IB Physics HL B 2 Greenhouse Effect Questions

Model Earth's energy balance by tracking incoming solar radiation, reflection, surface emission and infrared absorption and re-emission by greenhouse gases.

Exam points

Apply energy conservation to track radiation absorbed, emitted and re-emitted in the Earth–atmosphere system.
Use solar constant, planetary geometry and albedo to calculate mean absorbed solar intensity.
Apply emissivity and Stefan–Boltzmann law to calculate radiated intensity and equilibrium temperature.
Explain greenhouse-gas infrared absorption and re-emission using resonance or molecular energy levels.
Use energy-balance models to explain the natural greenhouse effect and surface warming.
Explain how changing ice, cloud or surface albedo alters reflected and absorbed solar energy.
Explain how increased greenhouse-gas concentrations from human activity augment the greenhouse effect.

Covered syllabus points

B.2.1—Conservation of energy B.2.2—Emissivity B.2.3—Albedo B.2.4—Earth’s albedo variation B.2.5—Solar constant S B.2.6—Mean solar intensity B.2.7—Greenhouse gases B.2.8—Infrared absorption B.2.9—Greenhouse models B.2.10—Enhanced greenhouse effect

[Maximum number: 1]

The diagram shows a simple model of the energy balance in the Earth surface-atmosphere system. The intensities of the radiations are given.

What is the average intensity radiated by the atmosphere towards the surface?

$100 \mathrm{Wm}^{-2}$

$150 \mathrm{Wm}^{-2}$

$240 \mathrm{Wm}^{-2}$

$390 \mathrm{Wm}^{-2}$

[Maximum number: 8]

The diagram shows a simplified energy-balance model for the Earth surface-atmosphere system.

The following data are given:

\begin{aligned} \text { Average albedo of Earth } & =0.30 \\ \text { Average global temperature of the surface } & =288 \mathrm{~K} \\ \text { Average Earth-Sun distance } & =1.5 \times 10^{11} \mathrm{~m} \end{aligned}

(a)

State what is meant by the solar constant.

The diagram shows a simplified energy-balance model for the Earth surface-atmosphere system.

The following data are given:

[ 1 ]

(b)

Outline the physical mechanism by which some of the radiation emitted by the surface is absorbed by greenhouse gases in the atmosphere and re-radiated towards the surface.

[ 2 ]

(c)

Show that the average global intensity of radiation absorbed by the surface is about $240 \mathrm{Wm}^{-2}$ .

[ 2 ]

Average incoming intensity $=\frac{S}{4}$ « $=340 \mathrm{~W} \mathrm{~m}^{-2}$ »

Absorbed intensity $=(1-0.30) \times 340$ or $238 \mathrm{~W} \mathrm{~m}^{-2}$

The steps in the calculation must be
shown.

(d)

Determine the average intensity re-radiated by the atmosphere towards the surface. Assume that the emissivity of the surface is 0.90 .

[ 3 ]

Emitted intensity $=5.67 \times 10^{-8} \times 0.90 \times 288^{4}\approx351 \mathrm{~W} \mathrm{~m}^{-2}$

Intensity leaving Earth $=238 \mathrm{~W} \mathrm{~m}^{-2}$

Re-radiated intensity $=351-238=113 \mathrm{~W} \mathrm{~m}^{-2}$

Marking guidance:

Ignore units as they are not required for the answer.

The steps in the calculation must be checked.

Accept outgoing intensity $=240 \mathrm{~W} \mathrm{~m}^{-2}$ for MP2.

[Maximum number: 1]

A planet has an albedo of 0.30 . A simplified energy balance for the planet is shown.

What is the intensity radiated by the surface of the planet?

$70 \mathrm{Wm}^{-2}$

$90 \mathrm{Wm}^{-2}$

$100 \mathrm{Wm}^{-2}$

$130 \mathrm{Wm}^{-2}$

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Covered syllabus points

Question 1

Question 2

Question (a)

Question (b)

Question (c)

Question (d)

Question 3