1. Meeting Ecological Challenges
Read the lesson title aloud to students.

2. Learning Objectives Explain the concept of ecological footprint.
Identify the role of ecology in a sustainable future.
Click to reveal each of the learning objectives.
To build a background understanding of what is meant by a “global commons,” explain the concept of a village commons.
Tell students that many old English villages once had shared pastures called “commons” where any villager could graze cattle. Grass there belonged to no one, so everyone grazed as many cattle as possible.
Ask: What do you think happened?
Answer: Overgrazing usually caused the commons to deteriorate until there was nothing left for cattle to eat. Then everyone was out of luck.
Point out that this has been called “the tragedy of the commons.”
Ask: Why didn’t villagers preserve their shared resource?
Answer: Because each villager thought only about his or her own immediate needs, rather than about their neighbors’ needs or about their shared future.
Explain that today, several “tragedies of the commons” face humans. Ocean fisheries and the atmosphere are common resources that have no borders. They belong to everyone and to no one. And they pose humanity’s biggest challenges.
Distribute the worksheet for this lesson and tell students to use it to create a table to compare the challenges associated with the ozone layer, fisheries, and global climate. Tell them to note the problem observed, the causes identified, and the solutions implemented.
Make sure students understand that at the end of the presentation, they should be able to explain the concept of an ecological footprint and identify the role of ecology in a sustainable future.

3. Ecological Footprints
The total land and water needed to provide the resources for and absorb the wastes of an individual or population
Explain to students that to preserve ecosystem functions, each of us and our governments must recognize that long-term survival of our species depends on resource bases that are limited. Some cities and states and some countries are learning to address local ecological challenges through local actions.
Tell students: Ecological science can help us understand our ecological impact and shape our future. Although science doesn’t have all the answers, ecological research can play an important role in helping us toward a sustainable future.
Explain that ecologists often use a concept called an ecological footprint to help us understand our impact. An ecological footprint is the total area of functioning land and water ecosystems needed to provide the resources an individual or population uses and to absorb the wastes that individual or population generates. Ecological footprints include resources such as energy, food, water, and shelter, and wastes such as sewage and greenhouse gases.
Tell students that the food they eat, the miles they travel, and the electricity they use all contribute to their—and the population’s—ecological footprint.
Call on students to identify items representing uses of resources in the analogy, such as the boat, airplane, electric plant, and planted fields.
Ask students to describe how the natural resources used for each item shown contribute to the community’s ecological footprint.

4. Comparing Footprints
The average American has an ecological footprint over four times larger than the global average.
Tell students that there is no single, universally accepted formula for calculating ecological footprints.
Explain that although determining absolute ecological footprints is difficult, footprints can help make useful comparisons among populations, as shown in this illustration. To determine a country’s ecological footprint, researchers calculate the footprint for a typical citizen and multiply that by the size of the population.
Tell students that according to one calculation, the average American has an ecological footprint over four times larger than the global average. Each average American uses almost twice the resources used by an average person in England, more than twice the resources used by an average person in Japan, and almost six times the resources used by an average person in China.
Direct students to examine the map shown. Tell them that this world map shows each country in proportion to its ecological footprint.
Tell students: The United States has an ecological footprint about twice the world’s average.
By contrast, the African nation of Zambia has a footprint a little over one-fourth the global average.
Ask for a volunteer to locate Zambia.
Click to highlight Zambia.
Tell students to compare each country’s footprint size to its actual size on the smaller map below.
Click to point out this comparison for the United States.
Make sure students understand the color key and why the continents are shaped as they are.
Ask: Why is North America so much larger than South America on this map?
Answer: Areas that have larger relative footprints are shown to be bigger than areas that have smaller footprints.
Tell students to compare the ecological footprints of regions and countries with the lesson opener image of Earth from space. (Return to slide 1 if necessary.)
Ask: What do you notice about the areas with the largest ecological deficits?
Answer: These areas—United States, Western Europe, South Korea, and Japan—are also the areas with the densest lights as seen from space, which makes sense because those areas are the most developed.
Ask: How have you contributed to your ecological footprint today?
Answer: waking up to a clock radio, turning on lights, using water to take a shower, flushing the toilet, preparing food for breakfast, wearing manufactured clothing, talking on a rechargeable cell phone, riding in a car to school, listening to music on a battery-powered MP3 player, sitting in a heated classroom

