In early March, Hailey Summers helped publish a study that quantified the greenhouse gas emissions produced by commercial indoor cannabis cultivation. For the next few weeks, journalists called the Colorado State University Ph.D. candidate’s phone nonstop, trying to get an interview about the paper’s findings.    

“I am a nerdy engineer who sits at home and programs all day,” Summers says. “So it has been cool, but it has also been a learning experience. You don’t get professional training on this. I’ll just say that.”

The study, on which she was the lead author, was picked up by media outlets far and wide. “Indoor Weed Farms Are Hotboxing The Planet,” declared Gizmodo. “Cannabis cultivation has an enormous carbon footprint, study finds,” read a headline in Yahoo Finance. Even India’s Hindustan Times ran a story titled “Does Smoking Cannabis Fuel The Climate Crisis?” And although the answer is a definitive yes according to Summers’ paper, she’ll be the first to tell you that’s not exactly news. 

“I didn’t blow the lid off of anything,” she says. “The industry knows. Their electricity and natural gas bills speak for themselves.”  

But the study did finally put a number to what the industry already knew. To do so, Summers created a model that calculated how much energy warehouse growing operations across the country use to mitigate the weather outside. Then she compared those numbers against the grid mix—which sources are used locally to generate electricity, whether hydroelectric, natural gas, nuclear, or coal—to estimate the local greenhouse gas emissions. For a complete picture, the model also incorporated the greenhouse gases created “upstream” in the manufacturing process to produce things such as fertilizer. 

The results? One kilogram of dried cannabis produces between 2,283 to 5,184 kilograms of CO2, depending on the region where it was grown. Put another way, producing one ounce of dried weed is equivalent to burning seven to 16 gallons of gasoline, according to Smithsonian Magazine. Colorado’s variable weather and mixed power grid mean it’s one of the worst offenders. Marijuana cultivation accounts for an estimated 1.3 percent of the state’s total greenhouse gas emissions.    

The easy fix would be shifting from indoor grows—which require massive amounts of energy to power the high-intensity lights that feed the plants, as well as to cool down those lights—to outdoor grows. Doing so could reduce greenhouse gas emissions by as much as 96 percent, according to the study. But making the switch is easier said than done, according to Alex Levine, chief development officer and co-owner of local cannabis retailer and cultivator Green Dragon.

There are security concerns; there are also strict zoning laws. Most Colorado counties also have a ban on outdoor marijuana cultivation, and areas that do allow it are far from needed infrastructure like electricity or natural gas lines. Ultimately, Levine says, regulations have made indoor grows the path of least resistance. 

Even so, there’s a perception that the cannabis industry would prefer to grow indoors anyway. One expert on solar-powered greenhouses, who was quoted by The Weather Network in a story about the study, said that he wasn’t surprised that marijuana’s greenhouse gas emissions were so high because the industry’s massive profits mean there’s little incentive to change. 

Not so, Levine says. “Nobody in their right mind wants to grow indoors. Sometimes you read these articles, and they make it seem like the industry is just, ‘Oh, we’re so happy we are indoors.’ Believe me, no one is happy with a $200,000-a-month electricity bill.”   

While opening up more land to outdoor cannabis cultivation may be the best solution, Levine and Summers both say it’s not the only one. Colorado currently doesn’t have any regulations requiring energy-efficient practices for indoor grows, such as mandating LED lights. Levine also pointed out that cannabis cultivators aren’t eligible for things like the Colorado Commercial Property Assessed Clean Energy program which helps businesses finance environmentally friendly improvements, like adding roof-top solar panels, because the program is underwritten by the federal government. And his company knows a thing or two about being green. It was one of the first cultivators to integrate solar-powered greenhouse designs into its operations. 

State and local municipalities have taken some steps to address the issue. In 2018, for example, the Colorado Energy Office (CEO) released a report that assessed the industry’s baseline energy and water usage and outlined improvements that could be made. Those findings then led the CEO to partner with local electric cooperatives and municipal utilities in a pilot program that provided free energy-use assessments for cannabis cultivation businesses in 2020. 

A spokesperson for Governor Jared Polis says addressing the environmental impact of Colorado’s legal weed industry is a priority for the current administration and that the Cannabis Cabinet, one of the state’s seven cabinet-level working groups, is focused on “reducing energy use and implementing energy-efficient upgrades by regulated cannabis cultivators over the next fiscal year.” But when asked what that might look like, the spokesperson didn’t provide any further information. 

Summers also isn’t sure what the industry’s future could be. “There just aren’t enough solutions yet. What we needed was this study to truly quantify it and then get the gears turning about what actually needs to change,” she says. “I think  we should be paying attention to it now so that these best practices become standard, or it will only continue to get worse, right?” 

Levine agrees. “[The current situation] is sort of untenable. The cannabis market in this country is only growing, and energy usage is not going to go down until this gets solved,” he says. “Lawmakers need to start having more sober discussions like, ‘OK, cannabis is not going away, and it’s an important part of our economy. Let’s treat it like it is a respectable industry and not some criminal enterprise.’”      

Nicholas Hunt
Nicholas Hunt
Nicholas writes and edits the Compass, Adventure, and Culture sections of 5280 and writes for