Does CO2 have diminishing returns with regards to warming the earth?

Yes. The relationship between radiative forcing and increasing CO2 is logarithmic.

http://www.grida.no/publications/other/ipcc_tar/?s...

However, this is offset by the fact that human CO2 emissions are accelerating.

http://www.epa.gov/climatechange/emissions/globalg...

http://cdiac.ornl.gov/trends/emis/glo.html

Increasing CO2 has diminishing returns, but it diminishes rather slowly. A doubling of atmospheric CO2 from the pre-industrial level of 280 ppm to 560 ppm is expected to raise global temperatures about 3°C when including feedbacks. We're already at 388 ppm and accelerating.

http://www.greenoptions.com/wiki/climate-sensitivi...

Others have already mentioned the logarithmic dependence of radiative forcing with increasing CO2 concentration. It is worthwhile to plot the curve to get an understanding of the rate that the CO2 sensitiivity changes. I think that the temperature sensitivity mentioned in the question refers to the shift in the maximum of the Planck distribution to shorter wavelengths with increasing temperature. While the fraction of radiation in the mid infrared decreases, the total radiation increases as T^4, so there would still be an appreciable infrared flux at the higher temperatures. CO2 will absorb and emit radiation at any temperature under the dissociation energy. At 580 K, KT (8E-21 J) < E (1.4 E-20 J) so most of the molecules are still in the ground state. For a more detailed calculation, list all of the available states and their energies and calculate the partition function.

whether 'diminishing return' isn't precisely the outstanding term to apply the respond is confident, each and each 1ppm does produce much less warming than the previous. finally, there could desire to be adequate CO2 to catch each and all of the suns potential on the wavelengths that CO2 traps. Then the temperature of the planet will upward push till an equilibirum is reached with radiative consequences back to area. yet, as bob factors out, we are an prolonged, good way from that, in terms of time, temperature and CO2 concentrations. P.S. to the two antarctica and Randall. The celsius scale is bigoted and could't be used for the comparisions which you do. to assert that 2 levels is two times as warm as a million degree means that the potential content textile has doubled that's relatively fake. in case you opt for to benefit temperatures in opportunities or quantum stages, you may desire to apply the Kelvin scale wherein Earth is 288 levels and Venus is 734 levels as a effect Venus is approximately 3X as warm because of fact the Earth.

The radiative forcing from CO2 is roughly calculated as follows

RF = 5.35*ln(C/Co)

where Co is the initial concentration, C the current concentration (in ppm). As the no-feedback response from increasing CO2 is linearly related to the radiative forcing, it's pretty easy see that each additional ppm of CO2 will have less effect than the last.

A qualitative comparison is paint over a window - the first coat blocks more light than successive coats.

Yes.

http://wattsupwiththat.com/2010/03/08/the-logarith...

"Is there another way that CO2 can have diminishing returns that I am missing?"

Each time carbon dioxide (or some other greenhouse gas) is doubled, the increase in temperature is the same as the previous increase.

Beers Law.

http://brneurosci.org/co2.html

http://en.wikipedia.org/wiki/Beer%E2%80%93Lambert_...

greshnab: Are you seriously saying that we don't know anything about the greenhouse effect? Are you stating that we don't know anything about how and why specific molecules are able to gain energy through the absorption and remission of certain wavelengths of radiation?

sure you are thinking of the earth as a simple engine .. it isn't...

as co2 goes up LOTS of things happen... plants grow faster.. co2 absorption by water goes up faster, cloud coverage changes... and affects we know nothing about go up.

it is interesting to me that people that state global warming is caused by man say CO2 hasn't been this high since before the last ice age.. and there is no recovery possible if it gets much higher....

saying it has been this high before says that there IS a recovery mechanism that we simply don't understand...