Our Changing Climate
By Kay Berglund Newhouse

To teach my fifth-grade students about climate change, a current topic in the news and in our lives, I start with a discussion of our local climate. What kind of rainfall do we have? How warm is it in the summer and how cold in the winter? We extend this idea to contrast our climate with others, such as the deserts of the western United States, the icy, dry Antarctic and the tropical climate of Ecuador. We also have discussions on historic climate, such as ice ages.

Demonstration 1
How our atmosphere helps warm the earth

A sunny-day demonstration. Given all the negative headlines about the greenhouse effect, my students are amazed to learn that if the earth did not have a greenhouse effect, we wouldn't be able to live here. The moon, our closest neighbor, is as cold as -153°C (-243°F) at night. Besides providing us with oxygen to breathe, our atmosphere keeps our nights (and our winters) from being as drastically cold as the moon's. But what if our greenhouse effect gets to be too much? Fortunately, Earth's air is just right for us now, but what about in the future?

A simple sunny-day demonstration can help your students understand how our atmosphere helps to warm the earth. Take two shoeboxes and paint the insides black (or line them with black paper). Set the boxes outside in the sun and put a thermometer in each box, preferably in the bit of shade formed by the side of the boxes. Cover one box with plastic wrap. Monitor the temperature in the boxes for 15 minutes or so, being careful not to cast a shadow on the boxes as you read the thermometers. Graph the temperature in each box on the same line graph, or have older students graph the data themselves.

In this demonstration, the plastic wrap on the boxes models the atmosphere's heat-trapping effect, letting sunlight through but keeping heat in. In the atmosphere, heat is not literally trapped; instead, it's absorbed and re-radiated by greenhouse gases. Greenhouse gases include water vapor, carbon dioxide, methane, nitrous oxide and hydrofluorocarbons, such as those used in refrigerators and air conditioners. All of these gases help to keep heat energy from escaping from the earth's atmosphere; most of them occur naturally in the atmosphere and are also added by pollution.

Demonstration 2
How gases mix into the atmosphere

The air we breathe. Brainstorm ways in which our lives are different from the lives of people a few hundred years ago. Guide your students to think about production of food and other items, transportation and even world population. Factories, cars and electricity have changed our lives and they have also changed our air. All of these inventions add carbon dioxide, a greenhouse gas, to the atmosphere. Fortunately, forests are carbon dioxide "sinks," meaning they take extra carbon dioxide out of the air. Unfortunately, forests around the world are being cut down. Ruminant animals such as cows, and even termites eating fallen wood, add methane (another greenhouse gas) to the air.

To dramatize the mixing of the atmosphere, try the following demonstration: Fill a large tank with water. Add a few drops of food coloring at one end of the tank. Ask a student to point a fan towards the water to create currents. What happens to the food coloring? Does it stay in one spot, or drift to other parts of the tank?

A whimsical picture book titled The Windy Day by G. Brian Karas (Simon & Schuster, 1998) describes a boy breathing in "air that touched the edge of outer space, that traveled along the Great Wall of China, air that ruffled the hairs of the polar bears living at the North Pole." The lovely images in this book beautifully support a lesson about the connectedness of the air we breathe, across the globe and across time.

Demonstration 3
How melting ice affects water levels

Rising sea levels. Ice in the Arctic is melting. Glaciers on mountains from Oregon to Peru to Switzerland are melting. What happens to all this water? To do this next activity, you'll need to plan ahead so you can make a good-sized block of ice to serve as your glacier. Fill a glass baking pan or aquarium halfway with water. Place an object such as an upside-down glass jar into the water to serve as your mountain. Make sure it extends above the surface of the water. Place the block of ice on top of the mountain to be the glacier (the bigger the block of ice, the more dramatic this demonstration will be). Carefully mark the water level, on either the mountain or the outside of the aquarium. Loosely cover the whole apparatus to slow evaporation, and then wait overnight until the ice melts. As it melts and the water flows off the "land" and into the "sea," the water level rises. Many people are worried that the sea-level rise due to global warming will hurt coastal wildlife as well as coastal cities.

Small actions, many people. We know that temperatures around the world are getting warmer; we know that greenhouse gases trap heat and warm the atmosphere; we know that we produce millions of tons of greenhouse gases every year. But we also know that each of us can help reduce greenhouse gases in the air. As a class, read the book If Everybody Did by Jo Ann Stover (BJU Press, 1989) for a humorous look at the power of small actions by many people. Then, together as a class or as individuals, why not implement some of these small actions?

Kay Berglund Newhouse is an elementary school science teacher and science education consultant in Bethesda, MD.

February, 2007, Vol.37, No.5