Jovial Monk
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How does AGW work?
A number of molecules present in the atmosphere that contain three atoms or more can absorb and re-emit infrared (IR) photons (think of them as rays of infra red light if you like.)
Some of the Greenhouse gases are:
H2O present as water vapor (clouds are not water vapor but collections of tiny droplets of water) H2 + O = 3 atoms
CO2 is present as a gas, unlike water vapor it doesn’t eventually precipitate out as rain etc. 3 atoms, see?
CH4, methane, also present as a gas. A much (30x) stronger GHG than CO2 but does get oxidised to CO2 and H2O so not present all the time. 5 atoms.
N2O, nitrous oxide. 200x as powerful a GHG as CO2. Hangs around for ever.
O3, ozone, 3 atoms of oxygen in an unstable molecule.
So what happens? Visible light from the sun (UV can be disregarded) hits the earth, some gets reflected some hits the surface, some gets reflected, some gets absorbed. A rock or a cement pavement that has been baking in the sun all day radiates heat at night—you can feel the warmth. Oceans absorb a lot of light, warming the water.
So, the earth radiates infrared. If it couldn’t do that—we would bake!
So imagine a ray (photon) of infrared heading out from the surface of the earth. It hits a molecule of a GHG. The molecule absorbs the photon which ‘excites’ the molecule meaning it vibrates and spins etc faster. The molecule can’t hold on to the photon for long so re-emits it. However, it could be pointing to the surface and sends the photon back down to the surface.
There are other molecules of GHG in the atmosphere, a photon could be absorbed and re-emitted several times, increasing the chance it heads back to the surface.
Now, this is not something I am spinning out of nothing. NASA has satellites studying the radiation from the earth. At the frequencies corresponding to the spectrum lines of the various GHGs there is less radiation than expected. Infrared radiation IS being trapped in the atmosphere, warming the globe.
AGW is a soundly based scientific theory.
You know it is happening:
1. Glaciers are retreating (bar a very few)
2. Greenland is losing like 200gigatons of ice a year
3. Arctic sea ice is thinning and decreasing in extent.
4. The Himalayan ice sheet is retreating—this may cause a second nuclear war between India and China.
5. We have seen Antarctica is losing more and more ice (tho East Antarctica is gaining ice West Antarctica is losing more than East Antarctica gains.
That is the story in a nutshell.
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