“Well, what would you say if there was such a plant that could substitute for all wood pulp paper, all fossil fuels, would make most of our fibers naturally, make everything from dynamite to plastic, grows in all 50 states and that one acre of it would replace 4.1 acres of trees, and that if you used about 6% of the U.S. land to raise it as an energy crop, even on our marginal lands, this plant would produce all 75 quadrillion billion BTUs needed to run America each year? Would that help save the planet?”

...

“Yeah? What is it?”

“Hemp.”

...

“Well, Mr. Herer, did you know that hemp is also marijuana?”

“Yes, of course I know, I’ve been writing about it for about 40 hours a week for the past 17 years.”

“Well, you know marijuana’s illegal, don’t you? You can’t use it.”

“Not even to save the world?”

“No. It’s illegal”, he sternly informed me. “You cannot use something illegal.”

https://jackherer.com/emperor-3/chapter-2/

Plants require water. Yes we can solve the plastic problem by growing more plants, but then we will have a water problem as plants, heavy industry, chemical production, recycling (which uses a lot of water), power production (most use steam), live stock, and human water consumption all compete.

I mean I guess we could melt the ice caps for more water...