A lake of volcanic mudflow lies trapped at the slopes of Mount Pinatubo on June 28, 1991 as the volc...


“Is this a pathway that we should be going down?”

How to Save the Earth

Bill Gates is funding a controversial climate fix that could save the Earth — or doom it

To its advocates, Solar Radiation Modification is cheap, easy to do, and it can be done on a global scale. Whether or not you think it is brilliant, SRM is controversial.

by Alexis Schwartz
Originally Published: 

In 1601 CE, China plunged into turmoil.

The spring and summer were unusually frigid, while the latter part of the year was unusually hot. Floods and frost conspired to destroy crops, and drought killed whatever was left alive. According to contemporary eye-witness accounts, with the autumn heat came disease epidemics and famine. An account dating to 1611 describes how people “ate tree bark and grassroots” to survive.

The rest of the world was not spared: European wine harvests failed. In Russia, perhaps 500,000 people perished within two years. The reason was not war, nor a virulent pathogen: It was a temporary climate apocalypse, now called the Little Ice Age.

The world’s suffering stemmed from an eruption: In 1600, the Peruvian Huaynaputina volcano violently spewed ash, dust, and toxic gases into the atmosphere. The sulfuric ash traveled from Europe to Japan, dimmed sunlight, and made temperatures around the world crash.

The result was a worldwide crop failure, destroying countries’ food reserves. Some historians speculate the cataclysm put an end to early efforts to colonize North America in Jamestown, Virginia, where many early inhabitants died of malnutrition.

How to Save the Earth: On Earth Day 2022, Inverse explores some of the most ambitious, exciting, and controversial efforts to save our planet.

A painting of the Laki volcano erupting by Ásgrímur Jónsson (1876-1958).

Public Domain

Similar catastrophes followed another eruption in 536 C.E.. which plunged the world into darkness and blocked out the Sun for 18 months. Summer temperatures dropped to 1.5°C (34.7°F), crops failed, and millions died. Ultimately, the ensuing Plague of Justinian would spur the collapse of the Roman Empire.

And in 1783 C.E., the world endured the Móðuharðindin, or “Mist Hardships” — environmental catastrophes stemming from the Laki volcano erupting on Iceland. Then, an estimated 11 million people perished in two famines in India; and tens of thousands of Europeans starved to death, and those who survived propelled the French Revolution.

To historians, powerful volcanic eruptions catalyze social upheaval. Yet to climate scientists, they make for great research — and for some, they even suggest a way to survive our ongoing, manmade climate crisis.

Solar radiation modification

A Peruvian volcano eruption in 1600 led to a famine in Moscow years later, depicted in this 19th-century engraving.

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During a Plinian eruption — when a volcano is powerful enough to eject a column of sulfur and dust into the stratosphere — the particles shoot up and spread out to an umbrella-like plume. The cloud of matter scatters incoming sunlight, cooling the Earth below. Over time, this cooling effect decreases global temperature.

It’s a straightforward concept: the Sun’s light shining on Earth hits the dense sulfuric clouds and reflects back into space, leaving the shrouded land below to cool down. Imagine sitting underneath a gazebo on a hot sunny day, and the temperature differentiation between shade and Sun.

This effect, known as “radiative forcing,” is interesting to a subset of climate scientists as it offers a potential Hail Mary option to a modern global warming problem.

During the 1991 Mount Pinatubo eruption, 15 million tons of sulfur dioxide were released into the atmosphere, cooling global temperature by 0.5°C. The relatively mild eruption, paired with mankind's advancements in technology and food security, helped solidify the idea.

To counter swiftly rising temperatures, some scientists proposed geoengineering the atmosphere using solar radiation modification (SRM). Retrofitted planes would release sulfuric aerosol clouds into our atmosphere, mimicking a volcano’s planetary cooling clouds and countering rising temperature. To its advocates, SRM is cheap, easy to do, and it can be done on a global scale. Whether or not you think it is brilliant, SRM is definitely controversial.

Ash raining on Arequipa during the eruption of Huaynaputina in 1600.

Public Domain

Even SRM proponents aren’t necessarily “fans.” In a New York Times Op-Ed, David Keith, Applied Physics professor and lead developer of Harvard’s Solar Geoengineering Research Program, phrases the argument thus: “What’s the Least Bad Way to Cool the Planet?

The Union of Concerned Scientists, a scientific watchdog agency, meanwhile, has recommended “a precautionary approach.”

The Intergovernmental Panel on Climate Change sits on the fence, while the National Academy of Sciences proposed deeply prefaced research, warning of the potential catastrophes regarding mismanagement, and even climate warfare.

Fear of mismanagement has stunted research for now, but given SRM’s low barrier to entry and the gathering sense of climate doom it may not be a matter of when SRM will be used, but how SRM is used.

Environmentally speaking, it’s unknown if increased cloud coverage would uniformly cool the planet or just exacerbate problems in local areas. Some scientists worry about disrupting India's monsoons, for example, which feed billions of people; or reducing rain around the equator. Others are concerned about ocean acidification from falling sulfuric particles. Computer simulations are limited by restrictive budgets, and federal funding for research is nonexistent.

The science, and subsequently scientific opinion, is hazy due to a general lack of peer-review opportunities. It’s why, in 2021, the National Academy of Sciences called for $100 million in research funding, and why some diehards like Keith are pursuing studies despite blowback.

“We have got all the complexities of bias of who believes what and so on,” Keith tells Inverse.

The science of SRM

A volcanic eruption in 536 (and the darkness and famine that followed) may have contributed to the fall of the Roman Empire.

