Do you see a problem with this?

The broad conclusions are right, but there are a few technical details that are not quite right.

1. You need to compare the longwave radiation of the sun and greenhouse gasses in absolute terms ie W/m^2 within a given frequency interval. The longwave radiation from an object does not decrease intensity when it gets hotter, the shortwave radiation just grows in intensity faster so the emission peak shifts to shorter wavelengths as an object warms. You can plot the Planck distribution in a spreadsheet to see the effect.

2. Molecules can absorb and emit radiation from the microwave region to the x-ray region via different processes. Radiation in the microwave region comes from molecular rotational transitions. Far infrared radiation comes from molecular rotations and intermolecular interactions. Mid infrared radiation comes from fundamental vibrational modes of molecules (with rotational fine structure superimposed) plus some combination and difference bands. This takes care of the region to about 2.5 microns. The absorption cross sections in the near infrared region (.8 to 2.5 microns) are typically smaller than mid infrared absorption cross sections by a factor of 1000, but there is activity in this region from greenhouse gasses. The near infrared absorptions are from combination bands. Molecules absorb and emit radiation at visible and shorter wavelengths via electronic transitions. The generalizations given above hold in most cases, but there are exceptions, for example semiconductors.

It is incorrect to characterize greenhouse gasses as active only above 4 microns. Your result is nevertheless correct for a different reason. Energy is partitioned between all available modes with a probability proportional to exp(-E/kT), where E is the transition energy, T is the temperature in Kelvins and k is the Boltzmann constant. For more information, study the partition function in statistical mechanics. Shortwave is not impossible, just unlikely at the low temperatures present in the atmosphere. If the atmosphere were 1000 K warmer, there would be significant shortwave radiation in addition to longwave radiation.

3. The increase in downward shortwave radiation is due to increased greenhouse gas concentrations. Further, it is possible to determine the relative contribution of each type of gas because each emits a unique spectral pattern.

Dana already addressed the issue of cooling rate from decreased solar irradiance.

Edit 1:

<However I'm lead to believe that the planet does not emit back radiation at these wavelengths and so it is largely inconsequential to the greenhouse effect.> Correct. The higher energy modes are possible, but are not used.

Edit 2:

@ Ottawa

<I understand that certain molecules have certain absorption bands, but I thought molecules radiating IR did so over the whole spectrum. How can a molecule EMIT over a narrow band?>

Molecules emit at the same frequencies they absorb and there is a finite set of discrete frequencies for which this is possible. The allowed frequencies correspond to the difference in energy between molecular energy states. For CO2 there are 3 atoms each contributing 3 degrees of freedom for a total of 9. 3 are translations x,y,z, two are degenerate rotations and 4 are molecular vibrations: symmetric stretch, assymetric stretch and doubly degenerate bending. All of the infrared activity is near the 3 modes noted above. Each vibrational mode has rotational fine structure, which at low resolution makes the absorptions appear as a band, but in reality the band is composed of hundreds of narrow spikes. The bandwidth of each "spike" absorption/emission is broadened by the Doppler effect and molecular collisions. In gasses the bandwidth is typically less than 0.01 cm-1. This is basic quantum mechanics.

You need to look at the earth's emission spectrum. The only references I have to this are in Copyright journals, and I will be asking a separate question appealing for public domain references to this. However, www.rsc.org/images/CA1_tcm18-137980.doc gives a good answer to your specific question, and Figure 4 shows the effect I will be talking about.

Basically, I think you've got it right, apart from some details which others have pointed out.

Dana, Trevor, and dy/dx are well-informed. OM is in error. Greenhouse gases absorb at specific wavelengths, not over the entire range. "Entropy" is a red herring with a history in one denialist argument, discussed and refuted in the open literature many years ago. John M is talking about a region of the spectrum whose impact on the energy balance is minimal.

If you look at the graph of the Earth's actual emission spectrum, you will see that it looks rather like the hot body radiation expected for an object at around 290° K, but with some deep gaps in it corresponding to where the greenhouse gases absorb. These gaps correspond to energy that would have escaped from the earth if it were not for that absorption. Since (roughly speaking) energy leaving the Earth has got to equal energy reaching the earth, the earth must be at a higher final temperature if the emission at these wavelengths is blocked.

One sophisticated denialist argument is that the absorption by greenhouse gases is "saturated"; they can't absorb more than 100% of what the earth emits. True but irrelevant. The absorption bands have shoulders which are not saturated, and where more greenhouse gases will correspond to more energy reflected back down and failing to escape. All of this, of course, is taken into account in any competent modelling of the greenhouse effect, and you may rest assured that the modelling, carried out under the direction of scientists like Sir John Houghton, FRS, former professor of atmospheric science at Oxford, is competent.