5. Ecology in Action Recognizing a problem Researching to determine cause
Guiding changes in behavior
Tell students that the health of the biosphere depends on our ecological footprints, global population growth, and application of technology to solve problems. Ecological data, properly collected, analyzed, and applied, can help us make useful decisions.
Ask: How can ecological research guide us toward a sustainable future?
Answer: Research can have a positive impact on the global environment by recognizing a problem in the environment, researching that problem to determine its cause, and then guiding changes in our behavior based on scientific understanding.
Click to reveal each step in turn.
Explain to students that the following case studies illustrate the potential impact of scientific research on society and the environment.
The first case shows how completing these three steps can lead to a positive result for humanity and the biosphere. In the second two cases, we have progressed through some, but not all, of those steps.

6. Case Study: Atmospheric Ozone
Recognizing the Problem: “Hole” in the Ozone Layer
The ozone concentration over Antarctica has been decreasing.
Explain to students that between 20 and 50 kilometers above Earth’s surface, the atmosphere contains a relatively high concentration of ozone called the ozone layer. This natural ozone layer absorbs harmful ultraviolet (UV) radiation from sunlight, so it acts like a global sunscreen.
Ask: What are the risks of UV radiation?
Answer: Overexposure to UV radiation causes sunburn and can also cause cancer, damage eyes, and lower resistance to disease. UV radiation can also damage plants and algae.
Tell students: The scientific study and worldwide response to a problem with the ozone layer led to one of the first effective and workable responses by the international community to an ecological challenge involving a global commons.
Point out that the first step was recognizing the problem.
Explain that beginning in the 1970s, satellite data revealed that the ozone concentration over Antarctica was decreasing during the southern winter. This area of lower ozone concentration was called an “ozone hole.” It isn’t really a “hole” in the atmosphere, of course, but an area where ozone concentration is unusually low. For several years after the hole was discovered, ozone concentrations continued to drop, and the hole grew larger and lasted longer each year.
Ask: What does the figure show?
Answer: The figure shows the progression from 1981 to 1999.
Ask for a volunteer to explain what the image shows. Guide the volunteer to pointing out the dark blue areas.
Click to emphasize the “ozone hole” progression.
Explain to students that the darker blue color in the later image indicates that the ozone layer had thinned since 1981.

7. Case Study: Atmospheric Ozone
Researching the Cause: CFCs
CFCs act as catalysts to destroy ozone molecules.
CFCs were widely used:
as propellants
as coolants
in plastic foam production
Explain to students that in 1974, a research team led by Mario Molina, F. Sherwood Rowland, and Paul J. Crutzen demonstrated that gases called chlorofluorocarbons (CFCs) could act as catalysts to destroy ozone molecules under conditions in the upper atmosphere. This research earned a Nobel Prize in 1995.
Tell students: CFCs were once widely used as propellants in aerosol cans; as coolant in refrigerators (like those shown in the image), freezers, and air conditioners; and in the production of plastic foams.

8. Case Study: Atmospheric Ozone
Changing Behavior: Regulation of CFCs
191 countries signed the Montreal Protocol.
Tell students that once CFC research was published and accepted by the scientific community, the rest was up to policymakers and industry. In this case, their response was positive and effective. Following researchers’ recommendations, 191 countries signed the Montreal Protocol, an agreement that banned most uses of CFCs.
Manufacturers found alternatives to CFCs for most purposes. Because CFCs remain in the atmosphere for a long time, their effects on the ozone layer are still visible. But ozone-destroying halogens from CFCs have been steadily decreasing since about 1994, as shown in the chart. These data show that the CFC ban has positive long-term effects. In fact, current data predict that the ozone hole will fluctuate in size from year to year but should disappear around the middle of this century.
Ask: What trend does the graph show between 1996 and 2007?
Answer: The atmospheric concentration of ozone-destroying halogens steadily decreased.
Click to highlight this information.
Ask: What caused this trend?
Answer: the regulation of CFCs

