It is a simple question. With the data we have now, the estimates for at least the transient "sensitivity" to an equivalent forcing of a doubling of CO2, approximately 3.7 to 4.1 Wm-2, are decreasing to a range of roughly 0.8 to 2.1 C degrees. The base "no feedback" sensitivity to a doubling is 1 to 1.5 C degrees. All warming greater than that requires amplifying of positive feed backs that are not currently showing in the data.
The atmospheric effect or the limiting impact of "surface" heat loss due to all the properties of the atmosphere, is approximately 334 Wm-2 with an uncertainty range of 15 Wm-2 by my estimation and 345 +/- 9 Wm-2 per the Stephens et al energy budget, is produced by the total thermal energy stored by the "true" surface, mainly oceans. Since any amplification that may exist is include in the atmospheric effect, for a small change, 334Wm-2 to 338Wm-2 it is unlikely that there will be more than a minor amplification since the increase in "true surface" would offset warming near the rate it currently offsets warming.
The average energy of the bulk of the oceans is approximately 4C degrees or 334.5 Wm-2, the ocean quite likely produce the energy that creates the majority of the atmospheric effect. Land area in the habitable range, that excludes the Antarctic and most of Greenland is only 20 to 24% of the surface area and has already been developed to a great extent. There is little in the way of glacial expanses left to be impact other than Greenland with will take centuries of more to melt based on most estimates.
So is there any legitimate reason to expect warming greater than the no feed back climate sensitivity?
That is the center of the debate. Not that CO2 does not have some impact, just what is the reasonably expected impact. Most "advocates" tend to provide unreasonable, alarming, overly confident high estimates. Provide a valid reason to expect more if you do.