Future Tense

To Make Cannabis Green, We Need to Grow It Outdoors

Bright lights shine on tall marijuana plants indoors.
It takes a lot of energy to grow cannabis indoors. Josep Lago/Getty Images

Cannabis may look green, but the environmental metaphor mostly stops there.

Virginia—the latest state to approach full legalization—and the 46 others that have implemented some degree of liberalization all share the dubious honor of doing so with little or no consideration of environmental consequences, particularly those stemming from the prodigious energy use associated with indoor cultivation. In one mind-boggling illustration of this, a new study says that Colorado’s cannabis industry emits more CO2 than its coal industry.

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The Biden administration thus faces an acute disconnect between drug policy and environmental policy. Let’s hope it nips the cannabis carbon bomb in the bud before recent pushes from the House and Senate—together with a stock-trading frenzy—usher in a full-on national market.

The cultivation of cannabis has long prompted concerns about water, land use, and pollution. Now, questions about energy have come to the fore. Once the domain of barefoot gardeners, millions of pounds of cannabis—the nation’s highest-value cash crop—are now produced each year in Walmart-sized, windowless, energy-intensive factory farms. More than 40 percent of producers grow exclusively indoors. To some extent, this is a holdover from the stealthy black-market days, but it also provides farmers shelter from some of nature’s hazards, allows five or more harvests each year, and is easier to mechanize in the name of a more uniform and predictable product. Investors seem to love the glitzy multimillion-dollar ventures more than tractors, compost, and blue sky.

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Electric lights brighter than the sun and air-conditioning systems big enough to chill data centers make for a massive carbon footprint. One enormous planned cannabis “industrial park” in California seeks to enclose 55 acres—25 city blocks—powered by a private fossil-fuel power plant generating enough electricity to run 90,000 homes. It’s energy up in smoke.

A decade ago, I estimated that indoor cannabis cultivation across the U.S. was inhaling $6 billion in energy each year while exhaling carbon emissions of 3 million cars. A recent study I conducted suggests the average smoker in Colorado, the country’s highest per-capita usage state, unwittingly increases their household’s carbon footprint by 60 percent. There are always uncertainties in such numbers, but a major issue remains irrespective of whether the underlying energy use is half or twice these levels.

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Many have reasonably speculated that the carbon footprint should be dropping quickly, thanks to ostensibly more efficient cultivation methods. But the latest and most thorough peer-reviewed work on this suggests this is probably not the case.

Despite having decades to get organized since state-level legalization began back in 1999, policymakers have been ham-handed in addressing this threat to the climate. California is among the biggest and most surprising offenders. Indeed, many jurisdictions structure regulations in ways that favor indoor cultivation, such as setting license fees by the size of the growing area (yields are higher per square foot indoors) or by requiring that cultivation be co-located with (typically urban) retail sales. Others forbid outdoor cultivation altogether, including all of Illinois, where one can find massive indoor grow facilities plunked onto beautiful farmland. Massachusetts has only recently begun to allow it, the first trials meeting with success despite the northern climate.

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Even in legal states, black markets thrive by serving out-of-state demand, their ranks actually swelling with once-legal producers worn down by red tape and fees. Black-market indoor production tends to be far more carbon intensive, often powered by large, dirty diesel generators and heated at night with gas or oil furnaces.

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In the shadow of well-funded indoor operations, outdoor growers face an uphill battle. Utilities offer multimillion-dollar energy-saving “rebates” and cheap industrial rates to indoor growers, in effect subsidizing their energy use while putting outdoor growers at a competitive disadvantage. Adding insult to injury, budtenders at most dispensaries tend to toss outdoor-grown product onto the bottom shelf (not to mention taking a pass on environmental labeling), and advocate instead for indoor. This has the effect of suppressing demand and price for outdoor-grown, in turn making indoor-grown more profitable.

