Greenhouse Effect

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Albedo

Albedo (a) is the ratio of the total scattered (reflected) power to the total incident power for a surface.
The albedo of a planet is the ratio between the total scattered radiation and the total incident radiation of that planet.
Earth's albedo is generally taken as 0.3, meaning 30% of the Sun's rays that reach the ground are reflected back into the atmosphere.
An albedo of 1 represents a surface that scatters all incident radiation; albedo has no units because it is a ratio.
Earth's albedo varies daily and depends on cloud formations and season, latitude, terrain, and the incident angle of radiation.
Typical albedo values: fresh asphalt 0.04, bare soil 0.17, green grass 0.25, desert sand 0.40, new concrete 0.55, ocean ice 0.50–0.70, fresh snow 0.85.

Emissivity

Emissivity (e) is the ratio of the power radiated per unit area by a surface compared to that of a black body at the same temperature.
It is calculated using: e = (power radiated by an object) / (power emitted by a black body).
Calculations of emissivity assume the black body is at the same temperature and has the same dimensions as the object.
For a perfect black body, emissivity = 1 (this must be remembered; it is not in the data booklet).
For a non-black body, the Stefan-Boltzmann law becomes P = eσAT⁴, where P is total power emitted (W), σ is the Stefan-Boltzmann constant, A is total surface area (m²), and T is absolute temperature (K).

The Solar Constant

The solar constant (S) is the intensity of the Sun's radiation arriving perpendicularly to the Earth's atmosphere when the Earth is at its mean distance from the Sun.
Its average value is 1.36 × 10³ W m⁻² (about 1.4 kW m⁻²).
The solar constant varies year-round because the Earth's orbit is elliptical (distance from the Sun changes) and the Sun's output varies by about 0.1% during its 11-year sunspot cycle.
Calculations of the solar constant assume radiation is incident on a plane perpendicular to the Earth's surface and the Earth is at its mean distance from the Sun.
The intensity of solar radiation received by different planets varies with distance from the Sun; e.g., Venus receives higher intensity than Earth because it is closer.
Incoming radiative power: a planet's surface area is 4πr² but its radiative intensity covers a cross-sectional area of πr², so the mean intensity is S/4.

Greenhouse Gases

The main greenhouse gases, in order of decreasing contribution, are: water vapour (H₂O), carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O).
Each greenhouse gas has both natural and human-generated origins.
A greenhouse gas absorbs the long-wave (infrared) radiation re-emitted by the Earth's surface, trapping it in the atmosphere so it is not lost to space.
Greenhouse gases act similarly to the glass in a greenhouse, hence the name.
The two most significant contributors to the greenhouse effect are carbon dioxide and water vapour; ozone, methane, and nitrous oxides have lesser effects.
The relative significance of a greenhouse gas depends on its concentration in the atmosphere and how much it can absorb specific wavelengths of radiation.

The greenhouse effect: sunlight reaching Earth's surface and infrared radiation being absorbed and re-emitted by greenhouse gases

Absorption by Greenhouse Gases

About 25% of incoming short-wavelength solar radiation is absorbed by the atmosphere on its way to Earth, while about 80% of long-wavelength re-emitted radiation is absorbed on its way back out.
Ozone (O₃) absorbs close to 100% of incoming ultraviolet rays and strongly absorbs outgoing infrared between 9 μm and 10 μm, but is not a significant greenhouse gas due to its low concentration.
Carbon dioxide (CO₂) absorbs infrared with wavelengths between 1.5–30 μm, especially strongly at 15 μm; its increasing concentration makes it one of the most significant contributors.
Water vapour (H₂O) is the best absorber of infrared, with wavelengths between 0.8–35 μm; its concentration increases as air becomes warmer.
Overall, most ultraviolet, infrared, and microwave radiation is absorbed by the atmosphere, but the atmosphere is mostly transparent to incoming visible radiation.

The Greenhouse Effect

Incoming solar radiation is mainly ultraviolet and visible; visible light is not absorbed by the atmosphere but by the Earth's surface.
At night, the Earth re-radiates this energy as infrared radiation.
Greenhouse gases absorb infrared radiation and re-emit it in all directions, including back towards the Earth's surface.
The higher the concentration of greenhouse gases, the more infrared radiation remains in the Earth's surface-atmosphere system, trapping heat and raising average temperatures.
The greenhouse effect occurs due to the molecular structure of greenhouse gases: infrared light causes atoms to vibrate, and greenhouse gases have natural frequencies in the infrared region, so they resonate and heat up when absorbing infrared.
This absorbed radiation keeps Earth at a habitable temperature; imbalances in atmospheric composition can cause fluctuations in mean surface temperature.

