A Very Green Carbon Footprint

Sometimes psychedelic journeys can produce more carbon emissions than physical journeys.

As it turns out, the production of an ounce (28.3 grams) of dried weed can generate more carbon dioxide emissions than a road trip from San Francisco to Los Angeles. Smoking 10 joints, assuming half a gram of marijuana per joint, emits an amount on par with the climate impact of consuming an 8-ounce sirloin steak. Other than a serving of beef, no animal product even comes close to the carbon footprint of a single marijuana cigarette.

The upstream emissions from legally growing marijuana indoors can reach as high as 5.5 tons of CO2 eq/kg of dried weed, according to research from Colorado State University. This is because of the large amount of electricity required to control the temperature, humidity, and light conditions for indoor cultivation. As such, the exact emissions footprint from growing marijuana indoors varies depending on the climate of the region where it's grown and the carbon intensity of the regional electricity grid. The impressively detailed Colorado State model estimates that the carbon emissions to grow a kilogram of dried cannabis indoors range from 2.6 tons of CO2 eq in Long Beach, California, to 5.5 tons of CO2 eq in Kaneohe Bay, Hawaii. Even the low-end figure of 2.6 tons of CO2 would mean that a pound of marijuana carries a higher carbon footprint than a roundtrip flight from San Francisco to Tokyo in economy class (0.91 tons of CO2).

Is it time, then, for environmental activists to declare a new climate crusade against weed, to accompany the many ongoing crusades against beef, cars, flying, and video gaming? Must eco-socialists who champion more wholesome lifestyles with less opulence and more wilderness, organic wine, and weed now banish weed from that idealized vision?

The immediate, intuitive, and correct answer is no, stigmatizing marijuana use as a climate sin is by no means necessary. Marijuana could be grown more efficiently as an outdoor crop. Additionally, the electricity intensity of even indoor marijuana cultivation is irrelevant if powered with abundant, low-carbon energy sources. In other words, the path to low-carbon weed simply involves decoupling. It is by no means written in stone that marijuana consumption must necessarily produce substantial carbon emissions.

The most pragmatic routes toward reducing emissions from the marijuana sector don’t involve restricting how or how much weed gets grown or smoked, but actually involve expanding the freedoms available to growers and consumers. Broader national deregulation and legalization of marijuana would encourage lower-carbon outdoor or greenhouse cultivation. Decarbonization of agricultural inputs, transportation, and electricity take care of the rest, enabling a future with both abundant and sustainable cannabis.

There are multiple reasons why the carbon footprint of marijuana is so high: Cannabis requires expensive HVAC systems that recycle air at a much higher frequency (30 exchanges of air per hour) than for regular residential use (0.5 exchanges/hour). This is because marijuana has very strict requirements in terms of temperature and humidity, in addition to the electricity required for the growth lights and the energy necessary to keep the greenhouse at the right temperature year round. However, this hardly represents a fundamental connection between cannabis and high-carbon emissions, because growers could also plant marijuana outdoors in states with temperate weather, minimizing the emissions per kilogram of weed to just 1/25th of the emission footprint of indoor cultivation and also reducing the cost of running a cannabis operation.

This begs the question: Why is cannabis mostly grown indoors when more efficient alternatives are possible?

The answer to this question can be tracked to at least two pieces of legislation: The Marijuana Tax Act of 1937, which made cannabis possession and transfer illegal except for medical and industrial purposes, and the Controlled Substance Act of 1970, which classifies marijuana as a Schedule 1 substance, allowing no legally accepted medical use at the federal level. Even with cannabis legalized in 24 states and the District of Columbia, federal regulations still apply to interstate commerce, so it remains illegal to transport marijuana across state lines. This means that marijuana must be grown in the state where it will be consumed – regardless of the local climate or carbon efficiency of the power grid. To keep up with the ever-rising demand for cannabis, indoor growing is the only feasible method in many states because of seasonal weather variations.

