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There is often a hidden price to pay whenever explosive new trends take over the moment, and in the case of the $13-billion dollar cannabis industry, it happens to be environmental impact. There’s no stopping the future growth of the industry, but a new study by Colorado State University purports that the industry’s greenhouse gas emissions be considered before tomorrow’s policies and practices are created.

Published just this month, the study is the most detailed accounting to date of the industry’s carbon footprint. Scientists at CSU performed a life-cycle assessment of indoor cannabis operations across the U.S., analyzing the energy and materials required to grow their products, and tallying the corresponding greenhouse gas emissions.

They found that greenhouse gas emissions from indoor cannabis production come largely from the electricity and natural gas used for:

  • Air conditioning and heating to maintain proper temperatures for plants
  • High-intensity grow lights to mimic sunlight
  • Pumping carbon dioxide to increase plant growth
  • Treating and bringing in fresh air from the outside

All of this is energy-intensive, and although the scientists expected the amount of emissions to be large, they admit they were surprised by the actual numbers. Their findings are summarized in the accompanying chart, which shows relative emissions throughout the U.S. as defined as emissions per kilogram of dried cannabis flower.

In sum, U.S. indoor cannabis cultivation results in life-cycle greenhouse gas emissions of between 2,283 and 5,184 kilograms of carbon dioxide per kilogram of dried flower. Contrast this range to the electricity-only emissions used in outdoor growth: only 22.7 kilograms of carbon dioxide. It’s obvious that indoor cultivation has the much larger carbon footprint.

Fluctuations shown in the map naturally depend on the local climate. For example, Florida grow operations require excessive dehumidifying, while Colorado operations demand heating. Regulations also have an effect, such as an often-seen state requirement that grow operations be in close proximity to retail storefronts — leading to arguably too many indoor warehouses in urban areas where electricity costs are high.

The CSU researchers note that there are certainly security and quality control reasons to grow indoors, rather than outdoors or in greenhouses. The aim of this study, and of planned follow-up studies that will directly compare indoor and outdoor operations, is to help the industry tackle environmental concerns while legal cannabis is still relatively new in the U.S.