THE GREENHOUSE EFFECT AND GLOBAL WARMING
Carbon dioxide and other naturally occurring gases in the earth’s atmosphere create a natural greenhouse effect by trapping and absorbing solar radiation. These gases act as a blanket and keep the planet warm enough for life to survive and flourish. The warming of the earth is balanced by some of the heat escaping from the atmosphere back into space. Without this compensating flow of heat out of the system, the temperature of the earth’s surface and its atmosphere would rise steadily.
Scientists are increasingly concerned about a human-driven greenhouse effect resulting from a rise in atmospheric levels of carbon dioxide and other heat-trapping greenhouse gases. The man-made greenhouse effect is the exhalation of industrial civilization. A major contributing factor is the burning of large amounts of fossil fuels—coal, petroleum, and natural gas. Another is the destruction of the world’s forests, which reduces the amount of carbon dioxide converted to oxygen by plants. Emissions of carbon dioxide, chlorofluorocarbons. nitrous oxide, and methane from human activities will enhance the greenhouse effect, causing the earth’s surface to become warmer. The main greenhouse gas, water vapor, will increase in response to global warming and further enhance it.
There is agreement within the scientific community that the buildup of greenhouse gases is already causing the earth’s average surface temperature to rise. This is changing global climate at an unusually fast rate. According to the World Meteorological Organization, the earth’s average temperature climbed about 1 degree F in the past century, and nine of the ten warmest years on record have occurred since 1990. A United Nations panel has predicted that average global temperatures could rise as much as 10.5 degrees F during the next century as heat-trapping gases from human industry accumulate in the atmosphere.
What are the potential impacts of an enhanced greenhouse effect? According to estimates by an international committee, North American climatic zones could shift northward by as much as 550 kilometers (340 miles). Such a change in climate would likely affect all sectors of society. In some areas, heat and moisture stress would cut crop yields, and traditional farming practices would have to change. For example, in the North American grain belt, higher temperatures and more frequent drought during the growing season might require farmers to switch from corn to wheat and to use more water for irrigation.
Global warming may also cause a rise in sea level by melting polar ice caps. A rise in sea level would accelerate coastal erosion and inundate islands and low-lying coastal plains, some of which are densely populated. Millions of acres of coastal farmlands would be covered by water. Furthermore, the warming of seawater will cause the water to expand, thus adding to the potential danger.
Global warming has already left its fingerprint on the natural world. Two research teams recently reviewed hundreds of published papers that tracked changes in the range and behavior of plant and animal species, and they found ample evidence of plants blooming and birds nesting earlier in the spring. Both teams concluded that rising global temperatures are shifting the ranges of hundreds of species—thus climatic zones—northward. These studies are hard evidence that the natural world is already responding dramatically to climate change, even though the change has just begun. If global warming trends continue, changes in the environment will have an enormous impact on world biology. Birds especially play a critical role in the environment by pollinating plants, dispersing seeds, and controlling insect populations; thus, changes in their populations will reverberate throughout the ecosystems they inhabit.