page_title: Greenhouse effect
section_title: Greenhouse gases
hierarchical_section_title: Greenhouse effect / Greenhouse gases
caption_attribution_description: English: All atmospheric gases have a unique pattern of energy absorption: they absorb some wavelengths of energy but are transparent to others. The absorption patterns of water vapor (blue peaks) and carbon dioxide (pink peaks) overlap in some wavelengths. Carbon dioxide is not as strong a greenhouse gas as water vapor, but it absorbs energy in wavelengths (12-15 micrometers) that water vapor does not, partially closing the “window” through which heat radiated by the surface would normally escape to space. (Illustration adapted from Robert Rohde.)
context_page_description: The greenhouse effect is the process by which radiation from a planet's atmosphere warms the planet's surface to a temperature above what it would be without this atmosphere.
  Radiatively active gases in a planet's atmosphere radiate energy in all directions. Part of this radiation is directed towards the surface, warming it. The intensity of the downward radiation – that is, the strength of the greenhouse effect – will depend on the atmosphere's temperature and on the amount of greenhouse gases that the atmosphere contains.
  Earth's natural greenhouse effect is critical to supporting life, and initially was a precursor to life moving out of the ocean onto land. Human activities, however, mainly the burning of fossil fuels and clearcutting of forests, have accelerated the greenhouse effect and caused global warming.
  The planet Venus experienced runaway greenhouse effect, resulting in an atmosphere which is 96% carbon dioxide, with surface atmospheric pressure roughly the same as found 900 m underwater on Earth. Venus may have had water oceans, but they would have boiled off as the mean surface temperature rose to the current 735 K.
context_section_description: By their percentage contribution to the greenhouse effect on Earth the four major gases are:
  water vapor, 36–70%
  carbon dioxide, 9–26%
  methane, 4–9%
  ozone, 3–7%
  It is not possible to assign a specific percentage to each gas because the absorption and emission bands of the gases overlap (hence the ranges given above). Clouds also absorb and emit infrared radiation and thus affect the radiative properties of the atmosphere.
caption: Atmospheric gases only absorb some wavelengths of energy but are transparent to others. The absorption patterns of water vapor (blue peaks) and carbon dioxide (pink peaks) overlap in some wavelengths. Carbon dioxide is not as strong a greenhouse gas as water vapor, but it absorbs energy in longer wavelengths (12–15 micrometers) that water vapor does not, partially closing the "window" through which heat radiated by the surface would normally escape to space. (Illustration NASA, Robert Rohde)[24]
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