My belief in Global Warming is getting shaky

[modest]

Originally Posted by Biochemist

There is a limit to the amount of heat that can be trapped by CO2, since it only absorbs a narrow portion of the spectrum.

I see your line of thought. It assumes the amount of IR radiated from the surface over any given frequency range is constant. It is not. As earth warms, so then does the amount of IR emitted in the frequency range of CO2's absorption. More heat is then retained.

A limit to spectrum does not in any way equal a limit to temperature or "heat that can be trapped". Your further statements are based on this mistaken assumption.

~modest

[freeztar]

Originally Posted by Biochemist

That is why a 50% increase in CO2 over the last 100 years is associated with only a 0.5 to 1 degree rise.

50%?
0.5-1.0?

Source? Rise?

Realistically, even if you think CO2 is casual, it would probably not be the ONLY reason for the rise.

Indeed. CO2 is not the ONLY reason for temp increase. No one serious is claiming otherwise.

Further, the main greenhouse gas, water vapor (90% of GG is water vapor, 4% is CO2) absorbs in an overlapping spectrum. Once that spectrum is absorbed, there is not more retention.

Overlapping does not mean equal! Furthermore, H2O is much more complicated for reasons that we don't need to go into in this thread.

[modest]

Originally Posted by engineerdude

THESE MODELS IGNORE OVERALL CHANGES IN SUNLIGHT

Please don't shout.

Solar irradiance is a forcing.

Pubs.GISS: Abstract of Hansen et al. 2002

~modest

[freeztar]

Originally Posted by modest

Please don't shout.

Solar irradiance is a forcing.

Pubs.GISS: Abstract of Hansen et al. 2002

~modest

Solar forcing is included in the models!

[Biochemist]

Originally Posted by modest

I see your line of thought. It assumes the amount of IR radiated from the surface over any given frequency range is constant. It is not.

Help me with this, Mod. I was not assuming anything about IR from the surface. I was assuming only that the quantity of energy initially sequestered by the troposphere from sunlight is limited (in any bandwidth range) to the quantity of energy in that bandwidth range.

Ergo, once you have sequestered the majority of the energy in the CO2 absorption spectrum, incremental CO2 causes little or no incremental retention.

Per:Cold Facts on Global Warming

Originally Posted by Science Notes

The arithmetic of absorption of infrared radiation also works to decrease the linearity. Absorption of light follows a logarithmic curve (Figure 1) as the amount of absorbing substance increases. It is generally accepted that the concentration of carbon dioxide in the atmosphere is already high enough to absorb almost all the infrared radiation in the main carbon dioxide absorption bands over a distance of only a few km. Thus, even if the atmosphere were heavily laden with carbon dioxide, it would still only cause an incremental increase in the amount of infrared absorption over current levels. This means that a situation like Venus could not happen here. The atmosphere of Venus is 90 times thicker than Earth's and is 96% carbon dioxide, making the atmospheric carbon dioxide concentration on Venus 300,000 times higher than on Earth. Even so, the high temperatures on Venus are only partially caused by carbon dioxide; a major contributor is the thick bank of clouds containing sulfuric acid [7]. Although these clouds give Venus a high reflectivity in the visible region, the Galileo probe showed that the clouds appear black at infrared wavelengths of 2.3 microns due to strong infrared absorption [8]. Thus, Venus's high temperature might be entirely explainable by direct absorption of incident light, rather than by any greenhouse effect. The infrared absorption lines by carbon dioxide are also broadened by the high pressure on Venus [9], making any comparison with Earth invalid.

Correct my understanding, Mod.

[Biochemist]

Originally Posted by freeztar

Ten degrees is extreme. Who is predicting this?

Agreed. I was responding to Mod's post in #1185 about earth being like Venus if CO2 rose.

[modest]

Originally Posted by Biochemist

Help me with this, Mod. I was not assuming anything about IR form the surface. I was assuming only that the quantity of energy initially sequestered by the troposphere from sunlight is limited (in any bandwidth range) to the quantity of energy in that bandwidth range.

Ergo, once you have sequestered the majority of the energy in the CO2 absorption spectrum, incremental CO2 causes little or no incremental retention.

Per:Cold Facts on Global Warming



Correct my understanding, Mod.

There are two very real problems I see with this thinking.

The first is the frequency range itself. The range falls off parabolic-like. Increasing the amount then *does* increase the range. A photon of about 13 or 14 micrometers might currently have a very good chance of escaping the atmosphere. Increasing the amount of CO2 would decrease that probability.

The other thing, which I commented on already is the intensity (or brightness) of the radiation itself. As the temperature of the surface increases then the amount of radiation at any given wavelength also increases. This is wine's displacement law. Looking at measured intensity vs. wavelength diagrams:


-source


-source

Increasing the amount of CO2 would both broaden the CO2 depressions and raise the entire intensity line. So, of course, further heating can happen due to CO2 increase. What your link points out about Venus (thatCO2 doesn't act alone) is true, and it's also true that CO2 does not act alone in warming our planet above its emission temperature.

But, this is well-known. CO2 is one factor in many. This doesn't discount the effects of CO2 as a greenhouse gas—it just makes modeling our climate that much more difficult.

~modest

[Biochemist]

Originally Posted by modest

But, this is well-known. CO2 is one factor in many. This doesn't discount the effects of CO2 as a greenhouse gas—it just makes modeling our climate that much more difficult.

~modest

Thanks, Mod. Great post.

[Biochemist]

Originally Posted by freeztar

50%?
0.5-1.0?

Source? Rise?

Sorry FT. Can't find it. I was trying to find the logarithmic graphic (Lindzen did one, I am sure there are many) that showed the potential range of incremental absorption with increased CO2 and its effect on temprature. I could not recover it on Google.

Bio

[Essay]

Originally Posted by Biochemist

...its effect on temprature. I could not recover it on Google.

Bio

...There may be a reason for that deletion!

Biochemist:

I think you're referring to a brief blip in the denialist's blogosphere, from about a year ago. Hopefully it's not still being promulgated!

I could look it up after the Inauguration, if you'd like.

It came about [IMHO] because some self-proclaimed expert re-labeled the axes from a textbook graphic.
The graph related the absorbance of CO2 with CO2's concentration--a logarithmic function.

The bozo had simply scratched out the word "dog," and scribbled "cat" over it, with a crayon!
Oh sorry....

The bozo had written "Temperature," over the y-axis label of "Absorbance," with a computer.

...thus erroneously implying a logarithmic relationship between concentration and temp.

THis got a lot of circulation in the denialist blogosphere, and even made it onto the realclimate (or climate audit) blogs--whichever is the denialist one (I don't follow too closely).
I think I recall that even Steve McIntyre was duped by this one--for about a month--before someone pointed out the fallacy.
===

Catch you in a couple of days....
Enjoy the festivities!

~

p.s. ...thanks Monty Python.