Title: Carbon Dioxide and Global Temperatures Through Time

Overview & Outcomes:

The processes by which carbon dioxide is removed from the atmosphere and reservoired in "sinks" was the topic of Investigations Lesson 11. This lesson provides students will come to understand that climate change has been a natural part of the Earth's history and give reasons why the Earth's climate might change. Also, they will have an opportunity to critically evaluate the strongest evidence for global warming, and explore two opposite points of view currently held by scientists; that global warming will have negative consequences for life or that it will not. Human activities that contribute to global warming through carbon dioxide production are the topic of the next lesson, Investigations Lesson 13.

This lesson helps learners:

• interpret graphs showing increasing average global temperatures in the past 450,000 years.

• correlate increasing global temperatures with increasing concentrations of atmospheric carbon dioxide in the past 160,000 years.

• analyze current data that reveals increasing concentrations of atmospheric carbon dioxide over the past 30 years.

• describe the negative and positive consequences that may result from global warming.

• analyze the point of view held by some scientists that global warming will cause negative consequences for life.

• analyze the point of view held by some scientists that global warming will not have negative effects.

• understand that climate change has been a natural part of the Earth's history and give reasons why the Earth's climate might change.

The concept map shows model relationships among concepts this lesson seeks to develop. Concepts introduced in this lesson are bolded on that concept map and concepts from other lessons are in plain text (not bolded).

Background Notes for the Teacher:

To determine how the temperature of the Earth has changed over thousands of years, scientists study ice cores from the polar caps. Snow accumulates in these regions and changes to ice, in which a unique record of precipitation, air temperature, atmospheric composition, variations in solar activity and volcanic irruptions is preserved. In addition, the age of the parts of the ice core can be determined so that the variables of interest can be dated.

Air temperature is derived by analyzing oxygen isotopes in the cores. Most naturally occurring elements may exist as different isotopes, which are basically a variation in the mass of the atom in the element. While the number of protons (atomic number) in an atom's nucleus remains constant, the number of neutrons may vary, which produces different isotopes. For example, oxygen atoms always have eight protons, but the number of neutrons may range from 8-10, resulting in three different oxygen isotopes with atomic masses of 16 (light isotope), 17 and 18 (heavy isotope). The basis of isotope analysis is that the relative concentrations of the three isotopes of oxygen in air depending on the climatic conditions, and so isotope concentrations may be linked to temperature. The relationship between isotopes and temperature is that the lower the air temperature, the less "heavy" oxygen (O18) present.

The amount of CO2 (and other greenhouse gases) in the atmosphere is also recorded in the ice. As the ice forms air bubbles trap a "sample" of the atmosphere. Scientists can take a core and by analyzing the air trapped in the bubbles produce a record of atmospheric CO2 levels over time.

The average temperature of the atmosphere has risen from approximately 58o F in 1860 to approximately 59o F in 1990. While the average temperature has fluctuated over that 130 year period, overall, there has been a consistent rise. Scientists are concerned about this increase in temperature, not only because it is increasing steadily, but also because we are in one of the warmest periods for Earth's history (see AVERAGE GLOBAL TEMPERATURES IN THE RECENT AND DISTANT PAST). The temperature of the Earth has changed from about 54o F to 60o F over the past 450,000 years. This 6o F change was in the surface temperature of the ocean. Scientists think the average air temperature changed by about 9 F or 10 F. (The surface temperature change of the oceans was less because polar ice caps insulate the ocean.)

Because of the cyclic pattern of temperature change, some scientists say Earth will soon cool off. Others say human burning of fossil fuels may cause the average global atmospheric temperatures to rise an additional 2o F to 9o F by the middle of the next century making Earth hotter than it has ever been in the last 450,000 years. To realize how this small increase could result in dramatic differences in habitability, consider the situation about 500 years ago when the average world temperature dropped about 2o F. The "Little Ice Age" began converting Greenland from green to white (ice and snow). Also, temperatures were 9o F to 10o F lower during the last major Ice Age (which ended ten thousand years ago) than the current average temperature.

