We know it's not that simple. Allowing the discussion to be framed around it : "Hansen's CO2 sensitivity from 1988 is wrong, so the world is not warming all that fast" is a huge mistake.

CO2 is the biggest forcing, but a number of others, both positive and negative, are of the same order of magnitude. As a first approximation, the other forcings more or less cancel each other out, leaving a net forcing roughly equivalent to that of CO2. This does NOT mean that we can disregard other forcings!

In particular, the photochemical and particulate coolings are tied to levels of dirty industrial activity, and have varied a great deal in the past few decades. In my modest opinion, their decline in the 80s and 90s (cleanup of OECD heavy industry, decline of ex-Soviet bloc industry) steepened the global warming curve over that period; this decline has since been swamped by the dirty industry of China, India, et al, which is currently flattening the curve.

If one can't abstract that sort of influence (and especially if one declines to try), I find the idea of deriving a CO2 sensitivity from observed temperatures to be downright silly.

_{It is rightly acknowledged that people of faith have no monopoly of virtue - Queen Elizabeth II}