Earth's Climate

Science, Grade 6


Table Of Contents: Earth’s Climate

1. Climate and Its Causes

2.1. What Is Climate?
The weather is the condition of the atmosphere at a specific time and place. The climate is the average weather of a region over an extended period of time. If you travel around the world, you will find many different climates.
2.2. Causes of Climate
Temperature and precipitation are the most important factors that impact climate. Temperature is influenced by latitude, altitude, large bodies of water, and ocean currents. Precipitation is influenced by winds and mountains.
2.3. Latitude Affects Temperature
The latitude of a region affects temperature. The sun’s radiation is most concentrated at the equator, resulting in warm temperatures. In polar regions, temperatures are much colder because the same amount of energy is spread across a larger amount of land.
2.4. Altitude Affects Temperature
Regions that are located at higher altitudes experience cooler temperatures. The air on top of a mountain is much cooler than the air at the base of a mountain because air temperature gets colder as you move to higher elevations in the troposphere.
2.5. Oceans and Lakes Affect Temperature
Oceans and large lakes influence the climate. Water heats and cools more slowly than land, helping moderate the temperature of nearby land. The California coast has mild temperatures due to warm air blowing from the Pacific Ocean.
2.6. Ocean Currents Affect Temperature
The ocean has surface currents that help distribute temperatures around the globe. Polar currents carry cool water toward the equator, and tropical currents carry warm water away from the equator. For example, the Gulf Stream creates warm air temperatures around southern Iceland and significantly impacts the climate of this region.
2.7. Prevailing Wind Affects Moisture
Prevailing winds blow primarily in one direction and influence the moisture in a region. Winds that travel across water are humid because they carry water vapor. Winds that travel across broad regions of land tend to be dry.
2.8. Mountains Affect Precipitation
Mountains play a role in the climate. Moisture-laden clouds that run into mountains are pushed upward. As the clouds cool, rain or snow occurs. When the clouds move down the other side of the mountains, the dry air creates a desert climate. This effect is called a rain shadow.
2.9. Seasons and the Earth’s Tilt
Seasonal weather occurs because the Earth is tilted on its axis as it rotates around the sun. Throughout the year, the Northern and Southern hemispheres will be either pointing toward or away from the sun. Land near the equator has year-round warm and humid climates, while regions further from the equator experience more dramatic temperature changes.

2. Pause and Interact

3.1. Review
Use the whiteboard tools to complete the activity.

3. Climate Zones and Biomes

4.1. Climate Zones
Climate zones are geographic regions with relatively similar temperature and precipitation. The Earth has three major climate zones—tropical, temperate and polar.
4.2. Biomes
The areas within a climate zone can be further divided into biomes. A biome is a large geographic region that is characterized by a particular climate and the organisms that live in this region.

4. The Tropical Zone

5.1. Tropical Zone
The tropical zone extends from the equator to 23.5 degrees in latitude, north and south. Temperatures are typically hot in this zone. The three biomes found in this region include rain forests, savannahs and deserts.
5.2. Tropical Rain Forest
Tropical rain forests have high rainfall and high temperatures throughout the year. Although rain forests are lush, the soil is nutrient-poor because frequent rains wash away the topsoil. More plant and animal species are found here than in any other biome.
5.3. Tropical Savannah and Desert
A tropical savannah is a hot grassland that has a wet and dry season. A savannah covers a large region across central Africa. Tropical deserts are hot and dry. Many desert animals and plants have adapted to live in this extreme environment. The soil is nutrient-poor in both of these biomes.

5. The Temperate Zone

6.1. Temperate Zone
The temperate zone is located between 23.5 and 66.5 degrees latitude, north and south. Although the biomes in the temperate zone experience four distinct seasons, they have a wide variety of temperatures and precipitation. The four biomes include the forest, grassland, chaparral and desert.
6.2. Temperate Forest and Grassland
Temperate forest biomes have plenty of rain and are known for their evergreen and deciduous trees. The soil is fertile due to the dropping and decaying of leaves every year. Temperate grasslands have little rainfall, and very few trees grow in these biomes. This biome has the most fertile soil, and many crops are grown in these areas.
6.3. Temperate Chaparral and Desert
Temperate chaparral regions are cool and wet in the winter and hot and dry in the summer. Primarily short evergreen shrubs grow in the chaparral’s rocky, nutrient-poor soil. The temperate desert has a year-round dry climate and the soil is nutrient-poor. This type of desert biome is hot during the day and cool overnight.

