"Marijuana growers in the US are using $6 billion a year in electricity"

But hey, if the electricity is produced from hydrocarbons the added CO2 can boost yields by 20%!
From Quartz:

As more states legalize marijuana in the US, pot cultivation is sucking up an ever-growing amount of energy from the grid.

Since most of the legal weed is grown indoors, the pot industry burns through large quantities of electricity used to power lamps, ventilation systems, and air conditioning. A square foot of planting requires some 200 watts of electricity (pdf, p. 20), about the same as a data center, according to a report this year in the Columbia Journal of Environmental Law.

The paper notes that marijuana plantations soak up at least 1% of the country’s electricity at a cost of $6 billion a year....MORE

That's nothing. Back in 2007 our headline was "6% of all power produced by BC Hydro is used to grow marijuana.".