The Bigger Picture: Global Climate · 2018-09-07 · chapter 5 • THE BIGGER PICTURE: GLOBAL...

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chapter five

The Bigger Picture: Global Climate

A fter completing the investigations in Chapter 4, you should realize that your sense of what is “normal” weather at any particular time of the year may actually be very different from someone living elsewhere. Whether the days are cold or warm, rainy or dry, sunny or partly cloudy, you become used to the conditions you expect in your home place. But what if they started to change?

If you pay attention to the news, you’ve heard much talk about climate. Measurements show that climate change is happening, but there are different projections about what this means. As citizens, it’s hard to know how to react to all these warnings. You may be asking questions such as: Are these warnings valid? Is climate change really going to affect me? Or simply, why should I care?

The story in this chapter is somewhat different from the ones you’ve encountered earlier in the course, because it poses ques-tions not fully addressed in this chapter or even in this course: What is causing the climate to change, and what impact will this have on local communities during your lifetime? You will continue to follow the story of humanity’s quest to understand climate change and its implications as you watch and read news accounts over the coming years. Instead of trying to provide answers, this course will help you develop the basic understandings necessary so that you can assess what you hear about climate change and understand what this might mean to you.

This chapter covers the fundamental factors that cause energy to be absorbed and held in Earth’s atmosphere, and can cause the atmosphere near Earth’s surface to become warmer or cooler over time. In Chapter 6, you’ll look back millions of years into Earth’s history and investigate how these factors, coupled with long-term changes in Earth’s surface features and its orbit, have caused the planet’s climate to be very different in the past from the way it is today.

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eDc earth Science • Unit 2 • atmosphere and climate

Consider Investigate Process

Brainstorming Discuss the following with your partner and be prepared to share your ideas with the class. Don’t worry if you don’t know all the answers at this point. You will explore many of these questions in the next few chapters.

1. Describe what you currently know about climate change, based on what you’ve heard in the media or from previous science classes. a. What evidence do you know of that supports the idea that global

warming is happening? b. What have you heard about the potential impacts of climate change? c. Do you think climate change could affect you? If so, how? d. What are your ideas about what might be causing the global climate

to warm? The true story below is about one community that is already feeling the

effects of a warming climate. Read the story and answer the questions that follow in About the Reading.

WHAT’S THE STORY?

Washing AwayThe residents of Kivalina, a tiny village in Alaska, are feeling threatened by the sea.

Kivalina, a remote island 190 kilometers (120 miles) north of the Arctic Circle, as shown in Figure 5.1, is accessible only by plane or boat during the summer. The Inupiat residents have for generations lived their lives largely independently of other people and have relied on the ocean and land to sustain them. They hunt caribou on the tundra landscape and whales and fish at sea. They’ve adapted their lives to the rhythms of the seasons—the long, cold winters and short sum-mers. Recently, the patterns in their local climate have been changing, and the future for Kivalina doesn’t look good.

Enock Adams, Jr., a resident of Kivalina, considers his words and speaks carefully as he describes their worsening situation: “It’s getting warmer, we know that. We’re right in the middle of this and we know what’s been hap-pening. The sea ice is developing later, so that proves to us that there has been significant change in terms of the weather. Having to deal with it is very frightening. It’s created a situation that we really have no control over.”

Each fall in Kivalina there are storms that blow 20–50 mile winds off the ocean, and these strong winds create huge waves. Normally, a thick layer of

3861 EDPS Earth Science Student Book, Part 1Figure: 3861 EDPS EaSci SB05_01Cronos Pro Regular 8/9

KivalinaArctic circle

50º

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figUre 5.1Kivalina, Alaska, is located in the arctic at a latitude of 67°49ʹ North.

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slush has formed along the shore by the time the storm season arrives in late September early October. This slush buffers the effect of the powerful waves and protects the coastline from erosion. However, in recent years the slush hasn’t been forming until December or January, after the storm season has already been underway for several months. During the fall months, the shore is not protected from the storm waves, and as a result, the soft sand that forms the foundation of this village has been disappearing into the sea (see Figure 5.2).

Residents of Kivalina are wondering what is hap-pening, why it is happening, and what the future holds for their families, friends, and neighbors. Should they move their village away from the ocean and disrupt the way of living they have known for generations? This is one of many stories of communities around the world affected by a changing climate. If you lived in one of these places and you wanted to know the answers, how would you find them? Why are these changes happening, and what can be done about it?1

about the readingWrite your responses to the following questions in your notebook. Be prepared to discuss your answers with the class.

1. The villagers of Kivalina have experienced warmer temperatures recently. Why has this threatened their community?

2. Have you heard of other stories similar to this? Are you aware of any other communities that are feeling the effects of climate change? Describe what you know about this.

3. If you were a resident of Kivalina, what would your concerns be? What questions would you have?

• • • • • • •

Climate is something you take for granted: Most who live in the northern United States and Canada expect to get snow in winter. People who live in the southwestern United States expect it to be hot and dry in summer. You don’t even think about these expectations until the conditions you take for granted start to change. Then you want to know why it is happening and if the changes will last. Scientists have been concerned with these questions, particularly in recent decades, because signs of climate change have appeared. What causes Earth’s climate to be the way it is now, and what can cause it to change? That’s what you’ll explore in this chapter.

figUre 5.2A sandbagged seawall fights erosion from storm waves in Kivalina, Alaska.

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challenge

What factors cause Earth’s climate to be the way it is, and what can cause it to change?

to the residents of Kivalina, the future of their village looks grim. The very existence of their island depends on certain climate conditions, and these seem to be changing. how does earth’s climate work, and what causes it to change? scientists are working hard to find the answers to these challeng-ing questions and so will you in this chapter. You’ll play the role of a Kiva-lina resident and investigate the factors that cause climate to change. Then you’ll gather with your community at a public meeting to discuss what is happening and what should be done.

In this chapter, you’ll explore factors that influence global climate and that can affect communities such as Kivalina. To gather the knowledge you’ll need, investigate how Earth’s atmosphere regulates the planet’s surface temperature. Specifically, explore the following:• How carbon dioxide (CO2) and other greenhouses gases control the amount

of heat energy absorbed by the atmosphere.

• How variations in the materials on Earth’s surface and in the atmosphere control the amount of the Sun’s energy that is reflected back into space.

• How CO2 is added to and subtracted from the atmosphere.

• How negative and positive feedback loops can either stabilize Earth’s climate or accelerate change.

Then pull together what you have learned and prepare your recommendations.

gather Knowledge

Begin by reading about how the Sun delivers energy to Earth and about the role played by the atmosphere in creating conditions on Earth’s surface that are very different from a few miles away in space. As you read this, take notes about the path that light energy takes as it enters Earth’s atmosphere. You’ll use these notes to draw a diagram when you answer the questions in About the Reading at the end.

