Radiative Physics – Yes CO2 Does Create WarmingI'm forced to spell out again how I am so darn sure that CO2 causes some warming. Some of this seems like it's too obvious but that's probably because I work in optics and these equations are very familiar. When considering radiative absorption of CO2, we need to look at Plancks equation and the absorption curve of CO2.
The spectrum of CO2 is important to consider. Note that all the absorption is at the far right end of the curve – long wavelengths – with high transmission in the visible .3-.65 microns. Also for the water vapor guys, there is a couple of clear CO2 peaks which fall at water vapor valleys — bad luck guys. Anyway the absorption curve of CO2 in Fig 1, doesn't extend into the visible range. It is transparent to visible light though and you can confirm it by the total atmosphere curve which is an addition of the gasses shown.
Fig 1
Then there's this: From Wiki:
Planck's equation states that
where
- I(ν,T) dν is the amount of energy per unit surface area per unit time per unit solid angle emitted in the frequency range between ν and ν + dν by a black body at temperature T;
- h is the Planck constant;
- c is the speed of light in a vacuum;
- k is the Boltzmann constant;
- ν is frequency of electromagnetic radiation; and
- T is the temperature in kelvins
So sunlight is about 5600 kelvin and the earth emits at about 285 Kelvin. Plugging the raw values into the above equation results in the graph in Figure 2.
Figure 2 - nanometers. 5000 nanometers is 5 microns in Figure 1. 1000 is 1, 2000 is 2.
See the flat pink line at the bottom? There you go, nice job Jeff, you've just proven that the Sun is brighter than the earth, brilliant!!
We know that the energy which strikes the surface of the earth is very nearly equal to the energy which the surface emits. There's heat from the core, chemical energy released and not much else that I can think of that throw it a tiny bit out of balance, but these effects are very small in comparison to the total wattage from the sun. It's so close that I probably shouldn't have mentioned it as somebody may see it as a method of disagreement. Therefore the area under the energy-vs-wavelength transformed version of these two curves is equal for all intents and purposes.
So in Figure 3, I've scaled the graph to have equal incoming and outgoing energy.
So that's how we determine the color of a lightbulb and the outgoing radiation of earth. An excellent graph below contains all of the points in this post overlaid. The internet is great, global warming in a few plots.
That's all there is too it. The peak of the outgoing radiation lands almost perfectly on top of a CO2 spike. Incoming light goes right through the CO2, outgoing light get's absorbed and re-emitted.
Radiative physics proven again.
The point is that any skeptical argument having any credibility at all, needs to start from this point. Yes CO2 causes some warming. After this, the world is your oyster and I'm no longer the guide.
Tuesday, April 20, 2010
Radiative Physics – Yes CO2 Does Create Warming
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