What does Greenhouse Effect cover in IB Physics?

This topic covers the Earth's energy balance, the greenhouse effect, and human impact. Emissivity is defined as emissivity = fracpower radiated per unit areaσ T^4. Albedo is defined as albedo = fractotal scattered powertotal incident power.

Is Greenhouse Effect SL or HL?

Both. SL and HL students study Greenhouse Effect to the same depth.

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FourtyFive has 19 Greenhouse Effect questions. Every answer you write is marked mark by mark, IB-style, and you see where each mark was won or lost. Every part has a hint, the AI tutor helps you through the step you are stuck on, and your Study Profile picks what to practise next.

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Topic B.2 · SL and HL

Greenhouse Effect: notes and practice questions

Q: How do I revise Greenhouse Effect for IB Physics?

Start from the core idea: this topic covers the Earth's energy balance, the greenhouse effect, and human impact. In the exam: a reliable Paper 2 extended question, usually run together with B.1 and E.5 into one long stem. May 2025 SL Paper 2 TZ1 question 6 and HL question 8 were the same question: state what the solar constant means (1), outline the mechanism by which the atmosphere re-radiates towards the surface (2), show that the absorbed intensity is about 240 W m⁻² (2), determine the re-radiated intensity given emissivity 0.90 (3), then show the Sun's total power is about 4 × 10²⁶ W (2). Then practise exam-style questions, easiest first, writing out every step of your working before you check it.

13 min read Jump to 19 practice questions

Summary

This topic covers the Earth's energy balance, the greenhouse effect, and human impact.
Emissivity is defined as $\text{emissivity} = \frac{\text{power radiated per unit area}}{\sigma T^4}$ .
Albedo is defined as $\text{albedo} = \frac{\text{total scattered power}}{\text{total incident power}}$ .
The mean incoming solar intensity for a planet is $\frac{S}{4}$ , where $S$ is the solar constant.
Main greenhouse gases ( $\text{CH}_4$ , $\text{H}_2\text{O}$ , $\text{CO}_2$ , $\text{N}_2\text{O}$ ) absorb and re-emit infrared radiation due to molecular energy levels.
The enhanced greenhouse effect is caused by human activities, primarily burning fossil fuels.
Students should be able to estimate equilibrium temperature using energy balance.

How it is examined

A reliable Paper 2 extended question, usually run together with B.1 and E.5 into one long stem. May 2025 SL Paper 2 TZ1 question 6 and HL question 8 were the same question: state what the solar constant means (1), outline the mechanism by which the atmosphere re-radiates towards the surface (2), show that the absorbed intensity is about 240 W m⁻² (2), determine the re-radiated intensity given emissivity 0.90 (3), then show the Sun's total power is about 4 × 10²⁶ W (2). Note the two show parts: the answer is printed in the question, so the marks are entirely for the working.

Given in the booklet

The emissivity and albedo ratios, and the solar constant as a value. The factor-of-four projected-area argument is not a booklet equation: the student has to know why a sphere intercepts $\pi r^2$ but radiates from $4\pi r^2$ . The four named greenhouse gases must be recalled.

Key ideas

the conservation of energy
emissivity as the ratio of power radiated per unit area by a surface to that of an ideal black surface at the same temperature, as given by $\text{emissivity} = \dfrac{\text{power radiated per unit area}}{\sigma T^4}$
albedo as a measure of the average energy reflected off a macroscopic system, as given by $\text{albedo} = \dfrac{\text{total scattered power}}{\text{total incident power}}$
that Earth's albedo varies daily and depends on cloud formations and latitude

Guiding questions

How does the greenhouse effect help to maintain life on Earth and how does human activity enhance this effect?
How is the atmosphere as a system modelled to quantify the Earth-atmosphere energy balance?

Linking questions

What relevance do simple harmonic motion and resonance have to climate change?
How do different methods of electricity production affect the energy balance of the atmosphere?
How are developments in science and technology affected by climate change?
What limitations are there in using a resonance model to explain the greenhouse effect?

Practice questions

19 questions · 3 easy · 13 medium · 3 hard

Showing 19 of 19

Question 1

EasyPaper 1A · calculator1 mark

The greenhouse effect is the process by which certain gases in the atmosphere trap thermal energy. What is the primary mechanism for this trapping?

