There's a qualitative barrier there. The AI risk people in the know are afraid of is not a flood of AI-generated articles, but something that probably can't be achieved yet with current levels of AI (and more slop generated from current-day AI won't hasten the advent of). On the other hand, modern-day greenhouse gases are exactly the greenhouse gases that climate activists are afraid of in the limit.

The AI risks people in the know are afraid of, are indeed what I listed: pretty much any person, anywhere, using an existing model running off their laptop to foment real-world violence or spread disinformation en masse on social media, or use it on a cheap swarm of weaponized/suicide drones, for a few examples

That's what we're already seeing today, so we know the risk is there and has a probability of 100%. The "skynet" AI risk is far more fringe and farfetched.

So, like you said about climate change, the harm can come from 1 person. In the case of climate change, though, the risks people in the know are afraid of, aren't "some guy willing to spin a stick for long enough to start a fire, or to feed and protect a flock of cows"