Is This Climate Tech Start-Up Going Rogue?

Another day, and another weather balloon ascends gracefully into the clear blue skies above Northern California. But this balloon isn’t headed up to the stratosphere to predict the weather—it’s going there to change it.

Make Sunsets is a tiny start-up headquartered in South Dakota that is using balloons to release small quantities of sulfur dioxide into the upper atmosphere, in the hope of reflecting some of the Sun’s energy away from the earth. Each gram of SO₂, says Andrew Song, one of Make Sunsets’ founders, offsets the warming from one metric ton of carbon dioxide released by burning fossil fuels. Not everyone is convinced by Make Sunsets’ methods, however—and many researchers and environmentalists worry the startup’s unregulated operations are disrupting more responsible research into geoengineering, including a prominent effort at Harvard.

Make Sunsets’ name is a reference to the dramatic sunsets that high-altitude SO₂ particles can produce, as seen following the eruption of Mount Pinatubo in 1991. That eruption briefly depressed global temperatures by about 0.2 °C for a year, until the particles slowly returned to Earth.

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The 53 kilograms of sulfur dioxide Make Sunsets has released since February 2023 is the cooling equivalent of planting 2.5 million trees, again for about a year, says Song, although neither he nor anyone at Make Sunsets is a professional climate scientist. “The largest direct air capture facility in the world can only remove about 4,000 to 5,000 tons per year,” he says. “We could do that in literally one session with balloons, without the capital costs. We are only restricted by customer demand.”

Make Sunsets finances its operations by selling US $10 “cooling credits” for launching each gram of SO₂. Customers include both individuals and corporate customers like Numerous.ai, which was looking to offset emissions-related warming from its AI spreadsheet software.

“I believe that stratospheric SO₂ injection is now well-researched enough that the risks associated with it are smaller than the risks of the effects of the temperature rise it prevents,“ says Mehran Jalali, co-founder of Numerous.ai. “Dealing with Make Sunsets was very simple and their answers to my many questions made sense.”

Not everyone is happy with Make Sunsets

But although solar geoengineering promises one of the quickest routes to reducing warming quickly (if only temporarily), not everyone is happy with Make Sunsets. “There’s a lot of disagreement among folks thinking about solar geoengineering, but most agree that Make Sunsets is a bad idea,” says Sikina Jinnah, a professor of environmental studies at the University of California Santa Cruz. Jinnah was also the co-chair of Harvard University’s Stratospheric Controlled Perturbation Experiment (SCoPEX) advisory committee, one of the first efforts to design a governance framework for an outdoor solar geoengineering experiment.

“A couple of rogue tech bros taking action completely outside the scope of government authority or any public engagement are really embodying the nightmare of what folks think this could be,” Jinnah says.

The consensus among most atmospheric scientists is that we have only a very limited understanding of how to inject particles effectively into the upper atmosphere without triggering side effects such as damage to the ozone layer, disrupting weather patterns like monsoons, or causing pollution at ground level. Solar geoengineering could also lock us into having to continue to inject particles essentially forever, in order to avoid the “termination shock” of a sudden temperature rise.

“Slowing down the science has real drawbacks to safety. But if you are selling market credits right now, you’re basically selling hot air.” —Kelly Wanser, SilverLining

“There’s a bunch of science needed to understand how to monitor and detect and regulate this stuff, and to mitigate side effects,” says Kelly Wanser, executive director of SilverLining, a nonprofit focused on near-term climate risks. “Having a bunch of independent actors willy-nilly putting parcels of pollution into the air is almost certainly not the way to do this.”

Make Sunsets has been extremely controversial from the get-go. In January 2023, Mexico announced its intention to prohibit solar geoengineering nationally after learning of the startup’s release of two prototype SO₂ balloons from Baja California. Shortly after, 110 climate scientists published an open letter recommending research in solar radiation management but stating that “it likely will never be an appropriate candidate for an open market system of credits and independent actors.”

