Grass grown indoors spews carbon into the atmosphere

Back in the before legalization, cannabis production involved finding a rarely visited patch of land and cultivating outdoors, or it meant growing indoors – usually in a basement where your product would not be visible to the world. outside. But the energy consumption involved in lighting an underground grow space was legendary.

With legalization, only the scale has changed. The most legal marijuana is grown indoors, with enough electrical use to match. Now, researchers have tried to quantify the greenhouse gases emitted and have come up with impressive figures. Based on their calculations, cannabis production results in over 2,000 kilograms of carbon dioxide emitted for every kilogram of product (defined as dried flowers), and its legalization has had a measurable effect on the production of greenhouse gases. Colorado greenhouse.

In many places that have legalized cannabis production, there are many factors that make growing indoors a reasonable option, including simplifying safety, allowing year-round production, and simply the experience that comes from growers. now professionals with years of practice as amateurs. But Colorado – one of the first states to legalize wacky-tabacky – has added what is presumably an accidental inducement by requiring that the majority of cannabis offered for sale be grown at the site where it is sold. You can either use good farmland to cultivate it or sell it near urban centers and campuses where the demand is higher, but not both.

Everyone knows anecdotally that cannabis more and more to chew thanks to electricity. But the only figures we have on actual usage come from the days of pre-legalization. So Hailey Summers, Evan Sproul, and Jason Quinn, all from Colorado State, decided to provide up-to-date numbers.

To do this, they obtained hourly data on weather conditions and carbon intensity of emissions for the entire United States. These were fed into a model that used them to estimate the carbon emissions caused by the air conditioning requirements of cannabis production. The model also took into account all of the other ways indoor production resulted in carbon dioxide emission, ranging from the manufacture of fertilizers to the disposal of plant waste, and included the emissions associated with the transport of these materials. Overall, the model has been used to explore emissions associated with production in over 1,000 different locations in the United States.

The big unknown in all of this is how often the air in the grow room is returned. The rates reported range from a complete replacement of the air in the installation 12 times per hour to up to 60 times per hour. The team produces figures for the whole range but mainly communicates figures for 20 turnover / hour.

Ultimately, electricity consumption was the main driver of greenhouse gas emissions, as one would expect. But there were unexpected twists and turns in the details.

For example, the highest electricity use was typically in the Southeastern United States, where the need for dehumidifiers and air conditioning was greatest. For example, in Jacksonville, Florida, humidity management adds about 1,500 kilograms of emissions to every kilogram of product. Cooler climates, such as Alaska and Chicago, tend to provide natural gas heating, so the amount of renewable energy on the grid is less, but not negligible, given the large lighting needs. for indoor growth. Despite similar overall emissions in Jacksonville, it comes much more from heating and cooling needs than from humidity management.

Unlike traditional agriculture, the use of fertilizers is not a major factor in overall greenhouse gas emissions. However, many cannabis growers increase carbon dioxide levels in grow rooms, which can help plants grow faster under the right conditions. Typically, this carbon dioxide is the product of other processes, such as the production of ammonia, and would have been released into the atmosphere as waste if it had not been used this way. But there are still carbon emissions associated with compressing and shipping cannabis, so it ends up contributing around 500 kilograms of emissions for every kilogram of product.

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