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With marijuana legalization quickly approaching, academics and legal experts are warning that mass cannabis production could have a negative impact on the environment.

Indoor cultivation, the primary method of production for major distributors such as Aurora Cannabis Inc. and Canopy Growth Corp., has been shown to use large amounts of energy as a result of 24-hour lighting rigs, high-intensity air conditioning and dehumidifiers. The facilities can be as large as 1.2 million square feet and can use tens of thousands of dollars in electricity a month.

“It’s a worrisome state of affairs," says Werner Antweiler, a professor of business and environmental economics at the University of British Columbia. “The carbon footprint could be quite large given the intense production method.”

Most research on the environmental impact of indoor cultivation comes from the United States. One study from the University of California, Berkeley, estimates that indoor facilities across the United States account for 1 per cent of the country’s total annual electricity use and account for about 50 million tons in greenhouse gas emissions. Evan Mills, the study’s author, says that each average indoor-grown cannabis plant consumes the energy equivalent of 70 gallons of oil, while the energy required to produce asingle marijuana cigarette is roughly equivalent to the energy expended by leaving a 100-watt light bulb on for 75 hours.

Cannabis is also heavily dependent on water, making it a potential source of concern in regions that experience dry spells and drought.

Selina Lee-Andersen, an environmental lawyer based in Vancouver, says that one marijuana plant needs approximately 22 litres of water a day; in comparison, a wine-producing grape plant uses approximately 12 litres a day.

Cannabis is photographed growing in a MedReleaf facility in Markham, Ont., on February 2, 2018.Christopher Katsarov/Globe and Mail

In California, the United States Forest Service reports that illegal operations use vast amounts of water each year in the areas surrounding Sacramento and San Francisco.

“So you can imagine that would be an issue in places like California that succumb to drought,” Ms. Lee-Anderson says. “And we’re not immune to it here either.”

Ms. Lee-Andersen says that cannabis water consumption could be a problem in provinces that are prone to water shortages.

“If facilities are located near urban areas that have experienced drought, like Vancouver, then water becomes a serious consideration."

The legalization of cannabis comes at a time when the federal government has pledged to reduce the country’s greenhouse gas emissions by 30 per cent below 2005 levels before 2030, a goal research groups such as Climate Action Tracker have already deemed insufficient. In order to hit that target, environmentalists say industries such as agriculture will need to consider more energy-efficient modes of production in order to reduce their carbon footprints.

One such method is growing the plants outdoors, which a group of academics specializing in cannabis-related studies says is a significantly more sustainable alternative to indoor cultivation, given that it doesn’t require modified lighting, heating or cooling systems.

The academics, who authored a brief presented to the government’s standing committee on health in response to Ottawa’s marijuana legalization bill, said that the field production of cannabis is environmentally similar to growing crops such as corn, which require low energy inputs. They say marijuana plants are well suited to organic cultivation as well, meaning that outdoor crops could avoid the use of herbicides or pesticides.

But outdoor growing becomes difficult during the winter, making it an unappealing alternative to producers looking to maximize output. Nonetheless, licensed producers are expected to take advantage of new rules allowing outdoor growing next spring.

Some smaller producers in Canada are already using greenhouses as an alternative to other types of indoor facilities . This allows them to maintain a year-long production schedule while curbing emissions because of reduced use of lighting and air conditioning.

The cannabis produced by Hydropothecary Corp., a Quebec-based company that brands itself on sustainable cultivation, is grown entirely in greenhouses.

“In the summer we almost don’t need electricity because the days are so long and the sun is so bright,” says Terry Lake, a vice-president at the company. Hydropothecary also uses computerized watering systems that deliver the precise amount of water required for each plant. If there’s excess water, he says, it’s redistributed to other plants.

Still, the greenhouse method is limited in how environmentally sustainable it can be, the authors of the standing committee brief argue, given that during winter months it will require more heat to maintain the quality of the plants.

Indoor growers are also looking to reduce their environmental impact. Aurora Cannabis spokeswoman Heather MacGregor says that the producer aims to use “environmentally responsible technologies" in their indoor cultivation facilities. According to Ms. MacGregor, the company is experimenting more with LED lighting and special irrigation systems to recirculate water.

The Cannabis Act does not specifically address environmental standards for producers. However, cannabis growers are still subject to federal and provincial environmental laws governing emissions and water use.

UBC’s Dr. Antweiler suggests that the various levels of government will need to see the results of a legalized industry before imposing further environmental regulations. While the U.S. studies are a warning sign, he believes there needs to be more Canadian research on the issue.

“Once we know how and where production occurs here, we can really find better ways to regulate it," he says.

Legalization provides an opportunity for growers to find new ways to reduce their carbon footprint, Dr. Antweiler says, and for governments to implement incentives to encourage growers to be more socially responsible.

“By moving out of illegality, producers have more flexibility to try to find the most suitable locations in terms of efficiency and costs – and that could help lower the footprint in the long term.”

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