to proceed, the scientists plan to travel in June to a remote part of northern Sweden, where they’ll launch a giant balloon into the stratosphere to test whether they can adequately maneuver an instrument-filled gondola suspended below. If all goes well, the team later this year plans for the first time to inject a small amount of calcium carbonate — a common substance found in rocks — into the atmosphere to better understand how the chemical compound might be used to moderate temperatures on the ground.

Long considered too risky, solar geoengineering is now being more seriously considered as the threat of climate change grows more dire. But critics say such a test, which would spread a few pounds of the particles about 12 miles above ground, would set a dangerous precedent and open a door to more radical experiments that could ultimately cause grave harm to the planet.


“I’m fully aware of the moral hazards, but if we are to provide decision-makers with useful information about whether this could work, we need to ground-truth our models,” said Frank Keutsch, a professor of engineering and atmospheric sciences at Harvard who serves as principal investigator of the project, known as SCoPEx, or the Stratospheric Controlled Perturbation Experiment.

With global average temperatures in the coming decade likely to exceed 1.5 degrees Celsius above pre-industrial levels — a potentially catastrophic rise — scientists say staving off the worst consequences of climate change will require more than reducing carbon emissions. Even if it were possible to eliminate such emissions overnight, they note, that wouldn’t offset the dangers from the massive amount of greenhouse gases already in the atmosphere.


As a result, scientists expect it will be necessary to remove existing carbon from the atmosphere.

SCoPEx BalloonHarvard University SCoPEx

MIT researchers, including former energy secretary Ernest Moniz, are urging the incoming Biden administration to spend billions of dollars over the next decade to study a range of technologies that use machines to extract carbon from the air or enable trees and rocks to absorb greenhouse gases more rapidly.

But those technologies, at least in their current incarnations, remain highly expensive and unlikely to present a timely or practical solution to more than a century of accumulated greenhouse gases. So proponents of solar geoengineering say the technology deserves close analysis, as a relatively inexpensive way of moderating temperatures quickly.

“Solar geoengineering has potentially huge benefits to humanity, especially the most vulnerable,” said David Keith, a professor of public policy at Harvard University’s Kennedy School of Government and one of the leaders of the project. “No one doubts that it’s possible to cool the atmosphere with aerosols.”

As evidence, scientists point to the cooling that occurred after the 1991 eruption of Mount Pinatubo in the Philippines released an estimated 20 million tons of sulfur dioxide and ash particles into the stratosphere, which cooled the planet by nearly 1 degree Fahrenheit over the next two years.


But Keith and other scientists say they’re well aware of the potential problems of trying to cool the atmosphere in such a fashion. Solar geoengineering, they also note, shouldn’t absolve governments from cutting emissions, as reflecting more sunlight into space doesn’t address the underlying problems of increased amounts of carbon in the atmosphere. For example, the oceans would continue to absorb carbon and become more acidic if emissions aren’t reduced, threatening everything from coral to shellfish.

Injecting large amounts of particles into the atmosphere could also cause great damage to the planet, breaching holes in the ozone layer and increasing the incidence of skin cancer; changing weather patterns in ways that could cause droughts in some places and flooding elsewhere; and potentially even altering the color of the sky.

“We’re talking about fundamentally changing the planet in ways we do not understand,” said Dan Cziczo, chairman of the Earth, atmospheric and planetary sciences department at Purdue University. “I do not believe this is sound science.”

He and others worry that if the SCoPEx project proceeds it would clear a path for others to engage in similar, perhaps more perilous, experiments. The multimillion-dollar project, and others like it, could also draw away the limited private and public grants for other climate research, they said.

Peter Frumhoff, chief climate scientist at the Cambridge-based Union of Concerned Scientists, called solar geoengineering “the worst possible way to address climate change that we need to take seriously.”


He worries that focusing too much on solutions that don’t address the fundamental causes of climate change could dissuade policy makers from making the difficult decisions to eliminate the use of fossil fuels and other steps to reduce emissions.

“At its best, it could only make sense as something that would buy time,” he said.

Keutsch and Keith acknowledged there are reasonable concerns about the wisdom and efficacy of solar geoengineering but that it’s incumbent on scientists to determine whether the pros outweigh the cons.

“I am convinced that doing limited research on stratospheric geoengineering is needed,” Keutsch said, adding that policymakers must still make cutting emissions their priority. “Do I know that I am right? The answer is no, but I would argue nobody can know that at the moment.”

He added: “I see our role as providing facts, not deciding on any form of use.”

They also acknowledged that their research methods should be transparent and monitored closely, given the potential impact beyond national borders.

Creating an oversight model is why Shuchi Talati, a scholar who studies solar geoengineering at American University, decided to join SCoPEx’s advisory board.

“Because this is a technology that can affect every individual in the world, there has to be international and national mechanisms ensuring transparency and public participation,” she said.

For the initial test of SCoPEx, which will determine whether the scientists can effectively steer a balloon in the stratosphere, the board has been reviewing whether it complies with Swedish laws before they approve the flight, Talati said.


For the more controversial test that would involve dispersing particles, there will be greater input from the public, financial audits, and more legal reviews before approval, she said.

“As we cross the threshold into physical experimentation, it’s vital that we ensure this research is done responsibly,” Talati said.

David Abel can be reached at david.abel@globe.com. Follow him on Twitter @davabel.