Historical deforestation locally increased the intensity of hot days in northern mid-latitudes

Abstract

The effects of past land-cover changes on climate are disputed1–3. Previous modelling studies have generally concluded that the biogeophysical effects of historical deforestation led to an annual mean cooling in the northern mid-latitudes3,4, in line with the albedo-induced negative radiative forcing from land-cover changes since pre-industrial time reported in the most recent Intergovernmental Panel on Climate Change report 5 . However, further observational and modelling studies have highlighted strong seasonal and diurnal contrasts in the temperature response to deforestation6–10. Here, we show that historical deforestation has led to a substantial local warming of hot days over the northern mid-latitudes—a finding that contrasts with most previous model results11,12. Based on observation-constrained state-of-the-art climate-model experiments, we estimate that moderate reductions in tree cover in these regions have contributed at least one-third of the local present-day warming of the hottest day of the year since pre-industrial time, and were responsible for most of this warming before 1980. These results emphasize that land-cover changes need to be considered when studying past and future changes in heat extremes, and highlight a potentially overlooked co-benefit of forest-based carbon mitigation through local biogeophysical mechanisms. Deforestation in the northern mid-latitudes has generally been considered to cause biogeophysical changes that drive mean annual cooling in the region. Research now suggests that historical deforestation has led to substantial local warming of hot days.