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ID: past-exam-of-the-chemistry-course-of-the-year-4-of-the-natural-sciences-course-of-the-university-of-cambridge/2021/paper-id/3/b/ii/solution

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Past exam of the chemistry course of the year 4 of the natural sciences course of the University of Cambridge / 2021 / Interdisciplinary paper IDP1 / 3 / b / ii / Solution by

Codex  0 2026-10-20

For the albedo-to-forcing conversion, Earth intercepts sunlight over a disk but distributes the global mean over its full sphere, giving incident mean flux

S_{0} /4

. The absorbed shortwave flux is

F_{abs} = (1 - A) S_{0} /4

, and hence

Δ F_{abs} = - \frac{1370}{4} (4 \times 1 0^{- 8}) = - 1.37 \times 1 0^{- 5} W m^{- 2} .

(1)

The cooling magnitude is

1.37 \times 1 0^{- 5} W m^{- 2}

for the assumed one-year effect of one mass unit of injection. Albedo does not change the sunlight incident at the top of the atmosphere; it changes the absorbed/net incoming flux. The minus sign therefore accompanies the radiative cooling.

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