Global Climate Change 491

In recent years, it seems that almost everybody is noticing evidence of climate change. A person who fishes in the Maldives observes the seas rising higher on the islands’ beaches. A rancher in west Texas suffers a dry spell that lasts many years. A homeowner in Florida cannot obtain insurance against the hurricanes that are becoming more frequent. And, in addition to stories such as these, solid scientific evidence con-firms that Earth’s climate is changing.

evidence of a Warming earth Evidence of global climate change includes rising atmospheric

temperature, precipitation trends, melting ice, and rising seas.

When scientists talk about global climate change, they are referring to many climate characteristics, such as temperature, rainfall, wind patterns, and storm frequency. The term global warming refers specifically to an increase in Earth’s average surface temperature. Global warming is only one aspect of climate change.

In 1988, the United Nations and the World Meteorological Associa-tion established the Intergovernmental Panel on Climate Change (IPCC). The IPCC is made up of scientists and government officials from around the world. The group has published several reports, the most recent in 2007. Hundreds of scientists contributed to the report, and the report was reviewed by 2000 experts. The IPCC has concluded that global warming is indeed occurring, and that human activities have contributed. These conclusions are now widely accepted. Evidence of climate change includes Earth’s surface temperatures, precipitation patterns, melting ice, and ris-ing sea levels.

rising temperatures The IPCC notes that the average atmospheric temperatures near Earth’s surface increased by 0.74°C (1.33°F) between 1906 and 2005. Most of this increase has occurred in the last few decades. To date, the year 2005 was the warmest ever recorded.

LESS

ON 2Climate Change

• Identify evidence of global warming.• Explain three methods used to study climate

change.• State the probable cause of global climate change.

Reading Strategy Construct a concept map that summarizes the evidence that Earth is becoming warmer. Use the green headings in the lesson as the main subtopics in your map.

Vocabulary global climate change, global warming, proxy indicator, climate model, fossil fuel

Guiding Question: What evidence shows that global climate change is occurring, and why is it happening?

FOCUS Watch the ABC News video Climate Change in Our Backyards, which shows where the effects of climate change are visible in the United States. Use this video to launch a discussion about how changes occurring locally can encourage people to act.

16.2 LESSON PLAN PREVIEWreal World Students research specific examples of evidence of global climate change.Inquiry Students use tree rings to evaluate climate conditions.Differentiated Instruction Struggling students use cause-and-effect diagrams to orga-nize lesson concepts.

16.2 RESOURCESPaper and Pencil Activity, Tracking CO2 and Temperature • Bellringer Video, Climate Change in Our Back-yards • Graph It, Atmospheric CO2 and Temperature Change • Real Data Online • Lesson 16.2 Worksheets • Lesson 16.2 Assessment • Chapter 16 Overview Presentation

492 Lesson 2

Changes in Precipitation Changes in precipitation over the past 100 years have been complex. Some regions of the world, such as the eastern parts of North and South America, are receiving more precipitation than ever before. Other areas, such as the southwestern United States and parts of Africa, are receiving less precipitation than in the past. Meanwhile, heavy rainstorms have increased in both dry and moist regions. These severe storms have caused flooding.

Melting Ice Glaciers are large, slowly moving sheets of ice, and many have taken thousands of years to form. If you go to Glacier National Park in Montana, you can find 26 glaciers. In 1850, there were 150 glaciers in the same area. What happened between 1850 and the present? Much of the glaciers’ ice has melted away (Figure 7). Throughout the world, most glaciers are shrinking or even disappearing.

Warming temperatures are also reducing the snow and ice that cover the North and South poles. For example, along the coast of Antarctica, edges of glaciers called ice shelves extend into the ocean, where they float. One of these is the Larsen Ice Shelf. Since 1986, this ice shelf has lost an area more than three times the size of Rhode Island. Portions of the ice shelf have broken away and melted.

Rising Sea Levels Sea levels are rising in many parts of the world. Residents of the Maldives and other low-lying areas are anxiously watch-ing this trend. The reasons for the rising seas are complex, but the pri-mary cause according to the IPCC is global warming. When sea water becomes warmer, its volume increases, making sea levels rise. To under-stand this process, think of the liquid in a thermometer. As temperature increases, the liquid expands and its level goes up. Water from melting ice also contributes to rising sea levels. If ice sheets in the Antarctic and Greenland continue to melt, the liquid water released will soon become the most important part of global sea-level rise.

FIGURE 7 A Disappearing Glacier Both photos show Sperry Glacier in Montana’s Glacier National Park. Contrast the sizes of the glacier (a) in 1913 and (b) in 2008.

(a)

(b)

Real Data

Global Temperature Since 1850

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0.0

–0.5

20001850 1900 1950Year

Dep

artu

res

in t

emp

erat

ure

(°C

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om t

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1961

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Data from Intergovernmental Panel on Climate Change. 2007. Fourth assessment report.

