The above figure is taken from an often cited paper, including by the IPCC, titled “Earth’s Annual Global Energy Budget” by Kiehl and Trenberth from the Bulletin of the American Meteorological Society, 1997, with notations that we added.

The top curve shows how the intensity of the average heat leaving the earth’s surface varies with infrared wavelength. The lower jagged curve is that leaving at the top of the atmosphere under average cloudy conditions.

The area under a curve is its total heat in watts per square meter. Note the large downward notch leaving the atmosphere in the 12 to 18 microns range caused by CO2.

It is such a strong absorber here that it cannot release its heat outward until the density of its molecules drops significantly at high altitudes where the temperature is about –60 F. Hence the low radiation rate.

If the amount of CO2 increases, the escape altitude moves up causing both the temperature and heat loss to drop further. The area of the CO2 notch below the dashed line is about 22 watts per square meter and represents the impact of the total CO2 given the existing clouds and water vapor.

Doubling CO2, taking over 100 years at the current growth rate, would move the notch downward and increase the area by about 3.5 watts per square meter, or 16%. When the heat loss drops, since the net heat from the sun remains at 235, the atmosphere gains heat and warms about 1 degree C until its emissions rise back to 235, restoring balance. A warmer atmosphere reduces the heat loss from the surface, and it also warms about 1 C.

This is all that CO2 does. And very slowly. The feedback processes can increase or decrease this warming, as they do for any other temperature change.

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