CO2: How Much Is Too Much?


Students will investigate the probable causes of global warming, with an emphasis on the role played by carbon dioxide emissions. They will then solve a number of word problems related to carbon dioxide emissions.


The atmosphere of our planet is composed of layers of gases. The bottom layer, which we breathe, includes nitrogen (about 79%), oxygen (about 20%), carbon dioxide (less than 1%), and other gases, called trace gases. This layer is called the troposphere. Solar radiation, or sunlight, passes through Earth's atmosphere and is absorbed by animals and plants, and by water and land. Once absorbed, the energy from the sun returns to the atmosphere as infrared radiation. Some of this radiation passes back into space, but much of it is trapped in the atmosphere by what are called greenhouse gases.

Any gas that absorbs infrared radiation in the atmosphere is called a greenhouse gas. Greenhouse gases are concentrated in the troposphere, which is the bottom layer of our atmosphere. These gases include water vapor, carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), halogenated fluorocarbons (HCFCs), ozone (O3), perfluorinated carbons (PFCs), and hydrofluorocarbons (HFCs).

Greenhouse gases function much like the glass windows of a greenhouse: they allow sunlight to enter the atmosphere and warm Earth but prevent heat from escaping. Without greenhouse gases, Earth would on average be colder by 60 degrees Fahrenheit—too cold to support life as we know it.

The crucial role played by greenhouse gases in keeping Earth warm enough to sustain life is called the greenhouse effect. But if the greenhouse effect becomes stronger, our planet could become warmer than usual. Even a little extra warming may cause irreparable problems for humans, plants, and animals.


Over the past 100 years, Earth has warmed by about one degree Fahrenheit. This average increase in our planet's temperature is called global warming. A one-degree increase may not sound like much. But in fact, this extra warming may be responsible for some changes in weather patterns we are now seeing in many parts of the world, such as a rise in sea level, prolonged and sometimes deadly heat waves, and more frequent and severe storms.

Many of the world's leading climate scientists think that human activities are the primary cause of global warming and related changes in climate. In particular, say these scientists, as Earth's population grows and the use of fossil fuels for energy increases, a greater concentration of heat-trapping gases will continue to build up in our atmosphere.

Carbon dioxide is one of the primary greenhouse gases responsible for global warming. This gas is released when fossil fuels, such as oil and gas, are burned. Scientists calculate that about 6,567 million metric tons of carbon dioxide are released into the atmosphere worldwide each year. Because of our activities, they say, the amount of this greenhouse gas has increased by more than 30 percent in the last 250 years.

What You Need

What to Do

  1. Introduce the related concepts of global warming and the greenhouse effect to students.
  2. Explain that Earth's average temperature has increased by one degree Fahrenheit over the past 100 years.
  3. Add that most climate scientists agree that this increase is mainly due to an increase in carbon dioxide emissions from the burning of fossil fuels such as oil and gas.
  4. Give a copy of the Measuring Carbon Dioxide Emissions worksheet to each student.
  5. Tell students that the solutions to the word problems on this handout depend upon basic mathematical operations, such as multiplication, division, subtraction, or addition.