1a. What is the approximate spectral composition of the Sun's radiation before it interacts with Earth's atmosphere?

1b. Is the amount of solar energy that reaches the top of Earth's atmosphere constant? Explain.

1c. Are all wavelengths of solar radiation transmitted equally through Earth's atmosphere? Explain.


2a. What effect does absorption have on the amount of solar radiation that reaches Earth's surface?

2b. What additional processes (besides absorption) affect radiation reaching the surface of Earth?

2c. What percentage of incoming solar radiation is affected by absorption and scattering (or reflection)?


3a. What do we mean when we say that clouds have a high albedo while land vegetation has a low albedo?

3b. What factors affect the insolation at a particular location on a particular day? How do they affect it?

3c. What latitudinal regions experience least variation in day-to-day solar radiation? Which experience the greatest? Why?


4a. What happens to most radiation that is absorbed by the surface of Earth?

4b. What is the difference between sensible and latent heat?

4c. Why don't global temperatures rise as a result of incoming solar radiation?


5a. What is the greenhouse effect?

5b. What chemical compounds contribute to greenhouse warming?

5c. Mars and Venus both have high relative concentrations (~95%) of the greenhouse gas CO2 in their atmospheres. Why is Venus so hot while Mars is colder than Earth?

5d. What is global warming?


6a. What general mechanism is responsible for redistributing heat energy in Earth systems?

6b. What drives atmospheric circulation?

6c. Explain simply how atmospheric circulation develops.


7a. Are the oceans or the atmosphere more efficient at storing energy? Explain.

7b. Explain what effect ocean heat capacity has on global temperatures.

7c. Give an example of how atmosphere and ocean systems affect each other.


8a. Explain how humans can affect land surface albedos.

8b. Explain how the loss of land vegetation might modify local climates.

8c. What impact have humans had on concentrations of greenhouse gases? Give a specific example.



1a. The Sun's spectral output is composed of approximately 9% ultraviolet (and shorter) wavelengths, 41% visible light, and about 50% infrared radiation. See Section 1 and Figure 2.01.

1b. The solar energy that reaches the top of Earth's atmosphere is more or less constant. It does vary a little as Earth revolves annually around the Sun, and because of changes in solar activity. See Section 1.1.

1c. No. Different wavelengths of light interact differently with water and aerosols in the atmosphere. Some wavelengths are preferentially transmitted, some are scattered, and other wavelengths are absorbed. See Section 1.2 and Figure 2.03.

2a. Absorption reduces the amount of solar radiation that reaches Earth's surface. On average, about 15% of incoming solar radiation is absorbed by atmospheric molecules such as water vapor, oxygen and small particulates (aerosols). See Sections 1.2, 1.2.1 and Figures 2.02 and 2.03.

2b. Scattering of solar radiation within the atmosphere also accounts for a reduction of energy reaching Earth. See Section 1.2.1.

2c. Combining together the percentages of incoming energy absorbed (18%) and scattered (26%) by the atmosphere plus clouds, the overall effect is that nearly half (18% + 26% = 44%) of the energy entering the atmosphere doesn't make it through to Earth's surface. See Section 1.2.1.

3a. Albedo is the fraction of the reflected solar radiation to the incident solar radiation. Clouds have a high albedo, meaning they reflect a much greater percentage of the incoming light than does vegetation. See Section 1.3.

3b. The insolation (incoming solar energy) received on a daily basis depends primarily on 1) the angle of the Sun above the horizon (solar elevation angle, solar incidence angle), 2) the length of time the surface is exposed to the Sun, and 3) atmospheric conditions. The higher the sun in the sky and the longer a surface is exposed to the sun, the more insolation. The clearer the sky, the more insolation. As Earth revolves around the Sun over the course of a year, its orbital and tilt geometry cause seasonal and latitudinal variations in insolation. See Section 1.3 and Figure 2.05.