Heritage Images/Hulton Archive/Getty Images

Now, Keith splits his time between leading Harvard's Solar Geoengineering Lab and advising Bill Gates on climate policy, namely SRM. (Gates is now one of many funding the Harvard Solar Geoengineering Lab). His current research, he explains, contradicts earlier theories about SRM’s ecological effects.

“All the early papers suggested solar geoengineering may reduce droughts, and almost all recent reporting, including the front page of headlines of The Guardian, suggest it causes droughts. So it gives you a sense of the total disconnect of how this is written about and what the actual science says,” Keith says.

What does the science say? It’s complicated.

Trying to determine the effects of SRM costs money. A lot of money.

When creating SRM simulations, researchers are hampered by cash. To obtain data, and run a simulation with enough computational power, the expenses alone are stalling radical research. “We only get to do some simulations, we have to try and make them count,” says Walker Lee, a solar geoengineering researcher at Cornell’s Sibley School of Mechanical and Aerospace Engineering.

“In a perfect world, we wouldn't need solar geoengineering.”

Since SRM is a “problem-solving” question, the simulations themselves are formed around objectives, not hypotheses. What will happen if we need to reduce by .5°C or 1.5°C, and what does optimal SRM look like?

“We can figure out how to optimize solar geoengineering,” says Lee, “but optimization is kind of a misleading term as it implies that there's the best answer or a right answer. That is inherently subjective.”

“Whatever the best answer is, or the best solution or the best climate state is going to depend on who you ask. And so rather than trying to pick up the best one, we usually pick a goal that would be reasonable. Then see how hard it is or how easy it is to reach that goal, how much sulfur we need in the climate model, and then what happens to the rest of the climate.”

It’s a process further hindered by an inability to conduct real-world trials. And though, Keith fairly points out that “hundreds of little experiments you could do,” Lee acknowledges, “You certainly couldn’t put the shaving cream back in the bottle, metaphorically speaking. Once the aerosols are there, you wouldn't be able to do anything but just sort of wait for them to disappear.”

The eruption of Mount Pinatubo on June 15, 1991 was the second-largest volcanic eruption of the twentieth century.


Opponents of SRM are easy to find within academia and politics. In a January 2022 letter in WIREs Climate Change journal, 60 researchers and academics called for an “international non-use agreement” on not only SRM technologies but SRM research in general. The consortium called for a ban on outdoor experiments or deployment of aerosols, a prohibition of national funding, and a refusal of patents.

One of its signatories, Sheila Jasanoff, an expert on science policy at Harvard’s Kennedy School of Government, tells Inverse pursuing SRM is "potentially planetary quality of life-changing technology.” It’s not necessarily a good thing.

“The people who want to insist on a basic science-applied science divide and want to say, right now all they're doing is basic science, and that should be free because we're not deploying, I think that's a somewhat either naive or disingenuous point,” she says.

“Because after all, why are these basic science things being done? What needs to be decided is: is this a pathway that we should be going down?”

“Far more attention is being paid to the technology found than the social infrastructure of ensuring responsibility in the uses of these technologies. That asymmetry is something that needs to be addressed,” she adds.

It’s an honest response to the canyon between applied sciences and SRM opponents.

“You certainly couldn’t put the shaving cream back in the bottle.”

Are we politically prepared to implement SRM? Small countries will likely not be given the reins to implement SRM, and are often those most affected. But, given the low costs, and relatively easy technology, there is no stopping them. The international community is struggling to understand how SRM could be monitored and by whom. In a 2021 paper, the United Nations addressed solar geoengineering, but “the report makes no recommendations on whether to use either method.”

Some opponents believe SRM will negate solution-based approaches such as carbon extraction and emission mitigation. SRM is easier, cheaper, and quicker than carbon extraction, which involves complex air filtering technology or decades of reforestation.

Even more fear the nature of SRM research funding, with Bill Gates and other private billionaires writing checks. “Given the great disparities and wealth, and the huge concentrations of wealth in a few hands, we should be having the debate to what extent should foundations be allowed to sidestep governmental policy,” says Jasanoff.

“Bill Gates has been a major supporter of geoengineering and, you know, with the best intentions in the world, but that's not the point. The point is that by channeling money through the private sector, you avoid deliberation, and you avoid decision points at which you might come up with conclusions or constraints.”

A drawing of Mount Vesuvius from 1896.

Grafissimo/DigitalVision Vectors/Getty Images

Unfortunately, humanity is at an impasse: As emissions rapidly increase, do we have time to mitigate climate change through carbon extraction technology, emissions limits, and green energy, or must we go on the offensive?

“In a perfect world, we wouldn't need solar geoengineering, but there is a nonzero probability that climate change is going to hurt really, really badly,” Lee says.

NASA currently estimates, “global temperature is on track to rise by 2.5 °C to 4.5 °C (4.5 °F to 8 °F) by 2100” — far past the +1.5 °C scenarios the Paris Accord laid out. And, faced with the reality that even if reaching net-zero emissions was possible in the near-term future (it isn’t), it’d take many millennia for Earth to absorb excess greenhouse gases. If humanity stopped producing carbon today, the Earth’s temperature would still increase far past +1.5 °C by the early 2030s. The consequences: 70 to 90 percent of coral reefs lost, 25 percent of all marine life gone, sea levels will rise 1-3ft. risking 4 million US lives, and “once in a lifetime” storms will become commonplace.

“Based on where we are right now and the projections for the future, and regardless of whether you account for past patterns of human behavior, we are not guaranteed to reach a world with less than 1.5 degrees of warming,” says, Lee.

“And when or if that happens, what are we going to do?”

How to Save the Earth: On Earth Day 2022, Inverse explores some of the most ambitious, exciting, and controversial efforts to save our planet.

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