Exploring climate regimes for differentiation of commitments to achieve the EU climate target

Five climate regimes are explored:

1. the Brazilian Proposal, with differentiation of emission reductions based on countries' relative contribution to the global temperature increase realised.
2. Multi-Stage (MS) approach with a gradual increase in the number of Parties involved and their level of commitment according to participation and differentiation rules. 
3. Per Capita Convergence approach (PCC) or 'Contraction & Convergence', with universal participation and a convergence of per capita emissions. 
4. Preference Score (PS) approach, an allocation derived from a population weighted preference score voting for either grandfathering or per capita allocation. 
5. Jacoby Rule (JR) approach with both participation thresholds and burden allocation based on per capita income.

It is found that, on the short-term (2025) and under a emission profile for stabilising CO₂ concentrations at 450 ppmv (consistent with the EU-target), all approaches result into reductions of emission allowances of Annex I regions of about 20 to 60 percent compared to their 1990 emission levels. For Europe the reductions are 40-60 percent in 2025. 

At the same time, major non-Annex I regions (East Asia and South Asia) need to start participating in global emission reduction before the middle of this century, irrespective of the emission allocation approach and type of threshold chosen. In addition to the quantitative analysis the strengths and weaknesses of the various regimes were also explored in a qualitative way on the basis of a multi-criteria evaluation. Different types of criteria were identified: environmental, political, economic, technical and institutional and general policy criteria. 

Overall, the MS approach seems, in principle, to best satisfy the various types of criteria. However, other approaches could improve their performance by making adjustments in their design.