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reaDinGFollowing the Path of Light EnergyThe temperature of space outside Earth’s atmosphere is −270°C (−454°F). Yet the atmosphere near Earth’s surface is a much more comfortable average temperature of 15°C (59°F). It seems remarkable that the atmosphere could be so effective in pro-tecting Earthlings from the deep cold of space, especially because the atmosphere is very thin, as shown in the view of Earth from the International Space Station in Figure 5.3. In fact, compared to the diameter of the entire Earth, the atmosphere’s thick-ness is like the peel on an apple. If you got in a car and drove straight upward at 97 kph (60 mph), you would reach outer space in just about an hour. Yet the atmosphere has so successfully regulated Earth’s surface temperature that for nearly 4 billion years Earth has remained the only known planet to have supported life.

How does the atmosphere regulate Earth’s temperature? The Sun delivers energy to Earth in the form of light, or electromagnetic radiation. The atmo-sphere controls the amount of energy that is absorbed by Earth and warms it, and the amount that is radiated back into space.

On average, scientists have determined that for every 100 units of light energy falling on Earth, approximately 25 units (25%) are reflected by clouds back into space. Another 25 units (25%) of this light energy is absorbed by the atmosphere. The remaining 50% percent travels to the surface of Earth. Approximately 5% percent of the light energy striking Earth’s surface is reflected off the ground, polar ice, or ocean surface directly back into space. However, most of the light energy that reaches the surface (45% of the orig-inal 100 units) is absorbed into the water or ground. This energy absorbed by Earth’s surface is key to the greenhouse effect, which you will learn about in Activity 1.

The preceding description of what happens to light energy from the Sun is simplified. The percentages given are averages; they actually vary from one part of the globe to another and also vary through time. During Activities 1 and 2 that follow, you’ll explore two of the major factors that influence how much of the Sun’s light energy is absorbed by Earth’s atmosphere (the green-house effect) and how much is reflected back into space (the albedo effect).

figUre 5.3Earth’s atmosphere, although very thin, is what makes Earth habitable for living things.

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about the readingRecord your responses to the following questions in your notebook. Be pre-pared to discuss your answers with the rest of the class.

1. Draw a diagram that shows what happens to the light energy that is trans-mitted to Earth from the Sun, based on the information in the reading.

2. The reading points out that the description of what happens to the light energy from the Sun is simplified and that the percentages of absorbed and reflected light actually vary from place to place on the globe. Based on what you know from previous chapters, explain how and why the amount of energy absorbed by the oceans at the equator varies from the amount of energy absorbed nearer the poles.

3. The reading points out that on average 5% percent of the light energy that reaches Earth from the Sun is reflected off Earth’s surface back into space. Might the amount of light energy reflected vary from one region to another? How and why?

• • • • • • •

In Activity 1, you’ll explore how CO2 and other greenhouse gases control the amount of heat energy that is retained near Earth’s surface.

activitY 1The Greenhouse Effectsetting the stage: what is the greenhouse effect?The composition of a planet’s atmosphere can tell you much about that planet and what it is like on the surface. In fact, as scientists look for life on planets orbiting other stars, the first clues they will find will be in the composition of the alien planets’ atmosphere. Earth’s oxygen and methane are present because life is here and continually replenishing the atmosphere with these gases. It turns out that oxygen isn’t the only gas in Earth’s atmosphere that’s important to humans—there are other gases that are just as crucial to the comfortable life you live on this planet.

To understand what keeps Earth a comfortable temperature for Earthlings, you must focus on the light energy that is absorbed by Earth’s surface. Light energy has a relatively short wavelength, which can pass easily (back and forth) through Earth’s atmosphere. However, most of the light energy that is absorbed into Earth’s surface is transformed into longer-wavelength heat energy (also called infrared radiation), which you can feel but not see. Have you ever tried to walk barefoot on black asphalt that has been in the bright sunlight for sev-eral hours on a summer day? The light energy from the Sun is absorbed by the asphalt and transformed into heat energy, which warms the surface, sometimes making it very hot.

According to a basic law of physics, heat naturally flows from warmer areas to cooler areas. Therefore, the heat energy warming the surface of the


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asphalt begins to rise into the air (you can feel this happening as you stand on the asphalt). This longer-wavelength heat energy rises into the atmosphere, and this time, instead of passing easily through the atmosphere and back into space, some of it is trapped. This is because certain gases in the atmosphere, primarily water and CO2, allow shorter-wavelength light energy to pass through toward the surface easily but tend to trap some of the longer-wave-length heat energy and reradiate it back toward Earth. These heat-trapping gases in Earth’s atmosphere are known as greenhouse gases, and without them, Earth would be too cold for life to survive. The amount of reradiated heat that is trapped by the atmosphere depends on the concentration of green-house gases in the atmosphere. As the concentration of these gases increases, more heat is trapped and the temperature of Earth’s atmosphere rises. The warming that results when heat is trapped near Earth’s surface by greenhouse gases is known as the greenhouse effect.

During this activity, you will consider the composition of Earth’s atmo-sphere, and compare it to Earth’s closest twin in the solar system, Venus.

pre-activity discussionDiscuss the following question with your classmates to help you prepare for the investigation. Record your answers in your notebook.

1. Modify the diagram you drew showing the pathway of light energy from the Sun to show what happens to the longer-wavelength heat energy that is reradiated from Earth’s surface (you can’t show percentages in this case, but you can use labeled arrows to show what is happening).

procedure 1. Working with your group, read the Atmosphere Component Cards care-

fully and share with your group what you know about each gas.

2. As a group, predict the relative amounts of these gases in Earth’s atmo-sphere and arrange the components in order from highest to lowest percentage. Don’t worry if you’re not sure of your answers—use your group’s knowledge from previous classes or outside of school to make your best educated guess.

3. When your group has arranged the Atmosphere Component Cards in what you think is the proper order, show your teacher what you have done. Your teacher will give you a set of Data Cards. Use Card 1: Earth’s Atmosphere to compare the actual measured percentages with your pre-dicted order. Answer these questions in your notebook:a. How close was your educated guess to the actual order of the gases?

Did anything about the order surprise you?b. Why do you think the abundance of some of the gases is not only

shown as a percentage, but also in parts per million?

Materialsfor each Group of StuDentS

• set of 11 atmosphere Component Cards

• set of 5 greenhouse gas data cards

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4. Put aside your Atmosphere compenent Cards and use information from Greenhouse Effect Card 1 and Card 2: Composition of Venus’s Atmo-sphere, to create a table and another type of illustration (such as a graph or diagram) that compares the atmospheric composition of Earth and Venus. Below your table and illustration, write a few sentences summa-rizing the similarities and differences between the atmospheres of Earth and Venus.

5. Using the information in Card 3: Greenhouse Gases, do the following:a. Add labels to the table and illustration to show which gases are green-

house gases.b. How do greenhouse gases behave differently from other gases? What

effect does this have on a planet? Write your answers in your notebook.

6. Study the information you’ve gathered so far, and answer the following questions:a. Which greenhouse gas is found in the highest concentration in Earth’s

atmosphere? In Venus’s atmosphere?b. The CO2 abundance in Earth’s atmosphere isn’t as high as that of water

vapor, which is also a greenhouse gas. However, CO2 has a longer life-time, so it lasts much longer in the atmosphere. Why do you think the lifetime of a greenhouse gas in the atmosphere might matter?

