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GCSE level Physics
exam revision notes on radiation
Absorption and emission of electromagnetic radiation: Part 5.
The super 'greenhouse effect'
of the mainly carbon dioxide atmosphere of the planet
Venus
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EMR
shorthand for electromagnetic radiation
INDEX of physics notes: Absorption
&
emission of EM Eradiation by materials - temperature and surface factors
 5.
The super 'greenhouse effect' of the mainly carbon dioxide atmosphere of planet
Venus
Venus is the 2nd planet from the Sun and is named after the Roman goddess of
love and beauty - perhaps because it shone the brightest of the five planets
known to ancient astronomers - but looks can be deceptive, Venus has no love for
the human body!
The surface temperature of Venus is up to
465oC.
The surface atmospheric pressure is 90
atm (90 x that on Earth).
The lower atmosphere is mainly carbon
dioxide (96.5% CO2) and nitrogen (3.5% N2).
[in the lower atmosphere and upper
clouds there may be small amounts of sulfur dioxide (SO2),
oxygen (O2), water (H2O), noble gases - helium
(He), neon (Ne) & argon (Ar), carbon monoxide (CO), sulfuric acid (H2SO4),
basalt rock particles and iron(III) chloride (FeCl3)]
The surface area and volume are about 0.9
x that of Earth.
On Venus it rains sulfuric acid, but this
evaporates before reaching the very hot surface
The surface of Venus is dry because it is
too hot for liquids to condense on
The surface of Venus is relatively flat
but very volcanic with still some active volcanoes.
The dense lower carbon dioxide atmosphere is
encased in 80 km thick clouds of mainly sulfuric acid (H2SO4)
and some sulfur dioxide (SO2) - these clouds reflect 90% of
sunlight - which is why it seems so bright, as well as being closer to the
Sun than the Earth.
This reflection of sunlight would tend to
make the planet cooler - a global dimming effect.
BUT, the hot surface of over 460oC
is a powerful emitter of infrared EM radiation.
This thermal radiation is absorbed by
the lower carbon dioxide rich atmosphere (96.5% CO2).
This produces a super greenhouse
effect compared to planet Earth (0.04% atmospheric carbon dioxide).
Little (if any?) infrared
radiation escapes from the planet's atmosphere.
So the surface temperature is kept at a
much higher temperature than if the infrared could escape and the net effect
completely overrides the dimming effect of the outer reflective clouds.
Note:
(a) Compared to Earth the surface
temperature is much hotter - a much stronger emitter of infrared EM
radiation AND the atmospheric carbon dioxide concentration is 2400 x
that of Earth! - 2400 x the greenhouse effect of carbon dioxide gas
on Earth!
(b) The greenhouse effect on
Venus is different to that on Earth in one respect - it doesn't
actually involve the absorption and remission of infrared radiation
- the infrared source on Venus is only from the hot surface.
INDEX physics notes: Absorption
and
emission of EM radiation by materials
Key points for Physics -
Information
sources for Doc Brown's key points: IGCSE-GCSE physics are based on textbooks
& syllabus-specifications for students taking the UK AQA,
Edexcel, OCR 21st Century Science, OCR Gateway science suite, WJEC, CCEA &
CIE GCSE
physics 9-1 level science examinations.
A syllabus-aligned
revision summary on the super greenhouse effect on Venus,
tailored for GCSE/IGCSE Physics students across WJEC, CCEA, CIE, AQA, Edexcel, and OCR. This topic is often
used to contrast Earth’s natural greenhouse effect with
an extreme planetary example.
Venus and the Super Greenhouse Effect
Key Facts About Venus
- Second planet
from the Sun
- Similar in size and
composition to Earth
- Surface temperature:
~465°C — hotter than Mercury, despite being farther from the Sun
- Atmosphere:
~96% carbon dioxide (CO2), with thick clouds of
sulfuric acid
Why Is Venus So Hot?
| Factor |
Effect |
| Thick CO2
atmosphere |
Traps infrared radiation extremely
efficiently |
| High atmospheric pressure |
Enhances heat retention |
| Sulfuric acid clouds |
Reflect sunlight but also trap
heat below |
| No water cycle |
No oceans to absorb CO2
or regulate temperature |
- Runaway greenhouse effect:
Once CO2 levels rose, positive feedback
caused more heat to be trapped, raising temperatures further and
evaporating any water that could have helped regulate the climate.
Comparison: Earth versus Venus
| Feature |
Earth |
Venus |
| CO2 % in atmosphere |
~0.04% |
~96% |
| Surface temperature |
~15°C |
~465°C |
| Greenhouse effect |
Natural, life-sustaining |
Runaway, extreme |
| Water presence |
Oceans regulate CO2 |
No liquid water |
Exam Board Emphases
| Focus Areas |
| Greenhouse gases, planetary
comparisons |
| Enhanced greenhouse effect, Venus
as a case study |
| Radiation balance, planetary
atmospheres |
| IR absorption, Venus versus Earth |
| Greenhouse gases and planetary
science |
| Thermal radiation, planetary
temperature regulation |
Student Tips
- Use Venus as a cautionary tale:
It shows what happens when greenhouse gases dominate.
- Explain the physics:
Link CO2 concentration to IR absorption and re-radiation.
- Practice comparisons:
Be ready to contrast Venus and Earth in terms of atmosphere and
temperature.
- Use diagrams:
Show incoming solar radiation and trapped IR on Venus.
- Think big picture:
This topic connects physics with climate science and planetary studies.
Keywords, phrases and learning objectives for absorption and emission of
radiation
Be able to describe and explain the super 'greenhouse effect' of the
high concentration of carbon dioxide
atmosphere of planet Venus which produce a much higher surface
temperature.
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revision notes and key points on the super greenhouse effect of the
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igcse/gcse physics notes on the super greenhouse effect of the carbon dioxide in
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physics notes on the super greenhouse effect of the carbon dioxide
in the atmosphere of Venus, OCR 21st century GCSE
physics notes on the super greenhouse effect of the carbon dioxide
in the atmosphere of Venus, OCR gateway
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INDEX physics notes: Absorption
and
emission of EM radiation by materials
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