Assessing countries' historical contributions to GHG emissions

One of the main principles in the UNFCCC is the recognition of parties' "common but differentiated responsibilities and respective capabilities". Countries' past contributions to climate change or global greenhouse gas (GHG) emissions differ, which has prompted discussion over their historical responsibility for current and future climate change. This report first assesses the countries' contribution to historical GHG emissions using different scopes of time and emission sources, both as cumulative emissions and cumulatively on per-capita terms. The choice over the scope used affects the countries' contribution significantly. Whether emissions prior to 1990 are accounted affects particularly the contribution of USA, EU and China, whereas the inclusion of LULUCF emissions has a tremendous effect on the contribution of Brazil and Indonesia. When emissions are measured on per-capita terms, the contribution of e.g. Brazil and Indonesia can become significant, while that of EU is decreased considerably. Different assumptions hence lead to very different conclusions on countries' responsibilities for climate change. The report also analyses the possibility to define per-capita based emission budgets to countries, from which the historical emission would be subtracted. The choice of scope has again large implications for the countries' remaining budgets, but regardless of the choice, such an approach would lead to unrealistic emission pathways for USA and Russia, making it unclear whether such tonne-per-tonne accounting of historical emissions is reasonable in burden sharing. Therefore, to make historical responsibility a usable concept in climate negotiations, the scope of countries' accountability for past emissions should be first settled and efforts should be viewed in a broader context than that of direct emission reductions.