At the UN’s COP28 summit yesterday, 197 countries resolved to move away from their reliance on fossil fuels—the first such pledge in history. The countries agreed to collectively achieve net-zero greenhouse-gas emissions by 2050, while tripling renewable energy use by 2030. But does it have teeth? As with the Paris Agreement of 2015, this accord leaves much up to individual countries to implement, offering leeway in how, and how quickly, they live up to the pact.