Talk:Greenhouse gas

Atmospheric Lifetime

The following statement in section 6.2 contradicts the preceding definition of lifetime and should be deleted: "The atmospheric lifetime of CO2 is often incorrectly stated to be only a few years because that is the average time for any CO2 molecule to stay in the atmosphere before being removed by mixing into the ocean, photosynthesis, or other processes. However, this ignores the balancing fluxes of CO2 into the atmosphere from the other reservoirs. It is the net concentration changes of the various greenhouse gases by all sources and sinks that determines atmospheric lifetime, not just the removal processes." If the inputs are included to balance out the outputs, then the lifetime for any gas with a stable concentration would equate to infinity (divide by zero). This is clearly wrong and it is the flux or flow of the substance through the atmosphere which is the denominator not the difference between the inputs and outputs. For a stable concentration the input equals the output, but as per water vapor, that does not mean that it has an infinite lifetime. This misunderstanding has propagated numerous incorrect statements such as "Recent work indicates that recovery from a large input of atmospheric CO2 from burning fossil fuels will result in an effective lifetime of tens of thousands of years." in the following section. It is quite apparent from the amplitude of the yearly CO2 concentration cycle that it's Lifetime is relatively short. The only way it could get to tens of thousands of years would be in situations like "snow ball earth" with no plants and no plankton etc. I suggest the above statement be replaced with "The atmospheric lifetime of CO2 is often incorrectly stated to be thousands of years or more, due to substituting the net input minus output flux through the atmosphere in place of the output flux. The atmospheric lifetime of CO2 is actually only a few years because that is the average time for any CO2 molecule to stay in the atmosphere before being removed by mixing into the ocean, photosynthesis, or other processes." — Preceding unsigned comment added by BFhybrid (talk • contribs) 13:13, 7 June 2011 (UTC)

The correct definition of atmospheric lifetime in the context of greenhouse gases is defined by what the literature states, and not what we as editors judge to be the correct definition. I've spent a bit of time looking in the TAR for its definition (which can be found here), and that one contradicts your personal definition of molecule lifetime, and is similar to the definition in 6.2. So that is the one that the preponderance of the literature seems to support. If you disagree, then i suggest that you find sources of equivalent merit to support yours. (suggestion: The U.S. Global Change Research Program or the AR4 might be a place to look) --Kim D. Petersen (talk) 15:59, 7 June 2011 (UTC)

The definition that I am discussing is not 'my personal definition' as you make out, it is the clear definition that is already referenced in 6.2 to Jacob, and includes the equation with explanations of each variable; maths is the universal language and it is unambiguous. I found no definition of atmospheric lifetime in your link, only one oblique reference to lifetime, in the obvious statement that well mixed gases have longer lifetimes. You have not addressed my objection that the second paragraph is contradicting the first paragraph, and the statement you are supporting is already tagged with 'citation needed'. What I don't understand is your claim that the definition you found in the TAR (what is this?) is similar to the definition in 6.2. Perhaps you could just extract the definition you are referring to from the TAR and post it here? Here is the first internet reference I found on Google on this issue BFhybrid (talk) 12:47, 8 June 2011 (UTC)

BFhybrid, you are absolutely correct. But I caution you not to pursue this matter because you will just get more frustrated. If you go back into the archives you'll see contributions from me on this subject. Physicists and engineers use half-lifes to describe exponentially decaying processes, and don't generally use the simple term "lifetime" except in casual conversation. Authors writing about greenhouse gas/effect make up their own definitions; you won't find a consistent definition. Indeed if someone attempted to create one, it would be torn to shreds or just ignored by others who have preconceived notions of what the end result should be. I've read some of the papers that assert lifetimes of the order of 100,000 years for CO2 in the atmosphere. While they may make some attempt to descibe how they arrive at a figure, they're not precise in describing where they set the concentration threshold on the way to an infinitely long lifetime. As for my understanding of the matter, when the terms are shifted to those physicists would use, the half-life of CO2 in the atmosphere (sources cease, decay only) is somewhere near three months (if I remember correctly). The more interesting observations that can be made are about the mechanisms. CO2 removal is a largely a surface effect, depending on how you view H2O condensation and the mass transport of CO2 to the surface by precipitation. H2O removal is a volume effect for the most part. Water vapor condenses at temperatures commonly found in the atmosphere; CO2 does not change state at temperatures found in the atmosphere. These are the underlying reasons why CO2 leaves the atmosphere far more slowly than H2O. blackcloak (talk) 09:37, 5 August 2011 (UTC)

Resource data ...

