Now that you know about winds and air pressure systems, let's talk about the impact of the hydrosphere on the climate. It starts with the oceans. Water does not heat and cool as rapidly as air, so the oceans stay about the same temperature year-round. The temperature of the water affects the air; this means the air near the ocean does not change temperature as dramatically as the air that is further inland. To see what I mean, let's compare the average monthly temperatures of North Dakota and Washington.

These two states are located at about the same latitude, which means they are about the same distance from the equator. However, Washington is near the moderating coastal waters of the Pacific Ocean while North Dakota is in the Central US and far away from any significant body of water. Because of these differences, the temperature patterns are very different in the two states.

Look at the Figure 4.2.1 above and compare the months of April in both states. Note how the average daily temperature is nearly the same. Now look at the month of September; once again, the temperatures are not that different. In fact, if the only data you had for these two states was from April to October, it would look like they have very similar temperature patterns. The big difference occurs from November through March. Compare the temperatures for January. Now look at December. As you can see, it gets considerably colder in North Dakota in the winter months than it does in Washington during the same time period. Now look at the months of January and July for Washington. There is a difference of 34.26 degrees between the average minimum winter and the average maximum summer temperatures. Now look at the same two months for North Dakota; we see a difference of 60.80 degrees between the average minimum winter and the average maximum summer temperature. Through these comparisons, we learn that the variations in temperature in North Dakota are much more dramatic than the temperature variations in Washington.