Energy-intensive indoor pot growth has become a sizable source of greenhouse gas emissions, but there are ways to lessen the environmental burden, new research finds.

Driving the news: The paper in Nature Sustainability provides a full and granular "lifecycle" accounting of the many ways indoor growth produces carbon emissions.

Why it matters: This cultivation is rising thanks to states including California, Colorado, Massachusetts and others legalizing recreational sales.

• "This industry is developing and expanding very quickly without consideration for the environment," Colorado State University researchers said in a summary at The Conversation.
• The findings can inform policymaking in states with legal weed or ones considering it, they said.

How it works: The biggest source of emissions is energy needed for sophisticated indoor air management to grow specialized crops at the right temperature and humidity.

• Other big ones include electricity needed for high-intensity grow lights, use of CO2 to enhance plant growth, and transportation of various supplies.

The intrigue: The authors find lots of regional variation in modeled emissions as they explored the natural gas and electricity needed for cultivation.

• That's due to differing climates and regional differences in how much clean energy is used for power production.
• "Areas such as the Mountain West and Midwestern United States are especially intensive for growing cannabis indoors," they find.

Of note: The regional data in the paper's modeling does not reflect the legal status of pot in the different areas.

Threat level: Comparing indoor cultivation to other industrial sectors in Colorado helps provide a sense of scale.

• Colorado State associate professor Jason Quinn said it creates about 2.6 million metric tons of CO2-equivalent annually.
• "This is similar to coal mining and waste management sectors that are 1.8 and 4.2 million metric tons of CO2-equivalent annually," the paper's co-author told Axios.
• "We've estimated that indoor cannabis is responsible for about 1.7% of the state's annual greenhouse gas emissions," he said.

Quick take: None of this is a civilizational threat! But rising sources of emissions are important at a time when scientists warn that steep emissions cuts are needed.

What's next: Changes to growing practices can reduce emissions, the paper notes, including...

• Making decisions based on geography and better engineering of indoor farms.
• Moving to greenhouses or outdoor growing, which can vastly curb emissions but can also bring their own environmental and security problems.

The chart above provides a sense of the big regional variations in estimated emissions from indoor cannabis growth.

• This doesn't show the small amounts of CO2 sequestered during the growing process.