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    Climate Change Is Making Weed Stronger

    Written by

    Brian Merchant

    Senior Editor

    In the midst of covering the worst drought to hit the Midwest in half a century, an NBC reporter kept stumbling upon a plant that didn’t seem to mind the water shortage. When she asked farmers in Iowa about the marijuana, which she spotted growing just about everywhere, even on the side of the road, they shrugged. They called it “ditchweed” and mostly seemed annoyed that the local police kept asking them to pull it up.

    As a weed, marijuana is pretty drought-friendly. It may come under fire for sucking down too much water in parched California, but it doesn’t actually need a ton of it to survive. Furthermore, marijuana has been shown to thrive under higher CO2 concentrations, as well as water scarce conditions. Some research even indicates that its psychotropic properties may become more potent in stressed conditions. Weed, it seems, was built to boom in our climate-changed world.

    "Marijuana is a very drought-tolerant plant. It's a weed, and they grow anywhere,” DEA agent Bill Weinman told the Rocky Mountain News during a dry spell in 2002. "Drought has little effect on pot crops: Plants prove hearty, surpassing yields of state's other crops." Authorities tasked with cracking down on illegal grow operations had long noted that marijuana seemed undeterred by drought.

    In fact, a 1988 AP story about the seizure of unusually healthy plants in Virginia—again, during a drought—came packaged with the headline “Drought May Make Marijuana More Potent.” The reporter interviewed a Virginia Tech researcher who believed that alkaloids in marijuana would grow more concentrated under hotter weather, as they do in tobacco and coca plants.

    Now we know that the active ingredient in cannabis is tetrahydrocannabinol, or THC, which isn’t an alkaloid. It is produced by the plant as a pest repellant, however, and research indicates that cannabis produces more of it when it's stressed—subjected to drought, or disease.

    Lewis Ziska, a plant physiologist with the US Department of Agriculture, and USDA ethno-botanist James Duke, both say their research shows that stressors will increase the plants’ “medicinal” properties.

    “[T]he more stress a plant gets—heat or cold or disease or just plain beating it—the more medicinal and less edible it becomes," Duke recently told the Daily Climate, which published a summary some of the reasons marijuana might become more potent under climate change.

    Ziska, meanwhile, has shown that as CO2 levels in the atmosphere increase, most plants, including marijuana, will benefit.

    The basic science of why this is the case takes us back millions of years: the vast majority of plant species, Ziska says, evolved in periods where the standard carbon dioxide concentration in the atmosphere was much higher, closer to 1,000 parts per million. Humans, meanwhile, evolved when CO2 levels were much lower—around 280-300 parts per million. While that level was ideal for people, with the temperate climes and all, most plants never truly adapted to the CO2 deprivation.

    Image: Robert A. Rhode

    Now, as humans are pumping more CO2 back into the atmosphere, at an unprecedented pace, those plants are loving it.

    Image: Wikimedia

    Further research backs this up: A 2009 study published in Physiology and Molecular Biology of Plants tested those hypotheses in a real-world environment, and found that marijuana grew quite well in carbon concentrations of 750 ppm, the highest amount tested. The authors concluded that their findings demonstrate marijuana's "potential for better survival, growth and productivity in a drier and CO2 rich environment.”

    A follow up study from the same authors confirmed as much: Primarily due to its “decreased stomatal conductance and subsequently the transpiration rate,” the researchers found that marijuana’s makeup “may enable this species to survive under expected harsh greenhouse effects including elevated CO2 concentration and drought conditions.”

    Meanwhile, weed was already getting too good. Add in the fact that growers have been on a decades-long quest to grow super-potent pot strains on their own accord—some recent indoor-grown strains have tested as high as 33 percent THC, while in 1978, the average strain of marijuana had a THC level of 1.37 percent—and the future is looking quite interesting for the nation’s preferred drug to pair with sitting on the couch and watching TV. (Which also happens to be how we have mostly reacted to climate change.)

    Marijuana is pretty much the perfect drug for the climate apocalypse—it thrives in elevated CO2, embraces drought conditions, and may even become stronger yet as the world warms.

    It’s a reminder that climate change is everywhere, propelling transformations that are sometimes minuscule, sometimes drastic. Not even weed is untouched by our fossil fuel habits. If we don’t cut back, I guess we can at least settle into those higher temps with a buzz, and watch the rising seas with a glazed-over mellow. Maybe get a few visuals to distract from the sunburn.