Let’s take a look at what Dr. Pierrehumbert says in the above video. Dr. Pierrehumbert is an expert on CO2 warming: https://en.wikipedia.org/wiki/Raymond_Pierrehumbert
At about 2:50, Dr. Pierrehumbert states that the surface temperature of the earth is accounted for by greenhouse gases. Having looked at and pondered the lapse rate— the rate the temperature of the atmosphere decreases with height, caused by decreasing pressure and well-explained by the gas laws— this proposition seems debatable.
A minor but important debate among those who don’t believe that CO2 is a major problem is whether or not atmospheric mass, by itself, can account for the “blanket” that warms the earth’s surface. Thinking in the simplest terms, anything that has mass can be warmed; the atmosphere has mass, so the atmosphere can be warmed and that atmospheric warmth can be and is in fact concentrated near the surface by virtue of conduction and convection with a surface heated by the sun. This is basic physics. From the surface the atmosphere cools according to the well-established lapse rate formulas which, it should be noted, have no terms for radiative effects. The actual way this happens is recorded daily in balloon launches all over the world, and the diagrams derived from probably by now tens of thousands of balloons show an atmosphere cooling according to lapse rate plots. No mystery about this.
The overall average environmental lapse rate is 6.5C/km: the atmosphere cools adiabatically (without actually “losing heat”) 6.5C for every kilometer of height gained, and this because as air expands it cools.
What Dr. Pierrehumbert goes on to say is that as CO2 increases, this raises the emissions height, which is the average height that the atmosphere starts net emitting infrared to space, thus cooling the planetary system. The average emissions height is roughly half-way up the troposphere, which is the lowest atmospheric layer where all our weather happens; this is also the layer where the lapse rate is in effect, as above the troposphere the temperature stays the same for a while (in the tropopause) while above the tropopause, in the stratosphere, the temperature starts increasing again. But, the lapse rate Pierrehumbert refers to is that of the troposphere, wherein the emission height lies.
Back to the 2:50 mark in the video. Pierrehumbert states that as we increase CO2 we don’t change the radiating temperature but we change the radiating height; thus, from a new height but the same temperature if we count down using 6.5C/km for the average lapse rate, we get a warmer surface, and that’s how CO2 warms the surface. So a minor rise in radiating height spells planetary disaster.
Except, it doesn’t. Here’s why.
As we move higher in the atmosphere, the atmosphere necessarily cools according to the well-established lapse rate formulas. So if we radiate from higher up, then we must be radiating from a cooler temperature, not the same temperature. In fact any place in the atmosphere that we want to find an emissions height, if we count down from there— as Pierrehumbert suggests— we find the exact same surface temperature because the lapse rate doesn’t change with height (well, it does, but for the purposes of our discussion, it doesn’t. We won’t complicate things by getting into the moist and dry lapse rates. We’re talking about the average lapse rate, just as Pierrehumbert is.)
Then what’s Pierrehumbert about?
Pierrehumbert simply assumes the conclusion. That is, the only way that the emissions height could be the same temperature but higher up is if the surface had already warmed, and then we “count up” using the lapse rate to get the same temperature but at a higher height. But instead Pierrehumbert (doesn’t) tell us that the atmosphere has already warmed, thus the emissions height is higher but the same temperature and we “count down”!
Nice trick.
The lapse rate is the lapse rate and it hasn’t changed. It’s established by atmospheric pressure, not CO2 and not even by greenhouse gases.