1. Climate, Weather, and Life
Read the lesson title aloud.

2. Learning Objectives Explain how weather and climate differ.
Describe how Earth’s climate and average temperature are determined.
Explain the causes of ocean currents.
Identify the factors that shape regional climates.
Explain the processes involved in climate change.
Click to show each learning objective.
Read the objectives aloud or ask a volunteer to do so.
Ask for a volunteer to describe the conditions outside today. (Don’t ask students to describe today’s “weather.”) Then, ask students whether this is a description of climate or weather. Point out that by the end of the presentation, they should be able to distinguish between climate and weather and describe the factors that combine to produce climate.

3. Climate and Weather
Weather: day-to-day conditions of Earth’s atmosphere
Climate: long-term patterns of temperature and precipitation over many years
Ask students: Is a hurricane an instance of weather or climate?
Answer: weather
Click to reveal the definition of weather.
Explain that atmospheric conditions include temperature, precipitation, sunshine, cloudiness, humidity, and wind, among other environmental factors. Point out that weather can change rapidly and can be difficult to predict. It may be sunny in the morning but rainy in the afternoon.
Click to reveal the definition of climate.
Point out that climate is more predictable. Tell students that climate includes long-term averages of wind, clouds, precipitation, temperature, and extreme weather events such as droughts, floods, and heat waves.
Emphasize that these short-term and long-term variations in external environmental factors determine which organisms grow and reproduce in particular areas. That, in turn, shapes populations, communities, and ecosystems.

4. Solar Energy and the Greenhouse Effect
Smaller amount of energy
passes back through walls.
Energy enters as light.
Ask students how many of them have heard of the “greenhouse effect.” Most, if not all, will undoubtedly have some familiarity with the term. Encourage students to share their understandings of what the greenhouse effect is.
For many students, the term will have negative connotations. Use this misconception as a jumping off point to discuss how a greenhouse works and what its function is.
Ask: Why do people use greenhouses?
Answer: to grow plants in regions or during times of the year that are not favorable to plant growth
Ask: Have you been in a greenhouse? Is it warmer or colder than the outside temperature?
Answer: generally warmer
Click to show the first callout.
Point out that the glass walls of a greenhouse function to let light pass through, trapping much of the energy as heat energy inside the walls.
Click to show the second callout.
Emphasize that the warmer conditions created within the greenhouse make it possible for many plants to survive when and where the natural climate conditions are too cold.
Click to show the third callout.
Much of the energy
is trapped as heat.

5. The Greenhouse Effect on Earth
Sunlight
Light reflected by earth’s surface
Heat lost to space
Heat reradiated
Use the diagram to describe the fate of incoming radiation to Earth’s atmosphere:
Earth receives solar energy from sunlight. Some of that energy is reflected into space, and some is absorbed and converted into heat. Some heat, in turn, radiates into space, and some is trapped within the biosphere. Earth’s average temperature is determined by the balance between the amount of heat that stays in the biosphere and the amount lost to space. This balance is largely controlled by the concentrations of three different “greenhouse gases” in the atmosphere—carbon dioxide, methane, and water vapor.
Help students understand why only some of the radiation represented by arrows in the diagram is reflected by Earth and passes back to space through the atmosphere. Tell them that the arrows represent either visible light or infrared light, which humans perceive as heat. Explain that visible light has shorter wavelengths and can pass through the atmosphere, whereas infrared light has longer wavelengths and can be absorbed by greenhouse gases.
Ask: What part of a greenhouse is analogous to the greenhouse gases in Earth’s atmosphere?
Answer: the glass
Click to reveal the various captions.
Explain that without the greenhouse effect, Earth would be about 30°C cooler than it is today. Point out that these three gases enter and leave the atmosphere as part of nutrient cycles. Their concentration in the atmosphere can therefore be affected by natural and human-caused changes in those cycles. If changes in nutrient cycles raise greenhouse gas concentrations, the atmosphere retains more heat, and Earth warms. If concentrations fall, more heat escapes, and Earth cools.
Greenhouse gases in atmosphere
Some solar energy reflected, some absorbed, and some reradiated as heat
Heat absorbed and reradiated by greenhouse gases and retained in the earth system

6. Latitude and Solar Energy
Explain that Earth’s climate zones are produced by unequal distribution of the sun’s heat on Earth’s surface. Polar regions receive less solar energy per unit area, and therefore less heat, than tropical regions do. The tilt of Earth’s axis causes the distribution of sunlight to change over the course of the year.
Ask: Why are tropical regions generally warmer year-round that temperate regions?
Answer: Tropical regions receive more direct sunlight year-round than temperate regions do.
Have students model the relationship between latitude and solar energy with a globe and flashlight. Ask one student to hold the globe in the same position as the drawing of Earth in the diagram. Ask another student to shine the flashlight straight ahead onto northern North America. Ask the class to observe the size of the area that is receiving light. Then, have the student shine the flashlight straight ahead onto the equator. Point out how a smaller area is now receiving the same amount of light.
Ask for another volunteer to describe the relationship between directness of incoming sunlight and concentration of light.
Misconception Alert: Some students may think that heat from the sun warms Earth. Be sure students understand that at the distance Earth sits from the sun, we cannot feel the heat from the sun. When we experience the sun’s warmth, we are experiencing the transformation of light energy to heat energy.

