Pot-smoking environmentalists take note: Grass might not be green. A new study reveals that indoor marijuana production carries a shockingly large carbon footprint.

GOOD reports that Lawrence Berkeley National Laboratory researcher Evan Mills, Ph.D., has released a surprising new independent report, “Energy up in Smoke: The Carbon Footprint of Indoor Cannabis Production.” Mills reports that indoor Cannabis production uses 1% of the nation’s entire electricity consumption. This comes to energy expenditures of $5 billion per year.

While 1% may not seem like a lot, the report claims that smoking one single Cannabis joint is equivalent to running a 100-watt light bulb for 17 hours. That Cannabis cigarette carries two pounds of CO2 emissions.

According to the report:

Each four-by-four-foot production module doubles the electricity use of an average U.S. home and triples that of an average California home. The added electricity use is equivalent to running about 30 refrigerators. Processed Cannabis results in 3000-times its weight in emissions. For off-grid production, it requires 70 gallons of diesel fuel to produce one indoor Cannabis plant, or 140 gallons with smaller, less-efficient gasoline generators.

Is this report ideal material for anti-drug activists? Not exactly. Mills is clear to write, “This study does not pass judgement on the merits of Cannabis cultivation” and he states that cannabis production is not intrinsically polluting, but rather currently engages in inefficient production. Mills proposes that energy use for indoor production could be dramatically reduced, with cost-effective efficiency improvements of up to 75%. He also suggests that by shifting cultivation use outdoors, certain aspects of energy consumption would be eliminated (although other environmental impacts might be imposed instead).

Fast Company finds this report to be further evidence that marijuana should be legalized. Writer Ariel Schwartz says, “Marijuana production needs to be legalized, so people will actually cast a critical eye on its energy usage. All the industry has to do is follow in the footsteps of the commercial agricultural industry, which has made strides in energy efficiency in recent years.”

Mills writes in his report that criminalization contributes to inefficient energy practices. Compared to electric grids, off-grid power production often produced more greenhouse-gas emissions. He also describes how long driving distances and odor suppression measures take away from ventilation efficiencies.

Ultimately, Mills concludes, “It is up to others to decide how to respond to the findings.” Whatever the response may be, indoor cannabis production must somehow reduce its carbon footprint.

