BYU Geography: Lesson 4

Terms in this set (106)

Another way that the lithosphere affects climate is its impact on precipitation levels. The shape of the lithosphere has a big influence on which areas receive precipitation. Look at Figure 4.3.2; the map shows precipitation levels in the US. Use the legend to find the areas that receive the most rain. On the east side of the country, notice how far inland the precipitation levels remain relatively high. Now look at the western side of the country. The northwest coast receives a significant amount of rain, but the pattern does not extend very far inland. What do you think explains this? One large factor is the mountainous nature of the western US.

Deserts are often caused by the orographic effect, which is the cooling effect that happens when air is forced to rise so that it can go over a mountain. As the air rises, the water vapor condenses and precipitation occurs. This means all of the water gets dumped on one side of the mountain, creating a humid environment, and by the time the air reaches the other side of the mountain it no longer has any water vapor left in it. This creates a desert.

Look at Figure 4.3.2 again. Notice how there is a dividing line down the continent where the dry desert air meets the humid air coming up from the Gulf of Mexico. The terrain across the central plains slopes downward from the Rocky Mountains towards the east. This slope makes a nice corridor for the dry air coming off the mountains to flow east. To the south, the Gulf of Mexico produces moist air that flows north. When the dry and moist air meet, a boundary line forms. It is along this line that a perfect environment sometimes exists for the creation of tornadoes. The area is often called Tornado Alley. There are more tornados in the US than anywhere else in the world because it has the right combination of terrain, water, and wind currents.
There is concern that humans may be influencing the biosphere in other ways. You have probably heard of the greenhouse effect; this is a process that traps heat in the atmosphere. Without this process it would be too cold on Earth to live. In lesson 3 you learned about Venus. Do you remember that Venus' atmosphere is very thick and hot? This is because the atmosphere on Venus is made mostly of carbon dioxide. Carbon dioxide is particularly good at trapping heat and is a major factor in producing the greenhouse effect.

Many scientists are worried because burning products such as coal, natural gas, and oil adds carbon dioxide to the atmosphere. Since carbon dioxide absorbs heat, the atmosphere may become warmer and disrupt the normal climate and weather patterns. Since the late 1800s the level of carbon dioxide in the earth's atmosphere has increased by 30 percent. During the past century, the average temperature of the earth has increased by 1° F. If the increase continues, some scientists fear that there could be serious and permanent consequences. The warmer weather could cause polar caps to melt, which would cause sea levels to raise. During the last hundred years it is estimated that warmer temperatures have caused the sea level to rise four to eight inches. The warmer water may cause other problems too. As you learned earlier, tropical storms begin over warm ocean water. Scientists worry that warmer oceans could result in more frequent and stronger tropical storms. In the U.S. that could mean more hurricanes.

Some scientists believe that there has always been a natural cycle of global warming and cooling, and they are not convinced that human activities can alter the cycle. Scientists are working to determine exactly what the consequences might be if we continue to add large amounts of carbon dioxide to the atmosphere.