Resource for comparative data on carbon emissions in the United States, China, and India from the United States Energy Information Administration ... http://www.eia.gov/oiaf/ieo/pdf/ieorefcase.pdf 216.250.156.66 (talk) 20:18, 28 July 2011 (UTC)

History of scientific research

There is a link in this section ( http://www.oppapers.com/essays/Global-Warming-Opposing-Viewpoints-Paper/733173?topic ) with a pay wall, it is to a purely commercial organisation trying to sell "teach you how to write". There is no access to samples of what they do or anything of that sort and it certainly does not have anything to say about GH gases unless you pay first. I will be removing this shortly unless a good argument is presented. --Damorbel (talk) 11:08, 12 September 2011 (UTC)

I created this link in this edit today. Previously the reference was "Opposing Viewpoints Resource Center. Detroit: Thomson Gale, 2005. From Opposing Viewpoints Resource Center" with no links. I have no idea who or what 'Opposing Viewpoints' is either. The problem is that the statements it provides a source for are self-evidently true. What we need is a better reference for this level of historical summary. --Nigelj (talk) 16:49, 12 September 2011 (UTC)

Typo in image

The image on the page has a typo in the bottom left-hand corner: "Absorbation" - instead of "Absorption"?

File:The_green_house_effect.svg

Can we fix it?

Drdrperry (talk) 00:22, 15 September 2011 (UTC)

"Absorbs and emits"?

Atmospheric absorption and scattering at different electromagnetic wavelengths. The largest absorption band of carbon dioxide is in the infrared.

The article begins, "A greenhouse gas (sometimes abbreviated GHG) is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range." Why do we have "emits" in there? The characteristic of a GHG is the existence of absorption bands in the IR region of the spectrum equivalent to the surface temperatures of the planet, so absorb is definitely right.

Does not any gas emit IR radiation equivalent to its blackbody temperature? I may not be correct here, as other gasses will be transparent and I'm not sure if transparent things emit IR like blackbodies, so this really is a question, not yet a suggestion and certainly not a criticism. Whichever is right, I didn't find the answer in the article. Maybe I missed it, or maybe we can improve something here. --Nigelj (talk) 18:49, 2 October 2011 (UTC)

The current phrasing is correct. Not all gases emit in the infrared when heated. For example, if you were to look at a heat gun through an infrared camera, you would not be able to see anything leaving the gun. This is because the primary components of air (oxygen and nitrogen) do not emit radiation in the infrared. However, if you were to introduce CO₂ into the heat gun intake, you'd very clearly see it show up on the infrared display because CO₂ does emit in that range. So it's very much correct to make the distinction that only some gases absorb energy and emit in the infrared. --Sean 130.253.30.70 (talk) 21:38, 2 October 2011 (UTC)

Nigelj, O2, N2, and Ar do not absorb or emit in the IR frequencies discussed in the greenhouse effect. In addition, many substances absorb in more frequencies than they emit. This is called fluorescence and phosphorescence. Q Science (talk) 00:51, 3 October 2011 (UTC)

You've stumbled into an area that has been discussed many times in the past. The current dumbed down wording is intended to provide the general reader with a simple statement about the critical link between thermal energy storage in the atmosphere and IR sources (absorption) and sinks (emission/re-radiation) of energy. The intro is not intended to be technically accurate, literate or complete. To get into some of the technicalities, even though these ideas do not necessarily belong in an introduction, I do not believe there are any molecular species found commonly in the atmosphere that exhibit phosphorescence or phosphorescence. It is a general rule that at any given wavelength, the absorption coefficient and the emissivity coefficient are equal, which simply means the a good absorber is an equally good emitter. What is missing in the intro is the idea that the non-GHG components (about 99%) of the atmosphere are the actual thermal reservoir (which we feel as the air temperature) and that GHG concentration controls the rate at which energy moves both into and out of the atmosphere (for a given temperature of the atmosphere and IR field strength). The problem, from a writer's point of view, is which facts need to be touched upon in the intro in order to give the reader enough to begin to understand the scope of the article. blackcloak (talk) 06:08, 26 October 2011 (UTC)

The atmosphere absorbs from a hot surface during the day and emits different frequencies at night (because the air is colder than the surface was). As I understand it, that meets all the requirements of phosphorescence.

