Concrete, stone, asphalt, and roofs tend to act as solar collectors and emit and absorb heat. The burning of fossil fuels also emit greenhouse gases like carbon dioxide that heat up the atmosphere around the source and usually the source is within urban environments. Cities also tend to be cloudier, rainier, and less humid than their surrounding areas. Average relative humidity is six percent less in urban areas because cities have large impervious surfaces and little surface or soil water to exchange by evaporation with the atmosphere. Urbanization and human activity creates a microclimate that is not environmentally healthful.
Urban environments produce air pollution that harm the natural environment.
Much of air pollution is concentrated in and around urban areas, where automobiles and industry emit mass amounts of waste into the environment. Visible air pollution, known as smog, is present in nearly all urbanized areas. Not only are humans affected adversely by bad air quality, animals also suffer. Air pollution can also curb vegetation growth and reduce crop yields. Air pollution from human activities harm all living creatures in the urbanized world.