Different parts of the world have different climates. Some parts of the world are hot and rainy nearly every day. They have a tropical wet climate. Others are cold and snow-covered most of the year. They have a polar climate. Between the icy poles and the steamy tropics are many other climates that help make the Earth a unique planet.
Average temperature and precipitation are important features of a climate. So are the day-to-day, day-to-night, and seasonal variations in temperature and precipitation. For example, San Francisco, California, and Beijing, China, have similar yearly temperatures and precipitation. However, the daily and seasonal changes make San Francisco and Beijing very different. San Francisco’s winters are not much cooler than its summers, while Beijing is hot in summer and cold in winter. San Francisco’s summers are dry and its winters are wet. The wet and dry seasons are reversed in Beijing—it has rainy summers and dry winters.
Climate features also include windiness, humidity, cloud cover, and fogginess.
A region’s climate is something like a person’s personality. It is usually constant, but there may be surprises. Just as someone with a cheerful attitude will sometimes become sad, an area with a generally mild climate will occasionally experience extreme rainfall or drought. But because climates are mostly constant, living things can adapt to them.
The enormous variety of life on Earth is largely due to the variety of climates that exist and the climate changes that have occurred in the past.
Climate has influenced the development of cultures and civilizations. People everywhere have adapted in various ways to the climates in which they live.
Clothing, for example, is influenced by climate. The warm clothing developed by Eskimo cultures of Asia and North America are necessary for survival in the cold, windy climate near the North Pole. Grass skirts, on the other hand, are part of many cultures in warm, humid climates, such as Tahiti, an island in the South Pacific Ocean.
Climate also influences where and when a civilization constructs housing or other buildings. The ancient Anasazi people of southern North America built apartments into tall cliffs. The sheltered, shady area kept residents cool in the hot, dry desert climate.
The development of agriculture was very dependent on climate. Ancient agricultural civilizations, such as those in Greece and India, flourished where the climate was mild. Communities could grow crops every season, and experiment with different types of foods and farming techniques.
Today, farmers are still in tune with the climate. They plant certain crops according to the expected amount of rainfall and the length of the growing season. A growing season is the time between the last frost of spring and the first frost of autumn. When the weather does not follow the typical climate pattern, it can mean hard times for farmers and higher food costs for consumers.
Of course, no climate is uniform. Small variations, called microclimates, exist in every climate region. Most are caused by topographic features such as lakes, vegetation, and cities. In large urban areas, for example, streets and buildings absorb heat from the sun, raising the average temperature of the city higher than the average temperatures of more open areas nearby. This is known as the “urban heat island effect.”
Large bodies of water, like the Great Lakes in the United States and Canada, can also have microclimates. Cities on the southern side of Lake Ontario, for example, are cloudier and receive much more snow than cities on the northern shore. This “lake effect” is a result of cold winds blowing across warmer lake water.
The most widely used system for classifying climates was proposed in 1900 by Wladimir Koppen. Koppen observed that the type of vegetation in a region depended largely on climate. He used this fact as the starting point for his classification scheme. Studying temperature and precipitation data, he and other scientists developed a system for naming climate regions.
According to this system, there are five climate groups: tropical, dry, mild, continental, and polar. These climate groups are further divided into climate types. The following list shows the climate groups and their types:
o Wet (or rain forest)
o Wet and dry (or savanna)
o Humid subtropical
o Warm summer
o Cool summer
o Subarctic (or boreal)
o Ice cap
All climates are the product of many factors, including latitude, elevation, topography, distance from the ocean, and location on a continent. The rainy tropical climate of West Africa, for example, results from the region’s location near the Equatorand its position on the western side of the continent. A constant amount of sunlight keeps temperatures in the area warm and steady. West Africa is also at the site where moisttrade winds meet, an area called the intertropical convergence zone (ITCZ) (pronounced “itch”). As a result, the region’s climate is warm and rainy.
There are three climate types in the tropical group: tropical wet; tropical monsoon; and tropical wet and dry.
Places with a tropical wet climate are also known as rain forests. Rain forests have the most predictable weather on Earth, with warm temperatures and regular rainfall. Annual rainfall exceeds 150 centimeters (59 inches), and the temperature varies more during a day than it does over a year. The coolest temperature, about 20-23 degrees Celsius (68-73 degrees Fahrenheit), occurs just before dawn. Afternoon temperatures usually reach 30-33 degrees Celsius (86-91 degrees Fahrenheit). Rain forests experience very little seasonal change, meaning average monthly temperatures remain fairly constant.
Tropical wet climates exist in a band extending about 10 degrees of latitude on either side of the Equator. This part of the globe is always under the influence of the intertropical convergence zone. The zone follows a pendulum-like path during the course of a year, moving back and forth across the Equator with the seasons. It moves north during summer in the Northern Hemisphere, and south during the northern winter.
Some tropical wet climates are wet throughout the year. Others experience more rainfall during the summer or winter, but they never have especially dry seasons. The U.S. state of Hawaii; Kuala Lumpur, Malaysia; and Belém, Brazil, are examples of areas with tropical wet climates.
Tropical monsoon climates are most common in southern Asia and West Africa. A monsoon is a wind system that reverses its direction every six months. They usually flow from sea to land in the summer, and from land to sea in the winter.
Summer monsoons bring large amounts of rainfall to tropical monsoon regions. People living in these regions depend on the seasonal rains to bring water to their crops. India and Bangladesh are famous for their monsoon climate patterns.
