Sharing the reduction effort to limit global warming to 2°C

In order to stabilize long-term greenhouse gas concentrations at 450 ppm CO2-eq or lower, developed countries as a group should reduce emissions by 25-40% below 1990 levels by 2020, while developing countries' emissions need to be reduced by around 15-30%, relative to their baseline levels, according to the IPCC and our earlier work. This study examines 19 other studies on the emission reductions attributed to the developed and developing countries for meeting a 450 ppm target. These studies considered different allocation approaches, according to equity principles. The effect of the assumed global emissions cap in these studies is analysed. For developed countries, the original reduction range of 25-40% by 2020 is still within the average range of all studies, but does not cover it completely. Comparing the studies shows that assuming a global emissions cap of 5-15% above 1990 levels by 2020 generally leads to more stringent reduction targets than when a global emissions cap of 20-30% above 1990 levels is assumed. For developing countries, the reduction range of 15-30% below their baseline levels by 2020 corresponds to an increase on the 1990 level from 70% (about the 2006 level) to 120%. Reducing deforestation emissions by 50% below baseline levels by 2020 may relax the emission reductions for either group of countries; for developing countries by about 7% or for developed countries by about 15% (but not for both).