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As marijuana becomes legal in more states for medicinal and recreational purposes, the expanding industry has also increased its environmental footprint. Marijuana has been legalized in more than half of the United States, and Prime Minister Trudeau plans to make Canada the second country worldwide to legalize the substance at the national level.

Because growing marijuana was a criminal offense in most states until quite recently, scant data exists about the environmental impacts of cultivating it. Researchers also have difficulty getting funding and procuring marijuana similar to that available to consumers, because it’s still illegal at the federal level. Some case studies, however, give us a glimpse of what effects larger-scale marijuana growing may have on the environment.

Marijuana grown indoors is a glutton for fossil fuels

Marijuana grown inside requires large numbers of grow lights, which means a great deal of power. Most often, these grow lights are high pressure sodium (HPS) lights, which use five to ten times more electricity than energy-saving LEDs. Estimates put the use of lighting for indoor marijuana growing at one percent of all electricity used in the United States, as much as the entire country’s home computers. Because most of this electricity comes from dirty power sources like coal, indoor marijuana growing operations have a significant carbon footprint.

Illegal growers may have an even bigger impact, relying on dirty diesel generators to avoid big power draws that could get noticed by authorities. That means in theory at least, the legalization of marijuana could reduce its impact, as illicit enterprises no longer have to stay off the power grid. Unfortunately the outcome is not that simple.

Scientists estimate that lighting for indoor marijuana growing uses one percent of all electricity generated in the United States, the same amount used by the entire country’s home computers.

The sharp increase in marijuana cultivation in states where the drug has recently become legal is straining local power suppliers. In Colorado, nearly half of all new power demand is from marijuana operations. Evan Mills, a researcher at Lawrence Berkeley National Laboratories, found that in California, the marijuana industry consumed as much electricity as one million homes.

There are distinct advantages to indoor cultivation for growers. Growing inside allows them to control the climate and amount of light plants receive while protecting crops from pests and disease. Indoor operations also may produce many more crops per year than outdoor ones, so they yield more income than those grown outdoors.

Some growers have made the logical move to greenhouses, which allow them to control the climate but also rely on free solar energy rather than artificial light. In these cases, their power bills–and energy footprints—decrease significantly, up to 90%.

Growing marijuana outdoors affects water and wildlife

Although outdoor grow sites avoid the emissions of electric-powered operations, they also have significant ecological impacts. Preparing an area for marijuana cultivation usually involves cutting down forests, bad news for both carbon capture and the wildlife that called the forest home.

A recent study in the journal Environmental Research Letters looked at over 4400 grow sites in Humboldt County, California, and determined that outdoor marijuana farms lead to landscape fragmentation, erosion, and stream degradation. Because outdoor marijuana grow sites tend to use remote parts of forested areas, clear-cutting and building of access roads increase the likelihood of chemical runoff and soil erosion. Polluted and silted streams endanger fish populations, while other animals lose their forest habitat.

Study authors Jake Brenner of the Department of Environmental Studies and Sciences at Ithaca College, and Van Bustic of the University of California Cooperative Extension, recommend that “Siting grows in areas with better access to roads, gentler slopes, and ample water resources could significantly reduce threats to the environment.”

Many illegal marijuana farms use public lands. Over the last fifteen years, for example, officials at Sequoia and Kings National Parks have removed roughly 270,000 plants valued at over $900 million. Officials of the parks worry about the water pollution and habitat destruction these operations leave in their wake. Logic implies legalization will halt these types of impacts. Yet other impacts will remain the same.

Like many agricultural products, marijuana requires a good deal of water, up to six gallons per plant per day. Pesticide use in marijuana farming is similar to other heavily sprayed crops, but because marijuana remains illegal at the federal level, no federal regulatory oversight exists. Researchers have raised concerns about the health effects of pesticides that would not be allowed on food crops.

Operations in California have poisoned bears, owls, foxes, and other creatures in who ingested poisons intended to kill crop pests. One of these pesticides, carbofuran, is a potent neurotoxin banned in the U.S., Canada, and the EU. Researchers have found traces of it on confiscated plants, which means it’s also likely winding up in the finished marijuana sold to consumers.

Study authors conclude, “The extent and magnitude of cannabis agriculture documented in our study demands that it be regulated and researched on par with conventional agriculture.”

Will legalization reduce marijuana’s footprint?

Though growth in the marijuana industry could increase its use of energy, water, land, and pesticides, legalization could also have some moderating influences. Firstly, when growers don’t need to hide their operations, their reliance on dirty generators to power grow lights should diminish. Second, regulations may restrict energy and water use, and place limits on pesticides. They may also limit the number of grow sites on environmentally-sensitive lands to better protect water and wildlife.

However, since numerous pesticides are allowed on food crops, there’s no reason to believe that legalization would lessen the overall use of pesticides in marijuana cultivation, though it might help reduce the use of banned pesticides, a good thing for the forest creatures currently exposed to them. A larger market may also create demand for organically-grown marijuana.

In a paper published in a recent UC Davis Law Review, Professor of Law at the University of the Pacific Michael Vitiello wonders whether legalization might actually reduce the market for marijuana, as some users enjoy it in part because it’s illicit. Further, taxation could increase its cost, making it less appealing financially. Others speculate that legalization may spur rapid growth in the market over the next few years.

Vitiello, however, urges us to “remain agnostic” about “whether legalization will lead to regulations that have the effect of making the marijuana trade pay for its environmental costs,” or better still, reduce them significantly. At present, there are simply too many unknowns.

What’s certain is that government bodies must be proactive in creating regulations for this burgeoning industry that ensure the safety of both ecosystems and consumers.

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