Richard Courtney has made a couple of comments on a WUWT discussion of a new paper studying temperature trend components which are worthy of a separate discussion.

richardscourtney says:

Barton Paul Levenson:

I am ignoring the invitation to debate the climate of Venus although that would be interesting. WUWT has a severe troll infestation today and discussion of Venus would be a disruption to this thread which is about the Earth’s climate.

I am replying to the statement in your post at October 18, 2012 at 7:15 am which says

Richard: at present levels of atmospheric CO2 concentration additional CO2 in the atmosphere has no discernible effect on the Earth’s climate. BPL: No. It’s up 40% since the industrial revolution began. It’s the absolute amount that matters, not the concentration. The nitrogen, oxygen and argon that make up more than 99% of Earth’s atmosphere is not radiatively active.

It seems you are unaware that the IR absorbtion of CO2 in the atmosphere is constrained to only two narrow bands with almost all being in the 15 micron band. These bands are so near to saturation that they only increase their absorbtion by band broadening.

Think of light (i.e. visible radiation) entering a room through a window. If you put a layer of dark paint over the window then much light is absorbed by the paint and, therefore, does not enter the room. Add another layer of paint and more light is absorbed by that layer, but not as much as by the first layer. Similarly for each additional layer of paint.

The IR emitted from the Earth’s surface is trying to pass the ‘window’ of the atmosphere to enter space. Adding more CO2 to the air is like adding more paint on the window that has seven layers of the paint. Each unit addition of CO2 has less absorbtion than the previous unit addition: this reducing effect is logarithmic.

Empirical – n.b. not model-derived – determinations indicate climate sensitivity is less than 1.0deg.C for a doubling of atmospheric CO2 equivalent. This is indicated by the studies of Idso from surface measurements

http://www.warwickhughes.com/papers/Idso_CR_1998.pdf

and Lindzen & Choi from ERBE satelite data

http://www.drroyspencer.com/Lindzen-and-Choi-GRL-2009.pdf

and Gregory from balloon radiosonde data

http://www.friendsofscience.org/assets/documents/OLR&NGF_June2011.pdf

If climate sensitivity is less than 1 deg.C for a doubling of CO2 equivalent, then it is physically impossible for the man-made global warming to be large enough to be detected because natural variability is much, much larger. If something exists but is too small to be detected then it only has an abstract existence; it does not have a discernible existence that has effects (observation of the effects would be its detection).

As you say, the concentration of CO2 in the air has increased by ~40% since the industrial revolution (i.e. from ~280 ppmv to ~390 ppmv). This takes the degree of absorbtion of CO2 to ~80% of a doubling of CO2 in the atmosphere because of the logarithmic effect. And the globe has only warmed about 0.8deg.C since the industrial revolution. Most – if not all – of this rise is certainly recovery from the Little Ice Age (LIA), but if it is assumed the entire temperature rise is from the CO2 increase then a further increase to reach double pre-industrial concentration (i.e. to ~560 ppmv) would only provide a further increase to global temperature of about 0.2 deg.C. And a further doubling of atmospheric CO2 (to 1,120 ppmv) would only raise global temperature by an additional 1.0 deg,C.

In summation, as I said, at present levels of atmospheric CO2 concentration additional CO2 in the atmosphere has no discernible effect on the Earth’s climate.

richardscourtney says: