Activity 2.

WHAT IS THE PROBLEM?

Index

What is the greenhouse effect? What problems could it cause?

Purpose

Task In your group, choose one person to be a recorder and take notes for your report to the full group. First, read aloud each of the next five information sheets (Worksheets A-D, pages 6-9 in this booklet). Discuss the information on each sheet as you read it - ask questions and add what you know to the discussion. Then, as a group, list at least three points about global warming that your group thinks are important.

You will have about 15 minutes for this activity.

Three important points about global warming:

1.

2.

3.

Other points:

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Worksheet A

THE GREENHOUSE EFFECT: HOW IT WORKS

The Earth's surface is warmed by sunlight, and then radiates some of the heat back into the atmosphere. Some gases in the Earth's lower atmosphere absorb much of the radiated heat. Due to the presence of these gases, the atmosphere is warmer than it would be otherwise. This process is called the greenhouse effect. Scientists agree on how it works. As greenhouse gases concentrate in the atmosphere, more heat is absorbed and then re-emitted -- eventually, the Earth's surface is expected to become warmer.

The characteristics of greenhouse gases

Many heat-trapping "greenhouse gases" - such as water vapor - occur naturally in Earth's atmosphere. Without them, our planet would be too cold to support life. Overall, there are over a dozen greenhouse gases, some natural, some human-made.

Greenhouse gases differ in:

The most important human-affected greenhouse gases are:

Greenhouse Gas Life Span in the Atmosphere Heat-Trapping Effectiveness
(1 is lowest)
Carbon Dioxide (CO2) 2-30 years 1
Methane (CH4) 6-11 years 20-30
Nitrous Oxide (N2O) 120-150 years 230
Chlorofluorocarbons (CFCs) 65-111 years 15,000-20,000

Source: Lashoff, natuer, Vol. 344,. April 5 1990, pp 529-531

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Worksheet B

GREENHOUSE GAS LEVELS ARE RISING

The levels of greenhouse gases in Earth's atmosphere have been increasing for over 100 years - and continue to rise today. For example, atmospheric concentration of one major greenhouse gas, carbon dioxide (CO2), increased slowly from 1750 until the late 1880s. Since then, C02 concentrations have been rising at a high, nearly exponential rate.

Researchers estimate that at current rates of fossil fuel consumption some greenhouse gas levels will double by 2030 to 2050. While much is still unknown about our complex climate, existing computer models predict that if the level of C02 (or its equivalent in, all greenhouse gases) doubles, the climate will warm by 1.5 to 5.5 degrees Centigrade (3 to 10 degrees Fahrenheit).

Source: Neftel and Keeling as cited by Flavin

Since preindustrial times, greenhouse gas concentrations
in the atmosphere have increased considerably...

Greenhouse Gas Increase from Preindustrial Era
Nitrous Oxide (N2O) 10%
Carbon Dioxide 30%
Methane (CH4) 100% to 200%
Chlorofluorocarbons (CFCs) (not present in preindustrial era)

Source: Abrahamson, Flavin

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Worksheet C

HAS GLOBAL WARMING STARTED?

Studies indicate that the average global temperature has risen about 0.5 degrees Centigrade (1 degree Fahrenheit) since 1900, but the rise has not been steady. Global temperatures rose rapidly from 1910 to 1940, then dropped between 1940 and 1970. Temperatures started rising rapidly again in the 1970s. In fact, the seven warmest years on record are (in order) 1990,1988, 1987,1983,1981,1980, and 1986.

Is this the greenhouse effect? Maybe. But it could be another decade before we can be certain. So far, the warming trend hasn't been strong enough to provide conclusive evidence, and we still do not fully understand natural climate fluctuations.
The question of whether or not global warming has already started remains controversial. But scientists agree that increasing the amount of greenhouse gases in Earth's atmosphere will ultimately change our climate.

Source: NASA Goddard Institute of Space Studies; Union of Concerned Scientists

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Worksheet D

POSSIBLE EFFECTS OF GLOBAL WARMING

The possible effects of global warming extendbeyond our limits of experience and accurate prediction. Some scientists predict that a temperature increase of 1 to 5 degrees Centigrade (3 to 10 degrees Fahrenheit) could:

Whatever the effects, they are predicted to occur relatively quickly - by 2030 to 2050.

Source: Abrahamson, Flavin, Roberts

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