Part one of term paper
, in environmental science, is a popular term for the effect that certain variable constituents of the Earth's lower atmosphere have on surface temperatures. These gases--water vapor (H2O), carbon dioxide (CO2), and methane (CH4)--keep ground temperatures at a global average of about 15 degrees C (60 degrees F). Without them the average wou ...

Part two of term paper
... are concerned that changes in the variable contents of the atmosphere (particularly changes caused by human activities) could cause the Earth's surface to warm up to a dangerous degree. Even a limited rise in average surface temperature might lead to at least partial melting of the polar ice caps and hence a major rise in sea level, along with other severe environmental agitation. An example of a runaway greenhouse effect is Earth's near-twin planetary neighbor Venus. Because of Venus's thi ...