7. Next investigate how differences in the composition of Venus’s and Earth’s atmosphere have affected conditions on their surfaces. Venus is often called Earth’s twin, because it is Earth’s neighbor and is similar in diam-eter. However, the surface conditions are so different that humans would never consider setting up a colony there—for one thing, the surface tem-perature of Venus is hot enough to melt lead! Why is it so different? Is it because Venus is closer to the Sun? Use the information on Card 4: Terres-trial Planet Comparison to investigate how the distance from the Sun relates to the surface temperatures of the terrestrial planets. Do this by drawing a graph to show if there is a clear and predictable relationship between distance from the Sun and surface temperature, and answer the following questions:a. Based on your graph, is distance from the Sun alone enough to explain

the difference in surface temperatures between Earth and Venus?b. What, other than distance from the Sun, could be affecting the surface

temperatures of the terrestrial planets?8. In addition to distance from the Sun and surface temperature, Card 4:

Terrestrial Planet Comparison shows more information about Earth and Venus. Use this information to answer the following:a. Surface pressure is the force per unit area exerted on the surface by

the weight of the air in the atmosphere above. Two factors influence atmospheric pressure: the thickness of the atmosphere and the molecu-lar weight of gases in the atmosphere. Describe what you think it would be like on Earth’s surface if the air were 90 times heavier than on Venus.

b. What questions do you have about the characteristics described in this Card? Do you understand what all of them mean and how they would


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affect your experience on the surface of a planet? Do some additional research to better understand them.

c. Do you see any other atmospheric characteristics that might affect the temperatures on the surface of the two planets? Explain your thinking.

9. Study the diagrams on Card 5: Energy Balance of Earth and Venus, also shown in Figure 5.4. The yellow arrows on these diagrams represent short-wave radiation and the red arrows represent long-wave (infrared) radiation. The thickness of the arrows shows the relative amount of radia-tion. Answer the following questions about Figure 5.4:

a. Why is the arrow showing incoming solar radiation thicker on the Venus diagram than it is on the Earth diagram?

b. How does the amount of sunlight reflected by clouds in the atmo-sphere compare between the two planets?

c. How does the amount of sunlight striking the surface compare between the two planets?

d. Venus’s surface is very hot, so a large amount of infrared radiation is emitted, as you can see by the thickness of the arrow. How much of the infrared radiation emitted from Venus’s surface makes it back into space? (Give an approximate proportion.)

e. Approximately what proportion of the infrared radiation emitted from Earth’s surface makes it back into space?

f. Use the answers to d. and e., and your understanding of the green-house effect to explain how Venus’s surface came to be so much hotter than Earth’s.

figUre 5.4This diagram compares Earth's energy balance with Venus's energy balance. Although much less of the sunlight that strikes the top of Venus's atmosphere reaches the surface, Venus's surface is much hotter than Earth’s, due to a run-away greenhouse effect. The yellow arrows represent short-wave solar radia-tion and the red arrows represent long-wave infrared radiation. The thick ness of each arrow shows the relative amount of radiation (generalized, not to scale).


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AnalysisWith your group, complete the following questions and record your answers in your notebook. Be prepared to share your answers with the rest of the class.

1. Explain in your own words:

a. How can greenhouse gases in the atmo-sphere of a planet affect the temperature of the planet’s surface?

b. How could an increase in greenhouse gases in a planet’s atmosphere cause the climate to change?

• • • •

The greenhouse effect is a key factor linked to global warming. As the concentration of CO2 in the atmosphere increases, more heat is trapped near Earth’s surface. Do rising CO2 levels alone explain the changes in climate that are happening now and what will happen in the future? The operations of Earth’s systems are not quite that simple. There are other factors that influence the amount of heat retained by Earth’s atmosphere, and these factors must be considered as well. In the next activity, you’ll look at how variations in Earth’s surface materials can affect the amount of radiant energy from the Sun that is reflected back into space.

activitY 2The Albedo Effectsetting the stage: what is the albedo effect?Another significant factor affecting Earth’s temperature is the albedo effect. The albedo is the percentage of incoming light energy that is reflected rather than absorbed by a particular surface. In the diagram of Earth’s energy balance you drew earlier in this chapter, you should have shown approximately 25% of the Sun’s light energy being reflected back into space by the clouds and 5% being reflected back into space by Earth’s surface. You know from your own experi-ence that the cloudiness of the sky varies from day to day. This means that the albedo effect, or degree to which the Sun’s radiant energy is reflected, varies as well. The effect of clouds is particularly complex because the water vapor within

Biogeology: Using Greenhouse Gases to Terraform Mars

some scientists have proposed that greenhouse gases could be used to warm the surface of Mars and make it habitable for humans and other earth organisms. solar-powered, greenhouse gas-producing factories could be placed on Mars. Additional factories could be used to simultaneously oxygenate the atmosphere. These machines would mimic photosynthesis by taking in carbon dioxide and releasing oxygen into the atmo-sphere. however, hundreds of these greenhouse gas-producing machines would be needed, and it would take an extremely long time to build up the atmo-sphere. The machines would also need to operate in perpetuity to maintain adequate levels of greenhouse gases in the atmosphere.

some scientists believe a quicker way to introduce greenhouse gases to Mars’s atmosphere would be to hurl large, icy, ammonia-rich asteroids into Mars. This would release large amounts of greenhouse gases and water from beneath mars’s surface. to accomplish this, rocket engines would have to be somehow attached to asteroids from the outer solar system. At 4 km/sec, it would take the rockets 10 years to propel the asteroids to Mars. This would be an incredibly complex process, and the bombardment of the red planet by an asteroid would release energy equivalent to approximately 70,000 one-megaton bombs. terraforming by asteroid smashing would delay human settlement of the planet for centuries.


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the clouds also serves as a potent greenhouse gas. High, thin clouds tend to warm the planet by trapping heat energy and reradiating some of it back toward Earth, whereas low, thick clouds tend to reflect more of the Sun’s energy back into space, having the reverse effect.

The albedo of a particular surface is represented by a number from 0 to 1. A surface with an albedo of 1 reflects 100% of the light energy that strikes it and will appear white. A surface with an albedo of 0 absorbs 100% of the light energy that strikes it and will appear black. A surface with an albedo between these two extremes might be represented (for example) by the number 0.3, which means that it reflects 30% of the light that strikes it.

Just as with the atmosphere, the surface of Earth varies in the degree to which it reflects light energy as well. The albedo is a key variable used by scien-tists in computer models used to forecast weather. Therefore, Earth’s albedo is monitored on a daily basis by satellites.

• • • • • • •

In this activity, you will develop hypotheses about the relative albedo of var-ious Earth surface materials using images of Earth from space. Then, perform an experiment to prove that light-colored surfaces reflect the most light energy.

procedureRecord all observations and answers in your notebook as you work.

part a: studying images of earth

1. Study the satellite images of Earth in Figures 5.5–5.7, and answer the Think About It question that goes with each image.