There is now indisputable evidence that global levels of carbon dioxide are increasing in the Earth's atmosphere (see ABUNDANCE OF CARBON DIOXIDE IN THE ATMOSPHERE MEASURED AT MAUNA LOA, HAWAII). Data from the Mauna Loa Observatory in Hawaii show a steady increase in atmospheric concentrations of carbon dioxide over the past 30 years. Peaks and valleys on the graph represent seasonal variations. The valleys correspond to summertime when active terrestrial plants are removing CO2 from the atmosphere through photosynthesis. During the fall and winter, plants are less active and atmospheric CO2 increases. It is the overall increase, however, that is significant.

Some scientists believe that if human activity producing carbon dioxide continues and average temperatures rise 2o F to 9 F, global warming could occur. Potential consequences include melting of the Southern Polar ice cap and mountain glaciers raising sea levels by a few inches or a few feet. Increased flooding could result and devastate low-lying coastal areas such as Bangladesh. Summers would probably be hotter with longer and more frequent droughts. This would also lead to changed agricultural patterns. Plants could become more vulnerable to pests and diseases. Also, depending on how quickly global warming occurs, forests and plants may not be able to migrate successfully in the direction of the preferred temperature range. Loss of wildlife habitats may also occur wiping out species that cannot adapt and disrupting the balance of ecological systems. Human health would be threatened. High temperatures lead to stress, especially for those with respiratory diseases and the elderly. The demand for air conditioning could lead to more carbon dioxide being added to the atmosphere.

Other scientists believe that the increased carbon dioxide will lead to the discovery of crops that grow well in carbon dioxide.

Additional Teacher References.

1. Caplan, R. (1990). Our Earth, Ourselves. New York: Bantam Books. p 16 - 24.

2. Ennis, C. and Marcus, N. (1994). Biological Consequences of Global Climate Change.. Global Change Instructional Program.

3. Hocking, C., Sneider, C., Erickson, J., and Golden, R. (1990). Global Warming and the Greenhouse Effect.. University of California at Berkeley: LHS Gems.
   a) See charts on pp. 19, 61, and 138.
   b) See readings on pp. 142 - 143.

4. Huff, D. (1954)How to Lie with Statistics. New York: W.W.Norton & Co.

Materials:

For the class.

1. Overhead of ABUNDANCE OF CARBON DIOXIDE IN THE ATMOSPHERE MEASURED AT MAUNA LOA, HAWAII

For each group.

1. AVERAGE GLOBAL TEMPERATURES IN THE RECENT AND DISTANT PAST
2. Study guide to the above
3. Articles that offer both points of view (LETTERS TO THE EDITOR included)

For each student.

1. GLOBAL TEMPERATURES AND CARBON DIOXIDE
2. Study guide to the above
3. Article that outlines potential consequences of global warming (AS THE WORLD WARMS and THE POTENTIAL CONSEQUENCES OF GLOBAL WARMING included)
4. Study guide to the above (two enclosed)

Preparation:

1. Prepare overhead.
2. Reproduce handouts.

Instructional Procedures: (2 Days, 40 minutes each)

Day 1. (40 minutes)

1. Put students into cooperative learning groups. To each group, distribute the graph, AVERAGE GLOBAL TEMPERATURES IN THE RECENT AND DISTANT PAST, and study guide. Make sure students understand the axes by answering questions one and four on the study guide as a class.

2. Share answers in a class discussion. Help students critically analyze the data pointing out that some scientists feel the Earth will soon cool off (according to the cyclic pattern of temperature change), while others feel the Earth will soon be hotter than it's ever been in the past 450,000 years.

3. Distribute GLOBAL TEMPERATURES AND CARBON DIOXIDE and the accompanying study guide to each student to complete individually.

