Heat influx varies with small variations in earth’s orbit resulting rom mismatch of orbital cycle of planets thus gravitational effect on earth. (Sometime adding up, sometimes offsetting.)
And there’s the fundamental physics of greenhouse gases - the saturation effect of overlap of spectra of carbon dioxide and dihydrogen monoxide limits effect of CO2 on climate temperature to a small amount most of which has already been realized. Climate was warmer yet stable in the Medieval Warm Period when Vikings farmed southwest Greenland.