Cannabis production is among the most energy-intensive industries in the U.S. But some experts, growers, utility companies and local government agencies in states where marijuana is legal point the way toward reducing pot production's energy consumption and the resulting greenhouse gas emissions.

In Colorado, where marijuana was legalized in a 2012 referendum and became available for sale through licensed growers in 2014, new official data on the industry's energy use signals the challenges ahead.

One study found that Colorado growing operations in 2014 used energy equivalent to that consumed by 35,000 households.

Legal marijuana production is still new, however, and some have begun to take action to reduce its energy use.

"The industry as a whole has gotten a bad rap for not being energy efficient, but we are definitely working to minimize our carbon footprint," said Stephen Lipton, general cultivation manager at The Farm, a grower and recreational marijuana dispensary in Boulder, Colorado. "Right now, it's still a work in progress."

A key challenge is that most commercial growing operations in Colorado are located indoors to create conditions conducive to reaping a maximum possible number of high-quality marijuana plants.

"Growing indoors is pretty energy inefficient, but in most places in the U.S. you can only get one or two seasons outdoors, so there's really not much of a choice," said David DeGraff, chief executive officer of The Grow School in Denver.

Indoor operations often use 1000-watt, high-intensity bulbs — which generate a lot of unwanted heat that then has to be removed from the indoor environment with air conditioners and ventilation systems.

In some cases, energy bills might represent 30 percent of the total cost of an operation, Lipton said.

Many marijuana growers in Colorado produce pot at their homes rather than in large operations. But home growers are also concerned about reducing energy to lower their electricity bills, experts said.

In addition to being expensive, the high level of energy use in marijuana production may become unsustainable as the world seeks to reduce greenhouse gas emissions to avoid the worst effects of climate change.

There is movement for greater efficiency.

“There are technologies and strategies for reducing electricity use in lighting, ventilation and dehumidification — you can cut energy use by 50 percent or more with state-of-the-art technology,” said Howard Geller, executive director of the Southwest Energy Efficiency Project, a nonprofit policy and advocacy group based in Boulder, Colorado.

“A number of grow houses have adopted these technologies,” Geller said.

Boulder County's government has stepped in. It mandated that licensed cannabis growers use 100 percent renewable energy to power their facilities starting in 2015, said Ron Flax, the county’s sustainability examiner for land use.

Most growers were unable to meet that requirement because of the “tremendous” amount of energy they use, insufficient roof space for solar arrays, and financial structures and lease arrangements that make investing in such infrastructure unattractive, Flax said.

So the county created what it calls an energy-impact offset fund, he said.

Cannabis growers pay into the fund if they are unable to use renewable energy in their operations. Also as part of the program, each operation is to receive an energy-monitoring device to allow them and the county to assess their energy use in real time.

Much of the money in the fund goes to educating growers about how to use less energy.

Growers in Boulder can also take advantage of a rebate program by utility company Xcel Energy that rewards businesses for improving energy efficiency.

“It could be [installing new] lighting or insulation — the same thing any building would do to improve efficiency,” Xcel spokesman Gabriel Romero said, adding that the program is not specific to the cannabis industry, but available to any similarly energy-intensive business.

At The Farm, cultivation manager Lipton said he works with both Xcel and an energy consultant to reduce his operation’s carbon footprint. The Farm has installed new lights, ventilation and air conditioning systems, and other technology to increase efficiency.

"It works both ways, it's beneficial to us as well to reduce our energy levels and it also benefits the environment," Lipton said.

Some growers are hesitant to change lighting and other equipment out of fear it will hurt their product, said Geller of the Southwest Energy Efficiency Project.

“They’re making a lot of money now,” Gellar said. “Therefore they’re concerned and reluctant to change.”

Energy efficiency improvements such as installing LED lighting can lead to both savings and increased yields of the cannabis crop, according to a 2014 report by Northwest Power and Conservation Council, which coordinates the electricity needs of four states —Washington, Oregon, Idaho and Montana.

And, Flax said he expects energy efficiency to improve as the commercial marijuana-growing industry matures.

In addition to the use of more efficient lighting and technology, Flax said he expects a gradual shift to outdoor cultivation and sophisticated greenhouse designs instead of indoor operations with artificial lighting.

Some cautioned that greenhouses also consume energy through their use of ventilation systems and supplemental lighting. During the winter, greenhouse cannabis operations would need five to six hours a day of supplemental lighting so that the plants don't think it's fall and begin flowering, DeGraff of The Grow School said.

But all the experts agreed that new technologies are currently being developed — including brighter LED lighting — that can make the industry more energy efficient and climate friendly.

“The industry hasn’t come to full fruition yet,” Flax said. “To some extent the industry hasn’t known how much energy its consuming … by installing energy-monitoring devices they have a tool to see in real time how much power they’re consuming — an important first step for anyone wanting to improve.”