Galloping greenhouse effect

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A galloping greenhouse effect (English runaway greenhouse effect ) is an unstoppable and self-reinforcing greenhouse effect , which ultimately leads to the evaporation of all liquid water on a planet. The effect has a well-known example with the climate on Venus and is therefore sometimes also called Venus Syndrome .

Galloping greenhouse effect on Venus

The former water oceans of Venus have probably evaporated due to a galloping greenhouse effect

It is generally assumed that a galloping greenhouse effect took place on Venus, which led to the evaporation of the possibly previously existing water oceans. Earth and Venus are similar planets in many ways. They have roughly the same diameter and the same mass. As early as 1970 Rasool and De Bergh showed that the closer proximity of Venus to the sun triggered a galloping greenhouse effect. Evaporation of certain amounts of water through this proximity (and thus heat) does not in itself constitute a greenhouse effect. However, water vapor - similar to CO 2 - acts as a greenhouse gas . The water vapor causes further warming, which in turn causes further evaporation of liquid water. The "galloping" thing here is the self-reinforcing effect, which ultimately led to a complete evaporation of the water oceans. Today the atmospheric pressure on Venus is about 90 times higher than on Earth; the equilibrium temperature without an atmosphere would average -46 ° C on the day and night side, but is 464 ° C due to the greenhouse effect. For comparison: The greenhouse effect on earth raises the temperature from a theoretical −18 ° C without an atmosphere to an average of approx. 14 ° C (pre-industrial) and currently approx. 15 ° C.

Possibility on earth

The possibility of a galloping greenhouse effect on earth is discussed again and again, although it seems that the threshold for such a completely destabilizing self-reinforcement is barely exceeded. Nevertheless, even a small increase in greenhouse gases due to global warming can trigger dangerous tipping elements in the earth system , which lead to further warming processes. This would lead to what is known as a greenhouse earth condition. Steffen et al. (2018) cannot rule out that this will already be the case with the two-degree target agreed in the Paris Agreement . That would mean that irreversible processes would already be triggered when the two-degree limit was reached, which would warm the earth very much, even if mankind completely stopped emissions of greenhouse gases. Such a state represents conditions hostile to life (temperatures that are physiologically unacceptable for mammals and a rise in sea level of approx. 60 meters), but in itself is stable and not galloping like on Venus. The extent to which a galloping greenhouse effect could occur on earth has not been conclusively clarified. Calculations by Hansen et al. (2013) suggest that burning all fossil fuels warmed the air over the continents by an average of 20 ° C and the poles by 30 ° C, making the earth practically uninhabitable for higher living beings, but that this did not trigger a galloping greenhouse effect can be. As early as 1970, Rasool and De Bergh calculated that a galloping greenhouse effect would occur on earth if it were about 7% closer to the sun.

Individual evidence

  1. ^ A b c I. Rasool, C. De Bergh: The Runaway Greenhouse and the Accumulation of CO 2 in the Venus Atmosphere. In: Nature. Volume 226, No. 5250, 1970, pp. 1037-1039, doi : 10.1038 / 2261037a0
  2. ↑ Barry Brook: Venus syndrome - the Claron's despair. In: Brave New Climate (bravenewclimate.com). May 9, 2010, accessed February 4, 2019 .
  3. ^ NASA, Venus Fact Sheet . December 23, 2016.
  4. ↑ Venus and Earth: worlds apart. In: Transit of Venus blog. European Space Agency (ESA), May 31, 2012, accessed on February 4, 2019 (According to ESA's own information, the blog is "an unofficial and in-depth source of information for the general public, media and anyone interested in the transit of Venus" ( Source )).
  5. ↑ Jérémy Leconte, Francois Forget, Benjamin Charnay, Robin Wordsworth, Alizée Pottier: Increased insolation threshold for runaway greenhouse processes on Earth-like planets. In: Nature . tape 504 , 2013, p. 268–271 , doi : 10.1038 / nature12827 (it says that the threshold value for such an effect would be 375 W / m² irradiation, of which the sun only reaches 341 W / m².).
  6. ^ A b Will Steffen, Johan Rockström, Katherine Richardson, Timothy Lenton, Carl Folke, Diana Liverman, Colin P. Summerhayes, Anthony D. Barnosky, Sarah E. Cornell, Michel Crucifix and 6 other authors: Trajectories of the Earth System in the Anthropocene. In: Proceedings of the National Academy of Sciences . Volume 115, No. 33, 2018, pp. 8252-8259, doi: 10.1073 / pnas.1810141115
  7. ↑ James Hansen, Makiko Sato, Gary Russell, Pushker Kharecha: Climate sensitivity, sea level and atmospheric carbon dioxide . In: Philosophical Transansactions of the Royal Society A . tape 371 , 2013, 20120294, doi : 10.1098 / rsta.2012.0294 .