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How Legalisation Can Reduce The Carbon Footprint Of Cannabis

Today is Earth Day, which means it’s time for all of us to evaluate the impact of our lifestyles on the environment. The cannabis industry is certainly not exempt from this, with large indoor growing facilities consuming considerable amounts of energy and contributing significantly to greenhouse gas emissions. However, it’s important to remember that legality has a major influence over the entire supply chain, and new research suggests that legalisation may be the only way to curb the cannabis industry’s carbon footprint.

The Carbon Footprint Of Cannabis

Just as it doesn’t make sense to try and grow mangoes, coconuts or pineapples in cold climates, cannabis cultivation becomes considerably harder once you take the plant out of its preferred environment. In the US, therefore, the logical way forward would be to grow as much weed as possible in places like California, and export this to other states that have legalised cannabis but don’t have the right climatic conditions for cultivation.

Frustratingly, though, the plant’s illegality at the federal level prevents it from being transported across state borders, which means each state has to grow its own supply. For colder locations like Alaska and Minnesota, this entails the use of intensive grow rooms, all of which adds considerably to the carbon footprint of local cannabis industries.

Research carried out in 2012 suggested that growing a single kilogram of dried cannabis flower indoors generates 4.6 metric tons of carbon dioxide emissions[i]. However, that study was based on data recorded from a single grow room, and failed to take into account the variations in the amount of energy required to run a growing facility in different states.

To more accurately represent the carbon footprint of cannabis production in the US, a team of researchers has published a new study that calculates the level of emissions produced by grow rooms in different states across the country. According to their findings, the greenest place to grow cannabis indoors is Long Beach, California, where a kilogram of dried flower can be produced at a cost of just under 2.3 tons of carbon dioxide emissions. At the other end of the spectrum is Kaneohe Bay, Hawaii, where almost 5.2 tons of carbon emissions are generated for each kilogram of cannabis produced.[ii]

Why Indoor Cannabis Cultivation Has Such A Large Carbon Footprint

Despite the fact that we’re talking about growing cannabis indoors, the reality is that external atmospheric conditions still have an influence over the production process. This is largely down to the fact that air must continually be pumped into the growing space in order to ensure good circulation, thereby helping plants to grow and preventing mould from setting in.

Yet the air that is introduced must be modified, either by heating, cooling or dehumidifying to optimal levels. According to the study authors, the treatment of incoming air is the single biggest source of emissions for any grow room, and therefore contributes significantly to the carbon footprint of cannabis production in each state.

In Denver, Colorado, and Anchorage, Alaska, heating is the main consideration, as outside air temperatures are often far too cold for cannabis. As a consequence, indoor facilities in both locations generate an average of around four tons of carbon emissions in order to produce one kilogram of dried cannabis flower.

Conversely, indoor growers in Hawaii have to dehumidify the air that is pumped into their facilities, which is why their emissions are even higher than those seen in cold climates.

A second major contributor to the carbon footprint of indoor cannabis cultivation is the use of high-intensity grow lights. Despite the fact that lighting requirements are unlikely to differ between facilities, the emissions associated with illumination can vary by as much as six-fold due to geographical variations in electricity grid mixes.

For instance, in Hawaii, where electricity is predominantly generated from oil combustion, 805 grams of carbon emissions are generated per kilowatt hour of electricity used. In California, meanwhile, the use of solar power and natural gas means that only 238 grams of emissions are produced per kilowatt hour. In other words, operating grow lights in California is considerably less harmful than using the very same lights in Hawaii.

The third and final major cause of emissions when growing indoors is the direct introduction of carbon dioxide into the growing space so that plants can increase their rate of photosynthesis and reach maturity faster. While the study authors admit that most of this carbon dioxide is normally captured as a by-product of other processes such as ammonia production, and therefore would have been released regardless of its use in cannabis cultivation, they also mention that the energy expended to compress and transport this gas adds considerably to the carbon footprint of indoor cannabis growing.

Is There A Solution?

The most obvious solution to this problem would be to simply switch to growing in either greenhouses or outdoors, which the study authors estimate would cut emissions by 42 percent and 96 percent respectively. For this to occur, however, the US government would have to legalise cannabis at the federal level, so that it can be transported around the country in order to meet demand in states that lack the environment for outdoor cultivation.

Failing this, though, changes to certain state laws could still help to decrease the carbon footprint of indoor cannabis growing. Colorado, for instance, was the first state to legalise recreation cannabis back in 2012, paving the way for a huge increase in production. According to the study authors, cannabis cultivation in Colorado now produces more emissions than the state’s coal industry, yet they also insist that better planning could have helped to reduce the climate cost of growing legal weed.

In particular, they mention a piece of legislation which states that all cannabis sold in Colorado must be grown nearby. However, they calculate that indoor growing facilities in mountainous locations like Aspen and Leadville generate 19 percent more emissions than those in plains locations like Denver and Puebla. By simply scrapping this law and allowing certain facilities to produce the state’s entire supply of cannabis, therefore, a considerable reduction in emissions can be achieved.

Obviously, the development of greener technologies and the adoption of more environmentally friendly growing practices must be pursued if cannabis growers are to curb their carbon footprints. However, as this analysis reveals, the power to create a truly sustainable cannabis industry in the US may ultimately lie with lawmakers.

[i] Mills E. The carbon footprint of indoor Cannabis production. Energy Policy. 2012 Jul 1;46:58-67. – https://www.sciencedirect.com/science/article/abs/pii/S0301421512002285

[ii] Summers HM, Sproul E, Quinn JC. The greenhouse gas emissions of indoor cannabis production in the United States. Nature Sustainability. 2021 Mar 8:1-7. – https://www.nature.com/articles/s41893-021-00691-w

Cultivation information, and media is given for those of our clients who live in countries where cannabis cultivation is decriminalised or legal, or to those that operate within a licensed model. We encourage all readers to be aware of their local laws and to ensure they do not break them.

This post is also available in: French

Ben Taub