Historical deforestation locally increased the intensity of hot days in northern mid-latitudes, Lejeune 2018

Deforestation has contributed to warming in the northern mid-latitudes of North America and Eurasia not only through a large contribution to global CO2 emissions, but also through biogeophysical effects. The latter refers to land-surface effects such as albedo and evapotranspiration, which vary according to the type of land cover. This study uses models to demonstrate that deforestation in the northern mid-latitudes has increased the intensity of hot days by about a third since pre-industrial times. Factoring in deforestation’s contribution to greenhouse gas emissions further increases deforestation’s heating effect.

Our best estimate suggests that the present-day contribution of deforestation to the TXx [yearly maximum temperature, or “hot days”] increase over this region still equals at least 50% once the warming entailed by the LCC [land cover change]-induced carbon emissions is considered [LeJeune 2018: 4].

“Extensive deforestation took place early in the industrial period over the northern mid-latitudes,” and then slowed down in the 20th Century [LeJeune 2018: 4]. By 1920, modeled increases of temperature “through biogeophysical effects had already reached 0.3°C (~75% of their present-day values) over the most deforested areas of North America and Eurasia. On average before 1920, local deforestation was responsible for most of the TXx [yearly maximum temperature] warming over these regions” [LeJeune 2018: 4]. Warming caused by greenhouse gases became more important during the 20th Century, “leading to a total warming of 1.3°C over North America and 1°C over Eurasia by the present-day” [LeJeune 2018: 4].