Think about it 1 Study Figure 5.5, an image of Earth taken by astronauts on the Apollo 17 mission in 1972. Based on what you see in this image, come up with a hypothesis about how the following three types of surfaces rank in terms of their albedo: clouds, land, and oceans. Make it clear which you think has the highest albedo (is the most reflective) and which has the lowest albedo (absorbs the most light energy). Record your hypothesis and the evidence that supports it in your notebook.

figUre 5.5View of Africa and Saudi Arabia from Apollo 17. This picture was taken by the astronauts as they left Earth’s orbit for the moon.

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Think about it 2 Study Figure 5.6, which shows a true- color albedo im-age of Earth taken by the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on NASA’s Terra satellite. This is like the image of Earth taken by Apollo 17 astronauts in Figure 5.5; however, the clouds are removed and Earth’s surface is unrolled to look flat. Based on this image, make a list of various types of Earth’s surface materials (including the oceans and the polar areas) and rank them according to albedo (make it clear which has the high-est albedo and which has the lowest).

Think about it 3 Figure 5.7 shows Earth’s average albedo for March 2005 and includes the cloud albedo. You can see from the color bar at the bottom that the lighter colors on the map represent areas with higher albedo, and the darker blue colors represent areas with lower albedos. Describe the patterns that you see in this image, and write your hypotheses about what causes these patterns.

figUre 5.7Image showing Earth’s average albedo for March 2005, measured by the Clouds and Earth’s Radiant Energy Sys-tem (CERES) instrument aboard NASA’s Terra satellite. White shows areas where Earth reflected the highest percentage of light energy.

figUre 5.6True color albedo image taken by the Moderate Resolution Imaging Spectro-radiometer (MODIS) instrument.


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Look at the image carefully and describe it in as much detail as you can.

part B: albedo experimentRecord all observations and answers in your notebook as you work.

1. Review the items you have available and discuss with your group how you might use these to compare the albedos of different colored materials.

2. Design an experiment to compare the albedos. Your experimental pro-cedures should be clearly written and include:• accurate descriptions/sketches of how the materials will be used• instructions for collecting precise measurements • a data table to record your measurements

3. Write the procedures in your notebook and obtain your teacher’s approval before proceeding.

4. Perform your experiment and record your data.

5. Make a graph of your data and write a brief summary of what you can conclude from your data.

6. Complete the Analysis questions.

AnalysisComplete the following questions and record the answers in your notebook. Be prepared to share your answers with the rest of the class.

1. Were any measurement errors possible in your experiment? Would you do your experiment differently if you did it again?

2. Thinking back to the satellite images in the first part of the activity:a. List the different types of surface materials found on Earth. Which

have an albedo closer to 1? Closer to 0? b. Which types of surface materials vary in extent by season? How would

you expect Earth’s albedo to vary by season?

3. Describe one of the surface materials that could change in extent so that it covers more or less of Earth’s surface over time. Referring to the light energy path diagram you drew, how would you expect this change to affect Earth’s average temperature?

4. Another factor influencing albedo is the angle at which sunlight strikes the surface. When light strikes at a lower angle, more is reflected. How does this factor affect the albedo of different parts of the globe?

5. In the introductory story, residents of Kivalina have noticed that snow and ice cover the water near their island for shorter periods during the winter than in the past. Over time, how would you expect this reduction in snow and ice to affect the region’s average albedo? How would you expect the change in albedo to affect the region’s average temperature?

• • • • • • •

Materialspart B for each Group of StuDentS

• 2 30-ml graduated cups

• 2 thermometers

• 30 ml white sand

• 30 ml black sand

• timer (or access to a clock with a second hand)

• access to sunlight (or light from a 100-watt bulb)


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So now you know that the temperature near Earth’s surface is related to whether energy is reflected into space or trapped by greenhouse gases such as CO2. The more CO2 in the atmosphere, the more heat will be trapped, and the more Earth’s temperature will rise. So where does this CO2 come from? Explore this in the next two activities.

activitY 3Moving Carbon Aroundsetting the stage: carbon in earth’s systemsThe element carbon is one of the essential components of every cell. Did you know that the carbon in your body has been around since before Earth formed 4.6 billion years ago? In fact, it formed in the center of a star that lived and died before Earth’s Sun was formed.

Since the carbon in your body first formed, it has combined with other atoms and changed form many times. It has resided in various parts of Earth— the soil, the rocks, the oceans, living things, and the atmosphere. These parts of Earth’s systems that contain carbon are also known as carbon reservoirs. Table 5.1 shows the approximate amount of carbon that resides in each of Earth’s major carbon reservoirs.

table 5.1: the approximate amount of carbon in earth’s major carbon reservoirs in gigatons (1 gigaton = 1 billion tons)2

Major Carbon reservoirapproxiMate aMount of Carbon (gigatons)

Vegetation 610

soils 1,560

Atmosphere (preindustrial) 600

Ocean mixed layer* 1,000

deep ocean 38,000

sediments and rocks 66,000,000

* Ocean mixed layer: the shallower parts of the oceans where more mixing with air occurs.

The carbon moves in and out of some of these reservoirs (such as vege ta-tion) relatively quickly. On the other hand, carbon typically is stored in other reservoirs—particularly rocks—for very long periods of time. The term carbon flux refers to the amount of carbon that is transferred from one reservoir to another during a given time period.

• • • • • • •

How does a carbon atom get from rocks to the atmosphere? From water to rocks? In this next activity, you’ll investigate the processes that move carbon atoms around.

MaterialspartS a anD c for each team of StuDentS:

• 1 calcium atom (green)

• 3 carbon atoms (black)

• 8 hydrogen atoms (white)

• 10 oxygen atoms (red)

• 20 covalent bonds (white tubes)

part B for each Group of StuDentS:

• 1 bottle of limewater, (ca(oh)2)

• 1 wide mouth bottle with plug-style cap

• 1 small candle

• 1 foil square

• access to matches or lighter


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part a: modeling combustion

1. Use the structural diagrams in Figure 5.8 and the molecular modeling pieces to create one molecule of propane (C3H8), a common fuel, and one molecule of oxygen gas (O2).

2. Model the combustion of propane by:a. Making 4 more O2 models then putting any unused modeling

pieces away.b. Modeling the breaking of the reactant bonds by removing all the

white bonds from the atoms of all six reactant molecules (one C3H8 and five O2).

c. Modeling the formation of the products by reassembling all the bonds and atoms from the “broken” reactant molecules to make as many water (H2O) and carbon dioxide (CO2) molecules as you can.

3. Count up the number of H2O and CO2 molecules you made in Step 2 then complete the chemical equation below that shows the combustion of propane. Write the completed equation in your notebook.

C3H8 + 5o2 ____ Co2 + ____ H2o

part B: producing and sequestering co24. Work in groups of 4. Obtain the Part B materials from your teacher.

5. Place the bottle cap upside down on the table and fill it almost completely up with limewater. Holding the bottle upside down, push it down firmly onto the cap. Then flip the capped bottle right side up. Observe and describe the limewater.

6. Gently shake the bottle 10 times then place it upright on the table. Observe the limewater and record changes, if any, to its appearance.

7. Uncap the bottle. Place the cap on the table and then carefully pour the limewater back into the cap. Place the cap with limewater somewhere safe because you will use it again in Step 10.