A. Greenhouse gases reflect incoming ultraviolet radiation back to space.

B. Greenhouse gases absorb incoming visible light from the Sun.

C. Greenhouse gases absorb and re-radiate outgoing infrared radiation.

D. Greenhouse gases scatter all wavelengths of electromagnetic radiation equally.

Question 2

MediumPaper 2 · calculator8 marks

(a)

A team of climate scientists is preparing a report on the Earth's energy balance. A key part of the report focuses on the role of the atmosphere in regulating the planet's surface temperature.

(a) Identify two primary greenhouse gases in the Earth's atmosphere, other than carbon dioxide and water vapour.

[2]

(b)

(b) Explain the mechanism by which greenhouse gas molecules absorb infrared (IR) radiation.

[3]

(c)

[3]

Question 3

HardPaper 2 · calculator20 marks

(a)

An exoplanet named Xylos orbits a star named Aethel. Scientists are studying its atmospheric conditions and the properties of its host star.

(a) State what is meant by the stellar constant for Xylos.

[1]

(b)(i)

(b) The following data are given for exoplanet Xylos:

Average albedo of Xylos $= 0.40$

Average orbital distance from Aethel $= 2.0 \times 10^{11} \text{ m}$

Average global surface temperature of Xylos $= 250 \text{ K}$

Luminosity of star Aethel $= 2.0 \times 10^{26} \text{ W}$

(i) Outline the physical mechanism by which some of the infrared radiation emitted by the surface of Xylos is absorbed by its atmospheric gases and re-radiated back towards the surface.

[2]

(b)(ii)

(ii) Show that the average global intensity of radiation absorbed by the surface of Xylos is about $60 \text{ W m}^{-2}$ .

[2]

(b)(iii)

(iii) Determine the average intensity re-radiated by Xylos's atmosphere towards its surface. Assume that the emissivity of the surface is $0.95$ .

[3]

(c)

[2]

(d)(i)

(d) A possible fusion reaction occurring in stars like Aethel is the deuterium-tritium (D-T) fusion reaction:

$^2_1\text{H} + ^3_1\text{H} \rightarrow ^4_2\text{He} + ^1_0\text{n}$

Relevant atomic masses are:

Mass of deuterium ( $^2_1\text{H}$ ) $= 2.013553 \text{ u}$

Mass of tritium ( $^3_1\text{H}$ ) $= 3.015501 \text{ u}$

Mass of helium-4 ( $^4_2\text{He}$ ) $= 4.001506 \text{ u}$

Mass of neutron ( $^1_0\text{n}$ ) $= 1.008665 \text{ u}$

(i) Calculate, in $\text{MeV}$ , the energy released in the reaction.

[2]

(d)(ii)

(ii) Outline the role of fusion reactions in maintaining a stable radius for a star like Aethel.

[2]

(d)(iii)

(iii) Outline how the presence of hydrogen in Aethel can be confirmed empirically.

[2]

(e)(i)

(e) Aethel has a surface temperature of $5200 \text{ K}$ and a luminosity $0.5$ times that of the Sun.

(i) State the star type of Aethel.

[1]

(e)(ii)

(ii) Discuss how nuclear fusion processes in a red dwarf star differ from those in the Sun.

[3]

Question 4

EasyPaper 1A · calculator1 mark

The albedo of a large glacier is 0.75. The intensity of solar radiation incident on the surface of the glacier is $I$ . What is the intensity of solar radiation absorbed by the glacier?

A. $0.25 I$

B. $0.75 I$

C. $I$

D. $1.75 I$

Question 5

MediumPaper 2 · calculator8 marks

(a)

A team of astronomers is studying a newly discovered exoplanet orbiting a distant star. The star has a surface temperature of approximately 6000 K. The exoplanet has an average surface temperature of 290 K.

(a) Outline the principal differences between the electromagnetic radiation arriving at the exoplanet from its star and the thermal radiation being emitted by the exoplanet's surface.

[4]

(b)

(b) The exoplanet's atmosphere is found to have a high concentration of methane and carbon dioxide. Explain how the presence of these gases leads to an average surface temperature that is higher than it would be without them.

