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Indoor Cannabis Cultivation Leaves a Large Carbon Footprint, Study Finds

By Alexander Beadle

Published: Mar 11, 2021   
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Across North America, the rising tide of cannabis legalization has upped the demand for domestic cultivation operations that can provide a consistent product year-round. But what’s been the environmental cost of this boom in indoor, energy-demanding farming? A heavy one, according to one new study.

Published in Nature Sustainability, the study mapped the energy and materials needs of hypothetical indoor cannabis grows in various locations across the United States. Its authors then calculated the resulting greenhouse gas emissions these operations would release to try to identify any trends or patterns that might affect emissions.

The researchers from Colorado State University found the greenhouse gas emissions varied significantly from region to region. Colder areas with less sunlight, unsurprisingly, were associated with more emissions, largely due the power requirements of the environmental control systems needed to regulate heating, humidity, and ventilation.

Policy makers may want to take into account these significant regional variations when planning cannabis cultivation regulations, the researchers say, to avoid more environmentally damaging practices becoming baked into regional cannabis law.

Growing cannabis can be energy intensive, depending on location

Unlike outdoor cultivation or even greenhouse cultivation, indoor cannabis cultivation warehouses create a fully artificial climate that allows the cannabis plants to thrive year-round. While this allows multiple harvests per year, these environments can be very energy intensive.

But until now, there were little data on how energy hungry these cumulated operations might be. Some previous estimates were calculated almost a decade ago, before the legalization of recreational cannabis anywhere in the United States.

“We knew the emissions were going to be large, but because they hadn't been fully quantified previously, we identified this as a big research opportunity space,” Hailey Summers, a graduate student in the CSU Department of Mechanical Engineering and lead author of the new study, said in a statement. “We just wanted to run with it.”

Using data collected from the Department of Energy, Environmental Protection Agency and the cannabis industry, the CSU researchers performed a life-cycle assessment of hypothetical indoor cannabis operations in over 1,000 locations across the US. Historical weather data and electrical grid emissions data were used to estimate the energy and materials needed to maintain ideal indoor climate conditions.

From this, the researchers estimated the current greenhouse gas emissions of indoor farms to range between 2,283-to-5,184 kilograms of carbon dioxide equivalent produced per each kilogram of dried cannabis flower (kg CO2-eq per kg-dried flower), depending on which US region an indoor farm is located in. Colder areas and regions with high humidity generally required more energy and produced more greenhouse gas emissions.

Heating and ventilation are the biggest contributors to emissions

There researchers identified several factors key to gas emissions. High-intensity lights, for one, require lots of electricity. Although the environmental impact of this power can depend on the region its produced in. In Hawaii, for example, the electricity grid is largely oil based, whereas in California there are some areas that can source from natural gas and solar power.

Another consideration is the common practice of pumping CO2 gas into the cultivation area to stimulate plant growth. While this CO2 is normally captured from other industrial emissions, and so is not itself a direct emission from the cannabis industry, the power needed to compress this gas and transport it to the cannabis grows has to be factored in. This means that for a state like Colorado, it is possible to lower the environmental impact of the industry by keeping cultivation operations in the plains areas with good transport links, rather than up in the mountains where the environmental impacts associated with transportation would be greatly inflated.

But by far the biggest contributor to the emissions of an indoor cultivation operation, the researchers say, are the environmental control systems, the one that controls the heating, humidity, and ventilation for the crops. Cannabis plants can require large volumes of fresh air brought in from outside the facility to maintain health oxygen levels and moderate humidity. The researchers estimate an average of 30 volumetric air changes are needed per hour in an average indoor cultivation facility, and all of this air must be treated to match the ideal temperature and humidity of the plants.

The heating, ventilation, and air conditioning (HVAC) systems needed to do can draw dramatic amounts of power from the local electrical grid depending on the location. An operation trying to maintain ideal growth conditions during a cold Missouri winter, for instance, will likely require even more energy that an operation in southern California.

Tackle cannabis’ carbon footprint through policy

Why do these trends matter? Well, compared to the estimated environmental impact of outdoor and greenhouse cannabis cultivation, it is clear that indoor cultivation could have a disproportionate environmental impact if left unchecked. And based on preliminary results from another study the CSU researchers are working on, they also estimate that the greenhouse gas emissions per serving of cannabis are significantly higher than per serving of beer, spirits, cigarettes, and other legal substances.

“We would like to try and improve environmental impacts before they have become built into the way of doing business,” explained Evan Sproul, a research scientist in mechanical engineering and one of the study co-authors.

“Our team is also interested in understanding where weed could be grown if federal legalization happens,” the researchers wrote in a comment article accompanying the publication of their research. “Legalization might allow policymakers and producers to grow weed in places and in ways that are much more environmentally friendly, but they need the knowledge to do so.”


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