Climate warming has caused a widespread increase in extreme fire weather, making forest fires longer-lived and larger^1,2,3. The average forest fire size in Canada, the USA and Australia has doubled or even tripled in recent decades^4,5. In return, forest fires feed back to climate by modulating land–atmospheric carbon, nitrogen, aerosol, energy and water fluxes^6,7,8. However, the surface climate impacts of increasingly large fires and their implications for land management remain to be established. Here we use satellite observations to show that in temperate and boreal forests in the Northern Hemisphere, fire size persistently amplified decade-long postfire land surface warming in summer per unit burnt area. Both warming and its amplification with fire size were found to diminish with an increasing abundance of broadleaf trees, consistent with their lower fire vulnerability compared with coniferous species^9,10. Fire-size-enhanced warming may affect the success and composition of postfire stand regeneration^11,12 as well as permafrost degradation¹³, presenting previously overlooked, additional feedback effects to future climate and fire dynamics. Given the projected increase in fire size in northern forests^14,15, climate-smart forestry should aim to mitigate the climate risks of large fires, possibly by increasing the share of broadleaf trees, where appropriate, and avoiding active pyrophytes.

气候变暖导致极端火灾天气的广泛增加，使森林火灾的持续时间更长、规模更大^1,2,3。近几十年来，加拿大、美国和澳大利亚的平均森林火灾规模增加了一倍甚至三倍^4,5。作为回报，森林火灾通过调节陆地-大气中的碳、氮、气溶胶、能量和水通量来反馈给气候^6,7,8。然而，日益严重的火灾对地表气候的影响及其对土地管理的影响仍有待确定。在这里，我们使用卫星观测表明，在北半球的温带和北方森林中，每单位燃烧面积的火灾规模持续放大了夏季长达十年的火灾后地表变暖。研究发现，随着阔叶树数量的增加，变暖及其随火势大小的放大而减弱，这与与针叶树物种相比，它们较低的火势脆弱性一致^9,10。火势大小的增强型变暖可能会影响火后林分再生的成功和组成^11,12 以及永久冻土退化¹³，从而对未来的气候和火动力学产生以前被忽视的额外反馈效应。鉴于预计北部森林的火灾规模会增加^14,15，气候智能型林业应以减轻大火的气候风险为目标，可能在适当的情况下增加阔叶树的份额，并避免活跃的火生植物。