It's not meaningless. CO₂ in the atmosphere causes the greehouse effect, which allows the sun to heat the earth more. To avoid greenhouse effect you can't have things that require CO₂ to constantly remain in the atmosphere. You need non-carbon sources like wind, solar, hydro, nuclear, geothermal, etc.

> To avoid greenhouse effect you can't have things that require CO₂ to constantly remain in the atmosphere.

But we don’t want to fully avoid the greenhouse effect. https://en.wikipedia.org/wiki/Greenhouse_effect:

“Earth's natural greenhouse effect keeps the planet from having the below freezing temperature that it would have if there were no greenhouse gases”

He's talking about the excess unnatural greenhouse effect.

I don’t see how one can read that from “To avoid greenhouse effect you can't have things that require CO₂ to constantly remain in the atmosphere.”

The natural greenhouse effect has CO₂ constantly (I think at least since there’s any carbohydrate burning on earth) remaining in the atmosphere.

It's all implied. Maybe he doesn't know about some of those things, but it is incredibly common to talk about it in those terms without spelling out that you mean excess / problem-causing amounts of the effect, etc. When he says can't have things he's talking about human energy use. He says right after you need to use wind, solar, etc.