Ok...with the caveat that saying "CO2 is only one minor factor" is self-serving. In fact, that's what's in dispute.
The fact that it is a minor factor is in no dispute as that factor is readily determined in relation to the heat capacity effects of other "greenhouse" gases.
The dispute lay in theinsistance of the focus on CO2 as if it were a major contributor to climate incomparison to water vapor, solar activity and astonomical factors the true principal determiners of the Earth's global climate.
If Mann, et. al. agree that co2 is a minor factor then what are they arguing?