As a radio amateur I am interested in all sorts of electromagnetic radiation. That includes thermal radiation in the infrared spectrum as well. Lately prof. William Harper visited The Netherlands with a remarkable presentation on climate. I was intrigued by one of his graphs:
The picture shows us the outgoing thermal flux spectrum from earth.
If there were no greenhouse gases, the (uv/visible/thermal) radiation going to space would be the area under the blue (Planck) curve.
The green curve is the computed spectrum with all the greenhouse gases present except for CO2.
The black and red lines are the energy fluxes for the CO2 concentrations for 400 ppm (part per million) and 800 ppm respectively.
When doubling the earth's CO2 concentration from 400 to 800 ppm, the outgoing flux will decrease from 277 W/m2 to 274 W/m2. A change of 3 W/m2
IPCC fully agrees with this model. However, the dispute is ongoing whether the 3 W/m2 change will raise earth's average temperature by 1.4 degrees C (Happer) or 4.7 degrees C or even more (IPCC).
It looks like the greenhouse effect of CO2 is already more or less saturated. Doubling CO2 concentration probably does not make much difference.
More on this subject:
A 40 minute YT-video from David Siegel shows the same graphs (and more..)
Interesting as well:
