Background

Venus and Earth are about the same size and 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, called greenhouse gases, tend to reflect radiant energy from the Earth 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 so cold that life as we know it couldn't 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, a primary source of CO2 is 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 (O2), whereas animals take in O2 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 Earth's atmosphere by burning fossil fuels. Driving automobiles, heating buildings, and producing consumer goods all add to the concentration of CO2 in 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 CH4 in the atmosphere. However, CH4 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 (Parts A and B) for this activity, you will plot curves for the CO2 (ppm) and CH4 (ppb) concentrations found in the atmosphere over an extended 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 as maximum and minimum concentrations during that same extended time period. The 20-plus year data record in Tables 6.1a, 6.1b, 6.1c, 6.1d, and 6.2 of this activity was provided by the National Oceanic and Atmospheric Administration (NOAA) – Climate Monitoring and Diagnostics Laboratory (CMDL), Boulder, Colorado.












































































































































































































































































































































Procedure

Part A

  1. Using the data from Tables 6.1a and 6.1b, plot the points corresponding to the monthly mean CO2 concentration at Point Barrow, Alaska on the eight graphs that follow. Use a colored pencil to connect the points.

  2. Using the data from Tables 6.1c and 6.1d, plot the points corresponding to the monthly mean CO2 concentration at South Pole Station, Antarctica on the eight graphs that follow. Use a different colored pencil to connect the points.

  3. Print a title at the top of your eight graphs.

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

Table 6.1a. Point Barrow, Alaska Monthly Carbon Dioxide Data (1971 – 1986).


Table 6.1b. Point Barrow, Alaska Monthly Carbon Dioxide Data (1987 – 2001).


Table 6.1c. South Pole, Antarctica Monthly Carbon Dioxide Data (1975 – 1988).


Table 6.1d. South Pole, Antarctica Monthly Carbon Dioxide Data (1989 – 2001).


Figure 6.1-1. Point Barrow, Alaska and South Pole, Antarctica Monthly Carbon Dioxide Concentrations (1971 – 1974).


Figure 6.1-2. Point Barrow, Alaska and South Pole, Antarctica Monthly Carbon Dioxide Concentrations (1975 – 1978).


Figure 6.1-3. Point Barrow, Alaska and South Pole, Antarctica Monthly Carbon Dioxide Concentrations (1979 – 1982).


Figure 6.1-4. Point Barrow, Alaska and South Pole, Antarctica Monthly Carbon Dioxide Concentrations (1983 – 1986).


Figure 6.1-5. Point Barrow, Alaska and South Pole, Antarctica Monthly Carbon Dioxide Concentrations (1987 – 1990).


Figure 6.1-6. Point Barrow, Alaska and South Pole, Antarctica Monthly Carbon Dioxide Concentrations (1991 – 1994).


Figure 6.1-7. Point Barrow, Alaska and South Pole, Antarctica Monthly Carbon Dioxide Concentrations (1995 – 1998).


Figure 6.1-8. Point Barrow, Alaska and South Pole, Antarctica Monthly Carbon Dioxide Concentrations (1999 – 2002).


Questions

Part A

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

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

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

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


Procedure

Part B

  1. Using the data from Table 6.2, plot the points corresponding to the annual globally averaged annual mean CO2 concentration on the graph in Figure 6.2 that follows. Use a colored pencil to connect the points.

  2. Using the data from Table 6.2, plot the points corresponding to the annual globally averaged annual mean CH4 concentration on the graph in Figure 6.2 that follows. Use a different colored pencil to connect the points.

  3. Calculate the rate of change for the annual globally averaged mean CO2 concentration. Use the following steps.

    1. First, subtract the lowest CO2 concentration shown in Table 6.2 from the highest concentration.
    2. Next, subtract the oldest year in Table 6.2 from the most recent year, then add 1 to account for the first year. As an example, if you have data from 1955 - 1975, subtract 1955 from 1975, which equals 20, then add 1, which equals 21 years of data.
    3. Now divide the concentration from your first subtraction in 3a by the result of your calculation in 3b, the number of years you have data. The final result is the rate of change in concentration per year.
    4. Round off your result to the nearest tenth and enter it in the left box below the graph and label with units.

  4. Repeat the procedures in 3a through 3d to find the rate of change for the annual globally averaged mean CH4 concentration.

  5. Print a title in the space provided above the graph.

  6. Draw a color-coded legend for your graph in the right box below the graph.

Table 6.2. Globally Averaged Annual Mean CO2 Concentration (ppm) and CH4 Concentration (ppb) Data.


Figure 6.2. Globally Averaged Annual Mean CO2 Concentrations (ppm) and CH4 Concentrations (ppb).


Questions

Part B

  1. What happened to the CO2 and CH4 concentrations between 1979 and 1999?

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

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


Conclusion

Review the problem stated at the top of this web page and write a detailed conclusion for this activity on "Greenhouse Effect".

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SAM II Activity 6 – "Greenhouse Effect – Too Much, Too Little, or Just Right?"