In layman's terms, let me show you the root of the Global Warming theory--Greenhouse effect--and how full of hot air it is.
The principle cause of any greenhouse effect is that of a one-way thermal blanket -- one which passes most wavelengths of the sun's energy, yet insulates infrared from the other direction -- energy radiated back up from the heated ground below. This is how a real greenhouse works -- most energy is in the visible bands, and it passes through glass panes to heat the ground. The ground heats up and re-radiates back in the infrared wavelengths for which the glass is opaque.
CO2 in the upper atmosphere does something similar. It acts as a thermal insulator by virtue of three infrared wavelength absorption lines at 2.7um, 4.3um and 15um wavelength. There's little energy in these lines from the sun, and when the earth absorbs the broader solar spectrum (mainly visible light), the ground gets heated. Any hot object is a so-called "blackbody radiator", meaning, it radiates energy proportional to its temperature, with a wavelength spectrum shifted towards the infrared. (Planck's formula describes the distribution of energy in this spectrum.)
You may note in the chart that most of the energy (vertical axis) lies at longer wavelengths than the CO2 absorption lines. The premise of global warming is that certain gases in the upper atmosphere -- principally water, CO2 and Methane -- are disposed to absorb infrared. In the simplified analysis, they absorb ALL the infrared coming up from the Earth. The absorbed radiation eventually is re-emitted, but isotropically -- in all directions. Consequently, 50% of the absorbed infrared is radiated up toward space, and the other 50% is "trapped" -- radiated back toward the Earth. This causes the Earth's surface temperature to rise till a state of equilibrium is reached, where the rate of re-radiation into space increases till it balances the energy absorbed from the Earth below.
You can understand this by personal example. Imagine running your home furnace constantly with some fixed outside air temperature... the temperature of your house will rise till the the rate of heat loss (which is proportional to the temperature difference between inside and outside) gets large enough to balance the heat input from your furnace. Replace your double-glazed windows with single pane windows, and the inside temperature will not rise so much -- the heat loss will be greater.
Thus, "greenhouse" gases retard the rate of energy loss, but don't eliminate it. They act as insulators, just like the gas in thermopane windows on your house.
Those are the essential principles of the Greenhouse Effect, but the theory of Global Warming enormously oversimplifies their application. In essence the Greenhouse hypothesis is developed like this:
1. The atmosphere is transparent to all solar energy (not true);Regarding Point 5, this site http://nov55.com/ntyg.html says,
2. The Earth absorbs all incident solar energy without reflection (not true);
3. The ground and heated air above the ground re-radiate the solar spectrum with a blackbody temperature shifted downward toward the infrared spectrum (true);
4. Certain atmospheric gases make the atmosphere mostly opaque to all this ground radiation (false);
5. The ground radiation is absorbed in thermally broadened atomic lines of certain gases concentrated in an infinitely thin atmospheric layer (reasonable);
6. The absorbed ground radiation is radiated isotropically, so half of it goes back toward Earth, raising the surface temperature (reasonable).
"Carbon dioxide absorbs infrared radiation (IR) in three narrow bands of wavelengths, which are 2.7, 4.3 and 15 micrometers (µm). This means that most of the heat producing radiation escapes it. About 8% of the available black body radiation is picked up by these "fingerprint" frequencies of CO2... before global warming was an issue, scientists concluded that carbon dioxide blocked 8% of the infrared radiation from going through the atmosphere. This is consistent with bandwidth. The width of the 15 micron peak is two microns wide from outer edges of shoulders. The total range of infrared radiation is about 100 microns, tapering off after 50 microns."That 8% number corresponds to 0.038% of CO2 in the atmosphere, by volume. A little more on that 8% number, shortly.
As for the assertion that the atmosphere is transparent to all solar radiation, look at this chart of total absorption:
In the scale on the left, "100%" corresponds to 100% absorption for any wavelength. I put red shading for the CO2 absorption regions.
Note where the 2.7micron, 4.3 micron and 15 micron absorption lines of CO2 are, and how small a fraction of the total atmospheric absorption they represent. (Note that the wavelength scale is logarithmic.) The 2.7um and 15um absorption bands of CO2 are completely dominated by water absorption -- in other words, this significantly diminishes the effect of CO2 as an atmospheric greenhouse gas for these wavelengths.
