This chapter discusses human influence on the severity of plant disease epidemics through changing environmental factors. It considers: (1) The impacts of man-induced climate change on the severity of disease epidemics; increased greenhouse gas emissions, increased temperature, changing weather patterns, and changing seasons all affect severity of epidemics. (2) The effects of environmental conditions influenced by agricultural practices for climate change adaptation and mitigation on the severity of epidemics. (3) The consequences of other man-made environmental changes (e.g., increase in air-borne pollutants) on the severity of epidemics of plant diseases.