The core of the Climate Equity Reference framework is still the dynamic Responsibility and Capacity Index approach. Or, as we sometimes call it, the "Responsibility, Capacity, and Need approach." However, the CERP approach has been substantively generalized, and much more generalization and extension is planned for the future.
We would also like to thank Kirk Smith, who as far as we can tell invented the Responsibility and Capacity Index, or at least the approach that it embodies. (We thought that we had done so, but in fact Kirk beat us by over a decade!) See Kirk R. Smith, Joel Swisher, and Dilip R. Ahuja, "Who pays (to solve the problem and how much)?," in Peter Hayes and Kirk Smith (eds.), The global greenhouse regime: Who pays?, United Nations University Press/Earthscan, London, 1993.