Why is it colder at higher altitudes?

21 February 2010


I was told that, the closer one is to the sun the hotter it is. So why is it that, the higher the altitude one is at, the colder it is?


Well, the reason, Dennis, is if you think about it, the distance between the Earth and Sun is a very long way. It's a hundred million miles or so. And therefore, the distance between the Earth's surface and the top of Everest at 29,000 feet is a tiny fraction of the total distance to the Sun: in the grand scheme of things, it's a trivial change in the actual distance.

So that isn't why the temperature changes and therefore also why it isn't hotter. The reason it's actually colder is because, as you go up in the atmosphere, the Earth's atmosphere feels less pressure the higher up you go. So as the gas in the atmosphere rises it feels less pressure, which makes it expand. When the gas expands it does some work. And and if it's doing work, it must be losing some energy; and if it loses energy, its temperature must drop because we define temperature as the average energy of the particles. Therefore, if the energy of the particles is lower, the temperature must be lower. That's why, at altitude, the temperature appears to fall. In space, outside the earth's atmosphere, if you're facing the Sun, you can actually fry. That's why space suits are specially designed in order to keep people from getting too hot in the sunny bits but also prevent them from becoming too cold in the non-sunny bits.


this is in relation to the higher you go the cooler it becomes. Assuming global warming is increasing as science has it, does this mean that water vapor will fail to condense at some point in time?

That's very unlikely to happen. Global warming considers ground surface temperatures and the changes that are being predicted are of the order of a few degrees. Unless we enter a runaway greenhouse state like Venus, which doesn't seem likely at the moment, water will still condense.

So if I had 2 clear boxes, one with low pressure air and one with high pressure air, after a few hours the one with high pressure air would be warmer than the one at low pressure? assuming they are well insulated

The important take-home point here is that the rising air is "doing work" against the atmosphere as it expands. When something "does work" then it must consume energy. Something with a lower average energy will have a lower temperature. 

Air in a sealed box is not doing work because it is at a constant volume; therefore its temperature remains constant. But if the air is allowed to escape and expand - for instance like air issuing from a pressurised cylinder - then it will produce a drop in temperature as it expands.

The answer given is the correct one. Perhaps you should research a topic a little more before making pronouncements like the one below that serves only to show how little you do actually know... What has been said in answer to this query is quite right.

To echo the thought posted below in hopefully a less condescending tone, I thought that any pressure allowed to sit for a time would eventually average out to a "room temperature" of sorts. I was under the impression that high altitudes were cooler because of distance from the surface (or whatever is absorbing most of the suns heat), which was why depths in the ocean are cooler despite their higher pressure. This however does not account for cold air on a mountain top on a calm day, so I'm looking for a better explanation.

hahaha...dumb answer above. The sun energy per unit surface is the same, this is correct, but the air is already thin at high elevations and is not expanding anymore to drop the temperature. Try again.

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