10., There are many greenhouse gases, including carbon dioxide (CO2), methane (CH4). and vaporized water (H2O). These and other greenhouse gases warm the Earth primarily by:, 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., Making more clouds, because clouds block the radiation from the planet, which is why cold, frosty nights are rare during cloudy weather.C., Raising the atmospheric pressure, because squeezing air warms it, as we saw at the Redwoods.D., Making politicians mad, so they give speeches that heat the air.E., Absorbing some of the infrared radiation emitted from the Earth. 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. Clouds are not caused by greenhouse gases, and while clouds warm nights, clouds cool days, and the net effect of clouds is probably slight cooling of the planet. Convection currents are blocked by the glass of greenhouses, but not by greenhouse gases. But CO2 does absorb some of the infrared radiation emitted from the planet. Absorbing an infrared photon puts a CO2 molecule into an excited state, and fairly quickly the molecule returns to its unexcited state by emitting a photon of the same energy. Some of those photons emitted by excited CO2 molecules head back toward Earth (the emission direction is random). So, the CO2 serves to trap energy in the Earth system, warming the planet so that it glows more brightly to shove infrared radiation past the CO2, achieving a new balance. , Points Earned:, 1/1 Correct Answer:, E Your Response:, E
11., The idea that human activities will cause global warming is well over a century old now. The United Nations has been sponsoring studies of this idea for almost two decades. The assembled scientists have concluded, with high confidence, that: , A., CO 2 levels in the atmosphere have been rising, warming the planet a degree or so, and burning all the remaining fossil fuels likely will raise the Earth’s temperature many degrees or more. B., CO 2 levels in the atmosphere have been rising, with no effect on the climate. C., CO 2 levels in the atmosphere have been rising because of natural causes, and this has been the primary cause of the ozone hole. D., Human activities have lowered methane levels in the atmosphere, causing cows to become more flatulent to achieve balance. E., CO 2 levels in the atmosphere have been rising, warming the planet a small fraction of a degree, and if we burn all the remaining fossil fuels, we may raise the temperature another small fraction of a degree. Human activities have raised CO2 in the atmosphere, causing warming of a degree or so. But if we continue with business as usual, we haven’t seen anything yet—we haven’t even doubled CO2, but a quadrupling or even octupling seems possible. Cow flatulence is not greatly affected by external methane levels, which are rising in any case. Besides, bovine belching is a larger methane source than is outlet through the other orifice.
- Fall '08
- Global Warming, Correct Answer, Coal, Pennsylvania, plant material, Points Earned