4. Share answers in a class discussion. Help students critically analyze data and emphasize the graphs represent a strong correlation between average global temperatures and concentration of carbon dioxide in the atmosphere.

5. Next, display the overhead, ABUNDANCE OF CARBON DIOXIDE IN THE ATMOSPHERE MEASURED AT MAUNA LOA, HAWAII. Ask students to explain and interpret results in a class discussion. They should conclude that this is strong indisputable evidence that CO2 levels have been rising over the past 30 years, and that global warming could be occurring. Help students explore possibilities for the seasonal fluctuations.

Homework Assignment. Distribute a global warming resource article (AS THE WORLD WARMS and THE POTENTIAL CONSEQUENCES OF GLOBAL WARMING included) and accompanying study guides to each student as homework.

Day 2. (40 minutes)

Put students into groups and have them compare answers from the homework assignment. They should complete any unanswered questions and be prepared to share answers in a class discussion.
1. In a class discussion, emphasize potential negative consequences of global warming.

2. Next, present the point of view held by some scientists that global warming will not have negative consequences. Students, in groups, should read the point/counterpoint article suggested or one chosen by the teacher (LETTERS TO THE EDITOR included). Encourage students to critically evaluate the articles by looking at how factual the material is and who the authors might be.

3. In a class discussion, emphasize the two points of view.

Optional.

1. If a storyboard is used, connect the increased carbon dioxide to the Industrial Revolution of the middle 1800s.

2. Instead of, or in addition to, reading an article outlining negative implications of global warming, show the video, After the Warming, Part 11. This video portrays life in 2050. Global warming has occurred resulting in climate change. The Northeast has become tropical while the South has become dry and barren. Flooding and starvation have occurred in low-lying coastal areas. Technology-rich Japan has become a dominant country in a world that has adjusted to global climate change but wishes it had changed lifestyles to prevent these changes.

Assessment/Portfolio Items:

• AVERAGE GLOBAL TEMPERATURES IN THE RECENT AND DISTANT PAST study guide
• GLOBAL TEMPERATURES AND CARBON DIOXIDE study guide
• Article study guide

Journal Entry.

Group Members:

1._________________________________

2._________________________________

3._________________________________

4._________________________________

Using the data provided in the accompanying graphs, please answer the following questions.

1. On the top graph, what is the independent variable on the x-axis (horizontal)?

   What is the dependent variable on the y-axis (vertical)?

2. What has happened to the average temperature of the Earth over the past 130 years?

3. What has been the range of temperatures (lowest to highest) over the 130 years?

4. On the bottom graph, what is the independent variable on the x-axis?

   What is the dependent variable on the y-axis?

5. During the past 450,000 years, would you say that the Earth has been generally warmer than now, or colder than now?

6. What has been the change in surface temperature of the oceans (lowest to highest) over the past 450,000 years?

7. How many warm periods or "interglacials" have there been in the past 450,000 years?

8. About how long has the earth been in its current "warm" period?

9. Referring to the top graph, how much has the atmospheric temperature changed in the past 130 years?

10. Does the data from these two graphs support that global warming is going to occur?

Name__________________________________________

1. On the top and bottom graphs, what is the independent variable on the x-axis?

2. On the top graph, what is the dependent variable on the y-axis?

3. On the bottom graph, what is the dependent variable on the y-axis?

4. The top graph shows how the global temperature has varied from 160,000 years ago almost up to the present. Notice the line in the graph stops before "0" years, which is today. We will say this line stops around the year 1800. Over the past 160,000 years, how many degrees colder has the temperature been than in the year 1800?

5. Over the past 160,000 years, how many degrees warmer has the temperature been than in the year 1800?

6. In the last 160,000 years, when was it at least as warm as in the year 1800?

   Look at the bottom graph. Analysis of air bubbles trapped in the same layers of ice shows the concentration of carbon dioxide during the same period. The vertical scale shows the concentration of carbon dioxide in the atmosphere (in parts per million) over the last 160,000 years. Notice again that the line in the graph stops before "0" years. Again, we will say this line stops around the year 1800.