• Emitted frequency is lower than absorbed frequency
• Delay between absorption and emission is greater than 1ms

Thus, the atmosphere itself is phosphorescent. Q Science (talk) 06:41, 26 October 2011 (UTC)

No, not phosphorescent. Phosphorescence, as far as I know, does not occur in gases. If you check the Wiki article it refers to the delay in re-emission characteristic of phosphorescence being "associated with "forbidden" energy state transitions in quantum mechanics", these transitions can only occur in solid materials. The IR absorption/emission associated with the so-called greenhouse gases is due to molecular vibrations that are directly related to the molecular temperature. Phosphorescence is not particularly dependent on temperature, whereas the absorption/emission of GHGs is an exact function of the temperature of the molecule.--Damorbel (talk) 09:10, 26 October 2011 (UTC)

That explains how it works in some solids. From The Free Dictionary

Persistent emission of light following exposure to and removal of incident radiation

From Merriam-Webster

luminescence that is caused by the absorption of radiations (as light or electrons) and continues for a noticeable time after these radiations have stopped

From dictionary.reference.com

any luminous radiation emitted from a substance after the removal of the exciting agent

a fluorescence for which the average lifetime of the excited atoms is greater than 10--8 seconds

The point of these is that

• Radiation causes the effect
• Emission continues for a noticeable time after the forcing radiation stops

BTW, to create a laser, the lasing material must be phosphorescent. That is true of solid, gas, and dye (liquid) lasers. HeNe and CO2 lasers are both fairly common gas lasers. Q Science (talk) 13:17, 26 October 2011 (UTC)

"to create a laser, the lasing material must be phosphorescent" Really? It doesn't mention this in the Wiki laser article. And a solid state laser's output is proportional to the input current (above the threshold). Also a laser can be modulated very quickly (many MHz) to give femtosecond pulses, which is rather different from phosporescent material, which can glow for an hour or more after the stimulus is withdrawn. --Damorbel (talk) 17:47, 26 October 2011 (UTC)

Well, we all know better than to trust wikipedia. (Grin) The trick is that if the material can store energy long enough, then it is possible to stimulate an emission and, by definition, any material capable of storing that type of energy for that long is phosphorescent. In some cases, the energy can be converted (via stimulated emission) into light in a femtosecond. Typically, the lasing wavelength is not the same as the pumping wavelength, another characteristic of phosphorescence. Q Science (talk) 18:00, 26 October 2011 (UTC)

And phosphorescence is coherent is it? And phosphorescence is stimulated is it? As you put it "any material capable of storing that type of energy for that long is phosphorescent" - and phosphorescence can have any characteristics you like, can it? --Damorbel (talk) 20:29, 26 October 2011 (UTC)

Phosphorescence is not coherent, but stimulated emissions are. Q Science (talk) 21:14, 26 October 2011 (UTC)

Re. - the line above Why then does, as you write, "the lasing material must be phosphorescent"? As noted Phosphorescence is a process whereby the emission is delayed minutes, hours and days; whereas lasing is in the femtosecond region. Do you not see any difference? Phosphorescence does not involve stimulated emission so it doesn't have anything to do with "light Amplification by Stimulated Emission of Radiation, LASER for short. Phosphorescence and lasing are very different (physical) processes, producing very different results, in any reasonable encyclopedia they should not be confused. --Damorbel (talk) 09:10, 27 October 2011 (UTC)

This may help

Spontaneoous emission from a triplet state occurs very slowly, by comparison with fluorescent transitions, and is called phosphorescence.

Molecular fluorescence is responsible for dye laser emission.

I was not aware that dye lasers were based on fluorescence. I have not been able to find many other references. The following reference supports the idea that the lasing medium is phosphorescent.

Stimulated emission depletion of triplet excitons in a phosphorescent organic laser

Perhaps you can find additional references. It appears that we need to add this to the laser and stimulated emission articles. Q Science (talk) 14:05, 28 October 2011 (UTC)

Both your refs. state that laser action arises from stimulated emission with the atoms (or molecules) in a highly excited state, also described as population inversion. With no stimulation some excited material may emit by slow process such as fluorescence and phosphorescence but there are plenty of ways other than these two to get the necessary population inversion, semiconductors can lase if driven hard enough but they are not phosphorescent; gas discharges do the same thing in the He/Ne laser but you will not get He/Ne to phosphoresce or fluoresce. I think you are just naming all light emitting processes 'phosphorescence' or 'fluorescence', which is not exactly scientific. The article on luminescence may help you to sort out the differences in the various sorts of light emission. Read the link and all the links in the article - you will then discover what a complicated subject the interaction of light and matter is; the terminology needs to be used precisely if confusion is to be avoided. --Damorbel (talk) 21:12, 30 October 2011 (UTC)

Associated Press resource

Biggest jump ever seen in global warming gases by Seth Borenstein, Associated Press (via USA Today) ... excerpt "The global output of heat-trapping carbon dioxide jumped by the biggest amount on record, the U.S. Department of Energy calculated, a sign of how feeble the world's efforts are at slowing man-made global warming." 99.109.125.146 (talk) 22:42, 3 November 2011 (UTC)