There is one key assumption that drives the system and the physics and that is the expected CO2 sensitivity values as establish by the 1979 NAS Charney report of 1.5C to 4.5 C with the expected value being 3.0 C. IF that 3.0C number is different than the GCM’s don’t work; and it seems that more current papers fall in the lower range or even below. If the CO2 is really .5C to 1.5C with an expected value of 1.0C than there must be other factors besides CO2 alone and than makes room for other factors.