Talk:Greenhouse gas

"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)

I agree; how arrogant can you be? You know a couple of characteristics of phosphorescence and so anything that has those two characteristics must be phosphorescent? Stores energy and releases it later. So, you would argue that a bouncing spring exhibits "a form of phosphorescence"? A Thermos flask? You need to understand that when a physicist speaks of things like lasers as "a form of phosphorescence", he or she does so because they know that "phosphorescence" is something that most people think they understand, or are familiar with. They have to refer to it in simple, familiar-but-not-technically-correct terms so people like us can understand the concepts at work, even if that understanding is extremely limited and so grossly oversimplified that it causes not just physicists but ordinary people like me to have to tell you to please stop embarrassing yourself by arguing about things you so very clearly have very much a layman's "casual understanding" of. Maybe read Wikipedia a bit more, and write a bit less. (124.168.202.62 (talk) 20:33, 28 January 2012 (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)

Question about conversions

Sorry if posting this in the wrong spot.

Isn't 59 deg F = 15 deg C?

Seems all the C to F conversions are off.

Brehart (talk) 10:02, 15 November 2011 (UTC)

Are you referring to the footnote that reads "Note that the greenhouse effect produces a temperature increase of about 33 °C (59 °F)? If so, it's correct. An increase in 33C is the same as an increase of 59.4F. (33/5 *9). It's about the change in temperature, not a specific temperature.VsevolodKrolikov (talk) 10:18, 15 November 2011 (UTC)

Understood (thanks for clarifying). Seems the average consumer would not read it that way, but makes sense now that I re-read it with your explanation.

Brehart (talk) 18:45, 15 November 2011 (UTC)

Introduction and recent growth in emissions

I've rewritten the introduction of the article. I'll outline what I view to be its problems below. Old revision:

Since the beginning of the Industrial Revolution, the burning of fossil fuels has contributed to the increase in carbon dioxide in the atmosphere from 280ppm to 390ppm, despite the uptake of a large portion of the emissions through various natural "sinks" involved in the carbon cycle.[5][6] Carbon dioxide emissions come from combustion of carbonaceous fuels such as coal, oil, and natural gas. CO2 is a product of combustion of carbon although burning coal for example, also produces carbon monoxide.[7] {{Since 2000 fossil fuel related carbon emissions have equaled or exceeded the IPCC's "A2 scenario", except for small dips during two global recessions.[8][9][10] In 2010, global CO2 emissions exceeded the IPCC's worst case scenario,[11] leading to concerns over whether dangerous climate change can be avoided.[12]}}

The part in braces is what I have a problem with:

{{ (1) Since 2000 fossil fuel related carbon emissions have equaled or exceeded the IPCC's "A2 scenario", except for small dips during two global recessions.[8][9][10] (2) In 2010, global CO2 emissions exceeded the IPCC's worst case scenario,[11] leading to concerns over whether dangerous climate change can be avoided.[12]}}

The SRES A2 scenario is not something most people will be familiar with, so mentioning it without explanation is not particularly helpful. Also, I feel that recent emissions growth is not sufficiently important to be mentioned in the introduction, at least in this form. Sentence (2) is really not that important, in the sense of one year's emissions exceeding a particular IPCC scenario. The scenario is described as "worst-case", which lacks objectivity, e.g., emissions growth has also corresponded in some regions with increases in income, which I personally do not see as a bad thing. The second subject of (2) concerns "dangerous" climate change, which is not defined. Since there is no objective definition of "dangerous" climate change, referring to it without explanation is, in my view, not appropriate. My new revision (in braces):

(as per existing revision) Since the beginning of the Industrial Revolution, the burning of fossil fuels has contributed to the increase in carbon dioxide in the atmosphere from 280ppm to 390ppm, despite the uptake of a large portion of the emissions through various natural "sinks" involved in the carbon cycle.[5][6] Carbon dioxide emissions come from combustion of carbonaceous fuels such as coal, oil, and natural gas. CO2 is a product of combustion of carbon although burning coal for example, also produces carbon monoxide.[7]

{{The governments of most countries in the world have agreed that the future increase in global mean temperature (i.e., global warming) should be limited to below 2 °C relative to the pre-industrial temperature level, and would require deep cuts in global GHG emissions from their present level. Analyses by the United Nations Environment Programme (published in 2011) and International Energy Agency (2011) suggest that current climate change policies to reduce emissions are inadequately stringent to meet the 2 °C target at reasonable cost.}}

Enescot (talk) 17:36, 25 November 2011 (UTC)

What's going on here? The intro now has all this stuff about global warming. This is not an article about that subject. Why is no one removing this material- or at least placing it in its proper place? blackcloak (talk) 20:01, 5 December 2011 (UTC)

I agree. The third paragraph in particular has no place in this article. Plantsurfer (talk) 21:21, 5 December 2011 (UTC)

I think "para 3" started here [1]. I agree: there is now too much of it. Only a brief mention is appropriate William M. Connolley (talk) 21:53, 5 December 2011 (UTC)

Agree also. If someone changes the subject, I have to question whether further information is reliable, regardless of whether I agree with them or not. I also don't want to have to sift through an article to glean the pertinent parts. — Preceding unsigned comment added by 65.102.59.64 (talk) 23:32, 5 December 2011 (UTC)

Deleted paragraph 3 of intro as per discussionPlantsurfer (talk) 23:42, 5 December 2011 (UTC)

I am uncomfortable with para 2 of the introduction because it launches into a statement about post-industrial CO2 rise without providing any background information about earth's atmospheric composition in the past. That is required for context and balance. Plantsurfer (talk) 00:03, 6 December 2011 (UTC)

Addition of current graphs/charts

Hello, I noticed that many of the images used in the article only included information up to 2000. Being as it is now 2012, are there current images that can be used in the article to demonstrate the points made? Thank you. Lucyburb (talk) 20:19, 21 January 2012 (UTC)