This company wants to cool the planet one balloon at a time. Some scientists aren’t buying it

Luke Iseman has a plan to cool the planet, inspired by a science fiction novel, using balloons full of heat-reflecting sulfur dioxide launched into the Earth’s stratosphere.

“To me, the question is whether doing nothing is better than doing something, given the reality we’re confronted with,” said Iseman.

Iseman and Andrew Song are co-founders of a company called Make Sunsets, a solar geoengineering startup that operates out of northern California. Its customers pay to have the company launch balloons full of sulfur dioxide (SO2) into the stratosphere, where it then releases the gas. Make Sunsets sells its SO2 by the gram.

In return, the customer receives what the company has dubbed “cooling credits,” which Iseman says indicates the customer is doing a small part to help cool the planet. 

As of October, the company has launched 90 balloons containing a total of just under 65,000 grams of SO2 to more than 600 customers.

But Iseman and Song’s idea has drummed up backlash and controversy. Although Make Sunsets says it isn’t releasing a large amount of SO2, scientists worry about the possible long-term effects of releasing sulfur dioxide into the stratosphere. Some say more research is needed, while others believe geoengineering shouldn’t even be an option. 

“The scientists can keep criticizing us. But at the end of the day, we are changing hearts and minds. And more people know about stratospheric aerosol injection than they did two years ago,” said Song.

How it started

Iseman got the idea for his balloons from a novel he was reading called Termination Shock by Neal Stephenson. In it, a billionaire decides to launch sulfur-filled rockets into the atmosphere in an effort to cool the earth. 

It introduced Iseman to the real-life story of Mount Pinatubo, a volcanic eruption in the Philippines in 1991. That eruption released sulfur dioxide into the atmosphere, cooling the Earth by half a degree Celsius for about two years. 

Research from the Quarterly Journal of Economics at Oxford Academic, which analyzed the positive effects of emissions reductions, says that half a degree of cooling could prevent hundreds of thousands of heat-related deaths a year.

“If we could copy this natural occurrence, we’d have to do it every year to maintain temperatures like that, but to me, that’s such a no-brainer,” said Iseman. 

At Make Sunsets, the balloons are launched into the stratosphere, which is the second layer of the earth’s atmosphere as you go up. Then they explode and expel either helium or hydrogen, depending on what was used to fill the balloon, mixed with sulfur dioxide. That becomes sulfuric acid, which reflects sunlight.

The company claims to speak regularly with leading scientists in the field, but declined to share any names. 

David Keith, a professor of geophysical sciences and director of the Climate Systems Engineering Initiative at the University of Chicago, believes  there could be a space for this type of geoengineering, with further research into the topic.

Despite that, he doesn’t support Make Sunsets, he said.

“After I talked with them early on, after I found what they were doing, I stopped talking to them because I don’t think they are doing anything interesting. I just don’t.”

However, he does say the science is sound.

Sulfuric acid takes that sunlight and the heat associated with it, and bounces it back into space, he says.

But he estimates that you’d need to put at least a million tonnes of SO2 in the stratosphere annually to continually cool the planet by half a degree. 

Make Sunsets balloons contain a little over a kilogram, meaning you’d need a billion of those launches every year to hit that target.

The company’s website claims that one gram of sulfur dioxide released in the stratosphere cools the planet enough to prevent the annual warming of one ton of carbon dioxide. That number came from public statements and articles by David Keith and a research paper by another scientist. 

Keith says the cooling calculation is a “very rough number,” so not something anyone should be using as a basis for a business. 

The controversy

While scientists agree that sulfur can play a part in cooling the planet, some believe there needs to be more research into the long-term effects first. Others believe it shouldn’t even be considered.  

Keith says we need to consider the fact that, at the end of the day, sulfur is a pollutant. 

According to his research, releasing sulfur dioxide into the stratosphere at the level needed for half a degree of cooling would also lead to thousands of premature deaths annually as a result of air pollution and ozone depletion, which causes higher skin cancer rates. 

