Group members preparing summary: Katy Schoel, Lisa Boeckman, Josh SierenSummary Information:
Energy enters the atmosphere as visible light. Some is used by global systems while some is released back into the atmosphere as infrared radiation (IR). This process determines our global climate. The energy that is absorbed will either raise the temperature of the object or evaporate surface water and create atmospheric water vapor. If an object absorbs enough energy to raise its temperature so that it is significantly higher than its surroundings it will release infrared energy to bring its temperature back down. The released IR is released into space or absorbed by greenhouse gases, including CO2, N2O, CH4, O3, and CFCs. This absorbtion is what causes global warming.
Clouds are the largest absorbers of infrared radiation. Humid places with a lot of cloud cover don't lose their heat as fast at night as dry places with no clouds. Clouds absorb the IR and re-radiate it back to the surface of the earth, keeping the temperature higher. Greenhouse gases work in the same way.
Greenhouse gases have different absorptive properties than ozone and oxygen, which block UV light while allowing visible light and IR to pass through. CO2 is a strong absorber if IR, which means the more carbon dioxide we have in the atmosphere, the more IR will be absorbed and reflected back to earth, increasing the temperature and contributing to global warming. Water vapor has the same property.
Class Figures:
Figure 0: This chart showed the amount of energy absorbed by a horizontal surface at different places on the globe. In class one of the questions brought up was why did the South Pole have more energy than the equator? One of the suggested answers was that the tilt of the earth on its axis meant that the south pole is closest to the sun during the northern hemisphere's winter. It is summer in the southern hemisphere then and the south pole is experiencing its longest days and receiving almost 24 hours of sunlight. The earth is closest to the sun in its orbit at this time, so the received radiation will be more intense. All of these factors could contribute to this phenomenon.
Figure 3: This chart illustrated the different wavelength absorbtivity of different atmospheric gases. The spikes on the graph show which wavelengths are absorbed, and can be translated into what type of light is being absorbed (i.e. visible, UV, etc.). notice that oxygen and ozone are the biggest absorbers of UV lights, so the destruction of the ozone layer will allow damaging UV radiation in.
Figure 4: Carbon dioxide produces the biggest change in radiative forcing with a factor of 6.3 W m-2.
Figure 7: This graph showed the increase in forcing due to increasing concentrations of greenhouse gases over the decades. Notice the significant increase in the majority of the gases between 1950 and 1970.
Figure 9: Changes in forcing due to aresols is almost equal to those produced by the natural changes of the sun or volcanic activity.
Figure 11: This graph showed the localized cooling effects due to sulfate emissions of industrialized countries. The reasons for this were discussed in a previous unit.
Dialog Summary:
It was pointed out that energy is changing form before it is released back into space as infrared radiation. Energy is not created or destroyed in this process. Another form of energy contributing to earth's temperature comes from the reaction's taking place at earth's core, but they are probably insignificant for the most part compared to the amount of energy received from solar radiation. Someone asked about the effects of smog on global warming, and most people responded that smog affects local temperatures but doesn't have a large effect on global temperatures, and we agree with this conclusion.
Another question asked was what can we do to reduce the effects of smog and ultraviolet radiation, but there were no responses to this query.
The following is an interesting website about ozone.