Children ages 8 to 13 construct a mobile that models the balance of warming and cooling influences, represented by craft materials, on Earth's global temperatures. The children find that the Sun's energy alone leaves the mobile unbalanced and Earth is too cold. They need to add additional warming and cooling factors to balance it and create Earth's moderate temperatures. Adding human sources of greenhouse gases, such as factories, power plants, cars, and farms, unbalance the mobile again, and Earth's temperatures become too warm.
Provide the children with coloring supplies, Styrofoam balls, and "Sun," "Too hot!," and "Too cold!" cards. Invite them to decorate the balls as Earth. Explain that they are going to build a mobile that will model the different sources of warmth and cooling on Earth.
Invite them to cut out and decorate their "Sun" cards with glitter, ribbon, buttons, and sequins to add the necessary weight for balancing the mobile.
- Where does our warmth come from? The Sun.
Distribute the mobile materials to the children and have them begin constructing their mobiles.
- Instruct the children to tie the middle of a yarn to the middle of one rod with a very tight knot. The two ends of the yarn should be the same length.
- Knot the "Too cold!" tag near one end of the yarn with a bell. Use the very end of the yarn to tie a loop from which to hang the mobile.
- Knot the "Too hot!" tag at the remaining end of the yarn with a bell.
- Attach the "Sun" card to one end of the rod with a red pipe cleaner. Push the Styrofoam© ball onto the other end. Cap both ends with pencil erasers.
Ask the children to lift their mobiles by the yarn loops next to the “Too cold” tags.
- What happened to Earth? It rose to hit the "Too cold!" bell. The mobile is out of balance.
- In this model, is Earth too cold, just right, or too warm? Too cold. The Sun alone would give Earth a global average temperature of -2°F (-19°C).
- Does it feel like -2°F here? Earth's actual average temperature is 57°F (14°C).
- How can we balance the mobiles so that Earth isn't too cold? Add weight to the "Earth end" of the mobile.
- Invite the children to attach the second rod to the mobile with yarn. Help the children tie one end of the remaining yarn tightly at the end of the first rod and between the Styrofoam© ball and pencil eraser. Have them knot the other end firmly around the middle of the second rod. The second rod should hang from the end of the first rod, adjacent to the Styrofoam© ball.
Explain that all Earth's warmth comes from the Sun, but that Earth also has greenhouse gases that trap some of the Sun's energy. These "warmers" will hang from one end of Earth's rod. Earth is a comfortable place to live because volcanos and bacteria living in natural wetlands have produced greenhouse gases like carbon dioxide (CO2) and methane. Those gases act like a blanket to trap the Sun's energy. Certain types of clouds also act like blankets and hold heat to Earth's surface.
Invite the children to cut out, color, and decorate their Warmer and Cooler Cards. Ask them to hang the natural warmers ("Heat-trapping Clouds," "Carbon Dioxide from Volcanos," and "Bacteria in Wetlands Releasing Gas") on one side of Earth's rod with red pipe cleaners.
Ask the children to investigate their mobiles. Invite them to lift the mobiles by their loops.
- What happened? Earth dropped to hit the "Too hot!" bell. The mobile is out of balance.
Explain that other factors keep Earth from getting too warm. These "coolers" will hang from the other end of Earth's rod. While the children attach the Cooler Cards to the mobile with blue pipe cleaners, discuss how the different coolers help keep Earth's temperatures balanced.
Other types of clouds, volcanic particles, and white ice and snow reflect the Sun's light back into space.
- Have you ever walked across a light-colored sidewalk on a hot day? How about dark asphalt? Which is warmer? Why? The light-colored sidewalk reflects light from the Sun and the dark asphalt absorbs it.
- Are white, fluffy clouds more like a sidewalk or asphalt? White snow and ice? Light gray clouds of particles from volcanos? Sidewalk.
Plants use carbon dioxide to make their own food — they are literally made mostly of a gas! — which they convert into hard trunks and swaying leaves.
- Can you think of a living thing that uses up carbon dioxide? Plants.
Ask the children to balance their mobiles. Have them hold the mobiles by their loops and adjust the pieces of the mobile so that they are balanced.
- Is Earth too cold, just right, or too warm for us — and plants and animals — to live here? Just right!
- When a volcano erupts, do you think it might tip the balance one way or the other? Yes. Volcanos add carbon dioxide to the atmosphere that causes warming, but also add particles and some gases that reflect sunlight and cause cooling.
- Can you think of a time when there was a lot of ice and snow on Earth? During the Ice Age.
- Which way would extra snow and ice tip the balance? Toward cooler temperatures. The snow and ice reflect the Sun's light and help Earth stay cool.
- Does the amount of heat we get from the Sun change? It does a little bit.
All the warming and cooling influences on Earth have changed through time — thats how we came to have ice ages! The Earth moves around the Sun every year. Over long time periods — thousands to hundreds of thousands of years — Earth's orbit changes a little. Its orbit gradually changes from circular to a little more elliptical over time. Earth's north and south poles also can tilt a little more or a little less toward the Sun as it orbits. Finally, the direction in which the poles are pointing at different times of year shifts gradually with time. These changes in our orbit around the Sun combine to provide more or less warmth to Earth over time, and these changes go through a natural cycle. Earth goes in and out of ice ages in step with those changes. In addition to changes in Earth's orbit, the amount of trees and bacteria growing on Earth has changed over time; sometimes there are many volcanos erupting; Earth is always changing!
