more carbon dioxide in the lower atmosphere means more little «point sources» for more absorbed
EM in the infrared part of the spectrum, (infrared that re-radiated from the earth's surface after sunlight
hit it and got absorbed); and since point sources radiate in a spherical pattern, that means more «back radiation» to earth,
on balance... and this changes the «standing pattern» of energy flow in and out of the earth system, creating a time differential, so it starts to re-adjust...