[4]

Question 6

HardPaper 2 · calculator12 marks

(a)

A rocky exoplanet, Planet X, orbits a star. The solar constant for Planet X is $1360 \text{ W m}^{-2}$ . The average albedo of Planet X is $0.15$ .

State what is meant by an albedo of $0.15$ .

[1]

(b)

Show that the average power absorbed per square metre of Planet X's surface is about $290 \text{ W m}^{-2}$ .

[2]

(c)

Assuming Planet X has no atmosphere and acts as a perfect black body, calculate its equilibrium surface temperature.

[2]

(d)(i)

Later observations reveal that Planet X has an atmosphere containing carbon dioxide.

Outline how the presence of carbon dioxide in the atmosphere leads to an increase in the surface temperature of the planet.

[3]

(d)(ii)

The surface of Planet X is covered by a large proportion of dark oceans. As the planet warms, some of the oceans evaporate, increasing the cloud cover in the atmosphere.

Discuss how this increase in cloud cover could affect the surface temperature of Planet X.

[4]

Question 7

EasyPaper 1A · calculator1 mark

The average temperature of the Earth is higher than it would be without an atmosphere. What is the principal mechanism by which greenhouse gases, such as carbon dioxide, contribute to this higher temperature?

A. They absorb ultraviolet radiation from the Sun, preventing it from reaching the surface.

B. They reflect incoming visible light from the Sun back into space.

C. They absorb infrared radiation emitted by the Earth's surface and re-radiate it in all directions.

D. They prevent convection currents from carrying thermal energy away from the Earth's surface.

Question 8

MediumPaper 2 · calculator13 marks

(a)

A newly discovered exoplanet, Exoplanet X, orbits a star similar to our Sun. Scientists are studying its potential for habitability. The following data is available:

The intensity of the star's radiation arriving at the top of Earth's atmosphere (if Earth orbited this star) $= 1360 \text{ W m}^{-2}$

The average distance from the star to Earth $= 1 \text{ AU}$

The average distance from the star to Exoplanet X $= 0.8 \text{ AU}$

Exoplanet X's average albedo $= 0.25$

Exoplanet X's emissivity $= 0.90$

Stefan-Boltzmann constant, $\sigma = 5.67 \times 10^{-8} \text{ W m}^{-2} \text{ K}^{-4}$

(a) Calculate the intensity of the star's radiation arriving at Exoplanet X's location.

[3]

(b)

(b) Calculate the average intensity of the star's radiation arriving per $\text{m}^2$ of Exoplanet X's surface. Assume Exoplanet X is spherical and the incident radiation is distributed over its entire surface area.

[3]

(c)

(c) Calculate the average intensity of the star's radiation that is absorbed by each $\text{m}^2$ of Exoplanet X's surface.

[2]

(d)

(d) State the average intensity of radiation that must be emitted by each $\text{m}^2$ of Exoplanet X's surface, assuming Exoplanet X's average temperature is constant.

[1]

(e)

(e) Predict the equilibrium temperature of the surface of Exoplanet X.

[4]

Question 9

HardPaper 2 · calculator7 marks

(a)

An exoplanet orbits a star that has a surface temperature of $5800\text{ K}$ . The exoplanet has an average surface temperature of $290\text{ K}$ and an atmosphere containing a high concentration of methane ( $\text{CH}_4$ ) gas.

Outline the differences between the radiation incident on the exoplanet's atmosphere and the radiation emitted by its surface.

[3]

(b)

Discuss the mechanism of the greenhouse effect on this exoplanet. In your answer, you must refer to:

the interaction between methane molecules and radiation

the energy balance of the exoplanet's surface

[4]

Question 10

MediumPaper 2 · calculator12 marks

(a)

Venus orbits the Sun at a distance where the intensity of solar radiation (the solar constant for Venus) is $S = 2600 \text{ W m}^{-2}$ . The average albedo of Venus is $a = 0.75$ due to its thick cloud cover.

(a) Define the solar constant.

[2]

(b)

(b) Venus has a radius $R$ . Show that for a planet to be in thermal equilibrium, its surface temperature $T$ is related to the solar constant $S$ and albedo $a$ by the expression $4\sigma T^4 = S(1-a)$ , assuming the planet behaves as a black body.