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States have largely dropped the ball and environmental groups seem to be missing in action, perhaps concerned about disturbing what is a sacred cow for many of their constituents. Mainstream journalists have barely covered this story. And national leadership has been conspicuously absent. Instead, criminalization at the federal level continues to drive cannabis indoors and underground. There has been no federal energy R&D or policy work to address the problem or identify best practices. As a result, the cannabis industry finds itself decades behind other sectors, passed over by energy programs and policies put into place in the wake of the oil crises of the 1970s. Meanwhile, the ongoing illegality of interstate transportation requires each state to host its own cultivation, irrespective of climate. Cultivation energy requirements vary by more than two-fold depending on location. Imagine the absurdity of forcing pineapples to be grown in frozen Alaska or sweltering Arizona.

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Beyond carbon, other concerns about indoor cultivation include destabilization of power grids, burdens on local water supply and water treatment infrastructure, worker safety, and mountains of solid waste–soil or artificial growing media are generally not reused, and the most common lights contain toxic mercury. Furthermore, air pollution from indoor grows, which are often located in densely populated areas, is increasingly a concern, particularly in Denver, which has more than 600 permitted indoor grow facilities. The problem is related to cannabis terpenes—among the more reactive volatile organic compounds released during cultivation and processing. They are said to offer health benefits, but their presence in the air also appears to exacerbate existing pollutants, such as ground-level ozone and particulates.

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Advocates of indoor growing tend to rely on largely debunked arguments to support their case.

They say that indoor growth results in product that has stronger medicinal or recreational effects. But the feds grow 98 percent of their research-grade medical cannabis outdoors. (Yes, it is a much smaller amount than needed for the medical market, but it shows that indoor cultivation isn’t necessary.) Meanwhile, indoor cannabis uses more energy than all other pharmaceutical manufacturing. Let’s not forget that climate change itself compromises health and well-being. When it comes to recreational cannabis, lab tests, seasoned experts, some retailers, and thousands of boutique outdoor growers have shown that cannabis cultivated outside can bring both quality and potency. Finally, advocates of indoor growing claim that their product just looks better. But carefully crafted products grown outdoors are increasingly getting top scores on looks as well. In any case, is slowing climate change truly less important than picturesque weed porn?

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Practical concerns about theft and odor do merit attention. But other sorts of high-stakes outdoor areas are routinely secured, and at far lower cost than constructing a building. Pharma companies grow tens of thousands of acres of opium poppies outdoors, and feedlots are certainly far more skunky, yet tolerated. Once again, outdoor and rural cultivation is the lesser of the evils.

Defenders of indoor operations also offer a host of pseudo-environmental arguments and bandaids. They claim it conserves water and that they can save energy by using greenhouses and solar, or just purchase indulgences in the form of green power generated elsewhere. But running an indoor operation doesn’t just require watering plants—fossil-fired power plants need water to cool them, and hydroelectric dams involve significant evaporation. All of that unseen water to run indoor operations vastly exceeds that used to irrigate outdoors. Perhaps surprisingly, the efficiency of artificial heating, cooling, and supplemental lighting in greenhouses isn’t sufficiently better than in windowless facilities. One can’t put solar panels on a greenhouse roof, so offsetting carbon is actually harder. The inconvenient truth is that even energy efficient operations with LED lighting, etc., require solar arrays spanning many times their own roof area. Meeting the Zero Net Energy goals and mandates (which call for all energy to be produced by solar or other renewables on-site) that many jurisdictions are embracing for all building types just isn’t practically or economically achievable by the indoor cannabis industry. The energy appetite of cannabis factories is already poised to outstrip all California’s wind energy production. Can we really afford to allow discretionary indoor cannabis to siphon off clean energy needed for activities that can’t be performed outdoors?

Outdoor cultivation has sufficed for five millennia. In a warming world, indoor cultivation is an unessential and unaffordable luxury. It’s incumbent on the new class of federal policymakers to avoid the cannabis carbon trap, which threatens to undermine their much-anticipated and urgent initiatives to rekindle the nation’s climate change strategy.

Future Tense is a partnership of Slate, New America, and Arizona State University that examines emerging technologies, public policy, and society.

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