Carbon In the Atmosphere - My Life as a Greenhouse Gas

Part A: CO₂ : It's a Gas!

View the image below; on which planet would you like to live?

The greenhouse effect

Since the 1800s, scientists have known that carbon dioxide is one of several greenhouse gases that naturally traps heat from infrared radiation that would otherwise escape to space. These scientists invented the term "greenhouse effect" when they compared their observations to how the sun warms a greenhouse. Scientists now know that the carbon compounds—carbon dioxide, methane, and halocarbons—are greenhouse gases that absorb a wide range of energy, including infrared energy (heat) emitted by the Earth, and then re-emit it. The re-emitted energy travels out in all directions, but some returns to Earth, where it heats the surface. Without greenhouse gases, Earth would be a frozen -18 degrees Celsius (0 degrees Fahrenheit). With too many greenhouse gases, Earth would be like Venus, where the greenhouse atmosphere keeps temperatures around 400 degrees Celsius (750 degrees Fahrenheit). Thus, by trapping infrared radiation, carbon dioxide and other greenhouse gases warm the atmosphere enough to support and sustain the "lifestyle" of living organisms here on Earth. As a matter of fact, if no natural greenhouse effect existed, the planet would be too cold to support and sustain the biodiversity that now exists on Earth.

Scientists are now seeing an amplified greenhouse effect. What causes this amplified greenhouse effect, and could it have consequences for the Earth's System? How do they know? Before you begin exploring these questions, begin by first reviewing the greenhouse effect using the Greenhouse Effect Interactive developed by the Norwegian Center for Science Education. If you get most of the answers correct in the quiz at the end of the interactive, you are ready to continue with the lab investigation. Good luck!

Carbon Dioxide as a Greenhouse Gas

Does carbon dioxide have a role in the amplified greenhouse effect? If so, what is the evidence? Let's begin the exploration of this question by looking at a simple pie graph of the different gases that comprise the atmosphere.

As you can see by the graph, above right, nitrogen and oxygen make up 99% of the atmosphere. While both nitrogen and oxygen are important in supporting life on Earth, they are not greenhouse gases and play almost no direct role in warming the atmosphere. The 1% slice of the pie chart is comprised of those gases found only in trace amounts.

Consider the table below and then answer the Checking In questions that follow:

The Case of the Dancing Molecules

Why do some gases in the atmosphere contribute to the greenhouse effect whereas others do not? For example, why isn't nitrogen or oxygen a greenhouse gas? If carbon dioxide is just a trace gas, how can it contribute to the greenhouse effect? It turns out that the ability of an atmospheric gas to trap infra-red radiation depends on how the radiation interacts with the structure of the molecule. To help you understand this important concept, first explore an interactive animation that compares the greenhouse warming potential of carbon dioxide to nitrogen. Then, watch a video of geoscientist, Dr. Scott Denning, using a molecular dance to explain this concept in greater depth.

When you enter the interactive, Molecules on the Move, do the following:

1. Follow the directions on in the pop-up screen before you begin the interactive animation.

2. Don't start adding in the molecules until you see how the solar and infrared radiation waves are behaving.

3. As you add the molecules, take notes on the similarities and differences in how carbon dioxide and nitrogen respond to solar radiation (yellow) and infrared radiation (red). Be prepared to share your notes with your partner or group.

Enter Molecules on the Move

Next, watch atmospheric scientist, Dr. Scott Denning, use his own personal dancing style to explain why greenhouse gases absorb infra-red radiation. As you watch and listen, note the following:

• How his molecular dance changes when he talks about the different molecules – nitrogen, carbon dioxide and water vapor.
• His explanation of the relationship between carbon dioxide, the greenhouse effect, and current atmospheric warming.

When you finish, share your notes from the interactive and Scott Denning's molecular dance with your partner or group and answer the Stop and Think questions.

View Scott Denning's molecular dance