8. Place the candle in the center of the foil square as shown in Figure 5.9.

9. Carefully light the candle then hold the bottle upside-down so that the bottle-mouth is 2–5 cm (1–2 inches) over the candle flame. Hold it there for about 20–30 seconds to catch the combustion gases.


H

H

C HH

H

H

C

H

H

C

propane

O O

oxygen

figUre 5.8The molecular structure of propane and oxygen.


candle

flame

foil square

figUre 5.9Setup for producing and sequester-ing CO2 in Activity 3.


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10. Keeping the bottle upside down, quickly, but carefully, move it over the cap filled with limewater and push the bottle down firmly onto the cap.

11. Gently blow the candle out then flip the capped bottle right side up, gently shake it 10 times, and place it upright on the table. Observe the contents and record your observations.

12. Put the bottle someplace safe so it can sit undisturbed while you com-plete Part C.

part c: forming limestone (working in pairs)

13. Use the structural diagrams in Figure 5.10 and the molecular modeling pieces to create one molecule of carbon dioxide (CO2) and one molecule of calcium hydroxide (Ca(OH)2). Put any unused modeling pieces away.

14. Limestone rock is made of calcite molecules (CaCO3). To model lime-stone formation, remove all the white bonds from between all the atoms of the CO2 and Ca(OH)2 molecules.

Reassemble all the bonds and atoms from the “broken” reactant mole-cules into a calcite molecule (CaCO3) and a water molecule (H2O).

15. Write down the chemical equation for the formation of limestone.

16. Observe the bottle of limewater again and record your observations.

AnalysisWith your group, complete the following questions and record your answers in your notebook. Be prepared to share your answers with the rest of the class

1. The combustion of any hydrocarbon results in the production of the same two substances. Name these two substances.

2. What happens when CO2 is mixed with limewater? Explain why you think this happens.

3. CO2 dissolves readily in seawater, which contains abundant Ca2+ ions. What do you think would happen to Earth’s climate if a lot of CO2 were to dissolve from the atmosphere into seawater? Explain why you think this would happen.

• • • • • • •

Carbon dioxide is an important greenhouse gas, and its concentration in the atmosphere is an important driver of climate change. What are the factors that can cause CO2 levels in the atmosphere to rise? What processes in Earth’s systems subtract CO2 from the atmosphere? What types of human activities affect CO2 levels in the atmosphere? In Activity 4, explore these questions.


O HH OCacarbon dioxideO C

calcium hydroxideO figUre 5.10

The molecular structure of carbon dioxide and calcium hydroxide.


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activitY 4Calling All Carbonssetting the stage: the carbon cycleThe element carbon is critical to life on Earth. All living organisms contain many different and essential carbon-based molecules. Food is made from carbon-based molecules. Carbon dioxide (CO2) is needed for plants to survive and if the atmosphere did not have any, the Earth would be much colder, per-haps too cold for living things to survive. However, too much CO2 in the atmo-sphere could make the planet too hot for living things. Several Earth processes work together to cycle carbon from one carbon reservoir to another and to keep the amount in each reservoir stable. There are several major transfer processes that occur constantly that help carbon—most often in the form of CO2—move from reservoir to reservoir. These carbon reservoirs and transfer processes work together to create Earth’s carbon cycle. Because the actual carbon cycle is so vast and complex (it includes every plant, animal, microbe, ocean lake, river, puddle, soil, sediment, volcanic eruption, etc.), it is often simplified to show only the most important reservoirs and processes, as shown in Figure 5.11.

Because the amount of CO2 in the atmosphere is so critical to Earth’s climate, you will focus on how CO2 is added to and subtracted from the atmo-sphere in this activity. Some processes add CO2 to the atmosphere and are called CO2 sources; other processes remove CO2 from the atmosphere and store it in various places called carbon sinks. This movement of carbon from one res-ervoir to another is called the carbon flux and when properly balanced, it keeps the amount of carbon in each place relatively constant. This helps maintain stable conditions in Earth’s biosphere, hydrosphere, atmosphere, and geosphere. figUre 5.11

Simplified diagram of the carbon cycle, showing reservoirs in blue and carbon transfer processes in red.


1950

plant respiration and decomposition

ocean di�usionanimal respiration

combustion during forest fires

volcanism

combustion of fossil fuels

chemical weathering

burial of sediments and fossil fuel formation

oceans

rock

atmosphere

vegetation

soils

rivers

photosynthesis

fossil fuels


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1. With your group, study the information on all 8 Carbon Cards and make sure everyone in your group knows the name of each process and understands how the process works. You might do this by splitting up the cards and explaining the processes to each other.

2. Sort the 7 Carbon Transfer Process Cards into groups, based on whether each process is a CO2 source or contributes to a carbon sink. Record your results.

3. Sort the cards within each group (sources and sinks), in order from highest annual carbon flux to lowest carbon flux. Record your results.

4. Summarize your findings by drawing a table in your notebook with seven rows beneath the headings shown in Table 5.2 below. Then fill in the information.

table 5.2

naMe of proCess

How proCess works

sourCe or sink

annual Carbon flux

5. Write answers to the Analysis questions in your notebook. Be prepared to discuss them with the class.

Materials for each Group of StuDentS

• 1 set of 8 carbon cards

Carbon Transfer Process: Chemical Weathering of Rocks

net effect: removes CO2 from atmosphere and stores it in the ocean

carbon flux: 0.1 billion metric tons/year

rainwater (h2) and carbon dioxide (CO2) from the atmosphere combine in soil and rock crevices on the land to form a weak acid called carbonic acid (h2CO3). This carbonic acid weathers and chemically breaks down the rocks, as shown in figure 5.12, and rainwater washes away dissolved ions. These ions are carried by rivers to the sea where some of them (si+4, Ca+2, and c03

−2) are taken up in the growing shells of microorganisms (CaCO3 and sio2). These shells settle to the bottom of the ocean when they die. The net effect of this entire multistep process is that CO2 is removed from the

atmosphere and stored in the shells of organisms. A generalized chemical equation for this process is

Casio3 + Co2 CaCo6 + sio2rocks from the

atmospherecalcite

in shellsquartz dissolved

in seawater or incorporated

into shells

figUre 5.12Weathered rocks.


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Carbon Transfer Process: Volcanism Associated with Tectonic Plate Processes

net effect: adds CO2 to the atmosphere that was previously stored in rocks

carbon flux: 0.2 billion metric tons/year

rocks of earth’s crust containing carbon are recycled by tectonic plate processes. This carbon is released in the form of CO2 when the rocks are melted, and the gas sepa-rates out and is erupted from volcanoes, such as the one shown in figure 5.13. These volcanoes most commonly occur near plate boundaries, along subduction zones and seafloor spreading ridges. The net effect of this process is that carbon stored in rocks is released in the form of CO2 to the atmosphere.

