SOUTH HERO, Vt. (WCAX) – Research shows indoor cannabis cultivation emits significantly more carbon, with one study estimating 30 times more emissions than outdoor growth.

Of Vermont’s four hundred and sixteen licensed cannabis cultivators, just over 40% are indoor. Others grow indoors and outdoors depending on the season.

Compared to massive indoor cannabis growers across the country, Vermont’s are mostly small, but their emissions can add up.

It’s the start of the season at Sunset Lake Cannabis in South Hero, where seedlings will grow in the greenhouse for a few weeks before taking root outside.

For the second year in a row, Sunset Lake achieved climate-neutral certification.

They purchased carbon offsets outside of Vermont to make up for last year’s 100 tons of emissions. They believe their emissions would be even higher if they were growing indoors.

“Indoor growing is like this crazy engineering project of like, you’re really dialing in the humidity and the light and the temperature and the CO2 levels, whereas outdoors we’re like, ‘how’s it look today?’” said Cy Kupersmith of Sunset Lake Cannabis.

Vermont’s Cannabis Control Board Commissioner, Kyle Harris, explains the lighting and controls used for indoor growth is a major energy suck.

“You’re keeping grow lights on for, you know, 12 hours a day, or 18 hours a day. That’s a lot of energy production to maintain, not to mention your age, back equipment, your fans,” said Harris.

The exact breakdown of CO2 emissions from Vermont’s indoor versus outdoor growers is blurry.

The state says it doesn’t track individual growers’ carbon footprint, but it requires energy-efficient equipment for indoor growers and tracks its use.

“To make sure that folks are kind of moving in a direction that we think is best for the state and all the other folks that are tapped into the grid,” Harris said.

Back in the islands, Sunset Lake Cannabis searches for localized ways to curb rather than offset its emissions.

“Can we source better products closer? Can we find other companies with a similar mission to ours so that we can reduce our inputs overall and have a smaller carbon footprint?” asked Kupersmith.

As the industry becomes more established, Harris says he hopes to hone in on more efficient growing.

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