The greenhouse effect

The Enhanced Greenhouse Effect

Human activity is increasing greenhouse gas concentrations: atmospheric CO₂ has risen by more than 100 ppm to 420 ppm in 2020.
The enhanced greenhouse effect means less long-wave radiation (heat) can escape the atmosphere.
Average global temperatures have increased by over 1°C since pre-industrial times.
Human sources of CO₂ include burning fossil fuels (power stations, vehicles), burning wood, and deforestation (fewer trees remove less CO₂ via photosynthesis).
Human sources of methane include decay of organic matter (manure, landfill waste, crops); nitrous oxide comes from artificial fertilisers and burning fossil fuels.
The greenhouse effect arises from natural causes, but the enhanced greenhouse effect arises from human activity.

Energy Balance Problems

Earth's energy balance compares incoming solar energy with outgoing energy; if they are in balance, Earth's temperature remains constant.
Simple climate models help predict temperature fluctuations based on current and increased greenhouse gas concentrations.
The simplest model uses a one-layer atmosphere above the Earth's surface.
In simplified models, assume the Earth's surface and atmosphere act as black bodies (emissivity of the surface = 1) and remain at constant temperature.
For a body, intensity = power per unit area, given by I = eσT⁴.
The intensity absorbed by the Earth's surface is the sum of solar radiation reaching the surface plus the intensity radiated by the atmosphere.

Diagram of Earth's energy balance, showing solar radiation absorbed, thermal radiation into space, and greenhouse gas absorption in watts per square metre

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1.Which of the following contributes to the enhanced greenhouse effect?
Easy
- ABurning fossil fuels
- BDestruction of the ozone layer
- CCarbon dioxide from active volcanoes around the world
- DIncrease in ultraviolet radiation penetrating the Earth's atmosphere
2.Which equation is used to calculate emissivity?
Easy
- Apower radiated by an object / power emitted by a black body
- Bpower emitted by an object / power emitted by a black body
- Ctotal scattered power from an object / total incident power from a black body
- Dpower absorbed by an object / power absorbed by a black body
3.The average albedo of desert sand is 0.4. What is the ratio of power absorbed by desert sand to power reflected by desert sand?
Medium
- A0.4
- B0.67
- C1.5
- D4.0
4.Which of the following describes the role of carbon dioxide in the greenhouse effect?
Easy
- AIt absorbs incoming radiation from the Sun.
- BIt reflects incoming radiation from the Sun.
- CIt absorbs outgoing radiation from the Earth's surface.
- DIt reflects outgoing radiation from the Earth's surface.
5.The solar constant is the incoming radiative power of the Sun at
Easy
- Athe surface of a planet
- Bthe surface of the Sun
- Cthe average distance between the Sun and the planet
- Dthe top of the planet's atmosphere
6.Which factors affect the amount of solar power incident on a given point on the surface of the Earth? (select all that apply)
Medium
- AWeather conditions
- BLatitude
- CPosition of the Earth in its orbit of the Sun
- DThe Earth's albedo
7.The solar constant is quoted as an average rather than an absolute value. Which statements correctly explain this? (select all that apply)
Medium
- AThe Earth follows an elliptical orbit around the Sun
- BThe Earth rotates on an axis which is tilted at 23.5° to the plane of its orbit
- CThe energy output of the Sun varies according to an 11-year cycle
- DThe Earth's atmosphere absorbs some solar radiation
8.Certain gases, for example carbon dioxide and methane, are categorised as greenhouse gases because they:
Medium
- ATransmit incoming radiation from the Sun and then absorb outgoing radiation from the Earth
- BAbsorb incoming radiation from the Sun and also absorb outgoing radiation from the Earth
- CReflect incoming radiation from the Sun
- DReflect outgoing radiation from the Earth

