John, I think you are deliberately misinterpreting what I am trying to say, so let me be pedantic.
If, in physics you postulate a quantitative relationship between a dependent and independent variable, then in establishing what that relationship is, you must follow certain rules. In this case the warmists claim that as you add more CO2 (the independent variable) to the atmosphere, global temperatures (the dependent variable) will rise. The ratio of rise of CO2 and temperatures is the climate sensitivity.
In order to measure climate sensitivity, it is essential to prove that the observed rise in temperature was all caused by the rise in CO2, and no other factors were involved.
Since we do not know all the factors which affect global temperatures, this is impossible to do. So it is impractical. at the present time to measure climate sensitivity.