9. Case Study: North Atlantic Fisheries
Recognizing the Problem: More Work, Fewer Fish
The mass of cod caught has decreased since the 1980s.
Explain to students that ocean fisheries are another global commons facing a challenge. From 1950 to 1997, annual world seafood catch grew from 19 million tons to over 90 million tons. This growth led some to believe that the fisheries were endless, renewable resources. Then, dramatic declines in fish populations proved otherwise. National and international organizations are working on this challenge, but economic issues have made effective response difficult.
Tell students: Annual catches of cod have been rising and falling since the 1800s. Until the mid-twentieth century, some of that fluctuation was caused by natural variations in ocean ecosystems. But then, beginning in the 1950s, larger boats and high-tech fish-finding equipment made the fishing effort both more intense and more efficient. Catches rose for a time.
Click to highlight this portion of the chart.
Tell students: But then catches began falling. This time, catches continued to fall.
As shown in the graph, the total mass of cod caught has decreased significantly since the 1980s despite the most intense fishing effort in history.
Focus students’ attention on the information in the graph to discuss the case study of North Atlantic fisheries. Make sure students understand the meanings of “biomass” and “catch.”
Click to highlight the biomass portion of the chart.
Explain that biomass refers to the total mass of cod in the North Atlantic, while catch refers to the total mass of cod caught by the fishing boats.
Ask: What caused the sharp increase in the catch between the late 1970s and the early 1980s?
Answer: Larger boats and high-tech fish-finding equipment made fishing more efficient, and the catch grew larger.

10. Case Study: North Atlantic Fisheries
Researching the Cause: Overfishing
Fishing had caused the rates of commercial fish populations to exceed their rates.
death
birth
Tell students that fishery ecologists gathered fish population data including age structure and growth rates. Analysis of these data showed that fish populations and total cod biomass were shrinking. These declines in fish catches were the result of overfishing. Fish were being caught faster than they could be replaced by reproduction.
Ask for a volunteer to fill in the missing summary information.
Click to reveal the correct answers.
Tell students: In summary, fishing had caused the death rates of commercial fish populations to exceed their birth rates.
Explain that by the 1990s, cod and haddock populations had dropped so low that fisheries biologists feared these species might disappear forever.
Ask: How do you know the decline in catch in the late 1980s was due to overfishing and not to something else, like a decline in fishing?
Answer: The biomass line on the graph shows that there was a sharp decline in the number of cod in the Atlantic during that time.

11. Case Study: North Atlantic Fisheries
Changing Behavior: Regulation of Fisheries
U.S. National Marine Fisheries Service created guidelines for commercial fisheries:
specific number and size of fish
the Sustainable Fisheries Act (1996)
Tell students: The U.S. National Marine Fisheries Service used its best data to create guidelines for commercial fishing. The guidelines specified how many fish of what size could be caught in U.S. waters. In 1996, the Sustainable Fisheries Act closed certain areas to fishing until stocks recover. Spawning areas in places like Georges Bank are closed seasonally to allow fish to reproduce.
Explain to students that these regulations are helping some fish populations to recover, but progress is slow for several reasons. International cooperation on fisheries is not as good as it was on the ozone challenge. Huge fleets from other countries continue to fish areas outside U.S. territorial waters. Some are reluctant to accept catch limits because regulations that protect fish populations for the future cause job and income losses today. Both large companies and individual boat owners often take out very large loans to buy boats and other equipment, and those loans must be repaid.
Tell students that estimating size and population structure of oceanic fish populations is not an exact science, but it’s the best we have. Yet if fish stocks disappear, the result will be even more devastating than temporary fishing bans.
Explain that the challenge is to come up with sustainable practices that help maintain fish populations over the long term while keeping the fishing industry alive.
Discuss the regulation of fisheries.
Ask: Why do you think restoring fish populations has been a slow process?
Answer: Student answers will vary.

