The burning of coal, oil and natural gas, according to some scientists, is changing the earth into a planetary hothouse, changing climates worldwide. Coupled with the destruction of huge areas of tropical rainforests,the amount of carbon dioxide and other heat-trapping gases, the Earth is experiencing a change in its average temperature. This phenomenon is better-known as global warming, and represents one of the major environmental issues of the century.
Global Warming Issue Over the past century, the human species has turned the Earth into one huge unplanned experiment. By releasing unprecedented amounts of greenhouse gases (Figure 6.14) (carbon dioxide, methane, chlorofluorocarbons, nitrous oxide and gases that create tropospheric ozone) into the atmosphere, we have in effect, turned up the global thermostat. Greenhouse gases act in a fashion similar to the windshield of a car parked in the sun, allowing light-energy to pass through, but then trapping the re-emitted heat. The greenhouse effect occurs naturally and without it the Earth would be ice-covered and uninhabitable. However, over the past century, human practices have led to an increased buildup of greenhouse gases.
Scientists already have detected a 1 degree F temperature rise, which may be due to the greenhouse effect. They predict a further increase of between 4 and 9 degrees F by the middle of the next century if greenhouse gas emissions grow at expected rates. The 6 warmest years of the century have been in the 1980s, with 1987 and 1988 being the hottest on record. As world population and fossil fuel use grow, greater quantities of greenhouse gases will be released into the atmosphere. Although the U.S. has only 5 percent of the worlds population, we are responsible for 25 percent of the carbon dioxide that is released from burning fossil fuels.
Carbon dioxide (which accounts for approximately half of the global warming trend), nitrous oxide and tropospheric ozone are by-products of burning fossil fuels (coal, oil and gas) and wood. It is important to note that burning natural gas releases 70 percent as much carbon dioxide per unit of energy as oil, and half that of coal. Forests and oceans are natural sinks for carbon dioxide, but are unable to absorb the quantities currently being emitted. Deforestation releases large quantities of carbon dioxide as well as methane, carbon monoxide, ozone and nitrous oxide. Methane, which accounts for 18 percent of the greenhouse effects, also is produced by swamps, cattle, rice paddies, landfills, termites, swamps and fossil fuels. Chlorofluorocarbons (CFCs), used in refrigerators and air conditioners, as foam blowers, as circuit board cleaners and as aerosol propellants, account for 17 percent of the greenhouse effect.
Scientists predict that as global temperatures rise, life on Earth will face a series of potentially disastrous threats. Precipitation will decline in some areas, leading to crop failure and expanding deserts. Elsewhere, rainfall will increase, causing flooding and erosion. Changes in habitat could lead to mass extinctions of plants and animals that are unable to migrate to more compatible climates. And sea levels will rise, flooding coastal areas and causing salt water intrusion into coastal aquifers.
STS Actions.
• Ask students to make a diagram showing how they think the following contribute to create the "greenhouse effect." (Sun, Earth's surface, burning of fossil fuels, atmosphere, carbon dioxide). Use the results to identify student misconceptions.
• Ask students to predict how the following human activities would influence the "greenhouse effect:"
1. Using transportation systems such as high gas mileage cars, public transportation, and bicycles.2. Constructing buildings with superinsulated material, smaller windows and automated controls for thermostats and lighting.
3. Using fluorescent lights.
4. Buying efficient appliances.
5. Advocating renewable energy such as windpower, small-scale hydro, geothermal and solar.
• Climate researchers have predicted natural disasters would increase as a result of global warming. In the early eighties they predicted the following phenomena:
1. Drought in midcontinental areas2. More frequent and severe forest fires.
3. Flooding in India and Bangladesh.
4. Extended heat waves over large areas.
5. Superhurricanes