Considering the enormous carbon footprint and disproportionately high energy intensity of indoor marijuana cultivation, the fact that marijuana is legal in half the United States, including many of the most populous states, and the considerable economic activity generated by cannabis growth and consumption, the status quo represents a classic case of missed environmental and economic opportunities thanks to overly restrictive federal regulations. Removing burdensome restrictions would doubtlessly encourage a more efficient nationwide cannabis trade, producing considerable carbon benefits with virtually no public costs of implementation. With marijuana representing a major cash crop and a significant source of tax revenue in many states, including Colorado, California, and Michigan, a federal policy shift could even deliver a windfall to public coffers.

We evaluated the potential climate benefits of nationwide marijuana legalization by estimating the current energy and carbon footprint of U.S. cannabis cultivation, and contrasting the existing situation with hypothetical scenarios in which the distribution of cannabis production is shifted significantly toward outdoor, large-scale operations in states with more favorable year-round temperatures.

Modeling these scenarios made some issues very clear: despite detailed estimation of carbon emissions of marijuana cultivation down to the ZIP code level, data on where marijuana is grown inside states is not readily available, with even state-level data hard to acquire and not reported officially in states’ agricultural statistics, even when marijuana is one of a state’s main cash crops. To compensate for the lack of detailed geographical data, we calculated state-level averages for grow room electricity-related carbon emissions and multiply this emissions factor by either the total production of cannabis for states with harsh winters, and either 50% or 100% of the production of cannabis in states with milder weather. In the first scenario (S1), it is assumed that all production happens indoors, whereas in the second scenario (S2), 50% of the cannabis production occurs outdoors in the states where this is feasible. Since we lack data about growth patterns, we also use both these scenarios to estimate the carbon footprint of the federal prohibition policy.

For the counterfactual policy scenario, in both cases, we assumed that 75% of the current production of cannabis switched to outdoors growth. Some indoor growing continues, since we expect that a non-negligible fraction of marijuana growers will still try to retain as much control as possible over growth conditions, to offer specialty craft weed for different customers and markets, for example. Another important limitation of this approach is that we are modeling only the growth of legal marijuana. Some have estimated that the illegal marijuana market accounts for three-fourths of the total market size, so any emission estimates from this model could be as much as three times larger.

Nationwide, the total carbon footprint of annual U.S. legal marijuana cultivation is between 10.2 and 7.4 million metric tons of CO2 emitted for S1 and S2 respectively, to produce 2,834 metric tons of legal cannabis based on 2021 production. This is equivalent to 0.07%-0.1% of U.S. nationwide fossil CO2 emissions from electricity. But in some states, the electricity-related carbon footprint of indoor marijuana grow houses is remarkably high – potentially up to 6% and 3% of power sector carbon emissions in Oregon and Colorado, respectively, assuming all legal production is grown indoors. But what happens if more marijuana is grown more efficiently in warmer U.S. states?

We find that a more efficient pattern of cannabis production, with 75% of total U.S.-produced marijuana grown outdoors, would reduce sectorwide life cycle marijuana emissions by nearly 80%, avoiding 5.8 million to 8 million metric tons of CO2 emissions nationwide. Again, these results cover the legal maijuana market only, with multiplied emissions benefits if the changes to cultivation patterns extend to illegal production.

This represents only a fraction of the potential climate benefits from adopting less restrictive regulations on marijuana. Since marijuana is illegal under federal law, as previously discussed, U.S. government agencies, including USDA, cannot generally allow or authorize farmers to receive federal agricultural funding for farm equipment that is then used to grow or process cannabis. Additionally, farmers would be in violation of their real estate loan conditions if they grew, processed or stored marijuana anywhere on the premises of land acquired through federal loan programs, constituting a default under the loan conditions and leading to foreclosure of the property. Nor can farmers legally use federal water rights to grow cannabis, as this is illegal at the federal level even if state law allows marijuana cultivation. This requires farmers to maintain independent sets of equipment and infrastructure to care for both their conventional crops and their cannabis operations or be in violation of federal laws and their loan conditions and risk foreclosure and other legal consequences.

Regulation has been moving in the right direction following the legalization of hemp in the 2018 Farm Bill. However, poor public availability of cannabis agricultural data makes meaningful evidence-based marijuana policy research extremely difficult. Even in the absence of federal legalization of marijuana, better data sharing on marijuana cultivation would enhance policy discussions and improve our understanding of the impacts associated with both legal marijuana and the federal marijuana ban.

