Should We Stop the COPs?

Ten years after COP21, carbon emission trajectories remain far above the 1.5 ° C threshold, due to lack of international consensus. Breaking from cost-benefit approaches, we assess the maximum reduction in carbon emissions that could be accepted by all countries. We characterize the consistent target 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 a uniform carbon price of $250 per ton would be politically acceptable by all countries. It could reduce global emissions by 35%, but would require unprecedented international transfers: up to 3% of world GDP, with a large redistribution from high-income, low-emission countries to carbon-intensive emerging economies. Our analysis highlights the structural ambition gap imposed by voluntary cooperation and identifies two levers to overcome it: convergence in green technologies and stronger political support for mitigation. Without progress in these dimensions, international climate policy remains constrained to deliver only modest results.