The main factor that determines the climates of any place is its distance from the equator. This is because sun never rises high. Therefore the places close to the equator remains warm. Temperature typically decreases as altitude increases. At high altitudes the air is less dense, and it does not absorb and hold as much heat. On the average, the temperature drops about 3. 5 Fahrenheit for every 1,000 feet (2 Celsius for every 300 meters). Thus snow may fall on a cold mountaintop and stay there without melting while rain falls in the warmer valley below.
Land warms up rapidly when heated by the sun and cools off rapidly at night. But large bodies of water change temperature more slowly. This is mainly because water holds more heat than land can. Water is also transparent, allowing sunlight to warm the layers below. When water heats up more slowly than nearby land does, it has a cooling off more slowly, it has a cooling effect on the land. As a result, seacoasts usually have milder winters and cooler summers than mid-continental places with little water.
Winds affect climate because they carry heat and moisture. Winds that blow from the same direction most of the time are called prevailing winds. For example, the prevailing westerlies (winds that blow from the west) pick up moisture in the air brought northward from the Gulf of Mexico and carry that moisture in an eastward direction. This shift leads to less rainfall and short grasses in the western parts of Texas, Oklahoma, and Kansas. Rainfall is greater toward the Mississippi River, where forests and tall grasses are more common.
Pressure centers are large parts of the atmosphere where the pressure is much lower or much higher than in surrounding areas. Low-pressure centers usually cause stormy weather. High-pressure centers usually bring clear, sunny weather. If low- or high-pressure centers tend to form or move over an area at certain times of the year, this weather pattern helps determine the climate of that area. Heavy rains in warm belts of low pressure near the equator create near the equator create a tropical rain forest climate.
Dense tropical forests grow well in this climate. High-pressure centers are the primary cause of tropical desert climates like those of central Australia or the Sahara in northern Africa. Ocean currents are great streams of water moving in the oceans. Some currents carry warm water to cool regions. These currents affect climate in many parts of the world. The Gulf Stream, for example, is a warm ocean current. It carries warm water from the western tropical Atlantic toward the coasts of northwestern Europe.
As a result, winters in western France are warmer than winters in the state of Maine in the United States, even though both are at about at about the same latitude. Mountains form barriers that affect the movement of prevailing winds. As winds approach mountains, air is forced or rise. The air uses energy to rise and becomes colder in the process. If the rising air contains enough water vapor, the vapor cools and condenses to form clouds and precipitation. This creates a “ Rain Shadow” effect. More precipitation falls on the windward side of mountains than on the leeward side.
A clear example of this effect is the two different climates on either side of the Sierra Nevada mountains in California. The windward slopes on the west side are covered with trees. The leeward slopes on the east side have scrubby vegetation. Scientists have discovered that as cities and urban areas grow, local temperatures rise. This is partly caused by the greater amount of concrete and asphalt, which absorb the sun’s heat. The result is the creation of “urban climates” that may be different from the surrounding climates.