Using crowdsourced data to estimate the carbon footprints of global cities

•A hybrid method is established to estimate the carbon footprints of global cities.•The method integrates top-down input–output analysis and bottom-up crowdsourced data.•Carbon footprints of 465 global cities in 2020 are estimated.•10% of the global population in these cities account for 18% of global CO2 emissions.•Unproportionable benefits could be obtained by carbon abatement in a few cities.