According to research published today, growing cannabis indoors produces up to 5000kg of carbon dioxide per one kilogram of dried flower. 

That’s roughly 4850 times the emissions created by producing one kilogram of milk powder, or equivalent to burning 1540 litres of petrol into our atmosphere. 

The growing popularity of legal cannabis around the world, particularly in the United States, has led to the dramatic increase of indoor growing operations. Since Colorado legalised cannabis in 2012, a further 36 states across the USA have followed suit. The industry in the United States alone is estimated to be worth around $13 billion. 

The research, carried out by Colorado State University, and published in the journal Nature, found that greenhouse gas emissions from indoor cannabis production largely comes from the electricity and natural gas needed to control the indoor environments, high intensity grow lights, and supplies of carbon dioxide for accelerated plant growth (and as an aside, yes, talking to your plants does help them grow faster).

The research team found there would be substantial differences in emissions based on where growing was taking place, due to factors like climate and electric emissions. Emissions from producing one kilogram of dried weed bud could range from 2283 kg to 5184 kg of carbon dioxide.

But they said their research captures the potential cross-country spread of large commercial warehouses for growing cannabis, and models emissions for several high-growth locations around the country. 

The results include a map that shows relative emissions anywhere in the USA. They've also developed a GIS map that allows users to enter a county name and find local emissions estimates.

The research suggests moving to growing cannabis outdoors in greenhouses could lower energy requirements and reduce emissions. Current indoor operations could be made more energy efficient by switching to LED bulbs and retrofitting the climate-control systems. Making the change in Colorado alone would save 2.1 megatonnes of carbon emissions, or 1.3 percent of the state’s total emissions. 

However, the alternative to growing indoors is not appealing for those in the industry. Growing cannabis outdoors is risky business, as it depends on a number of variables, including consistent sunlight, temperatures, and levels of humidity, among many other factors.

While the research paints a dire picture, the likely reality is even worse, as transport and storage of the product was not accounted for. 

In Aotearoa, all growing operations for supply are currently illegal, so there’s no clear data on how much is being grown indoors versus outdoors, but it’s certainly something to think about if we move closer towards a legal industry.

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