1. Planetary Engineering 1
Climate Modeling
Class Exercise

2. Zero-Dimensional GEBM
Global energy balance: Radiative equilibrium (in = out)
Recall the energy balance in 0-dimensions and what it means for temperature.

3. Goal: Planets’ Temperatures
Important Fact: Sun heats less the farther it is.
What factor(s) affect change in S with distance from sun?
Important Factor: How does S change with orbit?

4. Change in solar flux: sun  earth
Recall from Topic 1:
Change in solar flux: sun  earth
At photosphere surface, solar flux ~ W-m-2
Note strong decrease from photosphere to Earth’s orbit.
At Earth’s orbit, solar flux ~ 1360 W-m-2

5. Two Spheres Surrounding Sun
Total energy flux the same through each sphere
R2 = 2 x R1 R2 R1
Consider 2 spheres surrounding the sun. Both intercept all the energy emitted by the sun. The larger sphere covers 4 x the surface area of the innner sphere. Thus the same amount of energy is spread over 4 times greater area.
The same area at R2 intercepts only 1/4 of energy it intercepts at R1
 Flux decreases as R-2

6. Global energy balance: Radiative equilibrium (in = out)
For Earth
Global energy balance: Radiative equilibrium (in = out)
Recall what we derived for Earth, based on observed S and albedo.
Thus, TRAD = 255 K

7. What about other planets?
How does Trad change with orbit?

8. What about other planets?
How does Trad change with orbit?
Planet Distance Albedo Outgoing IR Trad from sun [A.U.] [W-m2] [K]
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
This table can be easily filled in.

9. Tsurface ≈ Trad. How warm can we make its surface?
For Mars
Tsurface ≈ Trad. How warm can we make its surface?
Suppose we can alter the surface of Mars. How can we engineer a warmer surface?

10. Tsurface ≈ Trad. How cool can we make its surface?
For Mercury
Tsurface ≈ Trad. How cool can we make its surface?
Similarly for Mercury.

11. Why can’t we adjust Venus the same way?
What is different about Venus? (Hint: Why does Tsurface ≠ Trad for Earth?)

12. End Planetary Engineering 1