One other thing that may be relevant is the difference between the behaviour of a black body and of a gas. a black body absorbs all the radiant energy that falls on it, and emits according to its own temperature. That is possible because it can vibrate and absorb and emit energy at any frequency (or, as you prefer, at any wavelength). A gas like CO2 can only absorb and emit at specific wavelengths, corresponding to its own absorption frequencies. Very importantly, the efficiency of its absorption, and of its re-emission compared with a black body at the same temperature, depends on the amount of gas.

Congratulations on trying to get to the bottom of this very complex subject. I hope this helps.

Edit: see answers at

http://uk.answers/

.yahoo.com/question/index;_ylt=AoXUNpVgCeVQDYUXgXaVuekazKIX;_ylv=3?qid=20100727035301AABNl9w

and

http://uk.answers.yahoo.com/question/index;_ylt=Al...

If you have a question about any of the links there, please post it, to help educate all of us.

Shoulders: absorbance is logarithmic; that means that if you are in a region where the pre-industrial concentration let 1% of the light escape, the amount after the 40% increase so far will be (0.01)^1.4 = 0.0016 = 0.16%, so just 0.0084% more of the light will now be trapped. Not a bit difference; that's "saturation". But now go away from the band maximum to a point where it used to let through, say, 60% of the light. It now lets through 0.6^1.4 = 0.49, so an extra 11% of light at that wavelength will now be trapped thanks to the increased greenhouse effect caused specifically by anthropogenic CO2.

He might try a different type of shaving gel, some of them are designed to help soften up the stubble. Of course that is usually for the shave itself. Over time I would think your skin will become used to the abrasive nature of his chin. A lotion on your skin before making out might help also. Perhaps he could grow a goatee or a beard. Long facial hair does tend to be softer.

One of the factors for understanding the Earth's climate system is understanding the Second Law of Thermodynamics and entropy. This interesting quote comes from a story that in the late 1940s, John von Neumann, advised that one could start a discussion by using the term "entropy" because "no one knows what entropy really is, so in a debate you will always have the advantage". That is probably still just a true today.

You make quite a few statements in your question that you simply assume are true beyond doubt. Well, I doubt.

As well, most talk about heat in the atmosphere is usually about radiation of some sort. Why is there little discussion about convection and conduction, the other two methods of heat transfer? (hint: this is one of the main reasons that so many meteorologists have a problem with CO2 warming)

http://www.panspermia.org/seconlaw.htm

Edit: "Downward radiation between 14um and 16um is increasing."

I understand that certain molecules have certain absorption bands, but I thought molecules radiating IR did so over the whole spectrum. How can a molecule EMIT over a narrow band?

Hears the link that may start u of on a road to truth Check out when these started and see how they line up with hockey sick graph The introduction of radar and radio in the am band was the start then FM and now digitel all are in Microwave spectrum Don't forget these are only part of the network And I don't know what u know about HAARP but at least we know is it's used for communications experiments.

Hi Jeff,

By and large what you’ve got there is correct, there are one or two errors but they don’t affect the gist of what you’re saying

For example “All greenhouse gases absorb and emit radiation above 4um. For instance, one of the major absorption wavelengths of CO2 is between 14um and 16um”.

If you include water vapour within your definition if a greenhouse gas, which you should do, then the shortest absorption frequency is 0.75 microns.

Carbon dioxide has 3 main absorption bands in the infrared spectrum at about 2.7, 4.3, and 15 microns. It’s generally accepted that the concentration of atmospheric CO2 is enough to absorb nearly all the IR radiation in the main CO2 absorption bands (within a 1km range). Thus, even if the atmosphere were laden with CO2, it would only produce an incremental increase in IR absorption over current levels.

Only a small amount of radiation from the Sun at wavelengths for CO2 absorption directly reaches Earth’s surface. Similarly, very little radiation at these wavelengths emitted from the surface makes it to space. Most IR at these wavelengths comes from black-body radiation emitted by objects heated up by absorbing shorter wavelength radiation.

Even if the CO2 level increases, it will not have much effect on the total amount of IR radiation being absorbed from the sun. The primary effect would be trapping radiation from the surface at night-time and at lower levels in the atmosphere than before.

I won’t go into any more detail on the spectroscopy side of things as hopefully d/dx and / or Paul B will answer your question, both of whom are better qualified than I am to provide you with a suitable commentary.