[3]

(c)

[2]

(d)

(d) The actual mean surface temperature of Venus is approximately $735 \text{ K}$ . Outline the primary mechanism responsible for this much higher temperature.

[3]

(e)

(e) A simple model treats Venus as a grey body with an effective emissivity $\epsilon$ . Calculate the emissivity of Venus.

[2]

Question 11

MediumPaper 2 · calculator12 marks

(a)

The Arctic region is experiencing significant changes due to global warming, including the melting of large areas of sea ice. This has a considerable impact on the Earth's energy balance.

(a) Explain what is meant by albedo.

[2]

(b)

(b) The table shows typical albedo values for two surfaces found in the Arctic.

Surface	Typical Albedo
Sea Ice	0.60
Open Ocean Water	0.08

Explain, by reference to the properties of the surfaces, the difference in these albedo values.

[2]

(c)

(c) Climate models predict a continued decrease in the extent of Arctic sea ice. Outline how this decrease is expected to affect the net energy absorbed by the Arctic region.

[3]

(d)(i)

A satellite measures the solar radiation incident on a $1.0 \text{ km}^2$ area of the Arctic. The average intensity of the incident radiation is $340 \text{ W m}^{-2}$ .

(d) (i) Calculate the power reflected from this area if it is completely covered by sea ice with an albedo of $0.60$ .

[2]

(d)(ii)

(ii) The sea ice in this area melts completely, exposing open ocean water with an albedo of $0.08$ . Determine the change in the power absorbed by this area.

[3]

Question 12

MediumPaper 1A · calculator1 mark

The enhanced greenhouse effect is an increase in the average temperature of the Earth's surface. What is the principal mechanism by which greenhouse gases cause this effect?

A. Greenhouse gases absorb incoming short-wavelength radiation from the Sun, re-radiating it towards the Earth.

B. Greenhouse gases absorb outgoing long-wavelength infrared radiation from the Earth, re-radiating some of it back towards the Earth.

C. Greenhouse gases in the upper atmosphere reflect incoming short-wavelength radiation from the Sun back into space.

D. Greenhouse gases create a layer in the atmosphere that prevents convection, trapping thermal energy near the surface.

Question 13

MediumPaper 1A · calculator1 mark

A scientific probe lands on the surface of an exoplanet. The exoplanet receives radiation from its star, and when the star is directly overhead, the incident intensity of this radiation on the exoplanet's surface is $S_{star}$ . The surface of the exoplanet at the landing site has an albedo of $0.40$ .

What is the intensity of solar radiation absorbed by the surface of the exoplanet at the landing site?

A. $\frac{2}{5}S_{star}$

B. $\frac{3}{5}S_{star}$

C. $S_{star}$

D. $\frac{4}{5}S_{star}$

Question 14

MediumPaper 1A · calculator1 mark

A student makes three statements about the mechanism of the greenhouse effect.

I. Greenhouse gases primarily absorb short-wavelength radiation arriving from the Sun.

II. The Earth radiates energy at longer wavelengths than the energy it receives from the Sun.

III. Greenhouse gases in the atmosphere re-radiate absorbed energy, with some of this energy returning to the Earth's surface.

Which of the statements are correct?

A. I only

B. III only

C. II and III only

D. I, II and III

Question 15

MediumPaper 1A · calculator1 mark

The absorption of infrared radiation by greenhouse gases is a key part of the greenhouse effect. This absorption is particularly effective because

A. the greenhouse gases are at a much higher temperature than the Earth's surface.

B. the infrared radiation causes the gas molecules to undergo nuclear fission.

C. the frequency of the infrared radiation matches the natural vibrational frequency of the greenhouse gas molecules.

D. the greenhouse gas molecules are much larger than the other molecules in the atmosphere.

Question 16

MediumPaper 1A · calculator1 mark

A spherical asteroid with an albedo of 0.40 orbits a star. The intensity of the radiation from the star at the distance of the asteroid is $I$ . The asteroid has no atmosphere and is in thermal equilibrium. What is the average intensity radiated by the surface of the asteroid?