Thêm câu hỏi

9.Some of the energy incident on the surface of the Earth is emitted as infrared radiation. Why does this cause a ‘greenhouse effect’?
Medium
- AThe radiation becomes trapped in the troposphere
- BThe radiation heats the upper atmosphere
- CThe radiation is absorbed by the atmosphere and is re-radiated in all directions
- DThe radiation is absorbed by the upper atmosphere then all re-radiated back to the surface of the Earth
10.Which two assumptions are made when calculating the solar constant?
Medium
- AI. The Earth is in an elliptical orbit around the Sun. II. The Sun's output varies during its 11-year sunspot cycle.
- BI. Radiation from the Sun is incident on the Earth for one second. II. Radiation from the Sun is incident on one square meter of the Earth.
- CI. Radiation is incident on the Earth, parallel to its surface. II. The Earth is at its maximum distance from the Sun.
- DI. Radiation is incident perpendicular to the Earth's surface. II. The Earth is at its mean distance from the Sun.
11.Which of the following is the result of the enhanced greenhouse effect?
Easy
- Aincreasing global average temperature due to natural causes
- Bdecreasing global average temperature due to human activity
- Cincreasing global average temperature due to human activity
- Ddecreasing global average temperature due to natural causes
12.A perfect black body has an emissivity of 1.
Easy
True or false?
13.Albedo is defined as the ratio of the total scattered power to the total incident power of radiation reflected by a surface.
Easy
True or false?
14.Greenhouse gases primarily absorb incoming short-wave radiation from the Sun.
Easy
True or false?
15.The albedo of a surface can be greater than 1.
Easy
True or false?
16.The solar constant is the intensity of solar radiation at the Earth's surface.
Medium
True or false?
17.The greenhouse effect is solely caused by human activity.
Medium
True or false?
18.Match each material to its typical albedo.
Medium
- Fresh snow
- Green grass
- Desert sand
- Fresh asphalt
- 0.85
- 0.25
- 0.40
- 0.04
19.Match each greenhouse gas to its primary human-related source.
Medium
- Carbon dioxide (CO2)
- Methane (CH4)
- Nitrous oxide (N2O)
- Burning fossil fuels
- Decay of organic matter in landfills
- Artificial fertilisers
20.Arrange the following steps of the greenhouse effect in the correct order.
Medium
- Solar radiation reaches the Earth's surface and is absorbed
- The Earth's surface re-emits infrared radiation
- Greenhouse gases absorb the infrared radiation
- The absorbed radiation is re-radiated in all directions, warming the surface
21.Match each greenhouse gas to the range of wavelengths of infrared radiation it is best at absorbing.
Easy
- Carbon dioxide (CO₂)
- Water vapour (H₂O)
- Ozone (O₃)
- 1.5 – 30 μm
- 0.8 – 35 μm
- 9 – 10 μm
22.Arrange the following statements to describe the sequence of energy transfer in the greenhouse effect, starting with incoming solar radiation.
Medium
- Solar radiation, mainly ultraviolet and visible, reaches the Earth's surface.
- The Earth's surface absorbs the radiation and warms up.
- The Earth's surface re-emits energy as long-wave infrared radiation.
- Greenhouse gases in the atmosphere absorb the infrared radiation.
- The absorbed radiation is re-emitted in all directions, some back towards the surface.
23.Which of the following statements about the absorption of radiation by the Earth's atmosphere are correct? (select all that apply)
Medium
- AAbout 25% of incoming solar radiation is absorbed by the atmosphere.
- BAbout 80% of the infrared radiation re-emitted by the Earth is absorbed by the atmosphere.
- CThe atmosphere is mostly transparent to incoming visible radiation.
- DOzone absorbs incoming ultraviolet radiation.
- EThe atmosphere absorbs most incoming visible radiation.
24.In a simple energy balance model, the Earth's surface is assumed to be a black body. What is the emissivity of the Earth's surface in this model?
Medium
- A0
- B0.5
- C1
- DIt depends on the temperature
25.The greenhouse effect is caused solely by human activity.
Easy
True or false?
26.Which of the following are human sources of greenhouse gases? (select all that apply)
Medium
- ABurning of fossil fuels
- BDeforestation
- CVolcanic eruptions
- DUse of artificial fertilisers
- ERespiration of plants
27.The diagram below shows a simplified energy balance model of the Earth. Incoming solar radiation at the top of the atmosphere is 344 W m⁻². The atmosphere absorbs 20% of this, and the surface absorbs 50%. What is the albedo of the Earth in this model?
Medium
- A0.20
- B0.30
- C0.50
- D0.70
