International audienceThis study explores a situation of staged accession to a global climate policy regime from the current situation of regionally fragmented and moderate climate action. The analysis is based on scenarios in which a front runner coalition - the EU or the EU and China - embarks on immediate ambitious climate action while the rest of the world makes a transition to a global climate regime between 2030 and 2050. We assume that the ensuing regime involves strong mitigation efforts but does not require late joiners to compensate for their initially higher emissions. Thus, climate targets are relaxed, and although staged accession can achieve significant reductions of global warming, the resulting climate outcome is unlikely to be consistent with the goal of limiting global warming to 2 degrees. The addition of China to the front runner coalition can reduce pre-2050 excess emissions by 20-30%, increasing the likelihood of staying below 2 degrees. Not accounting for potential co-benefits, the cost of front runner action is found to be lower for the EU than for China. Regions that delay their accession to the climate regime face a trade-off between reduced short term costs and higher transitional requirements due to larger carbon lock-ins and more rapidly increasing carbon prices during the accession period
Transportation accounts for a substantial share of CO2 emissions, and decarbonizing transport will be necessary to limit global warming to below 2°C. Due to persistent reliance on fossil fuels, it is posited that transport is more difficult to decarbonize than other sectors. We test this hypothesis by comparing long-term transport energy demand and emission projections for China, USA and the World from five large-scale energy-economy models with respect to three climate policies. We systematically analyze mitigation levers along the chain of causality from mobility to emissions, and discuss structural differences between mitigation in transport and non-transport sectors. We can confirm the hypothesis that transport is difficult to decarbonize with purely monetary signals when looking at the period before 2070. In the long run, however, the three global models achieve deep transport emission reductions by >90% through the use of advanced vehicle technologies and carbon-free primary energy; especially biomass with CCS plays a crucial role. Compared to the global models, the two partial-equilibrium models are relatively inflexible in their reaction to climate policies. Across all models, transportation mitigation lags behind non-transport mitigation by 10-30 years. The extent to which earlier mitigation is possible strongly depends on implemented technologies and model structure.
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