What Is Runaway Greenhouse Effect And What Makes It Scarry

Greenhouse effect is caused by the presence of greenhouse gases such as carbon dioxide, water vapour and methane that trap the heat that is supposed to be radiated by earth back into space. The increase of the quantity of the greenhouse gases in the atmosphere ultimately leads to runaway greenhouse effect.

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What is runaway greenhouse effect?

Runaway greenhouse effect happens when a planet’s atmosphere contains greenhouse gas in quantities large enough to totally block all the thermal radiation from leaving the planet, preventing the planet from cooling.

How does runaway greenhouse effect occur?

The amount of warming a planet experiences due to greenhouse effect depends on various planetary feedback loops. For example, as the earth warms due to rising levels of greenhouse gases in the atmosphere:

  • more water evaporates from the surface.
  • the atmospheric concentration of water vapour increases, accelerating the greenhouse effect as water vapour is a greenhouse gas.
  • this in turn causes more warming, which increases the rate at which surface water turns into vapour, therefore positively reinforcing cycle the cycle.
  • this self- reinforcing cycle continues until the planet literally resembles hell.

The cycle is supposed to keep on running forever but however, there is a upper limit. Water vapour is opaque to infrared radiation of the long wavelength radiated by earth at current global temperatures. That is why this type of radiant heat is trapped. However, if the earth warms up, the wavelength of radiant heat it emits decreases. The water vapour becomes less opaque to the radiant heat emitted then.

The warming ceases when the earth’s surface temperature reaches about 1400K (1126°C) and and starts emitting radiation in the near-infrared, where water is not a good greenhouse gas. However this temperature is enough to evaporate the entire ocean and also make earth inhabitable. Venus experienced a runaway greenhouse in the past, and Earth is expected to experience it too in about 2 billion years as solar luminosity increases.


Sydney Chako

Mathematics, Chemistry and Physics teacher at Sytech Learning Academy. From Junior Secondary School to Tertiary Level Engineering Mathematics and Engineering Science.

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