28.Using the same model, the atmosphere radiates energy back towards the surface. If the atmosphere's temperature is 252 K and its emissivity is 0.95, what is the intensity it radiates? (Stefan-Boltzmann constant σ = 5.67 × 10⁻⁸ W m⁻² K⁻⁴)
Hard
- A154 W m⁻²
- B217 W m⁻²
- C229 W m⁻²
- D250 W m⁻²
29.Mars is further from the Sun than Earth. Compared with the solar constant at Earth, the solar constant at Mars is
Medium
- Alarger, because Mars is further from the Sun
- Bsmaller, because the Sun's radiation is spread over a larger spherical surface
- Cthe same, because the solar constant is a fixed property of the Sun
- Dsmaller, because Mars has a lower albedo than Earth
30.The diagram shows a simple one-layer energy balance model of the Earth. Incoming solar radiation at the top of the atmosphere is 344 W m⁻². The atmosphere absorbs 20% of this incoming radiation, and the surface albedo is 0.30. Which of the following statements about this model are correct? (select all that apply)
Hard
- AThe intensity of solar radiation reaching the Earth's surface is 344 × (1 − 0.20) × (1 − 0.30) W m⁻²
- BThe albedo of the atmosphere determines how much incoming solar radiation is absorbed before reaching the surface
- CThe Earth's surface radiates infrared radiation that is partly absorbed by the atmosphere
- DThe total power radiated by the Earth's surface must equal the total incoming solar power at the top of the atmosphere
31.A simple climate model predicts a mean surface temperature of 255 K for the Earth. The actual mean surface temperature is 288 K. Which statement best explains this difference?
Hard
- AThe Earth is not a perfect black body, so it radiates less than predicted
- BThe model ignores the greenhouse effect, in which the atmosphere absorbs and re-radiates infrared radiation back to the surface
- CThe solar constant used in the model is too high
- DThe Earth's albedo is actually zero
32.In a simple energy balance model, the Earth's surface is assumed to be a black body with emissivity equal to 1.
Easy
True or false?
33.Match each greenhouse gas to the wavelength range of infrared radiation it absorbs most strongly.
Medium
- Ozone (O₃)
- Carbon dioxide (CO₂)
- Water vapour (H₂O)
- 1.5–30 μm
- 9–10 μm
- 0.8–35 μm
34.Place the following stages of the greenhouse effect in the correct order, starting with radiation arriving from the Sun.
Medium
- Short-wave solar radiation passes through the atmosphere and is absorbed by the Earth's surface
- The Earth's surface warms and re-emits energy as long-wave infrared radiation
- Greenhouse gases in the atmosphere absorb the outgoing infrared radiation
- The absorbed energy is re-emitted in all directions, some returning to the surface and warming it further
35.A student writes the following statements about the enhanced greenhouse effect. Which are correct? (select all that apply)
Hard
- AHuman activity has increased atmospheric carbon dioxide concentration to about 420 ppm in 2020
- BThe enhanced greenhouse effect is caused by an increase in the number of greenhouse gases in the atmosphere
- CThe enhanced greenhouse effect is caused by a decrease in the number of greenhouse gases in the atmosphere
- DThe enhanced greenhouse effect has led to an increase in average global temperature of over 1°C since pre-industrial times
- EThe enhanced greenhouse effect is caused by the destruction of the ozone layer
36.A student sets up an experiment to determine the albedo of a grey card. They measure the total incident power as 250 W and the total scattered power as 90 W. What is the albedo of the card?
Medium
- A0.36
- B0.64
- C2.78
- D0.90
37.A satellite orbiting Earth has a flat solar panel of area 12 m² facing directly towards the Sun. The solar constant at the satellite's position is 1.36 × 10³ W m⁻². The panel converts 20% of the incident solar power into electrical power. What is the electrical power output of the panel?
Hard
- A3.3 kW
- B16 kW
- C1.6 kW
- D0.33 kW
38.In a simple one-layer energy balance model, the Earth's surface is a black body (e = 1) and the atmosphere has emissivity 0.72. The solar intensity absorbed at the surface is 248 W m⁻² and the intensity radiated by the atmosphere back to the surface is 154 W m⁻². What is the equilibrium temperature of the Earth's surface? (σ = 5.67 × 10⁻⁸ W m⁻² K⁻⁴)
Hard
- A290 K
- B255 K
- C288 K
- D303 K
39.Which of the following is the correct definition of the solar constant?
Medium
- AThe intensity of the Sun's radiation arriving perpendicularly to the Earth's atmosphere when the Earth is at its mean distance from the Sun
- BThe total power emitted by the Sun per unit area at its surface
- CThe intensity of solar radiation at the Earth's surface at noon
