The Greenhouse Effect
Recommended Age: Middle School
Guiding Question
Objectives
Concepts:
Global warming is a natural process that
keeps the planet warm and hospitable for living organisms. The
greenhouse effect (understood to mean an enhancedgreenhouse
effect) is the warming of the earth beyond this natural process of
global warming.
Principles:
- Greenhouse gases are in the earth’s
atmosphere.
- Some solar radiation is absorbed by
these greenhouse gases; some reaches the earth and is absorbed by
its surfaces. In both cases, light is absorbed as heat.
- Earth’s surfaces, warmed both by solar radiation and by warmth
from deep within the earth, radiate heat into the atmosphere,
where some is absorbed and some passes out into deep space.
The enhanced greenhouse effect occurs when more heat is absorbed
by the atmosphere, due to increased greenhouse gases, than can
pass by convection into space in a normal manner.
|
A diagram illustrating the process of the greenhouse
effect. Click on it to see a full-size version that you can print
out. |
Facts:
- Many of the greenhouse gases are naturally occurring, which is the
cause of natural global warming. Without naturally occurring
greenhouse gases, the earth’s surface temperature would average 33
degrees Celsius cooler.
- The first person to predict the greenhouse effect was a Swedish
chemist named Svante Arrhenius. Over a hundred years ago, in 1896, he
observed that when the industrial revolution began, more carbon dioxide was being released into the
atmosphere, and he believed that carbon dioxide levels would rise
as industry grew. He was the first to understand that this
increase meant a rise in the temperature of the earth. He was
ignored at the time, because the results of his predictions were
seen as too far into the future for the people of his time to
believe.
- When we burn fossil fuels and manufacture
other products, we release gases into the atmosphere, which are
greenhouse gases.
- Over the past 250 years, carbon dioxide levels have increased by
25%.
- Mass deforestation, as is occurring with our tropical rain forests,
is decreasing the amount of plant life on the planet. Trees and
plants are vital to us because they convert carbon dioxide into
oxygen. Industry will continue to pump carbon dioxide into the air
and, with the decrease of vegetation, more carbon dioxide will
remain in the atmosphere to cause problems like the enhanced greenhouse
effect.
- In the past 15 to 20 years, there has been an overall rise in
temperatures.
Skills
- Making Careful Observations and Recording Data
- Understanding Cause-and-Effect Relationships
- Drawing Conclusions
- Following Directions
- Making Inferences
Preparation
Materials:
- Cardboard boxes
- Black construction paper
- 3 thermometers for every box
- 1 classroom thermometer
- 3 glass panes for every box (have them cut to fit in the box at the
store)
- 6 blocks of wood for every box
- Glue
- Scotch tape
- Electrical tape
Room Preparation
Have materials ready and glass pre-cut to desired size (small enough
to just fit into boxes).
Safety Precautions
Caution! Danger of broken glass! Handle glass with care.
Cover edges of each pane with electrical tape to prevent injury from
cut edges.
Procedures and Activity
Prelab Discussion
- Introduce greenhouse effect concepts, principles, and vocabulary.
- Ask:
- What happens to a car that has been sitting in the sun on a hot
day with all its windows rolled up?
- Why does the car get so hot?
- What happens to the sunlight that passes through the windows into
the car?
- What is keeping the heat inside of the car?
- Many scientists believe that we are experiencing an enhanced
greenhouse effect. Unfortunately, accurate recordings of the
earth’s temperature go back only 100 years. This is not a long
enough period to be sure of what is happening. However, we can
simulate the greenhouse effect with a box and panes of glass. Keep
in mind that the mechanism is not the same:heat is trapped in
a car or a real greenhouse by the glass interfering with natural
convection. In the atmosphere, the heat is not literally trapped;
rather, enhanced global warming stems from the increased ability of
the atmosphere to absorb heat due to greenhouse gases.
Construction
- Using glue, completely line the inside of a cardboard box with black
construction paper.
- Tape down one thermometer towards the left side of the box, at the
bottom. Be sure the thermometer can still be read.
- Get two blocks of wood. Place one block to the far left and one to
the far right so that they will support a pane of glass.
