By some estimates, indoor marijuana cultivation is accountable for producing some 15 million metric tons of carbon emissions annually—the equivalent to the amount of emissions produced by three million American cars. Put another way, one single kilogram of processed marijuana is responsible for the same amount of emissions as driving a 44 mpg car across the country five times. How can this be? It’s due in most part to the significant amount of electricity required to grow marijuana indoors.Since there are now 320 million Americans, the first number comes to 0.05 ton CO2/person/year.
The second set of numbers gives, with 2900 miles between San Francisco and New York at 44 mpg, gasoline usage of 330 gallons. Since gasoline emits 8.92e-3 t CO2/gallon, that comes to 2.94 t CO2 per kilogram of pot, or 0.08 t CO2 per ounce, or 2,940 grams CO2/gram-of-pot*.
An ounce of pot is about 28 joints, so pot's carbon footprint is 2,980 g CO2/joint.
American per capita emissions are now 17.0 t CO2/yr, so a joint's footprint is 1.5 hours of per capita emissions*.
Assuming the entire event lasts for more than an hour and a half, you're reducing your carbon footprint by smoking. (If it comes from an indoor grow.)
To that you need to add the carbon footprint of a couple of bags of Doritos, and most of a day's worth of television, but hopefully you can subtract out the driving.
These numbers also imply Americans are partaking of 5,100 tons of indoor-pot per year, or an average of 16 indoor-joints/person/yr*. Which isn't obviously unbelievable.
Some, of course, more than others.
* If I did the math correctly. Corrections welcome.