Buyer beware: there’s a dubious new kind of climate credit for sale.

Traditional carbon offset credits, say, for planting trees or protecting forests, have a record of failing to actually reduce greenhouse gas emissions. Now, a startup is selling credits for its attempts to manipulate the planet’s ability to reflect sunlight, a controversial response to climate change called solar geoengineering.

A group of prominent scientists published a letter yesterday that warns that this kind of climate intervention is nowhere near ready to be commercially deployed and probably never should be. A big name on the letter is James Hansen, a former NASA scientist who’s now at Columbia University and is famous for sounding the alarm on climate change in a 1988 testimony to Congress.

The letter advocates for more research into the possible impact of solar geoengineering, which could minimize some of the dangers brought on by climate change or perhaps cause new problems. Given that uncertainty, the scientists stop short of actually endorsing solar geoengineering as a tactic for fighting climate change. They don’t think it should be implemented without a “comprehensive, international assessment” of its potential effects and “international decision-making” on how to use such technologies.

The statement comes after embattled solar geoengineering startup Make Sunsets attempted to release reflective particles into the atmosphere from Reno, Nevada, this month and from Baja California, Mexico, last year. The idea is to mimic the way debris from volcanic eruptions reflects solar radiation, which has temporarily cooled the planet in the past. What this actually looks like is a couple of co-founders lighting up fungicide on a grill, using the resulting gas to fill up weather balloons with reflective sulfur dioxide particles, and then releasing the balloons.

Make Sunsets sells “cooling credits” at $10 per gram of sulfur dioxide it releases. Each gram is supposed to offset “the warming effect of 1 ton of carbon dioxide for 1 year.” But the company isn’t having any measurable impact on the climate. To start, it’s released too little sulfur dioxide to make a difference against the billions of tons of pollution released each year by burning fossil fuels. And Make Sunsets hasn’t been able to collect concrete altitude data on the five balloons it’s launched so far, so it doesn’t know whether the reflective particles it released even made it to the stratosphere where they’re supposed to do their job.

Make Sunsets’ balloon launches have mostly succeeded in pissing people off who actually want to see more legitimate research into geoengineering. “There can be no room for selling snake oil,” says a February 13th press release from the nonprofit SilverLining that supports geoengineering research. “SilverLining strongly condemns Make Sunsets’ rogue releases of material into the atmosphere and its efforts to market fraudulent ‘cooling credits’.”

Mexico said it would bar solar geoengineering experiments following Make Sunsets’ balloon launches there. The move was meant to protect nearby communities and the environment, according to Mexico’s Secretariat of Environment and Natural Resources. Releasing a lot of sulfur dioxide has the potential to trigger acid rain, irritate people’s lungs, and even worsen the Antarctic ozone hole. There are still too many unknowns when it comes to potential side effects.

Even if scientists gain a better understanding of what impact solar geoengineering might have and decide that the benefits outweigh the risks, it’s still too risky to monetize. “It likely will never be an appropriate candidate for an open market system of credits and independent actors,” the letter published yesterday says, because it “does not address the cause of climate change.”

What’s causing climate change, of course, is greenhouse gas pollution from all of our fossil-fueled power plants, factories, and gas-guzzling vehicles. Humanity’s failure to slash that pollution is what got us into the conundrum that has some scientists considering a move as drastic as geoengineering now. Carbon credits, whether they’re from solar geoengineering or more traditional tree planting schemes, don’t do anything to prevent that pollution.

Sure, trees can take in and store planet-heating carbon dioxide. But when they die, burn, or are cut down, they release it again. It’s not a permanent fix. Neither is the kind of solar geoengineering Make Sunsets is attempting. Sulfur dioxide doesn’t linger very long in the atmosphere, which is why the startup’s $10 credit is only supposed to represent a year’s worth of cooling.

So if you want to make an impact this way, you have to develop a habit. If it’s ever effective at scale, this kind of climate intervention becomes addictive. Once you stop injecting reflective particles into the atmosphere, the world starts to heat up again — fast. Even volcanic eruptions that spewed enough sulfur dioxide to affect global temperatures have had a short-lived impact. The 1991 eruption of Mount Pinatubo cooled Earth’s surface for about two years.

The world is already struggling to kick its fossil fuel habit. Credit can be addictive, too. And if we’re not careful, we could squander what little time we have left to take real action on the climate crisis before it grows much worse.

“I wholeheartedly agree with most of this letter: more research is desperately needed,” Make Sunsets founder Luke Iseman says in an email to The Verge. “The question to me is what we do in the face of uncertainty. Do we take action we know will create cooling and hence save lives, or do we wait for some international consensus that may never come?”

There’s no evidence to back Iseman’s claims about geoengineering saving lives. But there’s plenty of evidence that switching to clean energy can.