- Carefully place one pane of glass on top of the wood blocks.
- Position a second thermometer in the center, on top of the glass
pane.
- Repeat steps 3 and 4.
- Position the third thermometer to the right on the topmost glass
pane.
- Repeat steps 3 and 4.
The result should
look like
this.
(Click on images to
see
full-size versions
you can print out). |
Top View |
Side View |
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 |
 |
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Testing Procedure
- Have students put their boxes in direct sunlight.
- Have students read their thermometers and record their data once a
day, at the same time. Example: At the beginning of each class
period.
- Also have students record the classroom temperature.
- The collected data should be placed in a chart that looks
like this
(Click on it to see a full-size version you can
print out):
- Compute the average daily temperature for each thermometer.
Discussion
Have students examine the relationship between increase in average
daily temperature and an increase in the number of panes of glass.
Think about why this is happening. Relate to greenhouse effect. A
pane of transparent glass allows solar radiation to pass through, but
interferes with the convection that would let heat out. This is the
kind of role that greenhouse gases play in the greenhouse effect:
they absorb more heat than normal atmospheric gases would.
Therefore, in this model, the effect of the increasing number of
panes of glass is similar to the effect of increasing greenhouse gas
levels.
Closing
Ask again: What is the greenhouse effect? Why does it
happen?
Evaluation
Have students share reasons why we need global warming to an extent.
Then have students share how we are changing the natural system of
warming with greenhouse gases. Have students share what they think
are the side effects of global warming.
Extension Ideas
- Discuss the impact of increasing temperatures on the polar regions,
aquatic life, humans, and the planet in general. Some possibilities
are: the effect on weather, rising sea levels, rise in ocean
temperatures and how this affects sea life, effects on agriculture,
etc. See other Web pages for more information on this topic: Global Change/Climate
Change (a report from Hawaii on NASA’s Mission to Planet Earth
studies of the greenhouse effect); the Consortium for International
Earth Science Information Network’s Thematic Guide Potential Increases in
Mortality Due to Global Warming; or the report Consequences:
Trends in U.S. Climate from the National Climatic Data Center in
North Carolina.
- Relate Earth to Venus
and its runaway global warming and to Mars and its deep
freeze in a page from the American Institute of Physics.
- The theory that we are experiencing unusual global warming now is somewhat
controversial. Some sites that try to help you make sense of the
conflicting information available include a chemistry professor’s article Debunking
Rush Limbaugh on the Environment, and another professor’s Bad Greenhouse
page, debunking myths and common misperceptions about the greenhouse
effect (including the idea that the atmosphere "traps" heat or reflects it
back to earth). NASA has a great Web page on this called Earth’s
Fidgeting Climate, and see the Environmental Protection Agency’s Climate Change page.
Vocabulary
- Atmosphere
- The air that surrounds the earth.
- Carbon Dioxide
- A heavy colorless gas that does not support combustion. It is
formed naturallyby the combustion and decomposition of
organic substances and is absorbed by photosynthesis of
plants.
- Fossil Fuels
- Fuels that are formed in the earth from plant or animal remains.
Examples are coal, oil, and natural gas.
- Global Warming
- The result of the greenhouse effect. It is the warming of the
planet’s atmosphere. Natural global warming is a result of the
natural greenhouse effect and is what makes the planet
hospitable to life. Sometimes, "global warming" is used to mean
"the greenhouse effect." That is, sometimes it is used to refer
to the warming that is a result of the enhanced greenhouse
effect.
- Greenhouse Effect
- The cause of global warming. It is the actual process of
greenhouse gases absorbing heat in the atmosphere. There is a
natural greenhouse effect which the planet needs to support
life. We amplify or enhance the natural greenhouse effect when
we load the atmosphere with an excess of greenhouse gases.
Usually, the term "greenhouse effect" is used to refer only to
the amplified greenhouse effect and not to the natural
greenhouse effect.
- Greenhouse Gases
- Gases, such as carbon dioxide, methane, and chlorofluorocarbons,
which are released into the atmosphere by burning fossil fuels
and by manufacturing. These gases trap additional heat in the
earth’s atmosphere.
- Solar Radiation
- Sunlight