- DThe average intensity of solar radiation received at the top of the atmosphere over a full year
40.The solar constant is 1.36 × 10³ W m⁻². What is the mean radiative power per unit area received by the Earth, assuming the Earth intercepts this radiation over a cross-sectional area of πr² and distributes it over its surface area of 4πr²?
Medium
- A340 W m⁻²
- B1360 W m⁻²
- C680 W m⁻²
- D170 W m⁻²
41.Complete the definition of emissivity.
Easy
Emissivity is the ratio of the power radiated per unit area by a surface to that of a ____ at the same temperature.
42.Complete the definition of the solar constant.
Medium
The solar constant is the intensity of the Sun's radiation arriving perpendicularly to the Earth's atmosphere when the Earth is at its ____ distance from the Sun.
43.List the two main greenhouse gases that contribute most to the greenhouse effect.
Medium
The two most significant greenhouse gases are ____ and ____.
44.The total incident power on a surface is 1500 W. The albedo of green grass is 0.25. Calculate the total scattered power.
Medium
45.The average albedo of fresh snow is 0.85. Calculate the ratio of energy absorbed by fresh snow to energy reflected by fresh snow. Give your answer to 2 significant figures.
Medium
46.What is the term for the fraction of incident radiation reflected by a surface?
Easy
47.What is the name of the model that explains the greenhouse effect by considering the natural vibrational frequencies of gas molecules?
Medium
48.In an experiment looking at solar energy, the total incident power is 1500 W. The albedo of green grass is 0.25. Calculate the total scattered power.
Medium
49.The solar constant is 1.36 × 10³ W m⁻². Calculate the mean radiative power per unit area received by the Earth, assuming the Earth intercepts this radiation over a cross-sectional area and distributes it over its whole surface. Give your answer in W m⁻² to 3 significant figures.
Medium
50.Complete the sentence about the solar constant.
Easy
The solar constant is the intensity of the Sun's radiation arriving perpendicularly to the Earth's atmosphere when the Earth is at its ____ distance from the Sun.
51.Calculate the mean intensity of solar radiation absorbed by the Earth's surface, assuming the atmosphere absorbs 20% of the radiation that is not reflected. Give your answer in W m⁻² to 3 significant figures.
Medium
52.A satellite in orbit around the Earth has a flat solar panel of area 12 m² facing directly towards the Sun. The solar constant at the satellite's position is 1.36 × 10³ W m⁻². Calculate the total power incident on the panel, in W, to 3 significant figures.
Medium
53.Define the solar constant and state its average value.
Hard
54.Explain how the greenhouse effect occurs due to the molecular structure of greenhouse gases.
Hard
55.Define the solar constant.
Medium
56.State the two main reasons why the solar constant varies year-round.
Medium
57.Explain how the molecular structure of greenhouse gases leads to the greenhouse effect.
Hard
58.The total incident power on a surface is 1500 W. The albedo of green grass is 0.25. Calculate the total scattered power.
Medium
- A451 W
- B375 W
- C413 W
- D337 W
59.The average albedo of fresh snow is 0.85. Calculate the ratio of energy absorbed by fresh snow to energy reflected by fresh snow. Give your answer to 2 significant figures.
Medium
- A2.18
- B0.18
- C-0.82
- D1.18
60.In an experiment looking at solar energy, the total incident power is 1500 W. The albedo of green grass is 0.25. Calculate the total scattered power.
Medium
- A413 W
- B375 W
- C337 W
- D451 W
61.The solar constant is 1.36 × 10³ W m⁻². Calculate the mean radiative power per unit area received by the Earth, assuming the Earth intercepts this radiation over a cross-sectional area and distributes it over its whole surface. Give your answer in W m⁻² to 3 significant figures.
Medium
- A408 W m⁻²
- B306 W m⁻²
- C374 W m⁻²
- D340 W m⁻²
62.The solar constant is 1360 W m⁻² and the Earth's albedo is 0.30. Calculate the mean intensity of solar radiation absorbed by the Earth's surface, assuming the atmosphere absorbs 20% of the radiation that is not reflected. Give your answer in W m⁻² to 3 significant figures.
Medium
- A190 W m⁻²
- B272 W m⁻²
- C238 W m⁻²
- D762 W m⁻²
63.A satellite in orbit around the Earth has a flat solar panel of area 12 m² facing directly towards the Sun. The solar constant at the satellite's position is 1.36 × 10³ W m⁻². Calculate the total power incident on the panel, in W, to 3 significant figures.
Medium
- A16300 W
- B17930 W
- C14670 W
- D19560 W

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