Audience-Pleasing Physical Models to Support CO2 Outreach

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Demo 3 — What is the Greenhouse Effect? [See materials and supplies]

How can increasing CO2 in the atmosphere increase global temperature?

This visual analogy (figure 3) provides a way to think about atmospheric physics in terms of familiar objects.

Figure 3. Model of interaction of atmosphere with light and heat.

Preparation:

Cut hardware cloth (wire mesh having ¼-inch openings) into two pieces about 10" × 10" square. Fold heavy tape over all sharp edges to make them safe to handle.

The hardware cloth helps us imagine how CO2 in the atmosphere interacts with light and heat energy. Whoosh the hardware cloth through the air to show its small resistance to wind—it is because only a little bit of wire is in the hardware cloth . It is like CO2 in the atmosphere in that only a little bit of CO2 is mixed in with other gasses to make up the Earth’s atmosphere.

A pipe cleaner represents the light energy coming from the sun, which has a short wavelength. The fuzz on the pipe cleaner represents the wavelength of light.

Have a volunteer hold the hardware cloth (CO2 in the atmosphere) horizontally above a table, so that it looks like the atmosphere as seen from space. Push the pipe cleaner through the hardware cloth to show how light from the sun can easily go through the atmosphere.

Ask: But what happens to the light after it hits the Earth? Does it all reflect back as light into space? Think about the effect of sunshine hitting the ground on a summer day. (Some light is absorbed by objects and the ground and then radiated as heat).

Heat energy has a longer wavelength than light. The pipe cleaner bent in five or six zigzags can represent this wavelength. Have participants bend the pipe cleaner into a long-wavelength spring.

Have participants try transmitting this long-wavelength heat energy through the CO2 in the atmosphere (hardware cloth). It will not go through because the “heat” is trapped and bounces around between the atmosphere and Earth.

Layer another sheet of hardware cloth over the first to represent more CO2 in the atmosphere. Ask: Will this make it harder for heat to escape? The CO2-rich atmosphere is trapping heat just like the glass roof of a greenhouse does (hence the name greenhouse effect).