7. Global Winds Warm air rising Cold air sinking Rising air mass
losing heat
Explain that unequal distribution of heat between the equator and the poles creates winds. This distribution is made possible in large part because of the differences in density between warm air and cold air.
Use the diagram to explain the patterns of air movement: Air that is heated in a warm area expands, becomes less dense, and rises. As this air rises, it spreads north and south, losing heat along the way. As that air cools, it becomes more dense and sinks. At the same time, cold air over the poles also sinks. These movements together create several cells of air that rise, travel north or south, then sink toward Earth’s surface, warm, and rise again. Between places where air sinks and places where it rises, air travels over Earth’s surface, creating winds, as shown in the diagram here. Earth’s rotation causes winds to blow from west to east over the temperate zones and from east to west over the tropics and the poles.
Ask for volunteers to go to the board and draw leader lines from the labels to an appropriate example.
Click to reveal the leader lines that show one possible example of each.
Remind students that all scientific models have strengths and weaknesses. Be sure students understand that the two concepts shown on the map are actually combined phenomena, but they are separated on the diagram for simplicity.

8. Ocean Currents
Point out that unequal distribution of heat between the equator and the poles creates ocean currents as well as winds, and that temperature differences drive ocean currents much the same way that temperature differences drive winds.
Use the diagram to explain that cold water near the poles sinks and flows along the ocean floor. This water rises in a few places through a process called upwelling. Surface water is also pushed by winds, creating surface currents that transport enormous amounts of heat. Air that passes over warm surface currents picks up moisture and heat. Air that passes over cool surface currents is cooled. In this way, winds and surface currents affect important external environmental factors, such as temperature and moisture content, of air above them. These interactions shape weather and climate on land areas near oceans.
Ask: What kind of current is found along the U.S. Gulf Coast?
Answer: a warm surface current
Ask: In what direction do cold currents in the Northern Hemisphere generally move?
Answer: Cold currents in the Northern Hemisphere generally move southward, away from the North Pole and toward the equator.

9. Regional Climate
Air descends, warms, and becomes drier, decreasing moisture.
Air rises and cools, releasing moisture.
Downwind side
Upwind side
Remind students that latitude and heat carried by winds and ocean currents influence regional climate. Point out, however, that Oregon, Montana, and Vermont are at similar latitudes and are affected by prevailing winds that blow from west to east, yet those states have different climates and communities. This is because an area’s location with respect to oceans, winds, and mountains is important.
Use the diagram to describe the effect of coastal mountains on regional climates: As moist ocean air rises over the upwind side of coastal mountains, it condenses, cools, and drops precipitation. As the air sinks on the downwind side of the mountain, it expands, warms, and absorbs moisture.
Click to reveal the labels describing changes in temperature and moisture.
Ask for volunteers to label the upwind and downwind sides of the mountain.
Click to reveal the correct answers.
Illustrate by explaining that Oregon borders the northern Pacific Ocean, where cold surface currents cool and humidify winds blowing over them from west to east. That moist air hits the Cascade Mountains, is pushed upwards, and cools, causing moisture it carries to condense and form clouds. Those clouds drop rain or snow, mainly on the side of the mountains that faces the winds, as seen in the diagram here. The resulting climate is cool, though not bitterly cold, and very wet. East of the Cascades, the air is drier and much warmer in summer, so different plant and animal communities live in Eastern Washington and Montana. Vermont, far to the east, has a different climate from both Eastern Washington and Montana.

10. Changes in Climate
Climate change involves changes in temperature, clouds, winds, patterns and amounts of precipitation, and the frequency and severity of extreme weather events.
Point out to students that changes in climate impact both the atmosphere and hydrosphere as indicated by the model. Also point out that these changes occur in the center of the circle labeled Measurable Changes in the Earth System. All items in the center of the circle can be measured qualitatively.

11. Nonhuman Causes of Climate Change
Not all factors that impact climate change are human caused.
Remind students that there are nonhuman causes of climate change as well. These are indicated in the outer circle of the model at the bottom
Click to reveal each factor and discuss each one. Ask students how they think those factors affect climate.