Greenhouse Gases and Climatic Change

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Earth climate is determined by the equilibrium between the amount and distribution of incoming radiation absorbed from the sun and the outgoing longwave radiation emitted at the top of the atmosphere. Several atmospheric trace gases, including water vapor, carbon dioxide, methane, and nitrous oxide, absorb far more efficiently the longwave radiation than solar radiation. These so-called greenhouse gases increase the amount of energy available to the earth and keep it much warmer than it would be otherwise. Although water vapor (and clouds that contribute both to the greenhouse effect and cooling through the back reflection of the incoming solar radiation) does not stay in the atmosphere more than ~2 weeks, most of the other greenhouse gases stay far more than 10 years. Anthropogenic use of fossil fuels, cement production, and deforestation already increased the atmospheric concentration of greenhouse gases and human activities also created new synthetic and powerful ones such as chlorofluorocarbon. The corresponding positive radiative already contributed to the ~0.8 °C increase of the global surface temperature since 1850 and will act as the main climate driver for at least the next century. This chapter outlines the bases of the greenhouse effect and its impact on the earth climate from ~1850 to 2100.