Cannabis production: the carbon footprint of new industry

Although the use, sale, and possession of cannabis is still illegal in the USA at a countrywide level, in 2012 the states of Colorado and Washington became the first to legalise it for recreational use. By the end of last year, 12 more states had followed suit, and 36 states have legalised it for medicinal purposes. This has taken what was an underground blackmarket of cannabis production into the mainstream, with legal cannabis sales projected to reach 22 billion dollars by next year. But cultivating cannabis on this scale is very energy intensive: the plants are grown indoors under powerful lights and with additional CO2 pumped in to maximise the yields. And this got Colorado State University researcher Hailey Summers wondering about the carbon footprint of all this “home grown” produce, as she told Eva Higginbotham...

Hailey - It's a windowless warehouse, the smell hits you right away, and there's just a canopy of green. And then you've got these really high intensity lights that almost feel like you're getting a sunburn inside. And then there's a suite of dehumidifiers around the room, and there's usually simple office fans mounted to the walls that are circulating air. And then there's a number of climate control systems on the wall because most growers really care about the environment that these plants are being grown in, and so they control it heavily to make the best product possible. In our study, the primary intent was to quantify the greenhouse gas emissions from growing cannabis plants indoors.

Eva - Why would someone choose to grow cannabis indoors, where they have to provide things like light, as opposed to growing it outdoors, when the sun's just there?

Hailey - Yeah, there's a number of reasons. A big one is being able to control the product. When you grow artificially indoors, you can keep your indoor climate, your temperature and your humidity, very regulated, and that allows you to make the best product possible. There's also some security or theft issues, an indoor warehouse is a very secure environment. Also it allows you to get multiple harvests per year because you can create an artificial environment and grow year round, you're not limited to just the weather outside, right? If we were to grow cannabis outdoors in Colorado, for example, purely outdoors, we would probably only be able to achieve one harvest per year, whereas indoors, you can get about six harvests per year.

Eva - What kind of factors did you have to consider?

Hailey - So we investigated two primary inputs, and that would be your energy inputs and then any material inputs needed. The energy inputs primarily break down to either electricity or natural gas, and then the material inputs we considered include things like water or fertilisers or carbon dioxide. And so we looked at basically all of the quantities of those inputs needed, and then we equated those inputs to greenhouse gas emissions using a standard methodology called life cycle assessment.

Eva - And what did you find?

Hailey - The total amount of greenhouse gas emissions was pretty significant. So we analysed over a thousand locations across the US and we accounted for variations in weather and electric grid mix., and so those play a pretty big role in determining your overall greenhouse gas emissions. In Colorado, we were able to obtain the amount of cannabis being produced, and that translates to about 1.7% of Colorado's annual greenhouse gas emissions.

Eva - How big of an impact is this intensive growing of cannabis having in comparison to other industries that we know release a lot of greenhouse gases too?

Hailey - In the past few years a previous study came out and said that about 4% of Denver's electricity is coming straight from these growth facilities. So that's a pretty big portion of our electricity use. And to put this into context, there's a couple other sectors that I can compare that to. One would be coal mining operations, those in the state of Colorado are about 1.5% of the state's annual total., so a little bit less.

Eva - If we just switched to renewable energy resources, which is hopefully on the horizon in lots of parts of the world coming up, would we solve the problem of this energy intensive farming?

Hailey - I think that growing indoors in the state that we are is probably the worst it will be. As we clean up the grid, it's certainly going to help, but there's still some of these material inputs such as the carbon dioxide supply that are not directly associated with the grid.

Eva - If it's so hard to grow cannabis in Colorado, where it is cold, why don't we just grow it all outside in California, where the weather is ideal for growing cannabis?

Hailey - So there's a couple of reasons why we can't do that in the current state. and the biggest one is legalisation. So currently for states that are either medically or recreationally legalised, you would have to grow that cannabis in the state that it's legal in. So right now we can't grow in a state and then transport across state lines. If federal legislation was to lift, we could probably come up with a centralised location to grow the majority of cannabis and then distribute from there.