Think of CO2 as the handle on a spigot. It provides huge leverage over climate, but is clearly not the whole story.

Water Vapor and Methane are far more potent greenhouse gasses. Melting permafrost release CO2 and methane. Rising temperatures enhance evaporation and increase water vapor. A small rise in T due to CO2 creates an even larger rise due to enhance water and methane in the atmosphere. And rising T cause rising CO2 as well. Their is no simple one-way cause and effect. McGrath used exactly the correct phrase above - positive feedback. Climate and all of the above gasses are in a feedback loop.

That has been true for billions of years. What has changed in the last few hundred to thousand is the increased anthropogenic emissions - CO2 among them.