Turning to your point about a decrease in total solar irradiance (TSI). They key thing would be just how much the Sun’s output fell by. TSI is pretty consistent with a variation of less than 0.1% from the annual mean of 1365 Watts per square metre per year.

There have been extended periods of low solar activity in the past and the effect only becomes noticeable after many years. If TSI were to remain at a minimum mean annual level then we could expect to see noticeable changes in the temperature after just a few years with a fall in the average global temperature of perhaps 0.05°C. After 100 years or so it may, given the right circumstances, lead to a drop in temperatures of as much as 1°C.

Given the 2 ppmv annual increase in CO2 concentration we would need to see a decline in TSI of 3.412W/m²/yr to compensate for this. However, a compensatory state of equilibrium would not be reached for several hundred years and the effect is a logarithmic one. Or… if CO2 increased by 2ppmv/yr and TSI drops by 3.412W/m²/yr for just one year then it will be about 500 years before the two balance each other out but as CO2 continues to increase the decline in TSI required to offset this will decline.

Regarding your final point. Working out the precise figure would take a long time but the question is kind of irrelevant anyway as the answer is that Earth could never become hot enough for CO2 not to have an effect. We’re too far from the Sun to warm the planet the several hundred degrees C that would be required to reach this stage.

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RE: YOUR ADDED DETAILS

Hmmm, the temperature at which an object emits radiation outwith the absorption bands of CO2? Good question, not one that I knew an answer to so I looked in some books and texts that I have but couldn’t find anything. There were data for solubility of CO2 in different solutions at different temperatures and pressures but not for IR emissivity or absorption. Here’s a useful point of reference http://www.licor.com/env/PDF/co2_abs.pdf it doesn’t answer your specific question but you may find it interesting. Here’s another source of info re the physics CO2 which I often find myself referring to http://brneurosci.org/co2.html

The trick is not to simply proove that CO2 will cause some warming, because that really isn't in dispute. The trick is to prove that this warming is significant compared to natural variations.

If you think you can find real evidence for this, then you better knock on Phil Jones' door and tell him you want his job because you can do it better than he can.

Modern warmers don't use evidence, instead they use inference. The recent warming does not fit their models, there was warming in the second half of the twentheith century instead of cooling so by inference, CO2 is the cause.

Analysis using fundamental principles of physics has been done over and over throughout the decades and the same conclusion has been reached. Yes CO2 affects temperature but the effect is very minor.

Here's a nice figure showing that solar radiation doesn't overlap with longwave frequencies. It cuts off at a wavelength of about 4 microns as you note.

http://en.wikipedia.org/wiki/File:Atmospheric_Tran...

The increase in downward longwave radiation is from the enhanced greenhouse effect, no question about it.

The global temperature begins to respond pretty quickly to changes in solar output. Generally the response time is only a few months, perhaps a couple years tops. Of course the larger the change, the larger the forcing, and the longer it will take the global temperature to reach a new equilibrium with the consequent energy imbalance. But the temperature will at least begin to change quite quickly in response to increased solar radiation.

NASA GISS estimated that if solar irradiance remains flat and we have a new 'Maunder Minimum' type event, "the negative forcing, relative to the mean solar irradiance is equivalent to seven years of CO2 increase at current growth rates." So even that wouldn't really cause any cooling, it would just offset 7 years of anthropogenic warming.

http://data.giss.nasa.gov/gistemp/2008/

Solar irradiance increased pretty significantly in the early 20th century, and it only caused about 0.1-0.2°C of warming over a 30 year period.

http://cawcr.gov.au/bmrc/clfor/cfstaff/jma/meehl_a...

CO2 on the other hand is causing about 0.2°C warming per decade right now. So basically to offset that, you would need solar irradiance to decrease at a rate about 4 times faster than it increased in the early 20th century, which would be about 5 W/m2 (or 0.4%) per decade.

http://www.mps.mpg.de/images/projekte/sun-climate/...

Over the past 1,100 years, solar irradiance hasn't increased any faster than it did during the early 20th century - certainly not 4 times faster. The increase at the end of the Maunder Minimum was about the same rate.

http://en.wikipedia.org/wiki/File:Sunspot_Numbers....

http://commons.wikimedia.org/wiki/File:Carbon-14_w...

In comparison, the change in solar irradiance over the past 30 years has been between a 0.012% decrease (PMOD) and 0.01% increase (ACRIM) per decade. So it's been at least 33 times too small to offset AGW, let alone cause cooling.

Bottom line, the Sun isn't going to be offsetting AGW, let alone causing global cooling.

Liar, its all lies wat u jus said,why u lyin to yahoo