Why a Startup’s Controversial Experiments to Cool the Earth Are on Pause

Make Sunsets, a company behind a recent controversial effort to cool the earth by releasing particles of sulfur dioxide (SO2) into the upper atmosphere to reflect incoming heat, is canceling its upcoming experiments in Mexico, following a rebuke from the Mexican government.

“We have decided not to do launches in Mexico until we come up with a way to collaborate with the Mexican government,” Luke Iseman, the company’s founder, tells TIME in reaction to Mexico announcing on Jan. 13 plans to ban geoengineering. “We want to be working hard with government partners to buy us time for others to solve the shared challenges that we have to prevent catastrophic warming.”

The two-person company made news in the climate world last month when the MIT Technology Review reported that they had launched weather balloons containing helium and SO2 in the Mexican state of Baja California last spring—the first recorded attempt to alter the stratosphere in the name of climate action.

The intent was that the balloons would burst when they reached the upper atmosphere and release the SO2, which would theoretically reflect solar radiation back into space. Such methods, known as stratospheric solar geoengineering, are one of the most controversial areas of study in the climate world, due to the possibility of large-scale SO2 releases affecting global weather and agriculture in unpredictable ways. Many environmental activists are also opposed to the possibility, arguing that geoengineering constitutes a moral hazard, since polluters could conceivably argue that it gives them license to continue emitting planet-warming greenhouse gasses.

Following news of the Make Sunsets launch, the Mexican government issued a press release saying that it would “prohibit and, where appropriate, stop experimentation practices with solar geoengineering,” citing a lack of international agreements and a 2010 UN moratorium on the practice. The announcement also noted that the startup had not consulted authorities before it carried out the experiments.

“It was surprising that people feel like we’re trying to sneak around some law when that is not the intent,” Iseman says. “There doesn’t appear to be some permit that I should have filed for and did not.”

Experts say that Make Sunsets’ SO2 release was small enough not to constitute an environmental danger, but many have criticized the company for attempting to profit off largely untested science. Make Sunsets sells $10 “Cooling Credits” on its website in exchange for releasing a gram of SO2 into the stratosphere, which it claims will correspond to eliminating the warming effect on one ton of carbon dioxide emissions for one year.

One of the concerns about geoengineering is the possibility that individual countries or even lone actors might take up the practice of their own accord, attempting to alter the climate without global buy-in or robust scientific support, a possibility that Make Sunsets might seem to illustrate.

Iseman, for his part, argues that there is no time to wait to pursue last-ditch climate efforts. He is hopeful that he can find another country more supportive of his work. “If someone, somewhere in the world wants to launch a balloon with us, I hope they reach out,” he says. “And if they are a government, I will bend over backward to be on the next plane to visit them.”