“What is the ratio of risk to benefits? So nobody has the right answer. Nobody knows what’s the right amount. It’s a matter of public policy, not science. Obviously for a lot of people the right amount is zero,” said Keith.

Shuchi Talati, founder and executive director of the Alliance for Just Deliberation on Solar Geoengineering, says Iseman is right to an extent. Incidents like the eruption of Mount Pinatubo have shown that sulfur can help lower Earth’s temperature.

“What we don’t know is how these impacts affect other things like precipitation, weather patterns, public health, biodiversity — especially if you use them for a long time,” said Talati.

Raymond Pierrehumbert, a physicist from the University of Oxford, says another problem is that we’ve already released so much carbon dioxide in the atmosphere, which isn’t going anywhere on its own anytime soon. He says releasing SO2 into the stratosphere is a Band-Aid solution. 

And it’s one the world would have to commit to. 

“If you become reliant on solar geoengineering to keep the earth habitable, you’re really committing all future generations to doing this essentially forever. And if they ever stop, then the Earth will heat up very rapidly,” said Pierrehumbert.

That rapid warm-up is called termination shock, which is where the novel by Neal Stephenson got its name.

“There are many problems with solar geoengineering, but the termination shock to me seems like the big show-stopper,” said Pierrehumbert.

Then the warming impacts over the past few decades would be replicated again, except they would happen rapidly, in the span of just a year or two. Pierrehumbert says that rapid warm-up would be a “huge catastrophic threat,” but more research is needed into the damage it would do. 

Further research

While Keith says there needs to be careful consideration of how geoengineering is done, he believes there could be a space for it. He is one of more than 100 academics who signed an open letter calling for more research into solar geoengineering last year.

He has tried, and so far been unsuccessful, to get outdoor research off the ground. But he says he’s not sure it’s even necessary, as almost all solar geoengineering research is based on computer-generated climate models, which may give us enough information. 

Some countries have committed to looking further into the potential of geoengineering, including the U.S. and Canada. 

Pierrehumbert, on the other hand, believes it isn’t even worth looking into. 

He is one of more than 500 academics who signed the Solar Geoengineering Non-Use Agreement in 2022. It calls for a global ban on all forms of the technology, including outdoor field experiments and research.

“The argument that we need to do these outdoor experiments in order to learn what would happen, that’s just completely fallacious, I think [it’s] just a smokescreen for developing the technology,” said Pierrehumbert.

Talati agrees that there needs to be continued effort to cool the planet, and that geoengineering could be a pathway to that. But like Keith, she believes more research is needed. She also says it shouldn’t be in the hands of businesses. 

“I think private companies should have no role in this space. And the notion that there’s a company out there doing this and trying to profit off of it, which they are by selling cooling credits, is offensive.”

Make Sunsets

While Make Sunsets is experimenting with the technology, it isn’t running any sort of scientific experimentation or studying the impacts of what it’s doing, and doesn’t intend to.

But it is creating a conversation around geoengineering. 

“It’s a kind of performance theatre that gets people talking about it. In that sense, it’s worked. And whether that ultimately helps move the policy along or not, I’m not really the right expert to say,” said Keith.

Iseman understands there’s some skepticism about what he’s doing. But he says we need to try everything we can to cool the planet. 

“Yes, any interference with nature we should be suspicious of. But the sad truth is that we’ve been geoengineering the climate for at least the last several hundred years with our carbon emissions,” said Iseman. 

“We can’t suddenly decide to get cold feet about taking this and many other measures to address the climate emergency.”

Iseman says his balloons are safe and legal, and they are going to keep making them. In fact, he hopes to make them bigger.

“Our mission is to cool Earth as quickly as we safely can, whether that’s us or someone else. I’m fine going back to semi-retirement, as soon as the responsible adults show up and start doing what needs to be done.”