7. In the last 160,000 years, when was there at least as much carbon dioxide in the air as there was around the year 1800?

8. Comparing the upper and lower graphs, what do you observe about the relationship between global temperature and carbon dioxide content of the atmosphere during the past 160,000 years?

9. Suggest an explanation for the relationship that you observe between the Earth's temperature and the concentration of carbon dioxide gas.

10. Does this data support a strong correlation between increasing global temperatures and increasing concentration of atmospheric carbon dioxide? Why or why not?

    ---

    THE POTENTIAL CONSEQUENCES OF GLOBAL WARMING

    Name___________________________________

    1. What effect will global warming have on the following?

       a. ice caps and glaciers?

       b. oceans?

       c. coastal areas?

       d. plant growth?

       e. agricultural patterns?

       f. clouds?

       g. water resources?

       h. forests?

       i. biodiversity?

       j. human health?

    2. What effect might global warming have on certain crops?

    ---

    AS THE WORLD WARMS

    Name__________________________________

    1. How much has the Earth's average temperature risen since the 1850s?

    2. Why do you think Congress was more willing to listen to the warning of scientists during the summer of 1988 than before?

    3. What were the five hottest years recorded before 1988?

    4. Scientists use sophisticated computer models to make predictions. Using these models, scientists have predicted that certain areas will be hardest hit by temperature changes. List those areas.

    5. How much of a temperature rise are scientists predicting and over what time period (how many years)?

    6. Will all regions experience the same increases? Explain.

    7. How are the oceans predicted to react to rapid climate change and how might these ocean changes affect weather?

    8. Describe some of the potential effects warming will have on plant and animal species.

    9. How might global warming affect farming?

    10. What health risks are associated with extreme temperatures?

    ---

Dear Editor,

I think that scientists should know better than to present hypotheses to the public and get everyone excited before they can give us all the facts. This whole idea that increasing the carbon dioxide in the Earth's atmosphere will cause major problems is over blown, in my opinion. A hypothesis like "global warming" - the idea that increased levels of carbon dioxide will produce an enhanced greenhouse effect, raising temperatures with dire consequences for the planet - may have some positive aspects that are being overlooked.

Didn't we all learn in science class that plants need carbon dioxide to photosynthesize and grow? With higher levels of carbon dioxide plants and trees will grow faster and larger. These benefits are no secret to farmers, foresters, and nurserymen who have been adding carbon dioxide to their greenhouses for years. Studies have been done that show with higher levels of carbon dioxide, vegetables mature earlier, bear larger fruit, and produce more fruit. Rice, wheat, barley, oats, corn, sugar, and rye all show increases in crop yield. Even potatoes, yams, and peas have responded with higher yields.

Let's be responsible in looking at this issue. Many people are aware that higher levels of carbon dioxide are a benefit to plants. So before we panic about this topic, let's make sure we have all the evidence to consider.

Sincerely,

A Concerned Citizen

Dear Editor,

I wish to write in response to a recent letter in your paper concerning discussing global warming responsibly. I agree that as citizens we need to be well informed about environmental issues that are altering our planet.

The author of the letter in question proposed that increased levels of carbon dioxide would make it easier for plants to photosynthesize. As a result the plants would grow faster and larger. The author neglected to mention that the types of plants that benefit most significantly from higher levels of carbon dioxide are often the weeds that can crowd out valuable food crops. Also, as Jack and the Bean Stalk found out, bigger is not always better. The larger size fruits and vegetables that were mentioned have been shown to be lower in nutritional value and more susceptible to insect damage. In this case more is actually less! The benefits to some plants from increased carbon dioxide levels do not necessarily mean benefits for the planet.

We must examine both the positive and negative aspects of this issue and think on a global scale.

Sincerely,

Another Concerned Citizen

Click Here to go to Investigations Lesson 13: Lifestyles and Global Warming-Any Connection?