Global Climate Change 493

Studying Climate Change Scientists study changes in climate by taking direct

measurements, inferring past climate characteristics, and using models to predict the future.

To understand something that is changing, we need to consider its past and present. Then we can use this information to predict what may hap-pen in the future. Scientists who study climate change can check present-day climate directly. But they have also developed clever ways to infer past climates and to predict future change.

Direct Measurement of Present Conditions To study Earth’s cli-mate today, scientists measure conditions directly. You know this if you’ve ever watched a TV weather report. Every day, weather reports give data about temperature, precipitation, wind patterns, and so forth. Over time, records of data such as air temperature and ocean temperature show that modern climate is changing.

Proxy Indicators: Clues About Past Climates To understand how climate is changing today, scientists must learn what climates were like thousands or millions of years ago. Environmental scientists use clues from the past to do this. Proxy indicators are types of indirect evidence that serve as proxies, or substitutes, for direct measurement. Proxy indicators shed light on past climate.

ReadingCheckpoint

What are three kinds of climate data that scientists can measure directly?

Changing Temperature of the AtmosphereThe graph shows how the temperature of the atmos-phere has changed since 1850. The zero point on the y axis marks the average atmospheric temperature for the years between 1961 and 1990. 1. Interpret Graphs What is the overall trend shown

on this graph? 2. Calculate Approximately how much has the

average air temperature changed since 1850? 3. Interpret Graphs Describe the temperature

pattern between 1850 and 1910. 4. Compare and Contrast Contrast the temperature

pattern after 1910 to the pattern before that year. 5. Predict How would the trend shown on the graph

affect the Maldives?

Atmospheric CO2 and Temprature Change

ANSWERS

Reading Checkpoint Sample an-swer: Temperature, precipitation, and wind patternsReal Data1. Global air temperature is rising.2. It has increased by about 0.8°C.3. It fluctuated, but was below the

1961–1990 average.4. Before 1910, the temperature rose

and fell; after 1910 it has risen fairly consistently except for the period between 1940 and 1950.

5. Steadily rising temperatures may cause sea levels to rise, increasing flooding in the Maldives.

494 Lesson 2

▶ Clues in Ice Earth’s ice sheets and glaciers hold clues to climate history. As glaciers and ice sheets form, tiny bubbles of air become trapped inside. Scientists use special tools to remove long columns, or cores, of ice. From these ice cores, scientists can determine such things as greenhouse gas concentrations in the ancient atmosphere and temperature trends. Even trapped soot particles have a tale to tell. The soot indicates how often for-est fires happened. Frequent forest fires can indicate a time of drought.

▶ Clues in Sediments Sediment consists of particles of rock and soil that have been deposited by wind, water, or ice. Researchers take samples from beds of sediment beneath bodies of water. Ancient sediments often pre-serve pollen grains and other parts of plants that grew in the past. Climate influences the types of plants that grow in an area. Therefore, if scientists know what plants grew in a location at a given time, they can often infer much about the climate at that place and time.

ReadingCheckpoint

How can sediments give information about past climates?

▶ Clues in Tree Rings The scientist in Figure 8 is examining rings in an old tree. Tree rings in old trees can be a proxy indicator. A pair of light and dark rings represents one year’s growth. The width of each ring of a tree trunk reveals how much the tree grew in a particular growing season. A wide ring means more growth, generally indicating a wetter year or in some areas a warmer year. By analyzing certain chemical characteristics of tree rings, scientists can get information about hurricane activity that happened hundreds of years ago. Long-lived trees such as redwoods and bristlecone pines can provide indications of precipitation and drought going back hundreds or thousands of years. And like ice cores, tree rings can show past forest fires. A charred tree ring indicates that a fire took place during that year.

Models: Predicting the Future Environmental scientists try to understand how climate functions. They then use this understanding to predict future climate change. To do both these tasks, scientists represent climate processes with computer programs known as climate models.

▶ Climate Models Programs that combine what is known about the atmosphere and oceans to simulate, or imitate, climate processes are called climate models. Climate models use enormous amounts of data and complex mathematical equations. Figure 9 shows the kinds of infor-mation that go into climate models.

FIGURE 8 Tree Rings as Proxy Indicators Scientists can infer some characteristics of past climates by examining tree rings.

ANSWERS

Reading Checkpoint Sediments of-ten preserve pollen grains and other parts of plants. Climate influences the type of plants that will grow in an area. Therefore, scientists can use plant parts trapped in sediments to infer what the climate of the area was like in the past.