Carbon Transfer Process: Formation of Fossil Fuels

net effect: CO2 is removed from the atmosphere and incorporated into rocks

carbon flux: < 1 billion metric tons/yearUsually, when living things die, they decompose, releasing the carbon from which they are built to the atmosphere. In some (rare) cases, these organic remains are instead preserved in an oxygen-poor environment such as the bottom of certain ocean basins or in stagnant swamps such as the coal swamp in figure 5.14. These remains accumulate and, over millions of years, are buried and incorporated into rock. heat and pressure transform the preserved organic material into oil, natural gas, and coal. Oil and natural gas form primarily from the remains of microscopic marine organisms. Coal forms from land plants. it is estimated that approximately 100 tons of ancient life is converted to 1 gallon of gasoline. The net effect is to store carbon in the rocks of Earth.

figUre 5.13Mount St. Helens.

figUre 5.14Picture of a coal swamp.


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Carbon Transfer Process: Photosynthesis

net effect: removes CO2 from the atmosphere and stores it in plants

carbon flux: 102 billion metric tons/year

plants such as the one in figure 5.16 remove co2 from the atmosphere and store it. photosynthesis uses co2 from the atmosphere, energy from the sun, and water to produce carbohydrates (sugar) and oxygen. light energy from the sun is stored in the chemical bonds of the sugar molecule. some of these carbohydrates are incorporated into plant tissue, where they are stored. The net effect of this process is that CO2 is removed from the atmosphere and stored in the tissue of plants. A generalized chemical equation for the process of photosynthesis is

6Co2 + 6H2o C6H12o6 (sugar) + 6o2

Carbon Transfer Process: Combustion of Fossil Fuels and Other Organic Matter (such as wood)

net effect: CO2 that was stored in rocks is added to the atmosphere


When fossil fuels such as oil, natural gas, and coal are extracted from Earth and burned (combusted), carbon and hydrogen in the fuel reacts with oxygen from the air to form CO2, water, and heat. The CO2, water vapor, and other by-products are released to the air through smokestacks such as the ones at the coal-burning power plant in Figure 5.15. The heat may be transformed into electricity and transported to people’s homes and businesses for power, or may be transformed into mechanical energy in cars, trucks, or other vehicles. When wood or other organic material is burned, it also releases CO2. The net effect of the combus-tion of fossil fuels and other organic materials is to release CO2 into the atmosphere.

figUre 5.15 Coal-burning power plant.

figUre 5.16: Plants use CO2, water, and energy from the Sun during photosynthesis.


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Carbon Transfer Process: Respiration and Decomposition

net effect: removes carbon from plants and adds CO2 to the atmosphere


respiration (the reverse of photosynthesis) involves the breakdown of sugar using oxygen to obtain energy and building blocks to form new biomolecules. These reac-tions release CO2, water, and energy as products and by-products. respiration occurs in both plants and animals, such as the dog in figure 5.17. another important way that CO2 is added to the atmosphere is decomposition. When organisms decompose, they are consumed mostly by bacteria and fungi, and CO2 is released. The net effect of respiration and decomposition is carbon stored in car-bohydrates within plants and animals is released into the atmosphere in the form of CO2. A generalized chemical equation for the process of respiration is

C6H12o6 + 6o2 6H2o + 6Co2

Carbon Transfer Process: Diffusion of Carbon Dioxide Into and Out of the Ocean

net effect: variable; depends on temperature of ocean

carbon flux: ∼ 92 billion metric tons/year from atmosphere into ocean; 90 billion metric tons/year from ocean into atmosphere

There is a certain amount of CO2 that can be dissolved in seawater. That amount depends on the temperature of the water. Cold water can hold more CO2 than warm water, so cold seawater tends to absorb CO2 from the atmosphere. Warmer water has higher kinetic energy. This higher kinetic energy increases molecular motion, which breaks intermolecular bonds and causes gases to

escape from the solution. Therefore, warm seawater tends to release CO2 to the atmosphere. so the net effect of the oceans on atmospheric CO2 varies with the ocean tem-perature, as shown in figure 5.18. higher latitude oceans tend to remove more CO2 from the atmosphere than they release (although as the water warms, this balance can change), and tropical oceans tend to release more CO2 to the atmosphere than they take up.

figUre 5.17This dog is breathing in oxygen and breathing out CO2.

figUre 5.18Sea surface temperature: The orange areas are the highest temperatures and the dark blue areas are the lowest.


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Analysis Complete the following questions and record your answers in your notebook. Be prepared to share your answers with the rest of the class.

1. List Earth’s major carbon reservoirs.

2. Describe a process that has the net effect of removing carbon from the atmosphere.

3. Describe a process that has the net effect of adding carbon to the atmosphere.

4. Describe a process that both adds carbon to and subtracts carbon from the atmosphere.

5. During the 19th century, much of the forested land area in the eastern United States was cleared for agriculture. What effect would you expect this to have on CO2 levels in the atmosphere? Explain your thinking.

6. If a large volcanic eruption were to occur somewhere on Earth, how would you expect this to affect CO2 levels in the atmosphere?

7. Compare the carbon flux rates of the various carbon transfer processes. Which processes absorb or release CO2 at a lower rate, and which pro-cesses have a higher yearly flux rate?

8. Scientists have related the increased use of fossil fuels by humans to the warming of Earth’s atmosphere that is occurring. Using data from the Carbon Cards and what you’ve learned about the greenhouse effect, explain how increases in fossil-fuel use could cause the climate to warm.

9. Energy can also be produced from biomass, such as corn and sugar cane, and proponents of biofuels say this is a better alternative than fos-sil fuels. Based on what you know about the carbon cycle, what do you think of this idea?

10. Describe and explain other natural events and processes or human activities that could affect CO2 levels in the atmosphere.

• • • • • • •

By now you should understand that, although there’s a clear link between CO2 levels and Earth’s temperature, there are many other factors that need to be considered. This next reading discusses how Earth’s systems can interact to either stabilize the climate or accelerate climate change.


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When the concentration of greenhouse gases in the atmosphere causes more heat to be retained, the warmer temperatures decrease the amount of snow and ice cover in arctic regions, and this can initiate a positive feedback loop (a feedback that tends to accelerate change), as shown in Figure 5.20. From your work in Activity 2, you know that decreases in snow and ice cover lower Earth’s albedo. When more heat is absorbed rather than reflected by the surface of Earth, this tends to increase the temper ature of the atmosphere even more. The warmer temperatures mean that more snow and ice melts, lowering the albedo and raising the tem-perature even more, and so on. These types of positive feedback loops accelerate the warming trend— particularly as the amount of snow and ice decreases and forests expand northward over significant portions of the globe.

Another type of feedback loop also occurs in Earth’s system: a negative feedback loop, which tends to stabilize systems, keeping them from changing. An example of a negative feedback in Earth’s climate system would be when warming temperatures lead to increased evaporation of water. If this evapora-tion leads to the formation of certain types of clouds—generally low clouds—

reaDinGThe Greenhouse Effect, the Albedo Effect, the Carbon Cycle, and Feedback LoopsSince the mid-1800s, when fossil-fuel burning began in earnest, CO2 emis-sions have significantly increased (Figure 5.19). When CO2 levels rise in the atmosphere, Earth’s surface warms, and this warming has a variety of effects within Earth’s systems. Some effects can actually accelerate the warming, making the climate change even faster. Other effects can reduce or reverse the warming trend and stabilize the climate.


