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Greenhouse effect

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The greenhouse effect is the warming of the Earth's surface caused by gases in the atmosphere that absorb infrared radiation. It is a natural process, and it keeps the Earth warm enough for life.[1][2] Without it, the Earth's average surface temperature would be about 255 K (−18 °C) instead of the actual 288 K (15 °C).[3][3]

How it works

The Earth is warmed by sunlight. To stay at a steady temperature, it must lose energy at the same rate as it gains it, which it does by giving off invisible infrared radiation.[3][4] The Sun's radiation is strongest at a wavelength of about 0.5 micrometres, in visible light, while the Earth's is strongest at about 10 micrometres, in the far infrared.[3]

Most sunlight passes through the atmosphere and reaches the surface, but the infrared radiation given off by the surface finds it hard to escape.[3] Some gases in the atmosphere, called greenhouse gases, absorb infrared strongly.[3] They absorb part of the radiation rising from the surface and send it back down to the Earth or out into space, so the surface stays warmer than it would otherwise be.[1][5]

The atmosphere is fairly transparent to infrared between about 8 and 12.5 micrometres, a gap called the "window", but it is opaque around 15 micrometres, where carbon dioxide absorbs strongly.[2][6]

Greenhouse gases

The most important greenhouse gases are carbon dioxide (CO2) and water vapour (H2O).[2] Water vapour has the biggest greenhouse effect of all.[7] The main gases in the air, oxygen and nitrogen, are transparent to infrared radiation.[5] Other greenhouse gases include methane, nitrous oxide and ozone in the lower atmosphere.[3]

Why it is called the greenhouse effect

The name comes from comparing the Earth and its air to a box covered with glass, which warms up when sunlight enters and the heat cannot escape.[5][5] The comparison is not exact. Real greenhouses stay warm mainly because the glass stops the warm air inside from drifting away, while the atmosphere works by absorbing infrared radiation.[5][5]

History

In the 19th century the scientist Fourier asked why the Earth does not keep heating up in sunlight. He realised that the warm surface gives off infrared radiation, and that the atmosphere must somehow hold in some of this heat.[4][4][5] In 1859 the British scientist John Tyndall tested gases in his laboratory. He found that oxygen and nitrogen let heat rays through, but that coal gas, carbon dioxide and water vapour block them.[5][5][5][8][9]

In 1896 Svante Arrhenius, a scientist in Stockholm, calculated that halving the amount of carbon dioxide in the air would cool the world by perhaps 5 °C, and that doubling it would warm it by 5 or 6 °C.[10][11][11] By 1910, however, most scientists thought he was wrong. One objection was that the greenhouse effect was already as strong as it could be.[12][12] Later work showed that the old measurements were faulty, and that adding carbon dioxide does make a difference.[13][13]

Human activity and climate change

Since the Industrial Revolution, which began around 1750, the amounts of carbon dioxide, methane and nitrous oxide in the atmosphere have risen sharply. This has been measured in air bubbles trapped in ice cores.[7] Burning fossil fuels and making cement release carbon dioxide; methane comes from sources such as rice fields and cattle; and nitrous oxide comes from microbes in fertilised soil.[14] Adding these gases strengthens the greenhouse effect and raises the surface temperature, which drives climate change.[3][1] Possible effects include more intense storms, changes in rainfall and rising sea levels.[1]

Some effects make warming stronger. These are called positive feedbacks. For example, melting ice and snow make the Earth's surface darker, so it absorbs more sunlight, and a warmer atmosphere holds more water vapour.[15][10][10]

