Early participation of key developing countries is critically important for the feasibility of achieving low greenhouse gas concentration targets. The IMAGE framework is able to identify mitigation strategies for radiative forcing targets as low as 2.6 W/m², but such targets become infeasible (i.e. no solutions with prices below 273 US$/tCO2) if there is a long delay in developing country participation. If participation of developing countries is seriously delayed as defined by the EMF-22 specifications the model was still able to achieve a 3.7 W/m² target, but not the 2.6 or 2.9 W/m² targets. Delayed participation leads to higher costs (25–90% in the 3.7 W/m² cases) and delay in mitigation action. As international climate policy currently only requires emission reductions in a limited number of countries, increasing participation is a key priority if one aims to achieve low concentration targets.
In this article we explore several scenarios that aim at meeting radiative forcing targets at 4.5, 3.7, 2.9 and 2.6 W/m2 by 2100. These scenarios are run under the assumption of participation of all countries by 2012 in climate policy and under the assumption of a significant delay in the participation of Russia and non-Annex I countries (up to 2030 and 2050). The study finds the lowest radiative forcing categories to be feasible under full participation, certainly if overshoot of targets is allowed and when bio-energy and carbon-capture-and-storage is added to the mitigation portfolio. In cases with severe delay in participation, the lowest targets become infeasible. For less strict targets (e.g. 3.7 W/m2), delayed participation leads to considerable costs increases (up to 90% for the stabilisation case). As a next step, scenarios with less delay in participation need to be explored.