Exhibit A, from the BBC:
There are natural fluctuations in the climate but scientists say temperatures are now rising faster than at many other times.
This is linked to the greenhouse effect, which describes how the Earth's atmosphere traps some of the Sun's energy. Solar energy radiating back to space from the Earth's surface is absorbed by greenhouse gases and re-emitted in all directions.
This heats both the lower atmosphere and the surface of the planet. Without this effect, the Earth would be about 30C colder and hostile to life.
1. As ever, they say "the Earth would be about 30C colder" instead of "the Earth's surface would be about 30C colder".
2. The Earth's atmosphere is, on average, about 30C cooler than the Earth's surface. They always gloss over that bit. The lowest part (where it touches the surface) is 30C warmer than average and the highest part is 30C cooler than the average.
3. The Barometric Formula explains that there has to be a temperature gradient going up ('adiabatic lapse rate' in Newspeak).
4. After we'd done out Physics O Level, the teacher said, let's stretch our mental legs a bit, and did some clever workings to show that if you know atmospheric pressure and density of air at sea level, you can extrapolate upwards to see where the top of the troposphere is, which contains 99% of the atmosphere (it gets a bit mad further up). I can't remember how he did it, but it all stacked up. To cut a long story short, pressure falls at a fairly constant rate, so it's not difficult to estimate pressure at a given height if you know pressure at sea level and that it's effectively zero 11 km up. And temperature also falls at a fairly constant rate. That's two of the variables you need for the formula without breaking a sweat. Expected temperature then just pops out of the formula, and is surprisingly close to observed results.
5. If the facts fitted the BBC's "really simple guide", then not only would the surface be 30C warmer, the top of Mt Everest would also be warmer - but it's not, it's a lot colder. They hedge their bets and fudge it with this claim: "This heats both the lower atmosphere and the surface of the planet." Are they trying to say that the top of Mt Everest would be warmer if there were no CO2?
6. To use a crude analogy, a perfectly efficient fridge doesn't change the average temperature of your kitchen. It causes the inside to be colder and warms up the rest of the kitchen to balance. The atmosphere does the same sort of thing. It can't change its own average temperature (how?), that's dictated by the Sun, but it cools the top half and warms the bottom half in equal and opposite measure.
--------------------------------------------------------
Exhibit B, from Wikipedia:
The temperature of the troposphere generally decreases as altitude increases. The rate at which the temperature decreases, -dT/dz, is called the environmental lapse rate (ELR). The ELR is nothing more than the difference in temperature between the surface and the tropopause divided by the height. The ELR assumes that the air is perfectly still, i.e. that there is no mixing of the layers of air from vertical convection, nor winds that would create turbulence and hence mixing of the layers of air.
The table below gives an ELR of 6.5C/km. You can measure this directly or work it out by plugging height and pressure into the formula. Rather infuriatingly, they give a variant of the formula in the section above, but don't draw any conclusions from it.
The reason for this temperature difference is that the ground absorbs most of the sun's energy, which then heats the lower levels of the atmosphere with which it is in contact. Meanwhile, the radiation of heat at the top of the atmosphere results in the cooling of that part of the atmosphere.
Sure, direct sunlight heats up the ground and that must warm the air directly above it. So the equilibrium is disturbed and tries to re-establish itself. But that is moving the goal posts. How much of the earth's surface is getting direct sunlight at any one point in time? It can't be more than half (day-night) and in the day time, maybe there's direct sunlight half the time (clouds). So overall, one-quarter? And two-thirds of the Earth's surface is water, which warms (and cools) much more slowly that the land.
Nonetheless, the temperature gradient is much the same by day or by night, when it could be argued that the surface cools the air above it. It is the same above the oceans (fairly constant surface temperature, day or night); it is the same above land (warms faster by day; cools faster by night); it is the same whether it's sunny or cloudy.
-----------------------------------------------------
We know all this stuff, or can easily find out. Why do they keep trotting out explanations that contradict each other and are completely at odds with known facts and basic physics?
(As ever, for sure, we also know that CO2 blocks/reflects infra red at a few frequencies, but that is a very marginal effect, no more than one degree here or there. There is twenty times as much C02 in the Martian atmosphere, but it is still bloody cold because it is further from the Sun, obviously, but also because the Martian atmosphere is only one-hundredth as thick as Earth's. The fact that is is 95% CO2 is largely irrelevant).
Debate Magazine
