Background Information

Venus and Earth are about the same size and are so close that they are frequently called the "twin planets" of our solar system. Yet, Venus is so hot that lead will melt on its surface! A runaway greenhouse effect makes Venus this hot.

The greenhouse effect occurs when the atmosphere of a planet acts much like the glass in a greenhouse. Like the greenhouse glass, the atmosphere allows visible solar energy to pass through, but it also prevents some energy from radiating back out into space. The greenhouse effect insures that the surface of a planet is much warmer than interplanetary space because the atmosphere traps heat in the same way a greenhouse traps heat. Certain gases in our atmosphere, called greenhouse gases, tend to reflect radiant energy from the Earth's atmosphere back to the Earth's surface, improving the atmosphere's ability to trap heat.

All greenhouse gases are trace gases existing in small amounts in our atmosphere. Greenhouse gases include:

  • carbon dioxide;
  • methane;
  • nitrous oxide;
  • some chlorofluorocarbons; and
  • water vapor.
We know that the greenhouse effect is necessary for survival. Without it, the Earth would be cold, so cold that life as we know it could not exist. However, scientists still have questions that must be answered. What kinds and amounts of greenhouse gases are necessary for survival? Are the amounts of greenhouse gases increasing, decreasing, or remaining the same? To answer these questions, scientists monitor the amounts of greenhouse gases in the Earth's atmosphere.

The atmospheric gas most responsible for the warming effect on both Venus and Earth is carbon dioxide (CO2). On both planets, primary sources of CO2 are volcanic eruptions. The difference between these two planets is that on Venus, 97% of the atmosphere is CO2, whereas on Earth, much less than one percent of the atmosphere is CO2. Why is there so much less CO2 on Earth? The carbon cycle holds the answer.

In the natural cycle of carbon, plants take in CO2 and give off oxygen, whereas animals take in oxygen and emit CO2. Further, CO2 dissolved in seawater is used by plants during photosynthesis and by other seawater organisms such as clams and coral to produce calcium carbonate (CaCO3) shells. These processes help control the amount of CO2 in our atmosphere.
Human beings complicate the natural carbon cycle because they increase the amount of CO2 in the Earth's atmosphere by burning fossil fuels. Driving automobiles, heating buildings, and producing consumer goods all add to the concentration of CO2 in the Earth's atmosphere.

Methane (CH4) is another greenhouse gas. It is produced in swamps, bogs, and rice paddies, as well as in the intestinal tracts of most animals, including cattle, sheep, and humans. Coal, oil, and gas exploration also contribute to the accumulation of methane in the atmosphere. However, methane concentrations are much less than CO2 concentrations.

Nitrous oxide (N2O), or"laughing gas," is another greenhouse gas accumulating in the atmosphere, although not as fast as CH4. Fertilizer decomposition, industrial processes that use nitric acid, and small amounts from automobile emissions all contribute to increasing atmospheric N2O.

In the procedures for this activity, you will plot curves for the CO2 (ppm) and CH4 (ppb) concentrations found in the atmosphere over a period of time.In much the same way a scientist would monitor concentrations of gases in the atmosphere, you will look for changes and trends, as well a maximum and minimum concentrations during that same time period.

The data in Tables 5.1, 5.2, and 5.3 were provided by
National Oceanic and Atmospheric Administration (NOAA)
Office of Oceans and Atmospheric Research (OAR)
Climate Monitoring and Diagnostics Laboratory (CMDL).






Procedure - Part A

  1. Using the data from Table 5.1, plot the points corresponding to the monthly mean CO2 concentration at Pt. Barrow, Alaska on Figure 5.1. Use a colored pencil to connect the points.

  2. Using the data from Table 5.2, plot the points corresponding to the monthly mean CO2 concentration at Amundsen - Scott South Pole Station, Antarctica on Figure 5.1. Use a different colored pencil to connect the points.

    Table 5.1. Monthly Mean CO2 Concentrations (ppm) at Pt. Barrow, Alaska.
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    Table 5.2. Monthly Mean CO2 Concentrations (ppm) at
    Amundsen - Scott South Pole Station, Antarctica.

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    Figure 5.1. Plots of Monthly CO2 Concentrations at Pt. Barrow, Alaska
    and Amundsen - Scott South Pole Station, Antarctica.

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  3. Print a title at the top of your graph.

  4. Place a color-coded legend on your graph in the space provided.




Questions - Part A

  1. During what season is the monthly mean CO2 concentration greatest in Pt. Barrow, Alaska?

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  2. If you were in the Southern Hemisphere, during what season would the monthly mean CO2 concentration be greatest at the Amundsen - Scott South Pole Station, Antarctica?

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  3. Why do CO2 concentrations vary less at the South Pole location than at Pt. Barrow?

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  4. Why do scientists collect CO2 data at remote isolated locations, such as Alaska and Antarctica?

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Figure 5.2. Part A - Questions Sheet
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Procedure - Part B

  1. Using Table 5.3, plot data points for the globally averaged annual mean concentration of CO2 in Figure 5.3. Connect the points with a colored pencil.

  2. Using Table 5.3, plot data points for the globally averaged annual mean concentration of CH4 in Figure 5.3. Connect the points with a different colored pencil.

    Table 5.3. Globally Averaged Annual Mean CO2 Concentrations (ppm)
    and CH4 Concentration (ppb).

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    Figure 5.3. Plots and Rates of Change of Globally Averaged Annual Mean
    CO2 Concentration and CH4 Concentration (ppb).

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  3. Calculate the rate of change for global annual mean concentration of CO2.

      a. Subtract the lowest concentration from the highest concentration shown on your graph.
      b. Now subtract the oldest year from the most recent year on your graph.
      c. Next, divide the concentration from your first subtraction by the number of years elapsed, the result of your second subtraction.

  4. The result of the calculations in Steps 3a, b, and c is the change in concentration per year.

  5. Enter your result in the box next to the graph in Figure 5.3.

  6. Repeat the procedure in Steps 3a, b, and c to find the rate of change for CH4.

  7. Print a title in the space provided above the graph in Figure 5.3.

  8. Draw a color-coded legend for your graph in the space provided in Figure 5.3.




Questions - Part B

  1. What happened to the CO2 and CH4 concentrations between 1983 and 1991?

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  2. Does CO2 or CH4 show the greatest rate of change relative to each other?

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  3. Do these data alone support the idea of global warming?_____________________________

    Explain.

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    ______________________________________________________________________

    ______________________________________________________________________

    ______________________________________________________________________




Figure 5.4. Part B - Questions Sheet
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Conclusions

Review the problem stated in the workstation screen graphic
at the top of this web page and write your conclusions here.



Figure 5.5. Conclusions Sheet
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