ABSTRACT
The activities of people influence the biosphere of the earth in many visible ways. When forests are replaced by cropland, when grasslands are replaced by deserts, or when estuaries are dredged or filled, changes in the number and kinds of living species in the vicinity are easily observed. The simplest climate model can only be compared with the long -term average of the global temperature. The range of global average temperatures that has occurred since the retreat of the last ice age and the beginning of settled agriculture seems to have been within plus or minus one degree of the average. The activity consists of changing, slightly, through industrial and agricultural activities, the composition of the atmosphere by adding long-lived, infrared absorbing gases, such as carbon dioxide, methane, chlorofluorocarbons, nitrogen oxides, and substances that affect the supply of ozone in the lower atmosphere.
