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Environmentally Unfriendly: Indoor Cannabis Production Is Hotboxing Our Atmosphere

The commercial cannabis industry is flowering. As waves of legislation legalizing adult recreational cannabis use have swept across the U.S., annual revenue from legal cannabis sales has risen by 48% in one year, climbing from $14.4 billion in 2019 to $21.3 billion in 2020. 

While weed has acquired a reputation for being “green,” natural, and eco-friendly, there has been little quantitative data to measure its environmental impact, until now. Recent research published in Nature and led by Hailey Summers at Colorado State University is the first study to quantify the greenhouse emissions from indoor cannabis production across the U.S. 

The authors found that yearly greenhouse gas emissions range from 2,283 to 5,184 kilograms of CO2-equivalent per kilogram of dried flower. To put those numbers in perspective, Summers extrapolated the data in Colorado, where indoor cannabis production accounts for 2.1 million metric tonnes of CO2e per year, a whopping 1.7 percent of Colorado’s total yearly carbon emissions. 

Summers’ research is groundbreaking. The only other study that has attempted anything similar was conducted in 2012, pre-legalization, pre-recreationalization, and pre-commercialization. The 2012 study looked at small-scale facilities and small-scale equipment in California, examining only emissions from energy use, while Summers and her team conducted a life-cycle assessment, accounting for the emissions of all material inputs, such as fertilizer. 

Indoor Cannabis Production Across the Nation

Interestingly, these emissions vary widely across the country. Summers and her team built a model using more than 1,000 locations across the United States, regardless of the legal status of cannabis production and sales, and analyzed the energy requirements in hypothetical grow facilities in all 50 states.

The distribution of energy consumption, natural gas consumption, and emissions was far from uniform, and salient patterns emerged. The Mountain West and Midwestern United States are particularly high in emissions, and the Southern U.S. and Hawaii stand out as major hot spots as well. 

Why the huge variation in emissions? Summers says two major factors are at play: “One is weather, and the other is electric grid mix: how many renewables are in your area’s grid versus [how much] coal.” 

It makes intuitive sense that weather would play such a big role in energy use. Summers explains that indoor cannabis production necessitates high ventilation rates—growers have to constantly bring in fresh air in order for the plants to perform photosynthesis. 

Cannabis requires very specific growing conditions: “If it’s winter in Colorado or Michigan or Minnesota, you can’t bring that air into the grow facility because it will shock the plants. In Florida, you’d need to dehumidify or cool it. You’re playing this game of modifying the weather.” 

And the more growers have to modify the weather and account for seasons, the more energy is required. 

Indoor cannabis production and the environment
The source of energy used in indoor cannabis production plays a role in how sustainable (or not) production in a given area might be.

The other piece of the puzzle is where the electricity comes from. Fossil fuels create a lot more greenhouse gas emissions than renewable energy sources; while all cannabis plants need about the same amount of light indoors, when the electricity comes from coal, the emissions will be a lot higher than if the electricity is sourced from solar or wind, for example. 

“One location might have emissions that are about five times higher [due to grid mix],” says Summers. “That range can really impact an indoor grow because electricity is one of the major inputs.” 

By mapping electric grid mix and weather, we get a much clearer picture of the locations most suitable to indoor growing. 

“California looks really good from our analysis because the weather is relatively stable and their grid mix is really clean: solar, wind, and even some hydro.” 

But the Midwest and Mountain West are more coal-reliant and experience huge temperature swings throughout the year, producing more emissions and requiring a lot of energy to moderate the indoor climate. 

Greening the Industry

If the United States legalized cannabis on a federal level, we could optimize growing locations on a national scale, explains Summers. Right now, interstate transportation of cannabis is banned, so any state that sells cannabis has to produce its own supply. 

In a perfect world, Summers hypothesizes, we’d “push most of the grow to the coasts [because] the emissions from transporting products from the coasts to the middle of the U.S. would be substantially lower than keeping grows in the Midwest.”

Still, federal legalization may be a long way off, so it’s important to focus on the changes that can go into effect immediately. Summers suggests policy solutions such as mandating LEDs, putting a maximum limit on lighting intensity and wattage per square foot, and subsidies for investing in energy-efficient equipment. 

Another solution would be to move more of the grow outdoors for certain products. For example, she explains, edibles can be made from flower grown in a less controlled environment; THC can be extracted from cannabis grown outdoors, and the flower doesn’t have to look as pretty or undergo such rigorous quality control. 

indoor cannabis production
When it comes to indoor cannabis production, the environmental costs of transporting equipment and materials to and from a facility can be enormous.

In order to bring about these types of changes, sustainability has to be strategic. Jake Mitchell, a senior environmental consultant for Resource Innovations, works on building sustainability practices into business and implementing long term plans for sustainability in the cannabis industry. 

One of his current projects involves a partnership with Xcel, a major electricity utility company in Colorado. Indoor cannabis production is energy intensive, and growers often want to make their energy more sustainable and reduce their energy costs, but it can be hard for them to justify those investments up front. 

Mitchell works with Xcel to help growers assess and manage their energy use, and then save more money on their projects and lower their electric costs over time. The utility company funds these evaluations so the service is free to the growers, and Mitchell is able to help build long lasting connections in the industry and make knowledge available to more growers. 

A Sustainable Future

If we’re serious about creating a sustainable industry, we’ll need to do more research. 

“We have really understood the indoor environment,” Summers says, as she and her team now turn their research focus toward greenhouse and outdoor conditions. 

“We speculate that those growth methods would probably have lower GHG emissions [than indoor production] but won’t know for sure until we study it.” 

As more states in the country legalize recreational cannabis, it will be critical for states to look at their practices and projected energy use for cannabis production, and make conscious choices accordingly based on data. While the research from Summers’ team provides a foundational understanding, Mitchell emphasizes that we need more data to drive decision-making. 

“You have to start from a basis of data…. That’s why sustainability is iterative,” he says. 

Mitchell describes the strategy of greening the cannabis industry from the ground up: “Start with the gems at the bottom,” he says, describing the projects with a return on investment that’s easy to capture. 

“Then move up the line until you have this massive chunk of money because of what sustainability has saved you.” At that point, it will be possible to invest in sustainable practices that don’t have a high return on investment, but will create lasting, positive change, he says.

Before he began working on making cannabis more sustainable, Mitchell had been retrofitting other industries for decades, a less feasible approach to lasting change. We’re in a unique position now, says Mitchell, because “this is an opportunity for us to become a sustainable industry from the start… instead of trying to fix the industry in 20 years.”