The US submission on elements of the post-2015 agreement is a good basis for further deliberation by countries, as it is exhaustive with only some elements needing to be debated for a global consensus.

The US quite rightly acknowledges that “with respect to CBDR/RC in particular, we endorse the view that national efforts will be differentiated across a broad continuum of all Parties based on a range of factors, including circumstances, level of development, mitigation opportunities, capabilities, etc. However, we would not support a bifurcated approach to the new agreement, particularly one based on groupings that may have made sense in 1992 but that are clearly not rational or workable in the post‐2020 era. There have been, and will continue to be, dramatic and dynamic shifts in countries' emissions and economic profiles that make such an approach untenable, environmentally and otherwise.”  The political challenge will be to determine how the changing trajectory of emissions at different levels of development will be reflected in the new agreement.

National contributions will have to distinguish between countries required to "limit/reduce" GHG emissions, as a legal agreement needs to be specific on this key commitment, otherwise it will meet the fate of the UNFCCC with its “aim” of returning emissions to a previous level.  There is clarity only on those who have to “limit” their emissions but not for those who have to “reduce” the growth of their emissions. Therefore, if contributions are not to be based on “groupings” the commitments should be specified in terms of a common metric of contribution to the "concentration of GHG's". This will be in accordance with the Objective of the Convention and the most recent science in the latest report of the IPCC, which frames the requirement in terms of the global carbon budget.

A "common time frame" for initial contributions assumes that all countries are at the same level of development and well-being. Again, if there has to be common metric, patterns of natural resource use in the civilization shift from rural agriculture to urban industry have to be taken into account. Climate change first came on the global agenda in the Stockholm Conference in 1972, and that could form the ‘common time frame’ for measuring the contribution of countries to the global concentration of GHG’s till 2050, when comparable levels of development should have been achieved by all.

Differentiation, on the basis of CBDR/RC, will then shift to the procedural aspects of the new arrangement, as the schedules and guidelines for reporting of information will need to recognise levels of development and circumstances of those countries who have to "limit" their emissions because of their acceptance of their responsibility and earlier commitment under the UNFCCC and those that will be taking new commitments at earlier stages in their growth to "reduce" emissions as they achieve a comparable level of development with the others, only then will the review "account for differentiation based on capability (to be replaced by the term ‘level of development’) and circumstances".

Assessment of the aggregate global effort will then be in terms of three parameters:  emissions reduction by those who have to limit their emissions, keeping well within their fair share of the global carbon budget by those who have to reduce the trajectory of their emissions and modification of consumption and production patterns by all countries.

The institutions related to Loss and Damage, Finance and Technology that have emerged under the UNFCCC, and have accumulated considerable knowledge, learning and experience, will need to be integrated into the new arrangement, and their effectiveness in supporting all countries to achieve comparable levels of development and further reduce the differentiation between countries, should be reviewed in 2032, in the global conference following Rio + 20.

Once there is an agreement on the new framework for ‘sharing responsibility and prosperity’ the details will fall in place. The outcome will depend on political willingness to deal with the causes of the problem of climate change by modifying consumption and production patterns rather than focus only on the symptoms of the problem by measuring emissions.