|Why is it colder at a higher altitude when
technically it is closer to the sun?
|Question Date: 2014-08-23|
This is a great question, but the answer is a
little complicated, so you have to help me out.
First, we have to understand air pressure. A
lot of people think that air has no weight. This
is not true. Air is matter and it has mass.
“Mass” is a fancy way of saying “stuff.” We
measure the mass by weighing it.
Picture yourself standing by the foot of a
mountain. There is a column of air on you that
goes all the way up into the end of our
atmosphere. It is pushing down on you, but you
don’t notice it. (If we swapped in water for air,
you would.) Now picture yourself on the top of
the mountain. The column of air is shorter now,
so it weighs less. It is putting less pressure on
you. Got that? More air pressure down by sea
level, less on the top of the mountain.
Pressure squishes things down so that they take
up less space. “Volume” is a fancy way of saying
“space.” The same amount of air is squashed into a
smaller space down at sea level. On top of the
mountain, it is more spread out.
Heat is energy, not stuff (matter). We can’t
see heat. We measure it as temperature.
This part is tricky, so help me out by grabbing
a piece of paper, a ruler, a pencil, and a red
crayon or marker.
1. Draw a square with the pencil. Make the
square about 2 inches on each side.
2. Now use the red crayon or marker to draw
20 lines from the top to the bottom of the square,
partly filling it in.
3. Next to this, use the pencil to draw a
second square that is about 3 inches on each side.
4. Now use the red crayon or marker to make
20 lines, each one 2 inches long, inside the big
In your drawing, the red lines are to show heat.
You can see that a lot less of the big square is
covered by red. If you were an ant walking around
in the big square, you would touch a lot less
When air is near sea level, air pressure squashes
it into a small space, like your small square.
When the air is high on the mountain, it spreads
out. This is like your big square. The same
amount of heat is now in a bigger space, so it is
more spread out. So the air is colder on top of
mountains because there is less air pressure.
Heat is not really red, and it’s not really
lines. The picture that you drew helps you think
about heat. Your picture is a model. Scientists
use models to help themselves think about things
and to communicate to other people.
Some places on land are actually below sea
level. Do you think they are hotter or cooler
than places at sea level?
If you like to think about this sort of
question, you may want to study atmospheric
Thanks for asking,
So you know that the sun is really hot, but space
is really cold. Since the temperature of the Earth
is so much hotter than space, you’d expect that
the closer you get to space the colder it gets.
Eventually as you get closer to the sun, the
temperature will start to increase. You may have
heard people say that the air is “thinner” at
higher altitudes. What this means is that it is
less dense. Generally, the less dense air is, the
colder it is. So the air is densest closest to the
surface of the Earth, then it gradually becomes
less dense until you get to the vacuum of space.
This density difference accounts for the
At higher altitudes, the air is thinner. That's
why it's harder to breathe at high
altitudes--there's less oxygen. There's also less
of everything else--carbon dioxide, water vapor,
etc. These gases, which are greenhouse gases, are
the part of our atmosphere which keep Earth at a
warm temperature compared to outer space. Without
this atmosphere, Earth would be uninhabitably
cold. So, even though higher altitude areas are
closer to the sun, they have less ability to
absorb the warmth of the sun because they have
less of these gases.
When air expands, it has to push the surrounding
air out of its way, which means that it expends
part of its energy to do the pushing. As a result,
the expanding air cools. When air contracts, it
gets pushed into a smaller space by the air around
it, which means that energy is put into it, which
heats it up. Eventually, the expanding or
contracting air will reach the same temperature
and pressure as the air surrounding it, and the
heating and cooling will stop. Air at higher
altitude is under less pressure than air at lower
altitude because there is less weight of air above
it, so it expands (and cools), while air at lower
altitude is under more pressure so it contracts
(and heats up).
Air in our atmosphere moves up and down as part
of the weather: the sun heats up the ground (which
absorbs more light than air and is thus warmer
than the air), and the air in contact with the
ground heats up, and expands (and then cools).
Elsewhere, cooler higher-altitude air sinks, is
compressed as it descends, and gets heated as this
occurs. This process is called "convection", and
it is responsible for nearly all of our weather.
You are correct that it is colder at higher
altitudes. However, the distance to the sun has
nothing to do with this – it is the lower
atmospheric pressure that results in lower
temperatures. Keep in mind that the Sun is about
93 million miles (490 billion feet) away from
Earth. Even if you hiked to the highest point in
Santa Barbara (La Cumbre Peak: 4,000 ft) or were
flying in a commercial airplane (cruising altitude
~ 30,000 ft), you are still relatively the same
distance from the Sun (REALLY far away).
The answer to your question deals with the
pressure and temperature relationship of a gas.
The Earth's atmosphere is thin layer of gases
composed of nitrogen (78%), oxygen (19%), and
other gases (~3%). As you go to higher altitudes,
there are less air molecules pushing down on you
(lower pressure). When the pressure of a gas
decreases, the temperature also decreases (the
reverse is also true – when the gas pressure
increases, the temperature increases). Therefore,
the air temperature is lower at higher altitudes.
Hope this helps!
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