Mitigation scenarios in a world oriented at sustainable development: the role of technology, efficiency and timing

The two scenarios differ in the timing of mitigation action (early action versus delayed response). Analysis of the scenarios has led to the following findings. First, stabilisation at a carbon dioxide concentration of 450 ppmv is technically feasible (requiring a 40% reduction of cumulative emissions between 2000 and 2100 compared to the baseline). Second, in the first quarter/second quarter of this century most of the reduction will come from energy efficiency and fuel-switching options, while the introduction of carbon-free supply options will later account for the bulk of the required reductions. Third, postponing measures foregoes the benefits of learning-by-doing, and, as a result, early-action seems to be a more attractive strategy for stabilisation at 450 ppmv than delayed response (about 30% lower cumulative investments between 2000 and 2100). Fourth, the most difficult period for the mitigation scenarios is the 2010-2040 period (exact timing depends on early action or delayed response), when 'bending the curve' towards a lower carbon emission system will have to be initiated. Finally, the real obstacles for implementing mitigation policies are related to (the large differences in) costs and benefits for individual countries and sectors. Hence, we believe that much political ingenuity will be required to find a method for fair burden sharing.