A. $0.10 I$

B. $0.15 I$

C. $0.40 I$

D. $0.60 I$

Question 17

MediumPaper 2 · calculator10 marks

(a)

An exoplanet orbits a star. The intensity of the radiation from the star at the distance of the exoplanet is $2400 \text{ W m}^{-2}$ . The average albedo of the exoplanet is $0.15$ .

Show that the equilibrium surface temperature of the exoplanet, assuming it has no atmosphere and behaves as a perfect black body, is about $310 \text{ K}$ .

[3]

(b)

The exoplanet is found to have an atmosphere containing water vapour and carbon dioxide.

Outline, with reference to molecular energy levels, how these gases absorb infrared radiation emitted by the exoplanet's surface.

[3]

(c)

Discuss the effect on the average surface temperature of the exoplanet of:

the presence of the greenhouse gases in the atmosphere

a subsequent decrease in the albedo of the exoplanet due to the melting of surface ice.

[4]

Question 18

MediumPaper 2 · calculator11 marks

(a)

An exoplanet of radius $r$ orbits a distant star. The albedo of the exoplanet is $\alpha$ and the stellar constant at its orbit is $S$ .

Explain what is meant by the stellar constant.

[2]

(b)

Explain what is meant by the exoplanet's albedo.

[2]

(c)

Assuming that the exoplanet behaves as a perfect black body radiator, show that it is predicted to reach an equilibrium temperature $T$ given by

$T = \sqrt[4]{\frac{S(1-\alpha)}{4\sigma}}$

where $\sigma$ is the Stefan–Boltzmann constant.

[3]

(d)(i)

The exoplanet with its atmosphere is not a perfect black body and has an emissivity of $e$ .

Explain what is meant by emissivity.

[2]

(d)(ii)

The mean temperature of the exoplanet is $295\text{ K}$ . The stellar constant is $S = 1800\text{ W}\,\text{m}^{-2}$ and the average albedo is $\alpha = 0.35$ .

Calculate the emissivity of the exoplanet.

[2]

Question 19

MediumPaper 2 · calculator10 marks

(a)

The exoplanet Zephyr-b orbits a star. The following data are available:

Luminosity of the star $= 3.8 \times 10^{26}\text{ W}$

Average distance from the star to Zephyr-b $= 1.2 \times 10^{11}\text{ m}$

Calculate the intensity of the stellar radiation arriving at the top of Zephyr-b's atmosphere.

[2]

(b)

Zephyr-b has an average albedo of 0.30.

Show that the average intensity of stellar radiation absorbed by the surface of Zephyr-b is about $370\text{ W}\,\text{m}^{-2}$ .

[3]

(c)

The surface of Zephyr-b has an average emissivity of 0.90. The planet is in thermal equilibrium.

Determine the predicted average surface temperature of Zephyr-b.

[3]

(d)

The actual average surface temperature of Zephyr-b is observed to be 315 K.

Explain this discrepancy with reference to the atmosphere of Zephyr-b.

[2]

Every Greenhouse Effect question, marked for you

Every answer is marked mark by mark, IB-style, and the AI tutor helps when you are stuck.

Where marks are lost

Stopping one step short of the conclusion. Two numbers and no sentence is two marks out of three.
Answering a procedure question with a platitude.
Losing precision in Paper 1B. Uniquely to this paper, quoting the right number badly loses marks.

Greenhouse Effect: notes and practice questions

How it is examined

Guiding questions

Linking questions

Practice questions

Question 1

Question 2

Question 3

Question 4

Question 5

Question 6

Question 7

Question 8

Question 9

Question 10

Question 11

Question 12

Question 13

Question 14

Question 15

Question 16

Question 17

Question 18

Question 19

Every Greenhouse Effect question, marked for you

Where marks are lost

Practise this topic as a session

Questions,
answered.

Start with the IB question
bank built for you.

How it is examined

Guiding questions

Linking questions

Practice questions

Question 1

Question 2

Question 3

Question 4

Question 5

Question 6

Question 7

Question 8

Question 9

Question 10

Question 11

Question 12

Question 13

Question 14

Question 15

Question 16

Question 17

Question 18

Question 19

Every Greenhouse Effect question, marked for you

Where marks are lost

Questions,answered.

Start with the IB questionbank built for you.

Questions,
answered.

Start with the IB question
bank built for you.