Climate Classification

Why does altitude affect air temperature?
Answered by HowStuffWorks
  • HowStuffWorks

    HowStuffWorks

  1. So you're climbing a mountain -- on top of the world and looking down on creation. But why on Earth does it have to be so cold up there? We all know that the higher you go, the colder it gets, but why?

    Altitude affects the temperature of the air because air pressure gets lower as the altitude increases. The higher the pressure of any gas -- like our air, for example -- the warmer it becomes. When you relieve that pressure, the gas cools. On Earth, the air pressure is approximately 14.7 pounds per square inch at sea level. By the time you reach 50,000 feet above sea level, the air pressure is reduced dramatically, to about 1.6 pounds per square inch.

    The pressure is generated by the force of gravity acting on the many miles of air molecules that make up our planet's atmosphere. The air pressure is not the same everywhere, however. It can be different at different points on the globe and can even change over time. Hot air, for example, is less dense and is lighter than cooler air. This means that deserts usually have low air pressure.

    Finally, just for comparison's sake, if you think we're taking a crushing blow walking around at sea level under that 14.7 pounds per square inches of pressure, you might enjoy buying a telescope and training it on Venus. It might make you feel better. There are four bodies in our solar system with atmospheres, and Venus's -- clocking in at 96% carbon dioxide -- is by far the most pressure-packed (the other three bodies are Earth, Mars and Titan). The pressure on the surface of Venus is about 90 times what we experience here. Scientists think we may have started out with a similarly crushing atmosphere, so it's a lucky thing Earth decided to lighten up a bit [source: planetary.org].

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