Outgoing heat energy

Snowcover

Realisticgeography

Oceanmodel layers

Atmosphericmodellayers

Seaice

Winds

Surface characteristicsand processes (snow cover, vegetation,topography,land use)

Incomingsolar energy

Evaporation of snow

Runo�

Soilmoisture

Ocean currents,temperature, and salt concentration

Precipitation and

evaporation

Global Climate Change 495

▶ Testing Models’ Accuracy Researchers use past climate data to test climate models. They compare the results of the climate model with what actually happened in the past. If a model accurately represents past climate, then it may accurately predict future climate. These comparisons show that global climate models can usually produce reliable predictions.

Finding the Cause of Climate Change

Evidence indicates that global warming has been caused largely by the increase in greenhouse gases in the atmosphere.

In 1958, a scientist named Charles Keeling started to measure carbon dioxide in the atmosphere. Keeling collected air samples every hour at the Mauna Loa Observatory in Hawaii and measured the carbon dioxide in the samples. Since then, scientists have continued to measure levels of carbon dioxide every day at Mauna Loa, around the clock.

The data collected at Mauna Loa show that in 1958, the concentra-tion of carbon dioxide was 315 parts per million (ppm). In contrast, the concentration was 387 ppm in 2009. The carefully recorded data of Keeling and his associates show that carbon dioxide concentration in the atmosphere is increasing. According to the IPCC, the rising levels of carbon dioxide and other greenhouse gases are reponsible for most of the increase in atmospheric temperature. The high levels of greenhouse gases are increasing the greenhouse effect.

FIGURE 9 Climate Model The computer programs for climate models include information about many factors, such as those shown in the illustration. Interpret Visuals In the diagram, where is the runoff coming from?

ANSWERS

Figure 9 From melting snow on the mountains

What are the causes and conse-quences of a warming Earth?Interpretation After students read about the causes of climate change, help them relate this information to their everyday life and actions. Ask each student to write a narra-tive about a day in his or her life. In the narrative, have students identify ways that their actions and choices affect climate change.

BIG QUESTION

500 1000 1500Year

Greenhouse Gas Concentration Through 2005

CO2 (p

pm),

N2O

(ppb

)

0

300

350

400

250

02000

200018001600140012001000800600

0

CH4 (p

pb)

Carbon dioxide (CO2)

Methane (CH4)ppm parts per millionppb parts per billion

Nitrous oxide (N2O)

Data from Intergovernmental Panel on Climate Change. 2007. Fourth assessment report.

496 Lesson 2

1. Use Analogies What is the main cause of the rise in sea level? How is this similar to the behavior of the liquid in a thermometer?

2. Apply Concepts What are climate models? What information do they use to predict what might hap-pen to climate in the future?

3. Relate Cause and Effect How has deforestation contributed to climate change?

4. Industrialization is the process in which a society develops industry and uses machinery on a large scale. Why has industri-alization been a cause of global climate change?

2

Increase in Greenhouse Gases Figure 10 shows that carbon dioxide is not the only greenhouse gas whose concentration has been increasing. Most other greenhouse gases cause more warming than car-bon dioxide, molecule for molecule. However, because carbon dioxide is so abundant, it is the greenhouse gas that is most responsible for global warming. Most scientists agree that the extra carbon dioxide in the atmo-sphere has come from human activities, such as the use of motor vehicles.

Burning Fossil Fuels The main source of extra carbon dioxide in the atmosphere is the burning of carbon-containing fuels, such as oil, natural gas, and coal, for energy. These fuels are called fossil fuels because they formed millions of years ago, from the remains of living things.

Use of fossil fuels has been increasing ever since the beginning of the Industrial Revolution about 200 years ago. The Industrial Revolution started a shift from farming to industry as a way of producing the goods that people use. Industry uses machinery, and machinery runs on fossil fuels. During the last two hundred years, people have used an increasing amount of fossil fuels in homes, cars, and industries. As the fossil fuels release carbon dioxide, the greenhouse effect increases and the tempera-ture of the atmosphere continues to rise.

Changes in Use of Land Land-use changes, such as the cutting of forests, have also caused an increase in greenhouse gases. Remember that plants, including trees, take in carbon dioxide. Therefore, the loss of for-ests contributes to an increase of carbon dioxide in the atmosphere.

FIGURE 10 Greenhouse Gases The graph shows how the concentration of different greenhouse gases has changed over time.

ANSWERS

Lesson 2 Assessment

1. When seawater becomes warmer, its volume increases, just as the liquid in a thermometer expands when it gets warmer.

2. Climate models are computer programs that simulate climate processes. Climate models use past climate data to predict future climate conditions.

3. Deforestation reduces the amount of carbon dioxide taken up by trees. This means that more carbon dioxide, a greenhouse gas, stays in the atmosphere.

4. Industry uses machinery, and many machines run on fossil fuels. Burning fossil fuels adds green-house gases to the atmosphere.