Climate and Earth's Energy Balance
Part D: Greenhouse Gas Lab
In the previous lab, you read about greenhouse gases and used computer models to investigate the effect of greenhouse gases on temperature. As you recall, greenhouse gases, which include water vapor, carbon dioxide, methane, nitrous oxide, and other man-made gases are relatively transparent to incoming shortwave (including visible) solar radiation however they absorb outgoing long-wave radiation emitted from Earth and the atmosphere, hence their name "greenhouse" gases. In this next lab activity, you will test the greenhouse potential of two easily acquired greenhouse gas samples: water vapor, carbon dioxide.
Note: this lab takes about 45 minutes to complete.
Lab activity instructions:
- If possible, divide up members of your class into several different groups (one for each bottle containing a different gas). Each group of 2-3 students will have one bottle into which one of the gases (regular air, water saturated air, CO2 ) has been placed. (For the saturated air, carbon dioxide, see above.)
- For each bottle, prepare a data chart with three columns: time, temperature, and notes. You will need to collect data for 25 minutes, once every minute. Be sure to locate a stopwatch or other clock showing minutes.
- Record the starting "room" temperature by holding the control temperature probe in the air for 1 minute. Record this temperature. NOTE: Do not set the probe on the desk. If you do, you'll be recording the desk temperature. Also, don't hold the tip of the probe because then you'll be taking your temperature.
- Place all the bottles at a designated distance from the light source (Recommend: 10-25 cm (4-10 inches) away from light source, if using an incandescent light source. If working outdoors, place the bottles all in direct sunlight be aware of shadows.)
- Either plug in the lamp and turn it on, or move the bottles into the sunlight. Immediately start collecting and recording temperature on a data chart. Continue to do so every minute for 15 minutes. After 15 minutes, turn the light off, or move the bottles into the shade, and continue recording the temperature for an additional 10 minutes. Safety Note: Be careful around the hot lamp.
- Plot the data you collected in step 5. Plot temperature on the (Y) axis and time on the (X) axis. Label your axes. If sharing data with the class, agree on a scale before plotting the data. If you have access to Excel or another graphing program, you can chart the graph electronically. Share the data / graphs so that each team has all of the data sets.
- Describe the general trends that you see in the temperature over time.
- Did one gas warm more quickly than the others? Was the increase in temperature gradual or were there changes in the slope of the line?
- Which gas had the greatest change in temperature while heating?
- How did the cooling of the gases compare to the warming? Which gas appeared to hold the heat the longest of the three that you tested?
- Recall that temperature is a measure of kinetic energy of molecules. Explain, in terms of kinetic energy, why the bottles remained warm after the light source was turned off or the bottles were shaded.
- How does the composition of the gases in the bottles differ from the composition of gases naturally found in the atmosphere?
- If you increased the concentration of CO2 in the bottle, how might this affect the temperature trend in the lab?
- How do greenhouse gases affect the Earth's radiation balance?
Stop and Think
Analyze your data. Consider the following questions: