Preindustrial human impacts on global and regional environment

Humans have had an impact on regional and global environments even prior to the Industrial Revolution through anthropogenic fire, agriculture, and the extinction of the Pleistocene megafauna. The preindustrial impact of anthropogenic fire to modify ecosystems and affect climate may have been small because in regions where impacts were once thought to be large, such as in Australia, the evidence now suggests a smaller effect. Both the extinction of the megafauna, which evidence indicates to be at least partially caused by humans, and preindustrial agriculture may have affected climate, but the effects may have offset each other. For instance, climate simulations indicate that megafauna extinctions may have led to a slight global warming, but later, agriculture led to a slight global cooling. Prior to the industrial era, the largest ecological and climate anomaly may have been associated with forest expansion during the early and mid-Holocene when there were few megafauna and agriculturalists to reduce this expansion.