"CO₂ isn't a pollutant" climate change deniers are missing the point, and hopefully this meme is simple enough for them to understand. I'd post it on Reddit too, but I'm trying to cut down on Reddit use.
Alt text:
Meme about Wreck-It Ralph (labeled “Fossil fuel emissions") overfeeding a pink rabbit (labeled “Plants") pancakes (labeled “C0₂")
The simple science is that plants do grow in heavier CO2 environments, sometimes very well. But they grow differently, which is a problem for food plants, because they don't produce what we want from them as food unless we also add heavy nutrients and water. In a greenhouse environment, this can increase production. In the outside, it's far more difficult to get good results.
So they aren't wrong, they just don't understand the bigger picture. Change one thing, other things change too, not always in the direction you want.