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Calculating the greenhouse effect
(Real Climate), 21 January 2006 -
In another forum (on a planet far, far away), the following quote recently came up:
"...the combined effect of these greenhouse gases is to warm Earth’s atmosphere by about 33 ºC, from a chilly -18 ºC in their absence to a pleasant +15 ºC in their presence. 95% (31.35 ºC) of this warming is produced by water vapour, which is far and away the most important greenhouse gas. The other trace gases contribute 5% (1.65 ºC) of the greenhouse warming, amongst which carbon dioxide corresponds to 3.65% (1.19 ºC). The human-caused contribution corresponds to about 3% of the total carbon dioxide in the present atmosphere, the great majority of which is derived from natural sources. Therefore, the probable effect of human-injected carbon dioxide is a miniscule 0.12% of the greenhouse warming, that is a temperature rise of 0.036 ºC. Put another way, 99.88% of the greenhouse effect has nothing to do with carbon dioxide emissions from human activity."
Realclimate has discussed the magnitude of the greenhouse effect before, but it might be helpful to step through this ‘back-of-the-agenda’ calculation and see what the numbers really give.
> www.realclimate.org: Calculating the greenhouse effect (21 January 2006)
Water vapour: feedback or forcing?
(Real Climate), 6 April 2005 -
Whenever three or more contrarians are gathered together, one will inevitably claim that water vapour is being unjustly neglected by ‘IPCC’ scientists. “Why isn’t water vapour acknowledged as a greenhouse gas?”, “Why does anyone even care about the other greenhouse gases since water vapour is 98% of the effect?”, “Why isn’t water vapour included in climate models?”, “Why isn’t included on the forcings bar charts?” etc. Any mainstream scientist present will trot out the standard response that water vapour is indeed an important greenhouse gas, it is included in all climate models, but it is a feedback and not a forcing. From personal experience, I am aware that these distinctions are not clear to many, and so here is a more in-depth response (see also this other attempt).
> www.realclimate.org: Water vapour: feedback or forcing? (April 6 2005)
Water vapour is not the dominant greenhouse gas
(Stoat), January 20 2005 -
OK, so it may not surprise you that I'm going to have to qualify the headline a bit lower down, but the point itself remains.
Why does anyone care about this? Answer, of course, that one of the std.septic arguments is "there is no point in worrying about human emissions of CO2, because water vapour is the dominant GHG". This argument is nonsense (which is why there is no k) but if you don't know the science thats no obvious. So...
Water vapour is not the dominant greenhouse gas (Jan 20 2005)
The 'Greenhouse effect'
(Wikipedia) -
The greenhouse effect is caused by an atmosphere containing gases that absorb and emit infrared radiation. Greenhouse gases trap heat within the surface-troposphere system, causing heating at the surface of the planet or moon. This mechanism is fundamentally different from that of an actual greenhouse, which works by isolating warm air inside the structure so that heat is not lost by convection. The greenhouse effect was discovered by Joseph Fourier in 1824, first reliably experimented on by John Tyndall in 1858, and first reported quantitatively by Svante Arrhenius in 1896.
en.wikipedia.org: The 'Greenhouse effect'
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