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.
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!
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.
A Complex Atmosphere
When you factor in how air pressure is highest at sea level and gradually thins out with altitude and the fact that air is insulating, it makes sense that the environmental lapse rate exists.
But the temperature does not consistently decrease with altitude. The change is steady at first, but in the higher parts of the atmosphere, it jumps around a bit. This is partially due to the fact that the gases that make up the atmosphere can be concentrated at different altitudes in the atmosphere and that heat moves vertically in the atmosphere.The process of advection, warm air moves laterally to a region of cool air, causes the cooler area to warm up.
Warm air is less dense than cool air, so due to convection warm air tends to rise and cool air tends to sink. This can cause a temperature inversion, where temperature suddenly increases with altitude instead of decreasing.The presence of water vapor influences heat retention as well; water vapor can trap heat at different altitudes, contributing to the inversion. Also, the atmosphere has a thick layer of ozone around 90,000 feet high. Ozone is a greenhouse gas made of three oxygen molecules that blocks out a lot of solar radiation. That radiation, including some heat, bounces off the ozone layer and is retained in the upper atmosphere. This is why we see an increase in temperature just above the stratosphere.
Earth’s environmental lapse rate is the decrease in temperature with increasing altitude in the atmosphere. The density of air molecules in the atmosphere affects the air pressure, the force of air exerted on Earth’s surface, which is the highest at sea level and steadily decreases with altitude. More air molecules at the surface means more heat is trapped there, especially given the presence of greenhouse gases, which trap heat, insulating the air and land beneath it.
Because the atmosphere’s composition is not consistent throughout and convection and advection cause heat to move around, the temperature experiences an inversion at different altitudes, a sudden increase with altitude instead of decreasing. The ozone layer and water vapor can also cause inversions at different altitudes. Earth’s atmosphere is complex, as are the temperature patterns within it!
Studying this lesson intensely could result in your expanded ability to:
- Realize why higher altitudes are colder than lower ones
- Examine the cause of air pressure and recognize its relationship to the temperature on Earth
- Discuss the atmosphere’s insulating properties
- Identify the atmospheric factors and discuss the processes that create Earth’s environmental lapse rate