From Envirowiki

The Atmosphere is the gaseous layer of a planet, and lies between either the lithosphere or hydrosphere of a planet, and space. Generally, the word atmosphere refers to the atmosphere of Earth, which includes the troposphere, exosphere, etc. The atmosphere contains part of the biosphere, and pretty much everything to do with weather, and a lot of climate.

The atmosphere is made up largely of nitrogen, oxygen, carbon dioxide, and trace gasses. The atmosphere and the hydrosphere are currently being affected by anthropogenic global warming due to the increased greenhouse effect, which is caused by larger concentrations of CO₂, Methane, and a number of other greenhouse gasses.