CHICAGO — David Keith was a graduate student in 1991 when a volcano erupted in the Philippines, sending a cloud of ash to the edge of space.
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Seventeen million tons of sulfur dioxide released by Mount Pinatubo spread through the stratosphere, reflecting some of the Sun’s energy away from Earth. The result was a drop in average temperatures in the Northern Hemisphere of more than half a degree Celsius in the following year.
Today, Keith cites that event as validation of an idea that has become his life’s work: He believes that by intentionally releasing sulfur dioxide into the stratosphere it would be possible to lower temperatures around the world, mitigating global warming.
Such radical interventions are being taken more and more seriously as the effects of climate change become more intense. Global temperatures have hit record levels for 13 consecutive months, unleashing violent weather and deadly heat waves and raising sea levels. The main driver of warming, the burning of fossil fuels, continues more or less unchanged.
In this context, there is growing interest in efforts to intentionally alter the Earth’s climate, a field known as geoengineering.
Major corporations are already operating huge facilities to suck the carbon dioxide that is warming the atmosphere out of the air and bury it underground. Some scientists are conducting experiments designed to light up clouds, another way to bounce some of the sun’s radiation back into space.
But it is stratospheric solar geoengineering that raises the greatest hopes and the greatest fears.
Its proponents see it as a relatively cheap and quick way to reduce temperatures long before the world stops burning fossil fuels. Harvard University has a solar geoengineering program that has received grants from people like Bill Gates, the co-founder of Microsoft. It is being studied by the U.S.-based Environmental Defense Fund along with the World Climate Research Program, an international scientific effort. Last year, the European Union called for an analysis of the risks of geoengineering and said countries should discuss how to regulate a rollout of the technology.
However, many scientists and environmentalists fear that it could result in unpredictable calamities.
Because it would be used in the stratosphere and not limited to a particular area, solar geoengineering could affect the entire world, possibly disrupting natural systems such as generating rain in an arid region and drying out the monsoon season elsewhere. Critics worry it will distract from the urgent work of moving away from fossil fuels. They oppose intentionally releasing sulfur dioxide, a pollutant that would eventually rise from the stratosphere to ground level, where it can irritate skin, eyes, nose and throat and cause respiratory problems. And they fear that once started, a solar geoengineering program would be difficult to stop.
Raymond Pierrehumbert, an atmospheric physicist at Oxford University, said he considered solar geoengineering a threat to human civilization. “It’s not just a bad idea in terms of something that would never be safe to implement, but even researching this topic is not only a waste of money, it’s actively dangerous,” he said.
Shuchi Talati, founder of a nonprofit called the Alliance for Fair Deliberation on Solar Geoengineering, called the technology “a double-edged sword.”
“It could be a way to limit human suffering,” he said. “At the same time, I think it can also exacerbate suffering if used in the wrong way.”
In interviews, Keith, a professor in the Department of Geophysical Sciences at the University of Chicago, responded that the risks posed by solar geoengineering are well understood, not as severe as critics portray and are dwarfed by the potential benefits.
If the technique slowed global warming by one degree Celsius over the next century, he said, it could help prevent millions of heat-related deaths each decade.
According to his calculations, A planet transformed by solar geoengineering would not be noticeably darker during the day. But it could produce a different kind of twilight, one with an orange hue.
By lowering global temperatures, solar geoengineering could help restore the planet to its pre-industrial state, recreating the conditions that existed before massive amounts of carbon dioxide were pumped into the atmosphere and began cooking the Earth, he said.
“There are definitely risks and there are definitely uncertainties,” he said. “But there is really a lot of evidence that the risks are quantitatively small compared to the benefits.”
Opponents of solar geoengineering cite several major risks.
They say that could create a “moral hazard,” giving people the wrong impression that there is no need to rapidly reduce fossil fuel emissions.
The second major concern has to do with unintended consequences.
“It’s a really dangerous path,” said Beatrice Rindevall, president of the Swedish Society for Nature Conservation, which opposed the experiment. “It could shake up the climate system, disrupt hydrological cycles and exacerbate extreme weather and climate instability.”
And once solar geoengineering began to cool the planet, abruptly stopping the effort could result in a sudden spike in temperatures, a phenomenon known as a “termination shock.” The planet could experience “a potentially massive temperature increase in an unprepared world within 5 to 10 years, affecting the Earth’s climate with something that has probably not been seen since the impact that wiped out the dinosaurs,” Pierrehumbert said.
Added to this are fears that solar geoengineering could be used by rogue actors and that the technology could be weaponized. And sulphur dioxide can harm human health.
Keith insists that such fears are exaggerated. Last year, he announced that he would leave Harvard, where he had been a professor for 13 years, to go to the University of Chicago, where he would develop a program around climate interventions, including solar geoengineering.
“I don’t know if those things will ever be used,” said Gates, a major investor in climate technology.Yes, I think it makes sense to investigate and understand it.”
After graduating from the University of Toronto, Keith enrolled in a PhD program at the Massachusetts Institute of Technology (MIT) to study experimental physics.
In 1992, he published a scholarly article, “A Serious Look at Geoengineering,” that raised the questions that would shape his career: Who should authorize the use of these technologies? Who is responsible if something goes wrong?
His academic path took him from Carnegie Mellon University in Pennsylvania to the University of Calgary, where he began researching ways to capture and store carbon dioxide. The next stop was Harvard, where he dove headfirst into solar geoengineering.
In 2009, Keith founded Carbon Engineering, a company that developed a process to extract carbon dioxide from the atmosphere. Investors included Gates, Chevron and N. Murray Edwards, who made billions of dollars extracting oil from the Canadian oil sands.
Last year, Carbon Engineering was acquired by Occidental Petroleum, a major Texas-based oil and gas producer, for $1.1 billion.
Occidental is now building a series of massive carbon capture plants. It plans to sell carbon credits to big companies like Amazon and AT&T that want to offset their emissions.
Academic energy in the field has followed Keith to the University of Chicago, which is allowing him to hire 10 full-time professors. and create a new program focused on various types of geoengineering. The total cost could reach $100 million.
The move has raised eyebrows among some. Pierrehumbert, who recently left the University of Chicago for Oxford University, said he was “dumbfounded” and argued that those research dollars could be better spent investigating ways to reduce fossil fuel use.
To celebrate his 60th birthday last October, Keith went hiking in the Canadian Rockies and came across a glacier that had shrunk dramatically in size in recent years. It was a visual reminder that global warming is upending the natural world, and it confirmed his core belief: Humans have already altered the planet, warming the climate with greenhouse gases. To repair the climate and return it to a more pristine state, we may need to take even more drastic measures and manipulate the stratosphere.
“Even now I am more motivated to push solar geoengineering because the rational arguments in favor of it seem stronger,” Keith said. “While there are still a lot of strong individual voices of opposition, there are a lot of people in serious political positions who are taking this seriously, and that’s really exciting.”
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