The climate mitigation potential of urban nature-based solutions (NBSs) is often perceived as insignificant and thus overlooked, as cities primarily pursue NBSs 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 yr⁻¹ of carbon emissions. Among the cities analysed, 1189 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.

人们通常认为基于城市自然解决方案（NBS）的气候缓解潜力微不足道，因此被忽略了，因为城市主要是为本地生态系统服务而寻求NBS。鉴于城市对此类项目的兴趣和能力与日俱增，因此需要更好地了解城市森林在缓解气候变化方面的潜力。我们对全球范围内城市重新造林的全球潜力和局限进行了建模，发现10.9 2.8 Mha的土地（占所有城市地区的17.6％）适合重新造林，这将抵消82.4 25.7 MtCO ₂ e yr ^-1的碳排放量。在分析的城市中，有1189个可能通过植树造林抵消了其城市碳排放量的25％以上。城市自然气候解决方案应在全球和地方议程中占有一席之地。