CO2 levels are 60% higher than in the late 18thC, and are still rising fast. There's a very simple mechanism which causes it to raise global temperature. Climate is far more complicated than we can understand: perhaps there is some not-yet-known feedback mechanism which means we won't get much warmer. But given the least worst science available, most likely it will make it quite a lot warmer rather fast, which is likely to be difficult for our grandchildren. If we had another planet or two for us to move to if it turns out badly, that might be a reasonable chance to take.
But we haven't got another planet.
We know how to stop adding CO2. It wouldn't even cost that much. We won't do it. That's amazingly stupid, and we don't like admitting to stupidity, so we grasp at straws. Or scandinavian tree-rings, of course.