1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

0

Mill

ion

met

ric to

ns o

f car

bon

20031751 1779 1807 189118631835 197519471919Years

totalnatural gasoilcoalcement

figUre 5.19Global CO2 emissions from fossil fuel use and cement production between 1751 and 2003.

figUre 5.20As warming temperatures decrease snow and ice cover in northern latitudes, this initiates a positive feedback loop and accelerates the warming trend.


decreased ice/snow extent, forests

migrate northward

decreased albedo (reflectivity)

warming

POSITIVE FEEDBACK ACCELERATES CHANGE


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the clouds tend to reflect more of the light energy from the Sun, cooling Earth’s surface and stabilizing the climate, as shown above in Figure 5.21.

However, the behavior of Earth’s climate system is not simple and easy to predict. Remember, that water vapor is a potent greenhouse gas and tends to trap heat energy radiating from Earth’s surface. Therefore, increased rates of evaporation can also initiate a positive feedback loop, accelerating the rate of global warming. Scientists have found evidence that this type of positive feed-back loop was responsible for the extremely hot conditions that exist today on Venus (although they don’t expect anything so extreme to happen on Earth). Venus may have been partially covered with water (like Earth) early in the history of the solar system. Because it was a bit closer to the Sun, more of this water evaporated into the atmosphere. The water vapor in the atmosphere acted as a greenhouse gas, warming the planet even more, which evaporated more water into the atmosphere. This positive feedback loop eventually warmed the surface so much that all of the surface water boiled away. The water vapor in the atmosphere was broken apart by sunlight and the hydrogen escaped into space, so water can’t form again. As you know from your work with the Carbon Cards in Activity 2, water plays a critical role in storing CO2 in carbon sinks (in the ocean and in rocks). Without water to serve this role, CO2 built up to extremely high levels in Venus’s atmosphere.

Many other factors make it difficult to understand exactly what is happening and what is in store for Earth’s climate. For example, fossil-fuel burning is also a major source of tiny airborne particles called aerosols. These aerosols have greatly increased in the lower part of Earth’s atmosphere since the Industrial Revolution began in the mid-1800s. The aerosols increase the albedo of the atmosphere and tend to have a cooling effect on Earth’s surface. Just how much of an effect these aerosols have is complicated to figure out, because the aerosols are difficult to measure. They vary in size and composition, are dis-tributed unevenly in the atmosphere, and are added to and washed out of the atmosphere in a matter of days.


increased evaporation from

the oceans

surface temperature increases slightly

more low clouds in the atmosphere

increasethe earth’s albedo

surface temperature decreases slightly

decreased evaporation from the oceans

decreased low clouds in the atmosphere

decrease the earth’s albedo

NEGATIVE FEEDBACK STABILIZES figUre 5.21The warming of Earth’s surface can increase evaporation rates, initiating a negative feedback loop and stabilizing Earth’s climate.


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about the readingWrite your responses to the following questions in your notebook. Be prepared to discuss your answers with the rest of the class.

1. Give an example of a positive feedback loop and a negative feedback loop from everyday life. Explain how these feedback loops tend to stabilize or change the conditions.

2. Scientists have determined that large amounts of carbon dioxide, and other greenhouse gases, such as methane, are locked in frozen ground (perma-frost) in arctic regions. As the climate warms, these greenhouse gases are released to the atmosphere. What type of feedback loop (positive or nega-tive) would you expect from release of these gases? Explain your thinking.

3. Describe some factors that make it difficult to predict the future of Earth’s climate.

• • • • • • •

At this point, you’ve gathered a great deal of information about Earth’s cli-mate and the factors that can cause climate to change. Now, pull together what you have learned and prepare to play the role of a resident of Kivalina, partici-pating in a public meeting in your community.

address the challenge

The citizens of Kivalina have called a public meeting to discuss what is hap-pening to their community. They are trying to understand why the climate is changing and make some decisions about what they will do about it.

Members of the community are coming to the meeting with some opinions already formed. Generally, their thinking falls into three categories:

1. “We need to move! Our climate is changing because humans are burning more fossil fuels, and with less ice on the ocean, more heat will be absorbed and it will get even worse. We need to start looking for another home, off the island.”

2. “Don’t worry, we can stay—all will be fine. Our climate has been chang-ing lately, but this is just temporary. The Earth will take care of us—whenever one thing changes, something else happens to bring it back into balance. I think we should just try to hold the sea back by building walls until the situation returns to normal.”

3. “Let’s wait a little longer to make a decision. The climate is complicated, and even if the global temperature is warming, we can’t know what will actually happen in our community in the future. We should wait awhile longer and see what actually happens before we make a decision.”

Now, prepare to attend the public meeting, representing one of the three viewpoints above. Join with others representing the same viewpoint, and get ready to convince your neighbors that your opinion is well founded. To make sure your group is ready, pull together your arguments and evidence, and prepare a written summary. Regardless of what you recommend, your written


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summary must include scientific information relating to all of the following concepts you studied in this chapter:• The greenhouse effect and how CO2 concentrations in the atmosphere can

cause the climate to warm

• Other factors, such as the albedo effect, that affect how much heat is retained near Earth’s surface

• Processes that contribute to or remove CO2 from the atmosphere

• How human activities add to or subtract CO2 from the atmosphere

• How positive and negative feedback loops can stabilize climate or acceler-ate change

Before the public meeting, share your written summary with your class-mates, and read the summaries written by the groups with the other two viewpoints. Remember that your recommendations are being presented to your neighbors, who are not scientists. Convince them that you have a sophis-ticated understanding of this topic, but be sure to explain your information clearly. Think about what helps you understand a topic—use explanations that are precise and easy to understand, and use pictures and diagrams that will make the information clearer and emphasize your key points.


share

You and your classmates will hold a public meeting, playing the role of mem-bers of the Kivalina community. Share your thinking about what the change in climate means for your community and what you should do. It’s important for you to listen carefully to the groups that have a different viewpoint, so that you can come to a consensus about actions your community should take.

discUss

Draw on the knowledge you’ve acquired in this chapter as you discuss these questions with your classmates. Your teacher may also ask you to record the answers in your notebook.

1. Think about how your personal ideas about the Kivalina situation were affected by the other ideas expressed at the public meeting. Describe something someone in another group said that you thought was convincing. a. Did your personal position initially differ from that assigned to your

team? If so, how?b. Did you find that your position changed as you prepared your

presentation?c. Did your position change after you listened to the arguments of the

other groups?


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2. Do you still have questions that need to be answered before you can decide what a community like Kivalina should do?

3. You probably found that you tried to persuade others by emphasizing information that helped your position, and deemphasizing other types of information. Give examples of how this might affect public discus-sion of scientific topics. How might you detect this type of bias?

4. Scientists can say with a high degree of confidence that Earth’s average temperature is rising, but it is very difficult to predict the effect that will have on individual communities. Thinking back to what you learned about regional climates in Chapter 4, why are local predictions so difficult?