6. The Polar Zone

7.1. Polar Zone
The polar zone extends beyond 66.5 degrees latitude, both north and south. It is the zone with the coldest year-round climate. The tundra and taiga are the two biomes found in this zone.
7.2. Tundra
The tundra has very short growing seasons, with almost 24 hours of light during the summer and 24 hours of dark during the winter. The very top layer of soil will thaw, but remain muddy. All the soil below this is frozen, and is known as permafrost.
7.3. Taiga
The taiga is located south of the tundra, and is characterized by its coniferous forests. The soil is acidic, and few plants grow on the forest floor. The boundary between the tundra and taiga is called the tree line.

7. Pause and Interact

8.1. Review
Use the whiteboard tools to complete the activity.
8.2. Biomes
Follow the onscreen instructions.

8. Climate Change

9.1. Ice Ages
Scientists use geologic evidence to study how the Earth’s climate has changed over time. The Earth has experienced several ice ages, which are periods of cooling that last thousands of years.
9.2. Glacial and Interglacial Periods
The most recent ice age occurred about two million years ago. Throughout an ice age there are episodes called glacial and interglacial periods. Glacial periods experience global cooling and massive ice sheets develop and move south. Interglacial periods experience global warming and the edges of glaciers melt and retreat.
9.3. What Caused the Ice Ages?
Theories that attempt to explain the occurrence of ice ages include the Earth’s changing motion, continental movement due to plate tectonics, volcanic ash in the atmosphere, and the impact of an asteroid hitting the Earth’s surface. A combination of these theories may have influenced climate change over geologic time.

9. Global Warming

10.1. The Earth is Getting Warmer
The Earth is currently in an interglacial period of warming. Many scientists believe that human activity is playing a role in global climate change. An increase in the greenhouse effect could be contributing to warmer temperatures.
10.2. Greenhouse Effect
A natural phenomenon called the greenhouse effect heats the Earth’s surface. This effect occurs when energy from the sun reaches the Earth as electromagnetic radiation and causes material to heat up. Atmospheric gases absorb and re-radiate this heat, keeping it close to the Earth’s surface.
10.3. Increased Atmospheric Carbon Dioxide
The burning of fossil fuels and massive deforestation are both human activities that are contributing to an increase in atmospheric carbon dioxide levels. Increases in carbon dioxide and greenhouse gases enhance the greenhouse effect.
10.4. The Impact of Global Warming
Global warming leads to environmental changes that impact worldwide climates and biomes. Changing regional weather patterns, increasing global temperatures, and melting polar ice caps are evidence of a current global warming trend. These changes may affect crop growth, flooding, desert formation, and a rise in sea level.

10. Ozone depletion

11.1. A Thinning Ozone Layer
The ozone layer in the stratosphere protects the Earth from harmful ultraviolet radiation. In the 1970s scientists noticed a thinning layer of ozone over Antarctica. Human-produced chemicals called chlorofluorocarbons (CFCs) were the primary cause of this ozone depletion.
11.2. Ozone Layer Recovery
Through an international effort, the production and use of CFCs has decreased, but the ozone layer may not recover for many years. This is just one example of how humans and pollution can have a significant effect on the Earth’s atmosphere.

11. Vocabulary Review

12.1. Vocabulary Matching Review
The Earth is currently in an interglacial period of warming. Many scientists believe that human activity is playing a role in global climate change. An increase in the greenhouse effect could be contributing to warmer temperatures.

12. Virtual Investigation

13.1. Earth's Seasons
Seasonal weather varies at different locations on Earth and impacts the climate of a region. Seasons are caused by the tilt of the Earth's axis as it revolves around the Sun. In this virtual investigation you will explore the sunlight's yearly patterns at different locations on Earth. Study the sunlight's patterns and analyze the data about each location to learn more about the relationship of seasons, the Earth's tilt, and the Earth's yearly orbit around the Sun.

13. Assessment

14.1. Earth's Climate