The Effect of CO2 Concentration on Atmospheric Temperature

Level: Senior high (and junior high for Part B)

Purpose

The purpose of this experiment is to determine the environmental effects of increased carbon dioxide (CO2) content in the atmosphere. It has been claimed that the Earth's climate is warming due to changes in the relative concentration of gases in the atmosphere. The gases involved include:

  • Methane
  • Carbon dioxide
  • Freon
  • Nitrous oxide

Of these, CO2 is building up in the atmosphere at a much greater rate. Several factors contribute to this build up. The use of fossil fuels in internal combustion engines and in the generation of electricity has greatly increased the amount of CO2 released to the air. Green plants remove CO2 from the air during photosynthesis and turn it into O2. Deforestation of large areas, especially the rain forests in tropical regions of the world, has decreased the amount of CO2 removed from the atmosphere by plants. The question must be asked as to how the increased amounts of these gases in the atmosphere could contribute to the hypothesized climate warming or "Greenhouse" effect. One possibility is that the changes in gas composition of the atmosphere increase the heat capacity of the atmosphere. The gases of the atmosphere are heated by the sun during the day. At night, some of this heat is radiated away from the Earth into space. The heat capacity of a substance can be regarded as the relative tendency to retain heat. Some materials lose heat to surroundings quickly, while others tend to retain heat longer. If the changes in the composition of the atmosphere allow its heat capacity to increase, less heat is lost to space during the night. The long-term effect of this decreased loss of heat would be a gradual warming of the atmosphere. Scientists have documented that the concentrations of these "Greenhouse" gases are increasing in the atmosphere today; for example, today the concentration of CO2 is approximately 350 parts per million (ppm), or 0.035%, versus the pre-Industrial Revolution concentration of 200-280 ppm (0.020 - 0.028%). We must determine the effect of the future increases in concentrations of these gases on air temperature.

Problem: How would doubling the concentration of carbon dioxide, as is expected to occur in the next few decades, affect the atmosphere? In this experiment air with increased concentrations of CO2 is produced and the rate of heat loss of that air is compared to today's "normal" air.

Equipment and Materials

Small aquarium

Small chunk of clay

Petri dish

Vernier thermometer

heat lamp

Alka-Seltzer tablet

Procedure:

You will treat the air in the large glass vessel as a model of the atmosphere. The vessel will be covered and heated by the "sun" (the heat lamp) until the temperature rises to 15 degrees C above the ambient (surrounding) temperature. The heat lamp is then turned off ("nighttime"), and the air allowed to cool naturally. Temperature readings are taken at definite time intervals and plotted on graph paper. This will show the rate of heat loss from "normal" air. Then, the CO2 concentration of the air will be increased and the experiment repeated. The results will demonstrate the effects of increased CO2 on the rate of heat loss from air. When Alka-Seltzer dissolves in water, a gas is released. This gas is CO2, so Alka-Seltzer tablets serve as a convenient source of this gas.

PART B: EFFECT OF CO2 CONCENTRATION ON HEAT GAIN AND LOSS OF AIR .

PART I: Measurement of heat gain & loss for today's "normal" air:

  1. Connect a thermometer to the USB ports on your computer.
  2. Open the Vernier Logger Pro software. The software should automatically detect your thermometer.
  3. Place a small petri dish filled with water along with a thermometer in your aquarium. NOTE: SEE THE DEMO SETUP ON THE CART TO MAKE SURE YOU HAVE CORRECTLY SET UP YOUR AQUARIUM!!!!!!!!
  4. Click the “collect” button to initiate data collection.
  5. Heat the air in the aquarium using the heat lamp "sun" until the temperature is raised by 15 degrees C.
  6. Remove the heat lamps to simulate "night". Record the temperature until the temperature returns to the initial ambient temperature.
  7. Determine the rate of heating and cooling by highlighting each portion of the graph, clicking the statistics menu and choosing “slope”.

PART II. Measurement of heat gain and loss from air containing increased CO2:

  1. Drop the Alka-Seltzer into the water in the small petri dish inside the aquarium.
  2. Repeat the process you completed in Part I to measure the heat gain and loss.

PART B: DETERMINING CO2 CONCENTRATIONS : SHOW ALL CALCULATIONS, WITH UNITS IN YOUR JOURNAL!

