Earth's Changing Atmosphere

Recent measurements have revealed that the characteristics of this atmosphere are changing. Figure 1 is a plot of atmospheric carbon dioxide, in parts per million, as a function of time since 1972. You can see that at all locations, the carbon dioxide concentration of the atmosphere is increasing. We know why it's increasing: the burning of fuels (coal, oil, natural gas), the burning of vegetation, and the production of cement. It is an uncontested fact that CO₂ in the atmosphere has risen from a pre-industrial (1780) level of 280 parts per million (ppm) to the current (2007) level of 382 ppm - a 34% increase.

There are other gases in the earth's atmosphere whose composition has changed in recent years. Methane is an example. Figure 2 shows the concentration of methane in parts per million over the last thousand years. You can see that for the first 700 years of this record, until the 1700's, the concentration of methane in the earth's atmosphere was fairly constant. But since the Industrial Revolution, methane concentration has increased quite dramatically to the levels more than double the pre-Industrial Revolution values. The sources of methane are reasonably well known: cattle, termites, rice paddies, boreal forests, and high latitude tundras are sources of methane gas.

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