Growing cannabis indoors produces a lot of greenhouse gases – how much depends on where it’s grown
Growing cannabis indoors is an energy-intensive process. Plantlady223 via Wikimedia Commons, CC BY-SA
The big idea
Indoor cannabis production is a major source of greenhouse gas emissions, and the environmental impacts vary significantly depending on where it’s grown, according to our new study.
The lamps used for growing grass indoors use a lot of electricity, but the facilities require a lot of energy to maintain a comfortable environment for the plants. That means air conditioning or heating to maintain the right temperatures. Producers also pump carbon dioxide inside to increase plant growth. This accounts for 11 to 25% of the greenhouse gas emissions from the plants.
The greatest energy consumption, however, arises from the need to constantly supply fresh air to the cultivation systems. All of this outside air needs to be treated so that it has the right temperature and humidity. This is a very energy-intensive process because the air exchange rate is typically so high.
All of these inputs contribute to greenhouse gas emissions, much more in some regions than in others.
Using data from the Department of Energy, the Environmental Protection Agency, and industry, we found that growing cannabis indoors results in higher greenhouse gas emissions in the mountains of the West, Midwest, Alaska, and Hawaii than on the Pacific and Atlantic coasts. This is because the coastal climate is milder, so you will need less heating or air conditioning, and because the electricity grids use more clean energy
Cannabis grown in Southern California has the lowest emissions at 143 pounds of carbon dioxide equivalent per ounce of dried cannabis. Meanwhile, east of O’ahu, Hawaii, has the highest emissions at 324 pounds of carbon dioxide equivalent per ounce. That’s roughly the equivalent of burning 16 gallons of gasoline.
Jason Quinn, CC BY-ND
Why it matters
Policy makers and consumers do not pay much attention to the environmental impact of the cannabis industry. In Colorado, the weed industry accounts for 1.3% of the state’s total annual emissions. This is comparable to emissions from coal mining and garbage disposal for the entire state.
There are currently little to no emissions regulations for growing cannabis indoors. Consumers do not think about the environmental impact either. Overall, this industry is developing and expanding very quickly, regardless of the environment.
Which is not yet known
The cannabis industry is so new that researchers don’t even know how much is being grown indoors. In addition, every indoor operation is unique. Some are old warehouses with outdated equipment while others are much more energy efficient.
Growing cannabis outdoors or in greenhouses could be a way to eliminate the need for lighting and environmental controls. However, the researchers are also unaware of the greenhouse gas emissions associated with these growth methods. All of these unknowns make it difficult to develop guidelines or best management practices.