From Pseudoscience of Doom:
We are still looking at how radiation travels and interacts with the atmosphere before anything changes.
There is a lot of fascination in the subject of the “average height of emission” of terrestrial radiation to space. If we take a very simple view, as the atmosphere gets more opaque to radiation (with more “greenhouse” gases) the emission to space must take place from a higher altitude. And higher altitudes are colder, so the magnitude of radiation emitted will be a lesser value. And so the earth emits less radiation and so warms up.
This “average height of emission” is often supplied as a mental model and it’s a good initial starting point.
Here is the result of the atmospheric model created with a surface temperature of 288K (15°C), 80% humidity in the boundary layer and 40% humidity above that (the “free troposphere).
This is a cloud-free sample – clouds are very common, but really make life complicated and we are trying to provide a small level of enlightenment. Simple stuff first.
There follows a tortuous series of calculations based on certain arbitrary assumptions which inevitably prove their point.
--------------------------------------
Q. Why do they always ignore clouds, which cover average two-thirds of the Earth at any one time? They are more than "very common". They are the norm.
A. It is because clouds actually explain pretty much the whole of the so-called 'greenhouse effect'...
1. The "average height of emission" concept is actually very useful in mathematical terms, although they are applying it to the wrong thing and in the wrong direction.
2. If we are going to simplify things, it makes more sense to round up that 'two-thirds of the surface' to 'all of the surface' instead of rounding it down to zero. The upper surface of clouds is on average 5 km above the surface. Earth and its clouds have an average albedo of 0.3, so let's assume these clouds have an albedo of 0.3.
3. As far as incoming solar radiation and 'effective temperature' are concerned, the 'effective surface' is the upper surface of clouds. When you calculate the 'effective temperature' you are in fact calculating/estimating the temperature of the upper surface of clouds. Unsurprisingly, a planet's 'effective temperature' is, in real life, very close to the actual observed temperature of the upper surface of clouds. Except on Mars, where there aren't any clouds, so the 'effective surface' and the hard surface are the same thing.
4. The temperature at the hard surface (land or ocean) is simply the temperature of the upper surface of clouds, plus their altitude x the lapse rate (the 'gravito-thermal effect' which is dictated by basic maths, GCSE level physics and a bit of common sense).
5. The simple approach from 4. neatly explains the hard surface temperature of...
a) Venus. 'Effective temp' and actual temperature of upper surface of clouds = 232K. Upper surface of clouds altitude (call it) 63 km. Lapse rate 7.9 K/km. Hard surface temperature = 232 + (63 x 7.9) = 733K.
b) Earth. 'Effective' and actual temperature of upper surface of clouds = 255K. Upper surface of clouds altitude = 5 km. Lapse rate 6.5 km. Hard surface temperature = 255 + (5 x 6.5) = 288K.
c) Mars. 'Effective' and actual temperature of hard surface (no clouds) approx. 215 K, no 'greenhouse effect'. Even though there is about thirty times as much CO2 above every m2 of Mars than there is on Earth!
6. There's always the question of cause-and-effect. What seems more plausible:
a) The "average height of emission" dictated by 'greenhouse gases' and the clouds just happen to form with their upper surface at the same altitude? Or,
b) The clouds have their own rules, they form where they form, and their upper surface is, in practice, the "average height of emission", because they are the only surface that can emit radiation directly to space? Or indeed absorb radiation directly from space?
7. Then *drumroll* there's the 'trapped radiation' myth. The hard surface is 288K and emits, mathematically, 390 W/m2. Measured from space, Earth emits 240 W/m2. The myth is that one-third of radiation emitted from by the hard surface is 'trapped' by 'greenhouse gases'. Nope. When you measure from space, you are measuring the radiation emitted by the upper surface of clouds, which are colder and emit 240 W/m2, the same as what they absorb from the Sun.
(8. There is a completely separate system going on between the hard surface and the lower surface of clouds, it's the clouds that do the 'trapping', they get radiation from the hard surface, absorb some and reflect some back down again. Let's not go there for now.)
Debate Magazine
