It occurred to me that a PDF is an inverted basin of attraction. If we are experiencing more extreme weather, the PDF is shifting. The basin of attraction is changing. A steep basin in the past would be consistent with low sensitivity. There is little variability and few chances of a regime change. A flattened basin like a flattened PDF is going to give us lots of variability. So we have the question, do GHGs flatten the basin? With a flattened basin, is it possible for the ball (the climate) to shift to another regime, perhaps like Trenberth’s step changes? Are past regime shifts such as a PDO shift, a flattening of the basin, and do they also explain the transitions in and out of glacials and interglacials?