Song notes that the Mexican government has not yet followed through on its threat, and dismisses it as “just a bunch of saber-rattling to get a bunch of gringos out of their backyard.” But the company did move its operation to the United States, where Song claims the federal government has not impeded any deployments, and that Make Sunsets is in full compliance with the law.

Rogue actors make solar geoengineering harder for everyone

Jinnah says that Make Sunsets is having a chilling effect on research in the field. “It’s making it much harder for scientists who are doing legitimate research to move through processes of public engagement,” she says.

Harvard’s oversight of its own geoengineering experiment, SCoPEX, did not go smoothly. On the scientific side, its researchers wanted to release a few hundred grams of non-toxic calcium carbonate into the stratosphere and track the way the material dispersed, altered atmospheric chemistry, and scattered light. They hoped this would allow them to improve the fidelity of future solar geongineering computer models. On the governance side, SCoPEX was intended to be a model of transparency, engagement, and open data sharing.

Neither aspect worked well.The group’s initial plan to release material over Arizona was criticized by Indigenous people, and another attempt in Sweden in 2021 was called off after the Indigenous Saami people protested.SCoPEX was finally cancelled in March 2024 and its principal researcher, David Keith, decamped to the University of Chicago.

“I wouldn’t say that Makes Sunsets was directly responsible for the cancellation of SCoPEX,” says Jinnah. “I will say that Make Sunsets made the political and social context surrounding SCoPEX more difficult.”

“A couple of rogue tech bros taking action completely outside the scope of government authority or any public engagement are really embodying the nightmare of what folks think this could be.” —Sikina Jinnah, University of California Santa Cruz

However, the challenges in governing such a controversial area of research go far beyond a few rogue actors. In a recent paper in Science, Jinnah reveals that tensions between and among the research team and her advisory committee also contributed to the project’s demise.

Jinnah notes the disconnect between some physical scientists, who might not feel a small experiment like SCoPEX needs any public engagement to proceed, and researchers in ethics, social sciences, and philosophy. Even if there’s no direct health impact or environmental impact, the social scientists “rightfully bring up that this particular set of technologies is so much bigger than just a small-scale experiment,” she says.

In a recent article in The New York Times, Keith implied that he would seek to avoid any public engagement in future geoengineering experiments, saying: “A lesson I’ve learned from this is that if we do this again, we won’t be open in the same way.”

Jinnah takes the opposite view. “There’s a massive amount of literature in the social sciences that talks about why engagement matters,” she says. “Engagement is a much deeper process of social legitimacy, of adhering to norms of international law. But there has to be broad widespread agreement, and standardization about how we’re going to engage as a community.”

There are efforts to move in this direction. The United Nations Environment Programmereleased an expert review on solar radiation management last year called One Atmosphere. It lays out the case for international governance of the stratosphere, centering on equity, ethics, and consent.

“More than 90 percent of all the public perceptions research about solar geoengineering is done by and about scholars from North America and Europe,” says Jinnah. “There’s this huge gap in understanding of what folks in the most climate-vulnerable countries actually think about this.”

The European Union has just started a multi-million Euro research project called Genie that aims to fill that knowledge gap, while non-profits The Degrees Initiative and The Alliance for Just Deliberation on Solar Geoengineering are also focused on building engagement and capacity globally.

Kelly Wanser of SilverLining sees a benefit to increasing understanding at a grassroots level, perhaps through funding museum exhibits or adding geoengineering to school curricula. However, she’s equally wary of dithering over the smallest experiments while time ticks away. “Slowing down the science has real drawbacks to safety,” she says. “But if you are selling market credits right now, you’re basically selling hot air.”

In fact, says Wanser, SilverLining has submitted a comment to the Federal Trade Commission about Make Sunset’s business, which she describes as false marketing. “We’re at an inflection point because the climate system is getting worse, and people are getting worried,” she says. “Regulators, policy makers, and the general public all have a sense that we don’t know very much about these things. Seeing people selling cooling credits raises more concerns than it helps.”