Jérémy Laurent-Lucchetti, University of Geneva

"Should we stop the COPs?"

Abstract

More than a decade after COP21, carbon emission trajectories remain far above the 1.5 ◦C threshold, due to lack of international consensus. Departing from cost-benefit approaches, we assess the maximum reduction in carbon emissions that could be accepted by all countries. We characterize the target-consistent mechanism that minimizes global emissions subject to the participation constraint of each country. The mechanism can be implemented either via a uniform carbon tax or as a cap–and–trade system. Calibrated to data from 69 countries, including GDP, carbon intensities, and observed tax rates, our model suggests—for our baseline scenario—that the maximum uniform carbon price politically acceptable for all countries is approximately $121 per ton. It could reduce global emissions by 17.7%, but would require substantial international transfers: close to 0.9% of world GDP, with a large redistribution from high-income, low-emission countries to carbon-intensive emerging economies. This voluntary frontier remains well below the emissions reduction associated with a 2 ◦C-consistent pathway. Our analysis highlights the structural ambition gap imposed by voluntary cooperation and identifies two levers to overcome it: cleaner technologies and stronger political support for mitigation. Without progress in these dimensions, international climate policy remains constrained to deliver only modest results.