In recent years, scientists have become increasingly concerned with the challenge of global change. Human life is causing a number of dramatic changes in the planet's ecosystem. Many of these changes are damaging to the ecosystem, and some of them are irreversible. The two most drastic changes that the planet will face in the twenty-first century are the greenhouse effect and the depletion of the ozone layer.
The greenhouse effect, also known as global warming, is caused by various gases which get trapped in the earth's atmosphere. Some of these gases, such as methane, are caused by the decomposition of organic matter. However, the worst greenhouse gases are those which are caused by human beings. These include carbon dioxide and nitrous oxide resulting from the burning of fossil fuels, and chlorofluorocarbons resulting from the use of aerosol sprays and refrigeration systems. Under normal conditions, much of the infrared energy of the sun bounces off the earth and reflects back into outer space. However, when these gases accumulate in the earth's stratosphere, the energy from the sun is trapped near the earth's surface (4:131). As a result, the earth's temperature is increased. This increase in temperature has a powerful effect on climate, as well as raising sea levels around the world.
Some of the pollutants in the air are also causing the depletion of the earth's ozone layer. Normally, the ozone layer shields plants and animals from the ultraviolet rays of the sun (3:103). In recent years, a hole has been discovered in the ozone layer above Antarctica (2:12). There is evidence that this damage has been caused by the emission of chlorofluorocarbons into the air. Human emissions are causing environmental damage in other ways, as well. For example, the chemical pollutants caused by automobiles and industries often fall back to the earth in the form of "acid rain" (3:131). This precipitation is known to cause p...