1. The Greenhouse Effect
Electromagnetic (EM) radiation, radiation processes
“Clear Sky” Exercise
Earth-Sun System
Greenhouse Gases
“Cloudy Sky” Exercise

2. Background Information
Electromagnetic (EM) radiation
Solar and Terrestrial Emission
Radiation Processes and Interactions
Water Vapor is a Greenhouse Gas (selective absorpotion)

3. Central Project Question
Knowing that water vapor is a potent greenhouse
gas, what do you expect is the short-term effect of
cloud cover on your local temperature?

4. The Greenhouse Effect
Electromagnetic (EM) radiation, radiation processes
“Clear Sky” Exercise
Earth-Sun System
Greenhouse Gases
“Cloudy Sky” Exercise
Earth vs Moon

5. Clear Sky Anticipation Questions
For a weather station located at Des Moines, Iowa ,
consider the following questions regarding the diurnal
cycle during both winter (January) and summer (July).
Why does temperature change through the day?
2) Assuming a cloudless day, plot your expectations
for the diurnal cycle of temperature using the blank
template figure.

6. Hour of Day
Hour of Day

7. Anticipation Questions (continued…)
Diurnal cycle during both winter (January) and summer
(July) at Des Moines Iowa.
3) Indicate the time of sunrise and sunset in your
figure.
4) What, specifically, causes temperature to increase
or decrease?
5) How do summer and winter differ? Why?

8. Hour of Day
Hour of Day

9. Anticipation Questions (summary)
Diurnal cycle during both winter (January) and summer
(July) at Des Moines Iowa.
Indicate the time of sunrise and sunset in your
figure.
What, specifically, causes temperature to increase
or decrease?
How do summer and winter differ? Why?

10. Realization
Data Source: Airport at Des Moines, IA from (NCDC Surface Airways)
Observation Variables: Temperature and cloud ceiling height (the height of the lowest cloud layer, if present)
Methodology:
Sort data and select only “clear sky” conditions
Compute the average diurnal cycle
Repeat for both January and July data

11. Hour of Day

12. Clear Sky Contemplation
Why does temperature change through the day?
How does temperature decrease?
How do summer and winter differ?

13. The Greenhouse Effect
Electromagnetic (EM) radiation, radiation processes
“Clear Sky” Exercise
Earth-Sun System
Greenhouse Gases
“Cloudy Sky” Exercise
Earth vs Moon

14. Radiation: Fundamental Principles
All objects emit EM radiation; the wavelength and energy emitted depends on the object’s temperature
As Temperature increases,
total emission increases
As Temperature increases,
wavelength of peak emission decreases

15. Solar and Terrestrial Radiation
UV | Visible | IR
NOTE:
Log
Scale!
Sun
Earth

16. (No Atmosphere Case)
Absorbed = Emitted =
Earth,

17. “Radiative Equilibrium”
Solar Radiation
Terrestrial Radiation
“Radiative Equilibrium”
Incoming = Outgoing
Stable Temperature

18. The Greenhouse Effect
Electromagnetic (EM) radiation, radiation processes
“Clear Sky” Exercise
Earth-Sun System
Greenhouse Gases
“Cloudy Sky” Exercise
Earth vs Moon

19. Earth’s atmosphere absorbs light at most wavelengths.

20. Selective Absorption in the Atmosphere

21. Greenhouse Gases are… …“transparent” for sunlight
…only partially transparent to
Infrared Radiation (…from Earth’s Surface)
… “warmed” via radiation
(However, sensible heat and convection also
“warm” the atmosphere)

22. The Greenhouse Effect
Electromagnetic (EM) radiation, radiation processes
“Clear Sky” Exercise
Earth-Sun System
Greenhouse Gases
“Cloudy Sky” Exercise
Earth vs Moon

23. Cloudy Sky Anticipation Questions
Diurnal cycle during both winter (January) and summer
(July) at Des Moines Iowa.
1) How might temperature differ between clear and cloudy sky conditions?
2) Draw your expectations on the figure provided,
labeling the clear and cloudy sky lines.

24. Hour of Day

25. Hour of Day
Hour of Day

26. Cloudy Sky Contemplation
Why is the cloudy sky temperature relatively flat?
How does clear sky temperature get both hotter and
colder than the cloudy sky temperature?

27. Greenhouse Process Incoming Solar Earth’s Surface Emits
Infrared Radiation

28. Greenhouse Process
Greenhouse Gases
Absorb IR

29. Greenhouse Process
Greenhouse Gases
Absorb IR
Emit IR

30. Greenhouse Process NET EFFECT: Earth’s surface Warmed by TWO
Heating sources

31. Greenhouse Process What if we add more Greenhouse Gases?? TWO
Heating sources

32. The Greenhouse Effect Summary
GHGs absorb IR emitted by Earth’s Surface
The gases also emit IR back to the surface,
providing an additional heating source.
An example of this effect is the relative warmth of
cloudy nights.
Additional GHGs will increase surface temperature
in the same way as enhanced cloud cover.