Land Use Model

( i ). If you use all the values proposed in the program and the changes in albedo listed in Section 3 what are the two surface temperature changes predicted? Did you expect them both to be negative? Why? Do you understand why they are different?

( ii ). If you input only the change in surface albedo due to tropical deforestation and make all the other changes zero what temperature changes do you get? Are they larger or smaller than from (i)? Why?

(iii) If you input only the change in surface albedo due to desertification and make all the other changes zero, what temperature changes do you get? Do they differ less or more from one another than for (i) and (ii)? Why? [Hint: think about the cloud fractions over tropical forest cf. over deserts].

(iv) Can you perform an experiment in which human land-use changes increase temperature?

(v) What happens to the predicted temperatures in any of (i)-(iv) if you make all the cloud fractions zero? Why?

(vi) What happens to the predicted temperatures in any of (i)-(iv) if you make all the cloud fractions 1.0 (i.e. 100% cloud)? Why?

(vii) What is the sensitivity of this model to the degree of uncertainty you can identify in the literature in either the current extent of anthropogenerated (human-induced) surface albedo changes or the albedo differences say between a tropical rainforest and land cleared for pasture? To establish model sensitivity you need to run at least two simulations: one with your best guess input (call this the control experiment) and another with a second estimate of the input values (called the experiment). Now compare how sensitive the results (here ΔT) are to the range in your input values.

(viii) Why do the two linear relationships between ΔR and ΔT differ? If there are two such relationships can both be correct? Do you believe either is correct? What do you mean by correct?

Sagan, C., and Toon, O.B. and Pollack, J.B. 1979, Anthropogenic albedo changes and the Earth's climate, Science, 206, 1363-1368.

Additional Readings:

Hansen, J., Johnson, D., Lacis, A., Lebedeff, S., Lee, P., Rind, D. and Russell, G., 1981, Climate impact of increasing carbon dioxide, Science, 213, 957-966.

Manabe, S. and Wetherald, R.T., 1967, Thermal equilibrium of the atmosphere with a  given distribution of relative humidity, J. Atmos. Sci., 24, 241-259.

Last updated on 10/13/09 02:22 PM by Zong-Liang Yang