Doubling of CO2 and Methane?

Question

I've just started to look into the effects of doubling both of these gasses in the atmosphere with regards to energy retention. For each doubling of CO2 in the atmosphere this produces an increase of 3.7 W/m^-2. This means that for each doubling, say from 180 to 360 and from 360 to 720, there will be an increase in downward radiation of 3.7W/m^-2. Correct?

The energy needed to raise temperatures of the atmosphere 1 deg. C is equal to roughly 4.0 watts per meter squared. Downward longwave radiation increased between 1973 and 2008 by 2.2W/m^-2 per decade according to Wang et al.

http://onlinelibrary.wiley.com/doi/10.1029/2009JD011800/abstract

The radiative forcing of CO2 between 1750 and 2005 is equal to +1.66 W/m^-2 methane is equal to +0.48 W/m^-2, and nitrous oxide is +0.16 W/m^-2.

http://www.mmm.ucar.edu/wrf/users/docs/Iacono_etal08.pdf

I'm curious as to what the overall temperature effect of doubling CO2 would be compared to doubling methane at the current concentrations. A doubling of methane, of course, would be smaller but, at less concentration, it would have a much larger effect per molecule. I recall an answer in here stating that even if methane and CO2 were at the same concentrations methane would still absorb more per molecule due to its makeup.

Answer 1

There is nothing inherently special about the methane molecule which makes it some super potent greenhouse gas--the only thing it has going for itself at the moment is that it is far less abundant. While it's true that CH4 has more vibrational modes being a higher order polyatomic, its most relevant band peaks around 1300cm-1, which falls in the tails of Earth's blackbody spectrum, making it less important. If we look at the radiative forcing from a doubling of methane, it's only something like 0.8 wm-2, but because we're talking about parts per billion rather than ppm, the radiative forcing per extra CH4 molecule is an order of magnitude higher than in CO2's case.

Answer 2

"There is nothing inherently special about the methane molecule which makes it some super potent greenhouse gas--the only thing it has going for itself at the moment is that it is far less abundant. While it's true that CH4 has more vibrational modes being a higher order polyatomic, its most relevant band peaks around 1300cm-1, which falls in the tails of Earth's blackbody spectrum, making it less important"



That's not the only relevant thing. The strength of the interaction is relevant. Some interactions are more likely to occure even at the same resonant radiation intensity.



The likelihood that a photon will excite a molecule is given by Fermi's Golden Rule. The transition probabilities are different for different resonances.



Unfortunately, it is not possible to understand where Fermi's Goldden Rule comes from without understanding differential equations, although I suspect some here might think they can derive it from spreadsheets.

Answer 3

The theoretical effect of doubling a greenhouse gas is not a logarithmic function, but the actual function can be approximated as logarithmic over a limited range of concentration. The rate of radiation to space is determined by the temperature of the last absorbing layer of gas. As greenhouse gas concentrations increase, the altitude of the last absorbing layer increases and temperature decreases. Cold gas radiates less energy to space, hence more energy is retained at lower levels. The logarithmic approximation for the effect of greenhouse gas doubling actually rests on the temperature profile of the atmosphere and an assumption of mixing. Water, for example, does not mix into the stratosphere very well and the emissions from water are characteristic of warmer layers. CO2 mixes well and the last absorbing layer is consequently much higher and colder.

Answer 4

How did you calculate the atmospheric cooling that happened between 1940 and 1980 using that formula?

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There's only one answer for the heating effects of the planet in your mind but there's so many other reasons for the cooling. I get it. Thanks Jeff!

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If your temperature records were completely accurate, then your question is a valid one. There's no evidence to support that your anthropogenic calculations are accurate. Despite some discrepancies between various data sets, the global temperature differences between 1942 and 1997 are small to none – except for land-based thermometer data outside the U.S. This disparity with your CO2 warming premise demands an explanation – as do the much larger in trends of the Northern Hemisphere compared to the Southern Hemisphere. Both satellite data and independent balloon data show a near-zero trend from 1979 to 1997. We all know what happened in the El Nino year of 1998.



Specific calculations on anthropogenic increases and the forcing effect of CO2 can also be found here : http://www.biocab.org/Radiative_Forcing_and_Heat_Stored.html

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Lest we forget that the past 10 years has shown no increase of temperatures. So now we are talking about a period between 1998 and 2003 of warming where the residual effects of an El Nino event may come into play. It's fair to say that there is hardly any additional warming due to the increase of CO2 in our atmosphere.

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The relatively minor warming of the ocean surface (71% of the Earth surface), stands in contrast to the reported global warming between 1970 and 2000. It suggests that land surface warming has been greatly over-estimated.

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A fact well known to all scientists is that the absorptivity-emissivity thermal property of carbon dioxide diminishes as its density increases and as the temperature augments. This happens because the infrared radiation absorption margin is very narrow (wavelengths from 12-18 micrometers) and so the opacity of carbon dioxide to infrared radiation increases with altitude. As the column of CO2 gains height, the opacity to infrared radiation increases.



Heat always moves from places of higher density of heat to places of lower density of heat. Thus states the Second Law of Thermodynamics. In daylight, air is always colder than soil; consequently, heat is transferred from the soil to the air, not vice versa. By the same physical law, the heat emitted by the Sun –a source of heat- is transferred to the Earth, which is a colder system.

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CO2 warming is enhanced by all of the other gases warming in our atmosphere and therefore it is not logarithmic. Doesn't matter what frequency or wavelength it receives radiation (energy) from. Your problem is that you think that CO2 and methane are the dominant heating gases. Of course they hold heat, but the heat in the atmosphere is generated by many gases. Oxygen and nitrogen also generate heat. How do you compensate for the "heat factor from other gases" in your formula? CO2 acts more like a thermostat and not the fuel for the fire.

Answer 5

In order to cause as much warming as a doubling of mrthane, carbon dioxide concentraton would have to increase by about 120ppm. That would be less than a doubling of carbon dioxide concentration. Doubling carbon dioxide concentraton would cause more warming than doubling methane concentration.

Answer 6

Your talking utter crap, the warming effect of CO2 logarithmically diminishes with concentration, a doubling of CO2 would produce a miniscule fraction of one degree centigrade rise.

Answer 7

<<>>



You did no such thing. There is a difference between theory and fact.

Answer 8

Interesting thoughts, but of course a doubling is only a thought experiment, nothing that radical could happen except over many decades at least, and as I understand it methane breaks down into CO2 after a decade or two. CH4 + 2O2 -> CO2 +2H2O

https://answersrip.com/question/index?qid=20080925155421AAwcLog

http://en.wikipedia.org/wiki/Atmospheric_methane