> a given CO2 level determines a rate of global heating

This IS the greenhouse effect. Increased levels of greenhouse gasses result in a warmer planet over time as Earth reflects less solar energy back into space. This warming leads to many known runaway feedback loops: increased wildfires that release more CO2 and destroy natural carbon sinks, reduced albedo from ice melt, increased moisture in the atmosphere, warmer oceans leading to less carbon sequestration by phytoplankton, methane release from ice melts.

There are more. Please read some recent literature to understand this better than anyone can summarize on HN. I recommend The Uninhabitable Earth