The third type of climate, tropical wet and dry climate, has three seasons. These areas are just outside the ITCZ, near the Equator. One season is cool and dry when the warm, moist ITCZ is in the opposite hemisphere. Another season is hot and dry as the ITCZ approaches. The last season is hot and wet as the ITCZ arrives and the region experiences months as a tropical wet climate.
Life in these tropical wet and dry regions depends on the wet season’s rains. During years when rains are light, people and animals suffer. Havana, Cuba; Kolkata, India; and Africa’s vast Serengeti Plain are in the wet and dry tropics.
Regions lying within the dry climate group occur where precipitation is low, including cool, high latitudes. There are two dry climate types: arid and semiarid. Most arid climates receive 10 to 30 centimeters (4-12 inches) of rain each year, and semiarid climates receive enough to support extensive grasslands. Often, these grasslands are known as savannas or prairies.
Temperatures in both arid and semiarid climates show large daily and seasonal variations. The hottest spots in the world are in arid climates. The temperature in the North African town of El Aziza, Libya, reached 58 degrees Celsius (136 degrees Fahrenheit) on September 13, 1922—the highest weather temperature ever recorded.
Although rainfall is limited in all dry climates, there are few parts of the world where it never rains. One of the driest places on Earth is the Atacama Desert of Chile, on the west coast of South America. There, the town of Arica averages less than 0.05 centimeters (0.02 inches) of rain a year.
Semiarid regions, such as the Australian Outback, usually receive between 25 and 50 centimeters (10-20 inches) of rainfall every year. They are often located between arid and tropical climate regions.
Arid and semiarid climates can occur when warm, moist air is blocked by mountains. Denver, Colorado, next to the Rocky Mountains in the U.S., has this type of dry climate.
Regions with mild and continental climates are also called temperate regions. Both climate types have distinct cold seasons. In these parts of the world, climate is influenced mostly by latitude and by a region’s position on the continent.
The mild climate type called Mediterranean climate has a warm summer and a short, mild, and rainy winter. It is found on the west coasts of continents between 30 and 40 degrees latitude, and along the shores of the Mediterranean Sea. Mediterranean summers feature clear skies, cool nights, and little rain. The city of Jerusalem, Israel, once had no rain in July for more than 100 years.
The type of mild climate known as humid subtropical climate is usually found on the eastern sides of continents. In cities such as Savannah, Georgia, in the U.S.; Shanghai, China; and Sydney, Australia, summers are hot and humid. Winter can be severely cold. Precipitation is spread evenly through the year and totals 76 to 165 centimeters (30-65 inches). Hurricanes and other violent storms are common in these regions.
Weather on both sides of a continent generally becomes cooler as latitude increases and areas are closer to the poles. The marine west coast climate, a type of mild climate typical of cities such as Seattle, Washington, in the U.S. and Wellington, New Zealand, has a longer, cooler winter than the Mediterranean climate. Drizzle falls about two-thirds of winter days, and temperatures average about 5 degrees Celsius (41 degrees Fahrenheit).
Areas with continental climates have colder winters, longer-lasting snow, and shorter growing seasons. They are thetransition zones between mild and polar climates. Continental climates experience extreme seasonal changes.
There are three types of continental climate—warm summer, cool summer, and subarctic. All these climates exist only in the Northern Hemisphere. Usually, continental climates are found in the interior of continents.
Warm summer climate regions often have wet summer seasons, similar to monsoon climates. For this reason, this climate type is also called humid continental. Most of Eastern Europe, including Romania and Georgia, has humid continental climates.
Cool summer climates have winters with low temperatures and snow. Cold winds, sweeping in from the Arctic, dominate the winter weather. People living in these climates have grown accustomed to the harsh weather, but those unprepared for such cold may suffer. Many of Napoleon Bonaparte’s soldiers, for example, were used to the mild Mediterranean climates of France. Thousands died in bitter cold as they retreated from Russia’s cool summer climate in the winter of 1812.
North of regions with cool summer climates are regions with subarctic climates. These regions, including northern Scandinavia and Siberia, experience very long, cold winters with little precipitation. Subarctic climates are also called boreal climates or taiga.
The range of weather in continental climate regions makes them among the most spectacular sites for weather phenomena. In autumn, for instance, vast forests put on their annual show of brilliant color before shedding their leaves as winter approaches. Thunderstorms and tornadoes, among the most powerful forces in nature, form mostly in continental climates.
The two polar climate types, tundra and ice cap, lie within the Arctic and Antarctic Circles near the North and South Poles.
In tundra climates, summers are short, but plants and animals are plentiful. Temperatures can average as high as 10 degrees Celsius (50 degrees Fahrenheit) in July. Wildflowers dot the landscape, and flocks of birds return from their winter migrations to feed on insects and fish. Whales feed onmicroscopic creatures in the region’s cold, nutrient-rich waters. People have adapted to life on the tundra for thousands of years.
Few living things exist in the ice cap climates of the Arctic and Antarctic. Temperatures rarely rise above freezing, even in summer. The ever-present ice helps keep the weather cold by reflecting most of the sun’s energy back into the atmosphere. Skies are mostly clear and precipitation is low all year. In fact, Antarctica, covered by an ice cap a mile thick, is actually one of the largest, driest deserts on Earth.