3c. Generally, equatorial regions experience less fluctuation in daily insolation throughout the year. Further from the equator, seasonal differences are more pronounced. Polar regions experience many more hours of sunlight than darkness in their respective summer, and many more hours of darkness than sunlight in their respective winter. On the equator, however, there is a nearly constant 12 hours of sunlight throughout the year. Moreover, the distance light has to pass through the atmosphere near the equator is less than the distance it passes through near the poles. See Section 1.3 and Figure 2.05.

4a. Most of the radiation absorbed by Earth's surface is reradiated (emitted) as long wavelength (longwave) radiant energy.

4b. Sensible heat is radiant energy that directly flows between objects or areas due to a temperature difference between them. Latent heat is released or absorbed when water changes state during the processes of evaporation, evapotranspiration, melting, freezing, condensation, and sublimation. See Section 2.1 and Figure 2.06.

4c. A balance exists between incoming solar energy and Earth system reradiation of longwave radiation back into space. See Section 2.1.

5a. The greenhouse effect is the warming of Earth's atmosphere caused by the absorption of longwave energy emitted by the surface of Earth. Atmospheric gases and clouds act like a greenhouse roof to keep heat in the system. See Section 2.2.

5b. Substances that have a significant effect on global warming are water vapor, carbon dioxide, methane, nitrous oxide, chlorofluorocarbons, and liquid water droplets. See Section 2.2.

5c. Venus has greater relative and absolute amounts of carbon dioxide than Earth and Mars. Despite a 95% relative concentration of carbon dioxide, Mars has a much thinner atmosphere overall so the absolute amount of carbon dioxide is too small to trap the solar insolation reemitted from the surface. See Section 2.2.

5d. Global warming is a consistent trend of increasing global temperatures caused by additional amounts of greenhouse gases accumulating in the atmosphere. See Section 2.2.

6a. The circulation of the atmosphere and oceans redistributes heat from areas of surplus to areas of deficit. See Section 2.3 and Figure 2.08.

6b. The heat differential between tropical and polar areas (generated by latitudinal differences in insolation) drives atmospheric circulation. See Section 2.3.1.

6c. Equatorial areas are heated more than polar areas; the warming equatorial air rises as it gets less dense. The rising tropical air gets replaced by cooler, denser air moving down from the poles by a process known as convection. Due to the rotation of Earth and the resulting Coriolis force, several circulating cells in each hemisphere are generated. See Section 2.3.1 and Figure 2.09.

7a. Oceans are more efficient at storing energy, due to the tremendous volume of water in the oceans and water's capacity to hold heat. See Section 2.3.2.

7b. The oceans impart a moderating effect on global temperatures. See Section 2.3.2.

7c. The El Niño-Southern Oscillation (ENSO) that occurs periodically in the southern Pacific Ocean is an example of how ocean circulation and atmospheric circulation interact. Changing moisture budgets, altered winds and decreased coastal upwelling become part of a chain of energy redistribution that affects global climate patterns. See Section 2.3.2.

8a. Albedo can be changed by modifying land surfaces. In general, presence of vegetation cover reduces albedo, while bare soil and concrete increase albedo. Moisture tends to lower albedos, lack of moisture raises albedos. See Section 3.1 and Figure 2.10.

8b. When vegetation is removed from a surface the localized radiation budget changes. Though the surface albedo usually increases and hence relatively more insolation is reflected and less absorbed, the localized area may become hotter overall due to less shading and less evaporative cooling as a result of reduced transpiration. The reverse may be true at times when vegetation is not transpiring; for example, during winter forested areas absorb more insolation and act as wind breaks, and thus may be warmer than cleared areas. See Section 3.1.

8c. Anthropogenic forces have increased atmospheric concentrations of methane ( rice cultivation, raising sheep and cattle, gas mining, trash landfills), carbon dioxide (consumption of fossil fuels, biomass burning), and chlorofluorocarbons (refrigerants, solvents, aerosol propellants). See Section 3.2.