ANALYZING GREENHOUSE GASES OVER TIME

OVERVIEW

Data on the concentrations of various greenhouse gases in Earth's atmosphere in recent history will be plotted by the students. They will look for trends in the data.

CONCEPTS

• Plotting data allows us to more easily see trends in the data.
• In the case of data taken over a period of time, graphs also make it easier to see what might occur in the future.
• The quantities of several greenhouse gases are increasing in our atmosphere. The production of chlorofluorocarbons (CFCs) is now decreasing.

MATERIALS

• Raw Data (provided below)
  • Carbon Dioxide Concentrations, Mauna Loa, Hawaii in parts per million by volume (ppmv)
  • Methane Gas Concentration in parts per million by volume (ppmv)
  • CFC (chlorofluorocarbon) Production
  • Nitrous Oxide in parts per billion by volume (ppbv)
• Pencil
• Graph Paper
• Ruler

PREPARATION

• Note that students can plot the data by hand or enter it into appropriate computer software, depending upon the desires of the teacher, equipment available, and level of the students.
• Divide the class into small research teams and assign each one table of data.

PROCEDURE

EXTENSION

• The following is an account of one scientist's study of carbon dioxide concentrations in Earth's atmo-sphere. Students can read this as an example of how science happens and where the numbers in Table 1 came from.
• Dr. Charles David Keeling was the geochemist at Scripps Institute of Oceanography who first studied atmospheric carbon dioxide (CO2) in the 1950s. He developed the first manometer to extract and measure CO2 in parts per million (ppm) and set up a measurement facility on Mauna Loa volcano in Hawaii. Air found there has been well mixed in the atmosphere and thus serves as a good example of global average air.
• The first decade of his data showed the CO2 levels to be increasing at a rate of 1 ppm each year. After that, data showed that CO2 levels are increasing at a faster pace - about 1.5 ppm per year. In the last 40 years CO2 levels have increased form 315 ppm to 350 ppm. The trend indicates the amount of CO2 in the earth's atmosphere will likely continue its increase.
• The amount of CO2 and other greenhouse gases in the atmosphere is increasing in large part due to human activity. Average global temperatures are also increasing. Is there a connection? It is not totally clear yet, but those who believe there is feel that the amount of CO2 being pumped into the atmosphere from human activities should be reduced.
• Discuss with your students the types of changes that can be made to reduce CO2 emssions. What is their county, state, or country doing (if anything) to help? Have the students ask older family members or friends about the impact that reducing CFCs has had on their daily lives. Do they feel changing their lifestyle or spending habits to help reduce CO2 is worthwhile?

VOCABULARY

• chlorofluorocarbons (CFCs): man-made substances used as coolant and computer-chip cleaner, which have been shown to destroy stratospheric ozone when they break down.
• global warming: increase in average global temperature. Some of the increases are due to build-up of gases such as CO2 , NO2, and chlorofluorocarbons in the atmosphere as a result of industrialization.
• greenhouse gas: atmospheric gas (water vapor, carbon dioxide, methane) that absorb energy radiated from Earth's surface.
• manometer: an instrument for measuring the pressure of gases and vapors.

SOURCE

• From "Visit to an Ocean Planet" educational CD-ROM, Copyright Caltech and NASA/Jet Propulsion Laboratory
• Adapted from Global Climate-Past, Present, and Future, S. Henderson et al. (Eds.), Environmental Protection Agency Report No. EPA/600/R126, pp. 77-89.