Is your joint smoking up the planet? How cannabis may be fuelling climate crisis

Is a beer, a cup of coffee or a spliff more damaging for the climate? If the cannabis is cultivated indoors on a commercial scale, the answer is probably the joint.

That’s the finding of researchers at Colorado State University, who say booming indoor marijuana production in the US is a major and growing source of greenhouse gas emissions that cause global warming.

The $13.6bn (about R207bn) industry has nearly quadrupled since 2012 when Washington and Colorado became the first states to open the doors to recreational use.

However, policymakers and consumers have largely ignored the environmental cost of energy-hungry indoor cultivation, the researchers said in a study.

Nearly a third of US states allow recreational use, while medical cannabis is legal in about two-thirds.

In Colorado, indoor cultivation accounts for an estimated 1.7% of the state’s annual greenhouse gas emissions - similar to that for coal mining, the study’s co-author Jason Quinn said on Tuesday.

Large contributors include the heating, ventilation and air-conditioning needed to maintain the right conditions for the plants, high-intensity grow lights and the use of supplemental carbon dioxide to boost growth.

Preliminary research suggests the level of planet-heating emissions per 0.1 grams of marijuana — about a third of a joint — was likely to be far greater than for a glass of beer, wine or spirits, a coffee or cigarette, the authors said.

“We were very surprised at how high the impact is,” said Quinn, director of the university’s Sustainability Research Laboratory.

“There’s a real opportunity to reduce that impact. Consumers can start asking whether the cannabis was produced indoors or outside.”

Moving to greenhouse or outdoor cultivation could cut emissions by 42% and 96% respectively, according to the study published in Nature Sustainability.

The research revealed a large variation in emissions across the country, and within some states, with indoor cultivation in milder climates requiring less heating or air conditioning to maintain favourable temperatures and humidity.

Producing 28g of dried cannabis in eastern O’ahu in Hawaii was roughly equal to burning 60 litres of fuel, creating more than twice the emissions from growing the same amount in southern California, the authors said.

They suggested states that had already legalised cultivation should steer indoor production towards regions with more optimal climates, while states legalising cultivation in the future should consider avoiding indoor production.

However, they said switching production outdoors could create security concerns and make it harder for growers to produce multiple harvests a year and ensure consistency.

Thomson Reuters Foundation