Earth's temperatures are shaped by various natural factors that interact to warm or cool the climate. Changes in Earth's orbit, in addition to less influential changes in the Sun's intensity, outgassing from volcanos and other sources, and changes in ocean currents, have resulted in long-term cycles of cooling and warming. While these influences are still not fully understood, the majority of scientists agree that their effects are minor compared to the contributions of human activities. Changes in solar intensity and volcanos produced most of the warming from preindustrial times to 1950, but are not implicated in the current global change. For instance, when Mt. Pinatubo erupted in 1991, the global average temperature dropped by 0.9°F (0.5°C) as volcanic particles in the air reflected some of the Sun's energy. (The volcano also released carbon dioxide, a warming agent, but this addition is thought to be small compared to human contributions.) Studies by the National Center for Atmospheric Research (NCAR) attribute less than one-third of the current warming to changes in the Sun's intensity.
Ice cores and other data provide evidence that the amount of carbon dioxide in Earth's atmosphere, and Earth's temperature, have fluctuated in a cyclical pattern through time. These cycles of cooling and warming are natural, and caused, over the last 750,000 years, primarily by cyclic changes in Earth's orbit. During that time frame we have experienced alternating periods of warmth and periods of glaciations. However, at present, the levels of carbon dioxide in the atmosphere far exceed even the highest levels of the past half-million years. Our global temperature is increasing in response to this added greenhouse gas.
Images from: UN Intergovernmental Panel on Climate Change (IPCC), Third Assessment Report, Climate Change 2001
- Who else lives on Earth besides plants and bacteria in wetlands? People, other animals.
- Do people release greenhouse gases into the atmosphere? Yes, from burning fossil fuels and by some of the ways we raise our food.
Some children may correctly state that we produce carbon dioxide when we breathe. It is important, however, that children not come away from this activity believing that their breathing is contributing to global warming!
People and animals release carbon dioxide when we breathe out, but animals have been breathing out carbon dioxide for millennia. During all that time, plants were taking that carbon dioxide out of the atmosphere. Animals breathing out carbon dioxide and plants "breathing" it in are part of a natural cycle on Earth. Animals (including humans) and plants are part of Earth's natural carbon cycle. Plants take up carbon dioxide from the atmosphere and transform it into the food they use to grow. When animals eat plants (or other animals that ate plants), they are eating carbon that ultimately came from the atmosphere. That carbon is released back into the atmosphere as waste when animals breathe out and when they decompose after death, becoming, once again, "food" for plants.
Fertilizers are often used to help grow healthy food plants, but these chemicals break down in the soil and release a greenhouse gas. Our farm animals also produce a greenhouse gas as they digest grass and grains.
- What are some examples of how people burn fossil fuels? When they drive cars, they burn gasoline, which is made from fossil fuels. When people burn gasoline, they release carbon dioxide to the atmosphere, which causes the atmosphere to trap more of the Sun's energy. Electricity that we use in our homes may come from a power plant that burns coal — a fossil fuel — to make the energy we use. Burning coal also releases carbon dioxide to the atmosphere.
Add the "warmers" that are caused by human activities to the mobile. Invite the children to add the remaining Warmer Cards to the natural warmers on Earth's rod with red pipe cleaner sections. Have the children attach the "Lights," "Air Conditioning," and "Computers and Video Game Consoles" cards to the electricity card with red pipe cleaners. Then have them attach the electricity card below the power plant card.
- What are some warmers that are caused by human activities? Power plants burning coal to
- make electricity; fertilizers, which are used to grow our food, breaking down into gas in the soil; cars and trucks burning gasoline; gas released by farm animals as they digest grass and grain.
- What do we use power plants for? They generate the electricity we get through outlets at home, at school, and in stores. Electricity powers our lights, air conditioners, computers, and other appliances
Invite the children to investigate their completed mobiles. Ask them to lift the mobiles by their loops.
- What happened? Earth fell to hit the "Too hot!" bell. The mobile is out of balance.
- How could we put the mobile in balance again? Take off some of the warmers; add more coolers.
- Could you use less of the warmers when you go home today? How? Turn off lights and computers when no one's using them, walk or carpool instead of asking for a ride in the car.
Scientists are measuring an increase in the amount of CO2
and other greenhouse gases in the atmosphere. Scientists have also been measuring Earth's temperatures and they've found that the global average temperature has risen over 1°F in the last 100 years.
Earth's global surface temperatures are rising at an unprecedented rate. The past century has seen an increase of a little more than 1°F (0.74°C). Today's global temperatures are the highest of the past 500 years, perhaps even for the past millennium. The scientific consensus is that the warming is due to greenhouse gases emitted as a result of human activities.
Scientists are especially concerned about Earth's polar regions, where there is a lot of ice and snow. Ice is melting at Earth's poles and at high elevations and scientists are concerned about what the loss of that cooler will do to Earth's temperature balance.
- Ice and snow are one of the coolers. What will happen to them as the Earth's temperatures warm? They will melt.
- What will that do to the mobile? Make the mobile (and Earth's temperatures) more unbalanced.
- Do we need greenhouse gases? Yes, they trap the Sun's energy and keep us warm.
- Do we need coolers like trees and ice and snow? Yes, they keep us from getting too hot.
- Are our Earth's warmers and coolers in balance right now? No, there are too many warmers.
Invite the children to take the mobiles home with them or display them at your site.