I am not aware of any physical mechanism that would lead to such limit
for total feedback.
The algorithm then adds «weight» (credibility) depending on various factors: rating frequency, total submissions, low value versus high value transactions,
total feedback on a given product and other parameters.
It is a strong positive
total feedback because even at effectively 2 C per doubling we are not keeping up with the forcing, and with no positive feedback, we would be nearer 1 C per doubling.
I do doubt however if one could easily get
a total feedback that is negative so I would think it might be difficult to go below 1C.
The Planck response is a negative feedback; including it,
the total feedback is -(1 / equilibrium climate sensitivity) and must be negative in order for equilibrium climate sensitivity to be finite.
The CO2 ERF is one - half the 4 × CO2 forcings from Andrews et al. (2012), and
the total feedback (ALL + Planck) is from Vial et al. (2013).
It is the water that is in
total feedback (negative) control of the global Temperature; it does that by the surprising, and unlikely mechanism of actually altering the incoming solar energy that drives the climate system; and it can easily eradicate any minor perturbation such as the minor effect on outgoing LWIR because of CO2 or Ozone or other GHGs (other than water).