10.Oxygen (O2) and nitrogen (N2) do not have much greenhouse effect, but several trace gases including carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and various chlorofluorocarbons are important greenhouse gases. The primary mechanism by which these greenhouse gases warm the Earth is: A.Preventing convection currents that take heat aloft, in the same way that the glass of a greenhouse stops convection currents and so makes the air in the greenhouse warmer.B.Raising the atmospheric pressure, because squeezing air warms it, as we saw at the Redwoods.C.Experiencing chemical reactions with each other, which release energy.D.Absorbing some of the infrared radiation emitted from the Earth.E.Making politicians mad, so they give speeches that heat the air. Although it is true that squeezing air warms it, the pressure does not set the temperature (change in pressure brings change in temperature), and, the greenhouse gases are really very rare and don't affect pressure much. The production and breakdown of the greenhouse gases roughly balance energetically, and any slight imbalances are tiny compared to the radiative effects of the gases. Convection currents are blocked by the glass of greenhouses, but not by greenhouse gases. But CO2 does absorb
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