12. Case Study: Climate Change
Recognizing the Problem: Global Warming
Physical evidence:
an increase in average worldwide temperature
a rise in global sea level
Explain to students that global climate is the ultimate global commons. It is also the ultimate test of the ability of scientific research to impact society and the environment.
Global climate involves cycles of matter that affect the energy balance of the entire biosphere. Climate also includes external factors, such as temperature and precipitation, that affect everything humans do—from building homes and growing food to manufacturing, driving cars, and generating electricity.
Tell students that the most reliable information on climate comes from the Intergovernmental Panel on Climate Change (IPCC). The IPCC is an international organization established to provide the best possible scientific information on climate change. IPCC reports contain data and analyses that have been agreed upon and accepted by 2,500 climate scientists from around the world and the governments participating in the study.
Tell students that ongoing IPCC reports confirm many independent scientific observations that global climate is changing. Researchers first noticed global warming—an increase in average worldwide temperature. Remember that winds and ocean currents shape climate and are driven by differences in temperature across the globe. So it isn’t surprising that more than temperature is changing. IPCC reports, along with many others, also note changes in humidity, winds, rainfall, and other abiotic external environmental factors. Many lines of evidence, both physical and biological, contribute to our current understanding of climate change and its effects on the biosphere.
Point out to students that the physical evidence of global warming shown in the graphs comes from several sources. These graphs show that Earth’s average temperature is rising and that sea levels are rising.
Click to emphasize the rising temperatures.
Tell students: Between 1906 and 2005, Earth’s average global temperature rose 0.74°C. The largest changes are occurring in and near the Arctic Circle. Average temperatures in Alaska, for example, increased 2.4°C over the last 50 years.
Click to emphasize the rising sea levels.
Satellite data confirm that Arctic sea ice, glaciers, and snow cover are decreasing. Sea level has risen since 1961 at a rate of 1.8 mm each year. This increase is caused by warmer water expanding and by melting glaciers, ice caps, and polar ice sheets.
Direct students to study the graphs.
Make sure they understand the source of the data.
Then, talk about the physical evidence of global warming.
Ask: Between 1860 and 1920, did the land-surface air temperature change?
Answer: Yes, but the fluctuations weren’t large enough to change the approximate average temperature.
Ask: What has been the trend in global sea level since about 1920?
Answer: The trend since about 1920 is a rising sea level.

13. Case Study: Climate Change
Recognizing the Problem: Global Warming
Biological evidence:
Many populations are experiencing rising temperatures.
Explain that small changes in climate that humans barely notice can be important to other organisms.
Tell students: Remember that each organism’s range is determined by its tolerance to external factors such as temperature, humidity, and rainfall.
Point out that if temperature rises, ecologists hypothesized that organisms would move away from the equator toward cooler places and from warm lowlands to cooler, higher altitudes. In addition, plant flowering and animal breeding are often cued by seasonal changes. If warming is occurring, researchers hypothesized that organisms should respond as though spring begins earlier.
Click to reveal the results of studies.
Tell students: Data from studies covering more than 1,700 plant and animals species confirm those hypotheses, because many populations are responding as though they are experiencing rising temperatures. The yellow-bellied marmot in the picture, for example, is ending hibernation over a month earlier than it used to.
Address the following misconception: climate versus weather
Some students may doubt predictions about climate change because they have witnessed many incorrect predictions about the weather. Explain that there is a big difference between weather and climate. Predicting atmospheric conditions in local areas is very difficult, but climate is much more predictable.

