Jim Wilson/The New York Times

Don’t bogart that megawatt, my friend.

A new study estimates that indoor pot-growing operations in the United States burn about $5 billion worth of electricity annually, or roughly 1 percent of national power consumption. That’s enough electricity to power two million average homes.

The electricity use of the typical grow operation approaches 200 watts per square foot, on par with the power usage of a modern computer data center, Evan Mills, a staff scientist at Lawrence Berkeley National Laboratory and author of the study, said in a statement. (The study was completed in his free time and without federal funds, Dr. Mills added.)

The study estimated that a single joint contains the equivalent of roughly two pounds of carbon dioxide emissions, the equivalent of running a 100-watt bulb for about 30 hours on the California grid.



Marijuana is considered the nation’s largest cash crop, with a production value estimated at about $40 billion annually. Legal restrictions have been steadily relaxed in recent years, with cultivation for medical purposes legal in 17 states.

Yet a continuing federal prohibition on virtually all forms of pot-growing has kept the industry in the shadows, contributing to substantial inefficiencies, Dr. Mills said.

“If improved practices applicable to commercial agricultural greenhouses are any indication, such large amounts of energy are not required for indoor cannabis production,” he wrote. “Cost-effective efficiency improvements of 75 percent are conceivable.”

Such energy savings could be substantial. In California, where about 400,000 people are licensed to grow marijuana for personal medical use or to sell to dispensaries, indoor cultivation is responsible for a whopping 8 percent of household electricity usage, costing about $3 billion yearly and producing the annual carbon emission of a million average cars.

“Current indoor cannabis production and distribution practices result in prodigious energy use, costs, and greenhouse-gas pollution,” Dr. Mills wrote. “The hidden growth of electricity demand in this sector confounds energy forecasts and obscures savings from energy efficiency programs and policies.”

However, Dr. Mills also noted that California’s cleaner mix of fuels for power generation meant that the state, despite its position as the country’s top marijuana producer, contributed only about 20 percent of national carbon dioxide emissions from the practice.