The only absorption line of CO2 with any appreciable effect is the 4.3um middle band. But now look at that first graph: The middle band is at the very edge of the Earth's blackbody energy spectrum. There is just very little total energy for CO2 to absorb in this band. Virtually the entire effect of CO2 is in the 15um band. But the 15um band is dominated by water vapor absorption. I conclude from this that even the 8% figure for CO2 absorption of longwaves from the Earth's surface is far too high. I don't know the source of that data, but it was probably a theoretical amount determined in the absence of water vapor.
Also note how much smaller methane absorption is than CO2. Where is the basis for all those assertion that methane is 100 times more absorptive of longwaves (ie, infrared) than CO2? Principally in the fact that the ratio of total absorption for methane relative to the fraction of methane in the atmosphere (0.000179%, or 200 times less than CO2) is greater. But note again how the methane absorption bands coincide with and are completely dominated by longwave water absorption by water vapor -- you can discern virtually no effect of methane in contributing to total atmospheric absorption (look carefully!). Even if methane was a more effective greenhouse gas, It would take a lot of cows to increase methane to any significance whatsoever, so long as there's water in the atmosphere. And remember -- global warming increases water in the atmosphere. So where's the beef?
The Wiki article calculates and asserts that ifthe atmosphere absorbs 78% of all radiation from the ground, it predicts the average global temperature of 288K to within 0.3 degree. Remarkable. I'm in awe. Exactly the same as the known value. All we need is that 78% figure. What hat was that rabbit pulled out of? The alleged accuracy of this prediction is presented as justification for calculating the accuracy of a temperature rise caused by a doubling in CO2, corresponding to (the author asserts) an increase in longwave atmospheric absorption from 78% to 80%:
ε represents the fraction of upward longwave radiation from the surface that is absorbed, the absorptivity of the atmosphere. ...ε=0.78 implies 22% of the surface radiation escapes directly to space"The author of the article (William M. Connolley, a self-described UK software engineer and climate researcher, see http://en.wikipedia.org/wiki/William_Connolley) calculates from this an average global temperature increase of 1.2K in the absence of water vapor (clouds). He then makes some hand-waving assumptions that says higher surface temperature increases water vapor with positive feedback (because water absorbs longwave radiation up from the Earth), so the real temperature rise from a doubling of CO2 will be 2.4K -- even more dire.
First of all, you will note that an increase in ε from 0.78 to 0.80 is not consistent with CO2 absorbing 8% of the longwaves. This is consistent with CO2 absorbing only 2% of longwaves from the Earth's surface.
So, Connolley supports my previous assertion that 8% is too high. We might wonder if even the 2% figure (the amount of surface radiation absorbed by CO2) is inflated. As I said, the 2.7um and 15um absorption bands of CO2 are completely dominated by water vapor absorption, and the 4.3um band is at the edge of the blackbody emission spectrum, where there's very little energy to absorb. So.
The article at this page (http://nov55.com/ntyg.html) makes some other interesting points about saturation effects that diminish CO2 absorption which I won't go into (and I have serious problems with other essays on this website, so don't take it as an endorsement), but here's the real problem with the Wiki article: Connolley says at the beginning,
"The planetary albedo αP is the fraction of the incoming solar flux that is reflected back to space..."and goes on to assume αP=0.3 for the remainder of his article, including when he makes his positive feedback water vapor correction, predicting a higher 2.4 degree rise in global warming from doubling CO2.
This is an interesting omission: higher water vapor (from evaporation of the Earth's oceans and lakes) means more clouds, and more clouds means more sunlight is reflected back into space. This will reduce the amount of solar energy absorbed by the Earth. To say that this is an egregious omission is being inadequate. It would be like saying ignoring the Nazi conquest of Poland was a minor omission in assessing whether Germany was a major threat to the rest of Europe. Connolley would have us spend trillions of dollars on cap and trade, impoverish industrial societies across the globe, and cost the lives of millions of people based on this one minor omission.
More could be said, but that's enough for me to conclude that the entire heat-trapping hypothesis has big holes in it. Nonetheless, there is great value in reading Connolley's analysis of greenhouse effect because with a little extra information you can see the false and misleading assumptions that go into the house of cards based on this premise.