The determination of the amount of CO2 released is an interesting laboratory procedure in itself, and we recommend that high school students be involved in this portion of the experiment. The first step is to determine the volume of the aquarium. If a gallon jar is used, use the conversion factor

1 gallon = 3.785 liters.

The remainder of this procedure will be described assuming you use a gallon jar. The next step is to calculate the mass of the air in the vessel. The true density of air is dependent on the amount of moisture present in the air (the humidity) and on the barometric pressure. There are tables and equations which allow a precise computation of the density of air under any set of conditions. These tables can be found in the CRC Handbook of Chemistry and Physics. This calculation is rather complicated; thus for the purposes of this demonstration/experiment, the density of dry air at a pressure of 760 mm of Hg will be assumed. This density is: 0.0012 gm/milliliter.

  1. Determine the volume (in mL) of your aquarium. Show your calculations in your lab manual.
  2. The mass of air in the aquarium should now be calculated using the density and your answer to #1:

Volume of container (mL) X Density of air (g/mL) = g of air in container

3. At this point, pretend you wish to determine the rate of heating and heat loss from an atmosphere in which the CO2 concentration has doubled, e.g. which contains 700 ppm (parts per million) CO2. The air in the gallon aquarium should contain:

g of air in container X (700 g CO2 /1,000,000 g of air) = g CO2 to be added

The CO2 will be obtained from the solution of Alka-Seltzer in water. Some kindly scientist types have performed the following simple test to help you determine determine how much CO2 is released from an Alka-Seltzer tablet:

  • A glass vessel containing 75 milliliters of water was weighed to the nearest milligram.
  • An Alka-Seltzer tablet is weighed to the nearest milligram.
  • The tablet is dropped into the water and allowed to dissolve.
  • After 10 minutes, the vessel, water and dissolved Alka-Seltzer is reweighed.
  • The initial weight of the vessel plus water is added to the weight of the Alka-Seltzer tablet (Add values from steps 1 and 2). Then the weight of the vessel, water and dissolved Alka-Seltzer is subtracted from this sum (Subtract value of step 4 from the sum of 1 and 2). The difference is the weight of the CO2 that was released from the Alka-Seltzer.

A typical determination gave the following values:

Mass of vessel plus water / 122.37 gm
Mass of Alka-Seltzer tablet / 3.35 gm
Total Initial Mass / 125.72 gm
Final of vessel, water, and Alka-Seltzer / 125.09 gm
  1. You should now use this information to determine the amount of CO2 given off by the Alka Seltzer tablet in grams.
  1. Finally, determine the total amount (in ppm) of CO2 that will be in the system when we dissolve an entire Alka Seltzer tablet, using the information you gathered from above. How does this number compare with the predicted change in atmospheric CO2 over the next decade or so?

PART III. Data analysis

  1. Obtain the EXPERIMENT results from at least 2 other groups of and determine the average rate of heat gain and heat loss for each test chamber.
  2. Now assume that the naturally-occurring atmospheric levels of CO2 have doubled and are now 700ppm. Based on your lab results, what would you predict to be the rate of heating of the atmosphere (assuming, of course, that there is a direct correlation)? How does your prediction compare with that of climate scientists? (whoa….you actually have to look this up???? What is this world coming to????)
  3. Based on your data, explain the relationship between CO2 in the atmosphere and the heating and cooling of the atmosphere, as well as the implications these data have for global ecosystems.

PART IV. More information

  • Watch the video segment link “Greenhouse effect”
  1. What is the greenhouse effect and what is its significance to life on Earth?
  2. What natural phenomena produce greenhouse gases? What are the sources of anthropogenic greenhouse gases?
  3. What are some everyday activities that result in carbon dioxide being released into the air?
  4. Explain the relationship between increased amounts of carbon dioxide in the atmosphere and the thermodynamics of the atmosphere.
  • Now view and interact with the “Carbon Cycle Flash”
  1. Draw a schematic of the carbon cycle in your notebook.
  2. Explain the major sources (releasers) and sinks (storehouses) of carbon on Earth.
  3. What major processes occur to liberate carbon from its sinks?
  4. Explain the interrelatedness of the Atmosphere, Lithosphere, Hydrosphere, and Biosphere in cycling carbon.
  5. How does understanding the carbon cycle allow us to better understand the phenomena of the greenhouse effect and changes in atmospheric temperature?