14. Case Study: Climate Change
Researching the Cause: Models and Questions
Greenhouse gases increased over the last 200 years.
Models predict average global temperatures will rise.
Explain that the first question for researchers is: “What is causing climate change?”
Earth’s climate has changed often during its history. So researchers had to test several hypotheses about whether current warming is part of a natural cycle of astronomical and geological changes or is caused by human activity.
Click to reveal the first bullet point and highlight.
Tell students: Data from many studies confirm that concentrations of carbon dioxide and other greenhouse gases have increased significantly over the last 200 years, as shown by the chart and graph.
Point out that several additional kinds of data support the hypothesis that this increased concentration is due to the burning of fossil fuels combined with the cutting and burning of forests. These activities disrupt the carbon cycle by adding carbon dioxide to the atmosphere faster than natural processes remove it. The vast majority of climate scientists agree that human activity is strengthening the natural greenhouse effect, causing the biosphere to retain more heat.
Explain that researchers use data to construct computer models to predict temperatures.
Click to reveal the second bullet point.
Tell students: Predictions of these models vary and are open to scientific debate. The most widely accepted models predict that average global temperatures will rise by the end of the twenty-first century 2°C to 6.4°C above their year 2000 level. Heat waves are expected to become longer and more intense in places that already experience them. Cold nights with frost will become less frequent in some places.
Tell students: Most models predict that North America will experience changes in rainfall and snowfall. The snowpack in our western mountains is likely to decrease, and some areas in the west and southwest can expect more droughts during the summer growing season. Some changes are likely to stress ecosystems ranging from tundra and northern forests to coral reefs and the Amazon rain forest. Rising sea level may flood some coastal ecosystems and human communities.
Talk about how much warming is expected to occur and what the consequences will be.
Ask: What are the possible effects for towns and cities along the coasts of the United States?
Answer: Because of the rise in sea level, some towns and cities may be flooded.
Ask: Why is it possible that global warming will cause the Sahara Desert to become greener?
Answer: Global warming will cause changes in weather patterns throughout the world. If weather patterns change in a certain way, the Sahara could receive more rain than is normal today.
Turn students’ attention to what might occur in your local region as a result of global warming. Have them predict changes for humans and for other organisms native to the region.

15. Case Study: Climate Change
Changing Behavior: The Challenges Ahead
Responses to climate change must be informed by scientific
and .
data
analysis
Explain to students that scientific research is informing efforts that are preserving the ozone layer and attempting to restore fisheries. Climate change poses much greater challenges. Scientists have been trying to communicate their studies of climate change to the public for decades in efforts to help the global community recognize and respond to climate change. Researchers continue to gather data and try to develop more accurate models.
Ask for volunteers to complete the sentence.
Click to reveal the correct answers.
Note that the answers can be in either order.
Tell students: Responses to climate change must be informed by scientific data and analysis, but they will also require input from economics and many other fields beyond biology.
Point out that changing behaviors involved in our use of fossil fuels will be difficult and will rely on new technology for renewable energy and increased energy efficiency. Other changes in behavior will also be major but may be somewhat easier. For example, changing patterns of rainfall and temperature may suggest that farmers should switch to growing different crops in different places.
Tell students: At international climate summits, countries are trying to work out agreements that will protect our global commons. As our government and the rest of the world work through these challenges, remember that the purpose of ecological science is not to predict disaster or to prevent people from enjoying modern life. The goal of science is to have positive impact on society and the environment. The world is our island, and our species depends for its survival on renewable resources provided by healthy ecosystems.
Explain that the hope is that scientific information and human ingenuity can help us preserve the quality of life on Earth for all.

16. Overview
The average American leaves an ecological footprint _____ the global average.
one-fourth the size of
one-half the size of
two times larger than
over four times larger than
Research can have an impact on the environment by:
recognizing a problem
Review with students the key points of this lesson.
Ask for a volunteer to answer the multiple-choice question.
Click to reveal the correct answer.
Remind them that according to one calculation, the average American has an ecological footprint over four times larger than the global average.
Ask for volunteers to fill in the list of ways in which research can have a positive impact on the global environment.
Click to reveal the correct answers.
Tell students: Research can have a positive impact on the global environment by:
- Recognizing a problem in the environment
- Researching that problem to determine its cause
- Guiding changes in our behavior based on scientific understanding
researching that problem
guiding changes in behavior

17. Student Worksheet Answers
Remind students that they should used their worksheet to compare and contrast challenges associated with the ozone layer, fisheries, and global climate as they gained information during the lesson.
Give students time to work individually or in small groups to review and complete their notes. Encourage interaction and the sharing of ideas.
Worksheet Answers:
Student answers will vary, but they should include information on ecological footprints and their impact on the ozone layer and global climate. The impact of fishery management should be included, as should the impact of global warming.
Details and notes on each of these should be included in the student’s table.