Another major niggle with the idea that CO2 "traps heat" and/or "traps radiation"

In moments of doubt, I turn to Skeptical Science, who advance superficially convincing but actually implausible explanations that reinforce my working assumption that it is all hokum (and/or that the site is clever counter-propaganda funded by Big Oil).

Today I shall dismantle this:

This is how the Greenhouse Effect works. The Greenhouse gases such as carbon dioxide and water vapour absorb most of the heat radiation leaving the Earth’s surface. Then their concentration determines how much heat escapes from the top of the atmosphere to space. It is the change in what happens at the top of the atmosphere that matters, not what happens down here near the surface.

So if we add more greenhouse gases the air needs to be thinner before heat radiation is able to escape to space. So this can only happen higher in the atmosphere. Where it is colder. So the amount of heat escaping is reduced. By adding greenhouse gases, we force the radiation to space to come from higher, colder air, reducing the flow of radiation to space. And there is still a lot of scope for more greenhouse gases to push ‘the action’ higher and higher, into colder and colder air, restricting the rate of radiation to space even further.

1. You literally can’t trap “heat” and heat can’t “escape”. I assume they mean “thermal energy” (which is temperature x specific heat capacity). “Heat” means the flow thermal energy that is transferred from something warm to something cooler. There’s no such thing as “heat radiation” either. I assume they mean “infra red radiation”.

2. The atmosphere is a mixture of gases that do not chemically react with each other (or not very much – or else they would have done). Each gas has its own properties (molecular or atomic mass; specific heat capacity; whether they absorb and emit radiation and if so at what wavelengths etc), and the average of each of those properties can be taken to be that property of the whole atmosphere. It is quite different to e.g. sodium and chlorine, which have their own properties which are totally different to the properties of household salt.

3. The atmosphere above each m2 of surface has a mass of about 10,000 kg. Each kg has a specific heat capacity of about 1,000 J/kg/C. So the total specific heat capacity is about 10 million Joules per degree C or K for each m2. CO2 levels have increased from about 4 kg/m2 to about 6 kg/mw2 since ‘pre-industrial times’. If those two extra kg CO2 have caused temperatures to rise by 1C, then each kg has somehow “trapped” 5 million Joules of thermal energy, permanently. That is a heck of a lot, the specific heat capacity of CO2 is about 800 Joules/kg, just to put it in perspective.

4. Radiation itself does not have a temperature, any more than it has colour, smell or taste. It’s not thermal energy. A litre of diesel or petrol holds 35 million Joules of chemical energy, that doesn’t mean that diesel is always very hot! There is no such thing as “hot” or “cool” radiation. It is just radiation, you measure it in Joules or Watts (= Joules/second), not in degrees C.

5. They assume, reasonably enough, that solar radiation coming in and radiation from the Earth going back out are roughly in balance. They then jump to the “water tank” aka “leaky bucket” analogy, and say if less is going out, then the atmosphere must warm up as a result.

Thought experiment – solar radiation coming in is fixed, but what if radiation is absorbed by plants or solar panels and converted to chemical or electrical energy? A good solar panel can absorb about one-quarter of the solar radiation that hits it each day. Those Joules end up in a battery (or are converted to potential energy if used to pump water uphill) and so can’t be radiated to space. So outgoing radiation must be less than incoming. That doesn’t make the atmosphere any warmer. (I’d love to know how much incoming radiation a plant can convert to chemical energy each day).

6. We are told time and again that the atmosphere is transparent to sunlight; that N2 and O2 are largely transparent to infra red radiation; and that CO2 absorbs and emits infra red radiation at certain wavelengths. All these things are largely true. But so what? If CO2 absorbs a photon’s worth of infra red, it can do two things:

a) absorb it and warm up slightly. As CO2 is only 0.04% of the atmosphere, it makes naff all difference if it is marginally warmer.

b) it can emit it again and cool down again. The emitted photon has no effect on N2 or O2 and can’t warm them up. It can only warm up other CO2 molecules, rinse and repeat. That’s like sunlight being converted to electrical energy by a solar panel, it has left the system and has no effect on total thermal energy (except that 0.04% is slightly wamer).

The only way to make this make sense is to somehow assume that CO2 can’t emit infra red radiation (which they keep telling us it can), so it warms up and then this extra thermal energy is transferred to neighbouring N2 or O2 molecules by conduction. The CO2 molecule then absorbs another photon and transfers the resulting thermal energy to a neighbouring molecule etc, so it’s a one-way street.

Or, we go back to the folksy and completely flawed explanation that the half the infra red emitted by CO2 hits the ground and warms it up a bit more than sunlight alone would. The IPCC can’t even make that add up, let alone make sense. Their infamous and much-quoted diagram shows that infra red “back radiation” from greenhouse gases warms the surface more than incoming sunlight!