This is an excellent overview on "infrared radiation and planetary temperature."
So I was recently told there is no evidence that CO2, being such an insignificant portion of the Earth's atmosphere, can drive global warming. It is difficult to believe the CO2 warming at the face of it. So how did the science develop? First it was just some experiments - to discover CO2 trapping the heat. And also some mathematical analysis to realize the Earth has an atmospheric blanket that traps heat - and CO2 then is the main means to trap the heat. This was based on spectroscopy - the "gaps" in the lines of prism light. So this science was way back in the 1800s - on the wavelength of light, as the absorption spectrum of heat, for CO2 - 1863, John Tyndall. The computer modeling is validated by satellite observations. It is based on warming as radiation due to quantum frequency. (youtube TED vid explains) So most people are trained in classical science - and so can not easily conceptual how the CO2 works as an "insulation blanket."
Now here comes the tricky part - it turns out that due to Earth's atmosphere - the CO2 quantum spectrum is logarithmic - so that as more CO2 is added above 300 ppm - there is an exponential increase in the heating ability of the CO2.
So a logarithmic scale means it grows exponentially (inverse of the logarithm).....How come no one explains this? I had to dig for this info. haha. So much for "science education" on global warming!
And so then people say yes but there's why more water on the atmosphere so obviously water is more important. He points out that the CO2 is higher up in the atmosphere so does not compete with the water but without the CO2 the atmosphere would not stay warm enough to hold the water. So yes water is about 2/3rds of the warming but without the CO2 the water would just rain down and the atmosphere would dramatically cool. The CO2, being a bigger molecule, holds the heat with greater stability. It takes longer for the CO2 to leave the atmosphere - 1000 years.
So CO2 absorbs the heat "so strongly" that it then creates a "heat spike" in the stratosphere - compared to the water vapor in the troposphere.
Notice the heat spike is precisely at the frequency proportional to CO2 - 667 (1/cm)
OK so now that Prof. Pierrehumbert covers the details of why CO2 is such a strong absorber -
We can see what else he has on the interwebs....
Here he is on youtube - interview
How does this logarithmic heating of increased CO2 work?
2016 - Pierrehumbert pdf - How to Decarbonize? Look to Sweden
For a positive feedback temperature dependence, warming increases Earth's sensitivity, while greater sensitivity makes Earth warm more. These effects can feed on each other, greatly amplifying warming. As a result, for reasonable values of feedback temperature dependence and preindustrial feedback, Earth can jump to a warmer state under only one or two CO2 doublings. The linear approximation breaks down in the long tail of high climate sensitivity commonly seen in observational studies. Understanding feedback temperature dependence is therefore essential for inferring the risk of high warming from modern observations. Studies that assume linearity likely underestimate the risk of high warming.Right - so this confirms how I had read his data above! Great.
Now for the details. So "Planck Feedback" means how much Earth's atmosphere radiates heat back into space.
Feedback temperature dependence determines the risk of high warming
Is this all just theoretical?
The present era of global sensing is unprecedented: high-precision instruments are tracking Earth’s energy flows on decadal timescales and regional spatial scales; an absolute accuracy of better than one part per thousand has been achieved in measurements of solar irradiance and is helping to close the TOA energy budget; networks of ocean-going floats are quantifying ocean heat uptake; and surface-based networks and profiling instruments are beginning to advance understanding of the surface energy budget.
Measurements from the Earth Radiation Budget Experiment (ERBE) (Ramanathan 1987) and now those from the Clouds and Earth’s Radiant Energy System (CERES) mission (Wielicki et al. 1996) have convincingly shown that Earth reflects less short-wave radiation and emits more long-wave radiation than previously thought (cf., Table 1) and have contributed to closure of the top-of-atmosphere energy budget to within a few watts per square meter.
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