National Carbon Reduction Commitments: Identifying the Most Consensual Burden Sharing

How could the burden of GHG emission reduction be shared among countries? We address this arguably basic question by purely statistical methods that do not rely on any normative judgment about the criteria according to which it should be answered. The sum of current Nationally Determined Contributions to reducing GHG emissions would result in an average temperature rise in 2100 of the order of 3°C to 3.2°C. Implementing policies that enable to achieve the objective of a worldwide average temperature rise below 2°C obviously requires setting a more consistent and efficient set of national emissions targets. While a scientific consensus has been reached about the global carbon budget that we are acing, given the 2°C target of the Paris Agreement, no such consensus prevails on how this budget is to be divided among countries. This paper proposes a Climate Liabilities Assessment Integrated Methodology (CLAIM) which enables to determine national GHG budgets compliant with any average temperature target and time horizon. Our methodology does neither resort to any scenario nor any simulation-based model. Rather, it computes the allocation of 2°C-compatible national carbon budgets which has a priori the highest probability of emerging from the international discussion, whatever being the criteria on which the latter might be based. As such it provides a framework ensuring the highest probability of reaching a consensus. In particular, it avoids the pitfall of arbitrarily assigning weights according, say, to "capacity" or "responsibility" criteria, and simultaneously unifies the different methodologies that have been proposed in the literature aiming at setting national GHG budgets. Sensitivity tests confirm the robustness of our methodology.