Global urban reforestation can be an important natural climate solution

The climate mitigation potential of urban nature-based solutions is often perceived as insignificant and thus overlooked, as cities primarily pursue nature-based solutions for local ecosystem services. Given the rising interest and capacities in cities for such projects, the potential of urban forests for climate mitigation needs to be better understood. We modelled the global potential and limits of urban reforestation worldwide, and find that 10.9 ± 2.8 Mha of land (17.6% of all city areas) are suitable for reforestation, which would offset 82.4 ± 25.7 MtCO2e y-1 of carbon emissions. Among the cities analysed, 1,189 are potentially able to offset >25% of their city carbon emissions through reforestation. Urban natural climate solutions should find a place on global and local agendas.