Making or breaking climate targets: The AMPERE study on staged accession scenarios for climate policy

TLDR

The study examines staged accession to a global climate regime from the current fragmented climate action. The authors model scenarios where a front‑runner coalition (EU or EU+China) adopts immediate ambitious action while the rest of the world transitions to a global regime between 2030 and 2050, assuming strong mitigation without requiring late joiners to offset earlier emissions. Staged accession relaxes climate targets and is unlikely to meet the 2 °C goal, though adding China to the front‑runner coalition cuts pre‑2050 excess emissions by 20–30 % and improves the chance of staying below 2 °C; the EU bears lower front‑runner costs than China, and delayed accession trades lower short‑term costs for higher transitional costs due to larger carbon lock‑ins and rising carbon prices.

Abstract

This 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.