Certainly, a more efficient nationwide pattern of cannabis cultivation suffices to decarbonize only a mere fraction of America’s national CO2 emissions. However, this example illustrates a few important principles to consider along the larger path toward a low-carbon society:

First, it is far easier to reduce the carbon intensity of a marijuana joint by 80% than it is to convince the American public to give up 75% of annual weed consumption. And with all likely scenarios suggesting that the U.S. electricity grid itself will only get cleaner over time, the remaining carbon footprint of marijuana production will diminish further. It is possible that competition from marijuana may also help displace tobacco cultivation, helping mitigate additional land-use impacts that growth in cannabis cultivation would otherwise entail.

Second, cannabis represents only one out of numerous policy cases where burdensome regulations obstruct a more efficient flow of goods and services that would also produce beneficial environmental side outcomes. Recently, U.S. Rep. Alexandria Ocasio-Cortez went viral for criticizing regulatory restrictions that have prevented adoption of improved sunscreen products. On a far grander scale, a maze of permitting hurdles and legislation might block a transmission line that would carry cleaner, cheaper electricity from one region to another. Bans on biotech crops, like BT eggplant and drought resistant corn, prevent the adoption of grain and vegetable varieties that would reduce pesticide use, improve crop resilience to extreme weather, and minimize land footprint.

The development of safer, smaller, and more versatile advanced nuclear reactors faces obstacles in the form of out-of-date and overly stringent requirements imposed by national nuclear regulatory agencies, like the Nuclear Regulatory Commission in the United States or the Nuclear Regulation Authority in Japan. Meanwhile, the Jones Act, which mandates that cargo transported between U.S. ports must be shipped on U.S.-built, U.S.-flagged, and U.S.-crewed vessels, stands as an obstacle to U.S. offshore wind farm development while raising the cost of fuel and other goods for islands, like Hawaii and Puerto Rico, among other negative effects. In many cases, all it takes to unlock emissions reductions is rewording a legal policy document.

Finally, the cannabis example demonstrates how the best environmental solutions embrace and enable abundance. In a future world with ample clean electricity and fertilizer, the carbon footprint of a marijuana joint will be virtually zero. Whatever amount of weed one imagines future generations might wish to consume, the low-carbon economy should be able to supply a sufficient amount with relatively minimal need for environmental management. If a thriving industry of artisanal growers wish to carefully cultivate the finest gene-edited, transgenic weed in controlled grow rooms, a clean energy-abundant future will allow proliferation of grow rooms to their hearts’ content, just as encouraging greater freedom of choice today encourages more outdoor growing and better sustainability in the near term.

But as things stand today, the environmental movement – eagerly encouraged by marketing efforts from corporations whose interests are aligned – insists upon sorting technologies, goods, and pastimes into either a sinful or a virtuous category. That environmental thinkers have long sermonized against video games, passenger jets, and meat consumption while sparing marijuana or pet ownership from criticism hints at how such judgments often originate from aesthetic biases, rather than quantitative calculations.

Rather, the elegantly simple solution of growing more weed outdoors highlights how senseless it is for climate advocates to continue declaring new crusades against this or that product. The path to a low-carbon future will require society to solve challenges that the average activist doesn’t think about and may not even be aware of – like the carbon footprint of cannabis, the most sustainable choice between concrete or steel transmission towers, or the energy intensity of wastewater treatment. Such challenges will require far more innovative, contemplative solutions than empty, trivial, and politically unpalatable proposals for ever more subtraction and self-deprivation. To obsessively count the emissions of our food and beverage to the point of basing our wine choice on a mere difference of 30 grams of CO2 per bottle, is just the climate version of orthorexia. Yes, we do need to pay attention to what we eat, but counting calories in a compulsive, all-consuming fashion is itself inefficient. The same goes for emissions.

Just as entrenched cultural and political resistance to marijuana legalization has perpetuated needless harms and inefficiencies, both social and environmental, it is long past time to consider whether the longstanding instincts of traditional environmentalism are similarly holding society back from sustainable progress.

Acknowledgements: We are grateful to Thomas Japhet, J.D., former USDA employee, for insightful feedback on U.S. Department of Agriculture marijuana policy.