Temperatures on Moon & Earth

In an earlier post I pointed out that there was a correlation between distance from the sun and surface temperature for Venus, Earth & Mars. I ended with this:

What detracts from my argument is that the Moon's average temperature is about -36 C, 50 C colder than Earth, despite it being the same average distance from the Sun, which I'd put down to a mixture of the Moon being paler in colour (so reflects more light) and not having a giant molten iron core, as well as it not having an atmosphere.

I have been reminded that The Moon is nowhere near as pale as it looks, it is in fact quite dark. In the jargon, it has an 'albedo' of 12%, as a against 30% for the Earth, so it must be the atmosphere that's the important bit. DK has referred me to this post of his, which in turn links to this fuller article, the important bits are as follows:

We know how much energy enters the Earth’s system from the sun. The Earth ought to settle at the temperature at which it radiates exactly the same amount to outer space. (Taking the average over time and latitude.) We can calculate this temperature fairly easily, and it turns out to be –24 C. But the average temperature of the Earth’s surface is about 14 C! This temperature difference and its dominant mechanism are what I’m choosing to call the Greenhouse Effect...

What keeps the [atmosphere] at 10 km so cold? –54 C is far below the –24 C we expect on energy-balance grounds, so it can’t be by radiating to space. And the fact that there is a straight line all the way down to the ground suggests that whatever the mechanism is, it’s the same one that keeps the surface at +14 C. Straight lines don’t happen by accident.

I won’t keep you in suspense any longer. The answer is pressure. Because of the weight of air, the pressure at the surface is greater than it is higher up. This means that if air moves up and down, the pressure changes, and the air expands or is compressed. And when air is compressed its temperature increases.

Air is driven to circulate up and down by convection. As it rises, it expands and its temperature drops. As it descends, it is compressed and its temperature rises. This maintains a constant temperature gradient of about 6 C/km. (It would be bigger, but evaporation of water carries heat upwards too, which somewhat counteracts the effect.)

No heat passes in to or out of the air to effect this change. It is solely an effect of the changing pressure. (If you really want to know, the compression does ‘work’ on the gas, which increases its internal energy. It doesn’t come from any flow of heat or radiation.)

This temperature gradient is called the adiabatic lapse rate, and is an absolutely standard bit of physics.

So now we know.

As it happens, the Warmenist explanation that carbon dioxide is transparent to visible light from the sun but reflects part of the infra-red coming from the surface of the earth and hence causes warming is sort-of-true, however, it is a logarithmic effect.

i.e. there is enough CO2 in the atmosphere to form a 'blanket' 6 yards thick (ten miles x 0.04%). Let's assume this reflects half the infra-red back down to earth and lets half through into space. If there were another layer, it would reflect half of the half of the infra-red that had made it through the first layer, but this quarter in turn would be partly reflected back upwards by the first layer and so on. Having scribbled some workings, each extra 'layer' would reduce the amount of infra-red going into space by a third or so.

Or, to put it crudely, if you feel cold, one blanket will make you feel noticeably warmer (let's say 10 C), adding another makes you warmer still (another 5 C), adding a third might make you another 2 C warmer and a fourth another 1 C, and so on. In other words, there is no particular 'runaway' effect, even if you had a thousand blankets on top of you (provided you were not crushed to death or suffocated), the extra warmth would never be much more than twice as much as with just one blanket.