17.2 World Climates

Lesson Objectives

• Identify world climates and where they are found.
• Define microclimate, and give an example.

Vocabulary

• alpine tundra
• biome
• continental climate
• desert
• humid continental climate
• humid subtropical climate
• marine west coast climate
• Mediterranean climate
• microclimate
• polar climate
• polar tundra
• steppe
• subarctic climate
• temperate climate
• tropical climate
• tropical rainforest

Introduction

The same latitudes should have the same types of climate all around the globe, but many other factors play a role in climate. Oceans and mountain ranges also influence climate in the same ways worldwide. You can see this in Figure below. The major climate types are determined by a lot of factors, including latitude. You can see where the climate types are on the map and then read about them below.

Find where you live on the map. What type of climate do you have?

Major Climate Types

Major climate types are based on temperature and precipitation. These two factors determine what types of plants can grow in an area. Animals and other living things depend on plants. So each climate is associated with certain types of living things. A major type of climate and its living things make up a biome. As you read about the major climate types below, find them on the map in Figure above.

Tropical Climates

Tropical climates are found around the equator. As you'd expect, these climates have warm temperatures year round. Tropical climates may be very wet or wet and dry.

• Tropical wet climates occur at or very near the equator. They have high rainfall year round. Tropical rainforests grow in this type of climate.
• Tropical wet and dry climates occur between 5° and 20° latitude and receive less rainfall. Most of the rain falls in a single season. The rest of the year is dry. Few trees can withstand the long dry season, so the main plants are grasses (see Figure below).

Africa is famous for its grasslands and their wildlife.

Dry Climates

Dry climates receive very little rainfall. They also have high rates of evaporation. This makes them even drier.

• The driest climates are deserts. Most occur between about 15° and 30° latitude. This is where dry air sinks to the surface in the global circulation cells. Deserts receive less than 25 centimeters (10 inches) of rain per year. They may be covered with sand dunes or be home to sparse but hardy plants (see Figure below). With few clouds, deserts have hot days and cool nights.
• Other dry climates get a little more precipitation. They are called steppes. These regions have short grasses and low bushes (see Figure below). Steppes occur at higher latitudes than deserts. They are dry because they are in continental interiors or rain shadows.

Dry climates may be deserts or steppes. Sonoran Desert in Arizona (22° north latitude), Utah Steppe (40° north latitude).

Temperate Climates

Temperate climates have moderate temperatures. These climates vary in how much rain they get and when the rain falls. You can see different types of temperate climates in Figure below.

• Mediterranean climates are found on the western coasts of continents. The latitudes are between 30° and 45°. The coast of California has a Mediterranean climate. Temperatures are mild and rainfall is moderate. Most of the rain falls in the winter, and summers are dry. To make it through the dry summers, short woody plants are common.
• Marine west coast climates are also found on the western coasts of continents. They occur between 45° and 60° latitude. The coast of Washington State has this type of climate. Temperatures are mild and there’s plenty of rainfall all year round. Dense fir forests grow in this climate.
• Humid subtropical climates are found on the eastern sides of continents between about 20° and 40° latitude. The southeastern U.S. has this type of climate. Summers are hot and humid, but winters are chilly. There is moderate rainfall throughout the year. Pine and oak forests grow in this climate.

How do these climates differ from each other?

Continental Climates

Continental climates are found in inland areas. They are too far from oceans to experience the effects of ocean water. Continental climates are common between 40° and 70° north latitude. There are no continental climates in the Southern Hemisphere. Can you guess why? The southern continents at this latitude are too narrow. All of their inland areas are close enough to a coast to be affected by the ocean!

• Humid continental climates are found between 40° and 60° north latitude. The northeastern U.S. has this type of climate. Summers are warm to hot, and winters are cold. Precipitation is moderate, and it falls year round. Deciduous trees grow in this climate. They lose their leaves in the fall and grow new ones in the spring.
• Subarctic climates are found between 60° and 70° north latitude. Much of Canada and Alaska have this type of climate. Summers are cool and short. Winters are very cold and long. Little precipitation falls, and most of it falls during the summer. Conifer forests grow in this climate (see Figure below).

Conifer forests are typical of the subarctic.

Polar Climates

Polar climates are found near the North and South Poles. They also occur on high mountains at lower latitudes. The summers are very cool, and the winters are frigid. Precipitation is very low because it’s so cold. You can see examples of polar climates in Figure below.

• Polar tundra climates occur near the poles. Tundra climates have permafrost. Permafrost is layer of ground below the surface that is always frozen, even in the summer. Only small plants, such as mosses, can grow in this climate.
• Alpine tundra climates occur at high altitudes at any latitude. They are also called highland climates. These regions are very cold because they are so far above sea level. The alpine tundra climate is very similar to the polar tundra climate.
• Ice caps are areas covered with thick ice year round. Ice caps are found only in Greenland and Antarctica. Temperatures and precipitation are both very low. What little snow falls usually stays on the ground. It doesn’t melt because it’s too cold.

Polar climates include polar and alpine tundra. Polar Tundra in Northern Alaska (70° N latitude), Alpine Tundra in the Colorado Rockies (40° N latitude).

Microclimates

A place might have a different climate than the major climate type around it. This is called a microclimate. Look at Figure below. The south-facing side of the hill gets more direct sunlight than the north side of a hill. This gives the south side a warmer microclimate. A microclimate can be due to a place being deeper. Since cold air sinks, a depression in the land can be a lot colder than the land around it.

Hills and other features can create microclimates.

Lesson Summary

• Climate types are based on temperature and precipitation. A major climate type and its living things make up a biome. Climate types include tropical, temperate, continental, and polar climates.
• A microclimate is a local climate that differs from the major climate type around it. For example, the south-facing side of a hill may have a warmer microclimate.

Lesson Review Questions

Recall

1. Define biome.

2. Identify two types of tropical climates.

3. How do steppes differ from deserts?

4. Where are Mediterranean climates found?

5. Describe a marine west coast climate.

6. What is permafrost?

7. What is a microclimate? Give an example.

Apply Concepts

8. Identify the type of climate in the green-shaded areas in the Figure below. Describe this type of climate.

Think Critically

9. Some tropical climates have rainforests. Others have grasslands. What explains the difference?

10. Compare and contrast two types of continental climates.

Points to Consider

Earth’s overall climate is getting warmer.

• Why is Earth’s climate changing?
• How is climate change affecting living things?