For the record, toward the left of this graph are the two (yellow) arrows that indicate the (visible) color (frequency) of the Sun's light coming in to the Earth. The spectrum of light that methane gas can affect is shown is shown in the (near infrared) purple portions. It only includes two very narrow colors, at about 3 microns and 8 microns. Please notice that methane gas CANNOT absorb or affect ANY of the incoming sunlight (yellow, which is all at about 0.7 microns).
We also include the far infrared radiation that the Earth gives off to space. both at the Equator (red, 15 microns) amd from the Poles (blue, 18 microns). Please notice that methane gas CANNOT absorb or affect ANY of the outgoing far infrared radiation from anywhere on Earth (which is all at about 15 microns and farther infrared).
It is sad that a few stupid comments made back around 2004 are still being repeated as having had any truth. People who did not have adequate scientific education or knowledge then claimed that Methane gas which is currently mostly trapped under Arctic ice (as Methane Hydrate) was allegedly going to cause even far greater Greenhouse warming effects than Carbon Dioxide is causing.
That theme has become amazingly universal! Even sources such as the Microsoft Encarta have articles which say "Methane is an even more effective insulator, trapping over 20 times more heat than does the same amount of carbon dioxide" (Global Warming, contributed by John Hart). We see in the graphs above and below that this statement is simply dead wrong!
It seems certain that people in the Petroleum Industry had given a few greedy but ignorant scientists a lot of money to cast aspersions on Methane gas, to try to minimize any Public Relations problems that Fossil Fuel burning is developing.
Let's first examine Carbon Dioxide.
The main problem with burning fossil fuels (CH4 → CO2 + H2O) is the ADDITION of carbon dioxide into the atmosphere. Look at this graph of the transmission / absorptance spectrum of carbon dioxide for various wavelengths of light. It is very transparent to UV and visible light (to the left in the graph), so the sun's energy easily comes through and in. But it is rather opaque to much of infrared light (to the right in the graph), which is what the Earth tries to radiate out to outer space. This results in the effect of "a stack of blankets" not allowing much of the Earth's heat to ever leave! Global Warming
We have also added some arrows at the top of the graph, which require some explanation! Any object that is heated releases RADIATION to get rid of some of that heat. The wavelength of the radiation is dependent on the temperature of the source. Scientists including Planck, Wein, Stefan, and Boltzmann developed equations that describe those effects.
Since the Sun's surface is around 5760°K, the wavelength of the MEDIAN radiation in is around 0.709 micron, a reddish color. This is represented by the LONGER downward (orange) arrow. There is also a different wavelength which is the one that is most intense, which is at 0.503 micron (a greenish color), which is represented by the attached shorter arrow to the left in the graph.
This results in carbon dioxide in NOT blocking the Sun's energy from getting to the Earth.
Different parts of the Earth are at different temperatures, so they radiate at different wavelengths. We show the MEDIAN (13.2 microns) and peak (9.3 microns) wavelengths for the radiation from the hotter Equator regions (as red arrows), and also for the radiation from the colder Polar regions (16.1 microns and 12.4 microns) (as blue arrows).
It might be noted that SOME of the radiation from the Equator regions has a chance of escaping, as the absorptivity of carbon dioxide is not quite as high for some of those frequencies. But the absorptivity of carbon dioxide for the Polar regions is consistently near 100%. Many scientists seem mystified as to why the North Polar region is warming up several times faster than the rest of the planet. Part of the explanation seems pretty obvious here when this differential absorption of carbon dioxide is considered.
Now let's examine the situation regarding Methane gas.
There is an additional troubling complication to this subject. There are spokespeople who are claiming to be scientists and then making statements that are horrifically misleading to the public.
In recent years, spokespeople have made many statements that carbon dioxide is nearly irrelevant and it is actually methane gas that must be feared regarding global warming. Such statements seem to trust statements such as that cited in the Encarta article to be true!
Unfortunately, none of the listeners to such statements have any way to either confirm or deny the validity of the claims. But look at the actual scientific facts! Where carbon dioxide is currently at a concentration of around 390 ppmv (parts per million by volume), methane gas is only around 2 ppmv. That is only about 1/200 as much. Now IF methane was astoundingly effective at blocking infrared radiation, maybe 2 ppmv should be feared! But look at the graph above which shows the absorptivity spectrum of Methane gas. It does NOT have massive bands of infrared absorptance. Instead, the reality is that methane only has two, rather narrow peaks regarding infrared absorption. And they are not even at wavelengths which would absorb the radiation the Earth is trying to send outward!
The claims of those spokespeople were entirely wrong or lies. However, their goal was greatly successful, where their lies convinced an immense number of people, including a lot of scientists, that we should be focused on methane and not on carbon dioxide. In this way, they have managed to continue to keep their green light regarding burning fossil fuels at astounding rates. But that was all based on blatant lies!
Here is another analysis, of a bunch of potential 'global warming gases'. The important factors here are a single vertical line at 16.1 microns (near the very right edge of this chart) since the colder surfaces near the Poles are at temperatures which radiate at this wavelength from the Earth's Poles, and also another vertical line at 13.2 microns which this is the wavelength that the warmer surfaces near the Equator radiate off. Most atmosphere gases do NOT affect outward radiation at these wavelengths, so they do NOT act as 'greenhouse gases'. Really, ONLY carbon dioxide absorbs large amounts of such radiation, although water vapor also does. However, water vapor tends to stay in weather patterns, very low in the atmosphere so it does not act much like a 'greenhouse gas'. Only carbon dioxide does.
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As we dig up coal and petroleum and natural gas to burn (oxidize) them, we wind up adding some more water vapor and carbon dioxide into the atmosphere, which had been buried for millions of years. THIS is the way that carbon dioxide is affecting the Earth's atmosphere, in adding blanket effects to cause the atmosphere and the Earth to gradually get warmer and warmer.
Coal has virtually no hydrogen in it, so when coal burns, only carbon is burning, which therefore creates somewhat more carbon dioxide. Not an enormous difference, but when you burn as much fossil fuel as we do, it adds up. Petroleum is made of very complex molecules, which contain a lot of carbon but also a modest amount of hydrogen (and even oxygen) atoms. It's effect is between coal and natural gas regarding producing carbon dioxide.
All three produce astounding amounts of NEW carbon dioxide which gets added to the atmosphere. So even though carbon dioxide is 'not quite as bad' as coal or petroleum, there is no reason to celebrate.
Whether fossil fuels are extracted from the earth by drilling for petroleum or natural gas , by mining for coal, or by fracking for natural gas, all contribute dangerous new amounts of carbon dioxide into the atmosphere.
There IS one effect of methane gas which is bad regarding Global Warming. When the atoms of Carbon and Hydrogen are OXIDIZED during burning, that CREATES (1) water vapor and (2) carbon dioxide. Not as much carbon dioxide as coal produces, but still a lot. So in one sense, but in a rather distorted way, burning enormous amounts of methane (or natural gas) still gets a lot of carbon atoms up out of the deep rock and therefore creates a lot of carbon dioxide as a result. As a scientist, I just wish that the 'experts' would get their facts right!
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