Factors that Influence the Environmental Lapse Rate

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  • 0:01 How Temperature Works
  • 1:13 Under Pressure
  • 2:30 Insulating Atmosphere
  • 3:31 A Complex Atmosphere
  • 5:12 Lesson Summary
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Lesson Transcript
Instructor: Meredith Mikell
Earth's atmosphere does not have a consistent temperature at different altitudes. There are several key factors that influence these phenomena. Here, we will explore those factors and finish the lesson with a short quiz.

How Temperature Works

Picture in your mind a mountain climber ascending Mt Everest. What is he or she wearing? What do the surrounding mountaintops look like? We don't have to read your mind to know that you probably are not picturing a shirtless figure in a swimsuit surrounded by lush, green vegetation. You're imagining a very cold scene: a climber bundled in layers of insulating clothing and standing over a vast expanse of snowy peaks. This is because we know higher altitudes tend to be generally colder than lower ones.

But why? Earth's environmental lapse rate is the decrease in temperature with increasing altitude, which occurs at a rate of approximately 3.5 degrees Fahrenheit per 1000 ft. To better understand why this happens, we first need to establish that temperature is the measure of kinetic energy present in molecules. In this case, the molecules are the gases that make up the atmosphere. Kinetic energy is the energy from movement of those molecules. So, for there to be temperature, there must be molecules present.

Under Pressure

If you've ever been on an airplane, you've likely experienced changes in air pressure that make your ears pop during take off and landing. Even though the air in our atmosphere might look the same when you gaze out the airplane window, the density of air molecules is not consistent.

Air pressure is the weight of air on top of Earth's surface and depends upon the density of air molecules. Because of Earth's gravity, more molecules are pulled closer to the surface, which means the density of air is highest at sea level. As you go up into the atmosphere, the molecules gradually thin out, decreasing in density, and thus decreasing the amount of pressure, until the atmosphere ends and space begins.

Put another way, if you are standing at sea level, there is a lot more air sitting on top of you than there is if you are sitting on top of Mount Everest. This is why mountain climbers often need oxygen tanks when they make their way up into the atmosphere: thinner air, less pressure, less oxygen to breathe. It is also why your ears pop in the airplane. The air pressure in your ears at take off is higher than the surrounding air way up at cruising altitude, so even though the cabin is pressurized, the difference between pressures causes that pesky popping!

Insulating Atmosphere

So the atmosphere is thickest at sea level and thins out with altitude. How does this impact temperature?

You're likely familiar with the greenhouse effect, the way that atmospheric gases trap solar energy, heating Earth's surface. Not all gases that make up Earth's atmosphere are greenhouse gases. Air is mostly nitrogen and oxygen, which do not help trap solar heat. But water vapor and carbon dioxide are two greenhouse gases that also make up the air that we breathe.

This means that heat is going to be trapped more in the lower altitudes - where there are more air molecules, and therefore, a higher air pressure - than at higher altitudes. Think of the atmosphere as a thick blanket covering the planet, trapping heat beneath it. The insulating properties of the atmosphere is a very big factor affecting the environmental lapse rate.

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