See also

References

  1. ↑ 1.0 1.1 1.2 1.3 Urone, Paul Peter; Hinrichs, Roger (2017) [2012]. College Physics. Houston: OpenStax. p. 544. ISBN 978-1-938168-00-0. Retrieved 2026-10-23.
  2. ↑ 2.0 2.1 2.2 Boeker, Egbert; van Grondelle, Rienk (2011). Environmental Physics: Sustainable Energy and Climate Change (3rd ed.). Chichester: John Wiley & Sons. section 3.2: The Radiation Balance and the Greenhouse Effect. ISBN 978-0-470-66676-0. Retrieved 2026-10-23.
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 Boeker, Egbert; van Grondelle, Rienk (2011). Environmental Physics: Sustainable Energy and Climate Change (3rd ed.). Chichester: John Wiley & Sons. section 1.2: The Greenhouse Effect and Climate Change. ISBN 978-0-470-66676-0. Retrieved 2026-10-23.
  4. ↑ 4.0 4.1 4.2 Weart, Spencer R. (2008). The Discovery of Global Warming. New Histories of Science, Technology, and Medicine (Revised and expanded ed.). Cambridge, MA: Harvard University Press. p. 1. ISBN 978-0-674-03189-0. {{cite book}}: |access-date= requires |url= (help)
  5. ↑ 5.00 5.01 5.02 5.03 5.04 5.05 5.06 5.07 5.08 5.09 Weart, Spencer R. (2008). The Discovery of Global Warming. New Histories of Science, Technology, and Medicine (Revised and expanded ed.). Cambridge, MA: Harvard University Press. p. 2. ISBN 978-0-674-03189-0. {{cite book}}: |access-date= requires |url= (help)
  6. ↑ Boeker, Egbert; van Grondelle, Rienk (2011). Environmental Physics: Sustainable Energy and Climate Change (3rd ed.). Chichester: John Wiley & Sons. section 3.2.2: Radiation Transfer. ISBN 978-0-470-66676-0. Retrieved 2026-10-23.
  7. ↑ 7.0 7.1 Boeker, Egbert; van Grondelle, Rienk (2011). Environmental Physics: Sustainable Energy and Climate Change (3rd ed.). Chichester: John Wiley & Sons. section 3.2.5: The Greenhouse Gases. ISBN 978-0-470-66676-0. Retrieved 2026-10-23.
  8. ↑ Weart, Spencer R. (2008). The Discovery of Global Warming. New Histories of Science, Technology, and Medicine (Revised and expanded ed.). Cambridge, MA: Harvard University Press. pp. 2–3. ISBN 978-0-674-03189-0. {{cite book}}: |access-date= requires |url= (help)
  9. ↑ Weart, Spencer R. (2008). The Discovery of Global Warming. New Histories of Science, Technology, and Medicine (Revised and expanded ed.). Cambridge, MA: Harvard University Press. p. 3. ISBN 978-0-674-03189-0. {{cite book}}: |access-date= requires |url= (help)
  10. ↑ 10.0 10.1 10.2 Weart, Spencer R. (2008). The Discovery of Global Warming. New Histories of Science, Technology, and Medicine (Revised and expanded ed.). Cambridge, MA: Harvard University Press. p. 4. ISBN 978-0-674-03189-0. {{cite book}}: |access-date= requires |url= (help)
  11. ↑ 11.0 11.1 Weart, Spencer R. (2008). The Discovery of Global Warming. New Histories of Science, Technology, and Medicine (Revised and expanded ed.). Cambridge, MA: Harvard University Press. p. 5. ISBN 978-0-674-03189-0. {{cite book}}: |access-date= requires |url= (help)
  12. ↑ 12.0 12.1 Weart, Spencer R. (2008). The Discovery of Global Warming. New Histories of Science, Technology, and Medicine (Revised and expanded ed.). Cambridge, MA: Harvard University Press. p. 6. ISBN 978-0-674-03189-0. {{cite book}}: |access-date= requires |url= (help)
  13. ↑ 13.0 13.1 Weart, Spencer R. (2008). The Discovery of Global Warming. New Histories of Science, Technology, and Medicine (Revised and expanded ed.). Cambridge, MA: Harvard University Press. p. 22. ISBN 978-0-674-03189-0. {{cite book}}: |access-date= requires |url= (help)
  14. ↑ Boeker, Egbert; van Grondelle, Rienk (2011). Environmental Physics: Sustainable Energy and Climate Change (3rd ed.). Chichester: John Wiley & Sons. section 3.2.5: The Greenhouse Gases, Table 3.3. ISBN 978-0-470-66676-0. Retrieved 2026-10-23.
  15. ↑ Boeker, Egbert; van Grondelle, Rienk (2011). Environmental Physics: Sustainable Energy and Climate Change (3rd ed.). Chichester: John Wiley & Sons. section 3.2.4.1: Effects Reinforcing Global Warming. ISBN 978-0-470-66676-0. Retrieved 2026-10-23.
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