Lesson 5: Global Warming Blankets the World

Global warming is a natural occurrence on earth. Without it, the earth would be too cold for humans to survive. Here's how it happens.

Sunlight is energy. When this energy reaches the earth's surface, the sunlight is changed into heat energy. The heat tries to escape back out into space, but some of it is trapped by clouds and certain gases like carbon dioxide (what we exhale), methane (swamp gas), and water vapor.

These gases act like a blanket to slow down the escape of heat. Eventually, it does to back out into space. However, the more these gases are present, the longer the heat will stay trapped.

The amount of carbon dioxide and methane present in the atmosphere has increased since the late 1800's. There has also been a noticeable upward trend in the earth's average temperature.

This doesn't mean every place on earth will just get warmer. Some areas that are now warm and dry may get cooler and wetter. As the earth's atmosphere and oceans adjust, weather patterns may be altered that create unexpected changes in temperature and precipitation.

Activity One – I'll Have an Arctic Melt

As the earth's temperature rises, ice at the poles may begin to melt. Will this raise ocean levels? It depends on whether the ice is sitting on land, like it is near the South Pole, or floating on water, like at the North Pole.

Materials: two baking pans, soil, ice cubes, water

Setting Up the Activity: Take one of the baking pans and fill one half of it with one inch of soil. Put one inch of water in the other half (you may have to add some water after a few minutes if the soil is dry, to maintain the one-inch water depth.) Put one inch of water in the other pan.

Place six ice cubes on the soil half of the soil/water pan, near the water. Place six cubes in the water only pan. After the ice has melted, measure the water depth.

Questions:

Q. Were there any changes in the water depth, in either of the pans?

A. There should be an increase in depth in the soil/water plan, but none in the water only pan.

Q. Why did this happen?

A. When water is in the form of ice, it takes up more space than water. Ice floating on water would make water levels higher than when the ice is melted. Ice on land will be added to water (oceans), making the water level higher when ice is melted.

Q. If only one of the Polar Regions could melt, which one would cause the least change in the sea level?

A. Arctic – most of the ice floats on water there.

Activity Two – Hey, Cool It!

Materials: None

Setting Up the Activity: Have a class discussion on what things we can do to decrease the amount of greenhouse gases (carbon dioxide and methane in particular) getting into the atmosphere. (Planting trees or decreasing the amount of trees being cut, decreasing the use of fossil fuels like oil and coal, etc.)

Discuss what things, other than human activity, may increase or decrease global warning. For instance, volcanoes spew huge amounts of dust into the air, reflecting sunlight back into space. An increase in cloud cover reflects more sunlight. An increase in microscopic ocean plants uses more carbon dioxide. A decrease in cloud cover decreases light reflection, increasing warming possibilities.

Global Warming and the Greenhouse Effect

How is Earth's atmosphere heated? What happens to this energy? What is global warming and the greenhouse effect? To answer these questions, one has to examine the relationship of solar energy and the Earth.

Earth receives almost all of its energy directly or indirectly from the sun. Solar radiation enters the atmosphere, but not all of it reaches the earth's surface. About a third is reflected and scattered directly back into space. Some is absorbed by the ozone layer, high above the earth. About 20 percent is absorbed directly into the atmosphere, and the remaining amount is absorbed by Earth's surface.

This energy does not stay forever stored in the earth- it is quickly released back into the atmosphere. As this energy tries to escape back out into space, some of it is absorbed by gases in the atmosphere- gases like carbon dioxide, water vapor, methane, and nitrous oxide. The energy absorbed by these gases are quickly released back into the atmosphere, but much of it gets directed back towards Earth's surface. Energy may go back and forth several times before it finally escapes. This is known as the Natural Greenhouse Effect. It is a process that has gone on for millions of years and creates global warming. Without it, the Earth's average temperature would be about -15 degrees Celsius (5 degrees Fahrenheit) instead of its current 15 degrees Celsius (59 degrees Fahrenheit)

However, if the amount of these gases are increased, they can absorb more energy, making it take longer for the energy to escape. This increased greenhouse effect also enhances global warming.

Studies in the last 100 years show that as the amount of greenhouse gases have increased, so has global warming. One of the biggest culprits is carbon dioxide. Carbon dioxide is added through the atmosphere by the burning of fossil fuels, deforestation, soil tillage, and other activities.

What will be the effects of increased global warming? To "look into the future," scientists use supercomputers to build climate models. These models try to predict what will happen. Not all models predict the same thing, because the Earth is a very complex system. Several things that may happen:

• Polar ice caps may melt, increasing sea level.
• The oceans will actually expand, just because of being warmer, increasing sea level.
• Weather and ocean patterns worldwide may change. Areas that are mild and wet may become warm and dry. Other areas may actually get colder, especially if it loses a warm ocean current.

What can be done? People must be willing to find ways to decrease the amount of greenhouse gases being added to the atmosphere. It will take an effort of everyone.