By Jaymi Heimbuch | Published in Treehugger Marijuana is a big industry in the US, especially as medical use of marijuana becomes more popular. And while we expect grow houses with tons of energy-sucking lights to have high bills, it might be a surprise to see the grand total the industry spends on electricity every year. It adds up to 20 terawatt-hours per year -- which is about 1% of national electricity consumption, or the output of seven large power plants. According to a recent report conducted and published independently by Evan Mills, Ph.D., a long-time energy analyst and Staff Scientist at the Lawrence Berkeley National Laboratory, the amount of energy we spend growing weed is rather extraordinary. A grow house can use lighting as bright as that of an operating room, use an air-change rate 60 times that of a normal home, and have the energy consumption of a data center. Yeesh!! Because of indoor cultivation of marijuana, and the need to grow indoors in order to hide operations from authorities, the industry has an outstanding footprint. The study states that Cannabis production results in: \t$5 billion energy bill each year \tElectricity use equal to 2 million average US homes \t1% of national electricity consumption \tGreenhouse gas pollution equal to 3 million cars What is even more fascinating to learn from the report is how much CO2 a single joint represents. " single Cannabis cigarette represents 2 pounds of CO2 emissions, an amount equal to running a 100-watt light bulb for 17 hours with average U.S. electricity (or 30 hours on California's cleaner grid)." Wow! Talk about ways to reduce your carbon footprint! We've discussed before on TreeHugger the ways in which legalizing marijuana could potentially benefit the environment, because of the disastrous effect illegal operations have on forests, watersheds, and now CO2 emissions. Knowing these figures, it wouldn't be surprising if one day soon we're hearing about buying only sustainably grown marijuana in the same way we should only buy sustainably grown coffee or beef. Dr. Mills, a member of the international body of scientists which has worked over the past two decades under the Intergovernmental Panel on Climate Change (IPCC), notes that there are ways to improve the energy consumption of Cannabis production. "If improved practices applicable to commercial agricultural greenhouses are any indication, the energy use for indoor Cannabis production can be reduced dramatically. Cost-effective efficiency improvements of 75% are conceivable, which would yield energy savings of about $25,000/year for a generic 10-module growing room. Shifting cultivation outdoors eliminates most energy uses (aside from transport), although the practice can impose other environmental impacts." As GreenTechMedia points out, "I'm sure there's a policy lever here -- if marijuana was completely decriminalized, prices would drop and the profit margin would diminish, but that might not translate into less usage." Especially if a marketing strategy were to latch on to the sustainability movement and show how your weed is greener.