claim: CO2 limits won't cool the planet, but they can make the difference between continued accelerating global warming to catastrophic levels vs. slowing and eventually stopping the warming at hopefully safe levels.
evidence: In the early and middle Ordovician, temperatures were mild, but at the beginning of the Late Ordovician, from 460 to 450 Ma, volcanoes along the margin of the Iapetus Ocean spewed massive amounts of carbon dioxide, a greenhouse gas, into the atmosphere, turning the planet into a hothouse.