A California researcher says indoor marijuana growing operations account for 1 percent of U.S. electrical consumption and produce greenhouse gas emissions equivalent to 3 million cars.
The high-powered lights, fans, dehumidifiers, generators and vehicles used in U.S. cannabis production and distribution rack up $5 billion a year in energy costs, analyst Evan Mills said.
Mills, an energy analyst with the University of California's Lawrence Berkeley National Laboratory, presented his findings in an April 5 paper titled, "Energy Up in Smoke: The Carbon Footprint of Indoor Cannabis Production."
Using the research techniques with which he analyzes the energy efficiency of appliances and cars -- the report has 22 footnotes -- Mills said a single "cannabis cigarette" represents two pounds of carbon dioxide emissions. That's equal to burning a 100-watt lightbulb for 17 hours.
Mills said professional curiosity led him to the topic. Like leaky furnace ductwork and power-gobbling computers, indoor pot grows appear to be among the nation's "previously unrecognized spheres of energy use," he said in the paper.
Areas reputed to have extensive indoor marijuana operations use substantially more electricity than other regions, Mills said. Humboldt County in Northern California had a 50 percent increase in per capita residential electricity use after cultivation for medical purposes was legalized in 1996, he reported.
Intense lighting systems that rival hospital operating rooms for brightness are the biggest energy users indoors, Mills said.
Growers' fear of getting caught or ripped off complicates the situation.
"Substantial energy inefficiencies arise from air cleaning, noise and odor suppression, and inefficient electric generators used to avoid conspicuous utility bills," he wrote.
Oregon, which has nearly 40,000 people enrolled in a medical marijuana program, probably has a similar situation, he said.
Shifting cultivation outdoors eliminates almost all energy use except for transportation, but poses other environmental challenges, Mills said.
Marijuana users, legal dispensaries and equipment manufacturers may have key roles in bringing about more energy-efficient growing operations, he said. Consumers increasingly look for assurances that food or other products were grown or made sustainably, and the same standards could be applied to pot.
"There's a precedent there," Mills said. "You can grow tomatoes or radishes in a smart way or a dumb way."