Conventional “CO2-equivalent” (CO2-e) emissions calculated using 100-year “Global Warming Potentials” do not consistently reflect the impact of emissions on global temperature: they overstate the impact of constant emissions of any short-lived climate pollutant such as methane by a factor of about four, while understating the large impact of changes in methane emission rates. Myles Allen and Michelle Cain from the University of Oxford explain how CO2-e emissions can nevertheless be used to calculate “warming-equivalent” emissions to inform burden-sharing discussions, mitigation policies in crucial sectors such as agriculture, and stocktakes of progress towards a global temperature goal.