EES 3310/5310

Energy Balance and Climate

Class #3 (Mon., Jan 24)

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Required Reading (everyone):

  • Understanding the Forecast, Ch. 2–3, pp. 9–23.

Reading Notes:

Note: There is an error in Table 3.1 on p. 23 of Understanding the Forecast: The observed temperature of the earth (\(T_{\text{observed}}\)) is 288 K, not 295 K.

As you read Understanding the Forecast, focus on pp. 13–23 . You need to understand the calculations of the “bare-rock” model on pp. 19–23. The intermediate steps are not as important as two equations: \[ F_{\text{out}} = F_{\text{in}}\quad\text{at equilibrium,} \] and equation (3.1), which describes the bare-rock model: \[ T_{\text{earth}} = \sqrt[4]{\frac{(1-\alpha)I_{\text{in}}}{4\epsilon\sigma}} \] (Helpful hint: to take a fourth root easily with your calculator, just press the square root key twice.)

Questions to think about (not to write up and turn in):

  • What is blackbody radiation? What is a “blackbody” anyway?

  • Why is it that the sun gives off visible light, but the earth does not?

  • When the earth absorbs energy from sunlight, where does the energy go initially? Where is the final destination of that energy?

  • What is the Stefan-Boltzmann equation, and why is it important?

  • What does the Stefan-Boltzmann equation tell us would happen if the sun got hotter? What would happen if the Earth got hotter?

  • Study table 3.1 on p. 23 of Understanding the Forecast (ignore the column “\(T_{\text{1 layer}}\)” because we don’t get to that until later in the chapter.):

    • Why is the sunlight brighter on Venus than on Earth, and dimmer on Mars?
    • Why is the “bare-rock” temperature of Venus lower than Earth, even though it gets more sunlight?
    • Why do you suppose the actual observed temperature at the surface of Venus is so much hotter than the “bare rock” temperature?
  • At the top of p. 20, why does Archer write, \(F_{\text{out}} = F_{\text{in}}\)? What would happen if \(F_{\text{out}} \ne F_{\text{in}}\)

  • Without getting bogged down in the details of the numbers, why are the areas used to calculate the incoming and outgoing energy fluxes different? (Figures 3.1 and 3.2 explain this)

  • If the sun got 5% brighter, approximately how many degrees warmer would the earth become?