5. Earth’s climate has changed significantly in the past, well before humans started burning fossil fuels. There have been ice ages and periods of time much warmer than today. If you wanted to figure out if the current warming trend is actually due to natural causes, how would you investi-gate this? Write a few questions you would have and explain how you would find the answers.

6. This chapter and the previous one provided an overview of many factors that influence regional and global climate. To understand the complex science involved in predicting climate change, you need to understand how all these factors relate to each other and how changes in one might affect the others. Create a concept map that relates the following list of terms to the concept of climate.

input of solar radiation

greenhouse effectalbedo effectocean currentsatmospheric

circulationwater vaporpositive feedbacknegative feedbackconvectioncontinents

oceansHadley cellpolar cellFerrel celllight energy

(shortwave radiation)snow and icecloudsprevailing windsweatherprecipitationmountains

temperaturevegetationdesertclimate zoneslatitudeelevationheat capacitycarbon dioxideheat energy

(longwave, or infrared radiation)

Digging Deeper

The concepts you have been studying in this chapter play out in many dif-ferent ways in the world. If you’re interested in exploring more about these concepts, below are some interesting topics to investigate or research.• Research other greenhouse gases, such as water vapor, methane, nitrous

oxide, nitrogen trifluoride, and ozone. How are they added to and subtracted from the atmosphere? How significant are their effects compared to CO2? Why?


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• Research the concept of an urban heat island. How is this related to albedo? How does this affect climate?

• Look in newspapers and magazines for articles about climate change. Find one article that particularly interests you and research it further. Which sci-entists are referenced in the article? What is their scientific background, and what institution(s) do they work for? See if you can find links to other articles about the same topic and try to learn more. What did you learn that particularly interests you? What questions do you have after researching this article?

review• Earth’s climate system is driven primarily by energy received from the Sun

in the form of light energy, or electromagnetic radiation. Some of this energy is absorbed by the clouds and Earth’s surface, and some is reflected back into space.

• Most of the light energy that is absorbed by Earth’s surface is reradiated as longer-wavelength heat energy. The greenhouse gases in Earth’s atmo-sphere trap the longer-wavelength heat energy, which warms the Earth. Without this greenhouse effect, Earth would not be habitable.

• Earth’s temperature is affected by the level of greenhouse gases in the atmo-sphere. As the concentrations of these gases increase, Earth’s average tem-perature increases.

• Another factor that influences Earth’s temperature is the albedo effect. Albedo is a measure of the percentage of incoming light energy that is reflected. Surfaces with an albedo of 1 reflect 100% of the light energy and will appear white. Surfaces with an albedo of 0 absorb all the light energy that strikes them and will appear black.

• Most of the surfaces struck by sunlight in Earth’s atmosphere, land, and oceans have albedos between these two extremes. As Earth’s albedo changes—the amount of heat energy absorbed versus reflected—the tem-perature at Earth’s surface rises and falls. This causes regional, seasonal, and long-term global changes in Earth’s temperature.

• Scientists relate the current global warming trend to increased levels of CO2, a greenhouse gas, in the atmosphere. CO2 is added to and subtracted from the atmosphere by way of a variety of human-induced and natural processes. Carbon continually cycles among vegetation, soils, the atmo-sphere, the ocean, sediment, and rocks via processes that occur over long and short time periods.

• CO2 is transferred into and out of the atmosphere over the short term via photosynthesis, respiration, the diffusion of CO2 into (and out of) the ocean, and the combustion of fossil fuels and organic material. Other pro-cesses also add CO2 to the atmosphere over the short term, such as the burning or logging of forests and the melting of permafrost.


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• CO2 is transferred into the atmosphere over the long term by the volcanic activity associated with tectonic plate processes. CO2 is removed from the atmosphere over the long term by the chemical weathering of rocks and the formation of rocks containing fossil fuels, such as coal, oil, and natural gas. These fossil fuels form over millions of years from the remains of plants and animals.

• Large amounts of carbon are stored as fossil fuels in rocks within Earth’s crust. Scientists believe CO2 levels are currently rising in the atmosphere because of the increased use of fossil fuels since the Industrial Revolution. These fossil fuels took millions of years to form, but the CO2 is released in a very short time period via combustion.

• Earth’s climate system is affected by negative and positive feedback loops. Negative feedbacks have a stabilizing effect and tend to keep conditions the same. Positive feedbacks are destabilizing and tend to cause a change in conditions.

• Earth’s climate is not determined by one factor but by multiple interacting factors that vary through time. To predict how changes in any one variable, such as albedo or the level of greenhouse gases, will affect climate in the long run requires an understanding of the complex interactions of many aspects of Earth’s climate system.

aSSeSSment1. Which of the following best describes how greenhouse gases raise the

average temperature of Earth?a. They allow more light to penetrate the atmosphere.b. They are naturally hotter than other, nongreenhouse gases.c. They allow in short-wavelength light energy but prevent some of the

long-wavelength heat energy from leaving the atmosphere.d. They have a very high albedo, which traps heat energy.

2. The walls of a building are to be painted to reflect as much light as pos-sible. What color should they be painted?a. whiteb. redc. blackd. pink

3. On a warm sunny day, you will feel cooler wearing light-colored clothes because theya. reflect more light energy.b. prevent sweating.c. are not as heavy as dark clothes.d. let more air in.


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4. Rank the following surfaces from lowest to highest albedo:a. temperate forestb. desertc. oceand. polar ice

5. Carbon can be stored in:a. vegetationb. rocksc. the atmosphered. all of the above

6. The following is an example of a process that subtracts CO2 from Earth’s atmosphere:a. photosynthesisb. volcanismc. combustiond. respiration and decomposition

7. The following is an example of a process that adds CO2 to Earth’s atmosphere:a. volcanismb. respiration and decompositionc. both a and bd. neither a nor b

8. Scientists have proposed that the burning of fossil fuels increases the concentration of CO2 in the atmosphere. This is becausea. the burning of fossil fuels is creating a hole in the ozone layer.b. humans are burning fossil fuels at a much higher rate than fossil

fuels are formed.c. fossil-fuel combustion creates particulate air pollution, which

reflects more sunlight.d. chemical weathering processes are releasing CO2 into the

atmosphere.

9. Draw a diagram of the incoming light energy from the Sun that shows its absorption and reflection by Earth’s atmosphere and by Earth’s sur-face. Use arrows to indicate direction and relative amounts.

10. What is the albedo effect and why is it important?

11. Scientists have documented that global warming is causing the melting of ice at high latitudes. Describe how this could initiate a positive feed-back loop.

12. As the temperatures near Earth’s surface warm, this can lead to increased evaporation rates and cloud formation. Describe how the increased formation of clouds could initiate a negative feedback loop.

13. Is it possible that the increased formation of clouds could also lead to a positive feedback loop? Explain your answer.

The Bigger Picture: Global Climate · 2018-09-07 · chapter 5 • THE BIGGER PICTURE: GLOBAL...

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Transcript of The Bigger Picture: Global Climate · 2018-09-07 · chapter 5 • THE BIGGER PICTURE: GLOBAL...