Humans have found it hard to quit fossil fuels, which is why some argue that we’ll soon need to start geoengineering — that is, modifying the atmosphere to prevent catastrophic warming of the planet.
The practice is controversial. Some argue it’s the only solution given that we’ve waited too long to reduce carbon emissions. Others say we shouldn’t be running two uncontrolled experiments on the Earth’s climate (the first being the global burning of fossil fuels).
That hasn’t stopped people from trying. And one approach championed by Make Sunsets has drawn the attention of the U.S. Environmental Protection Agency.
The startup is basically two guys from Silicon Valley who have been releasing weather balloons filled with hydrogen gas and sulfur dioxide particles. When the balloon floats somewhere past 66,000 feet in altitude, it bursts and releases the sulfur dioxide particles, which scatter and reflect sunlight, cooling the Earth a tiny bit.
The company sells “cooling credits” based on how much estimated warming each balloon release negates. Make Sunsets has raised $750,000, according to PitchBook, and the startup says its investors include Boost VC, Draper Associates, and Pioneer Fund.
Neither founder is a scientist, but the science behind sulfur dioxide and solar reflectivity is sound. Humans accidentally proved the importance of sulfur dioxide in global albedo — the average reflectivity of the Earth’s surface — when they slashed the sulfur content of marine shipping fuels in 2020; one prominent climate scientist has argued in favor of the practice.
Still, given the complexity of the global climate, it’s not clear what other effects the practice might have. It might seed rainstorms in one region while depriving other areas of rain. Several scientists have urged caution.
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San Francisco | October 27-29, 2025 REGISTER NOWPlus, if sulfur dioxide particles drift closer to ground, they could aggravate people’s asthma and cause other respiratory problems. Here, the EPA takes issue with Make Sunsets’ approach to geoengineering. Sulfur dioxide is regulated as an air pollutant. EPA Administrator Lee Zeldin said this week that the agency is investigating the company.
Make Sunsets argues its actions are legal. In an FAQ on its website, the company says, “Yes, our method to cool Earth falls under the Weather Modification Act of 1976 and report yearly to NOAA of our deployments as required.”
The law is fuzzy here, though. When it was written, the Weather Modification Act was likely intended to cover the practice of cloud seeding, in which particles like silver iodide are shot into clouds to induce rain or snowfall. Most weather modification today is done by entities like ski resorts and irrigation districts in the West. It’s not clear how the law applies to climate modification.
Still, while the EPA might be justified in its investigation, it isn’t exactly consistent with Zeldin’s approach to pollution.
The agency’s efforts to boost coal are likely to generate far more sulfur dioxide pollution than Make Sunsets will release with its balloons. A Make Sunsets balloon released on November 15, 2024, released 1,715 grams of sulfur dioxide. In 2023, U.S. power plants released 650,000 tons into the atmosphere, the majority of which came from coal. That’s approximately the same amount as 343,900,000 of the startup’s balloons.