Global Warming

Global warming is an example of global climatic change. To understand the concept of global warming and make decisions about how to respond to the seemingly contradictory information received from various sources, it is important to distinguish between climate and weather. Weather applies to short-term changes in properties of the lower atmosphere such as temperature, relative humidity, precipitation, cloud cover, barometric pressure, and wind speed. Climate is the general pattern of weather conditions, seasonal variation, and weather extremes over a long time—at least thirty years. A summer with record high temperatures is not a signal that global warming is occurring. A winter with record cold is not proof that global warming is not occurring. Climate change, especially global climate change, must be determined from global averages of weather conditions collected, averaged, and compared over decades.

Climate Change

Earth's climate has changed dramatically many times in the past and will almost certainly change many times in the future. Twenty thousand years ago, the places where Minneapolis, Milwaukee, Chicago, and Detroit now stand were covered with ice. Scientists do not know what caused the ice to spread or what caused it to retreat. Once the ice began to retreat, it did so very rapidly, completely disappearing in a few thousand years. Only a few remnants, such as the Greenland ice sheet, still exist. If the Greenland ice sheet were to melt, global sea levels would rise by 8 to 10 meters (26 to 33 feet), and many major seaports and coastlines would be flooded. If the Antarctic ice sheet melted, Earth's oceans would rise by 100 meters (330 feet).

Humans would survive climate changes of this magnitude, but social and political organizations probably would not. Scientists know this because past civilizations have not survived similar climate changes. Around 1000 C. E. , a well-established Norse colony thrived in what is now southern Greenland. The colony had been established during a relatively warm period when the temperatures in the area were 2 to 4°C (4 to 7°F) above average. It vanished almost without trace as the climate returned to normal, an ice sheet moved back over pastures, and the advancing sea ice cut off communications. That small temperature change made the difference between a thriving colony and disaster.

Earth's climate is still changing. Research strongly indicates that Earth is gradually warming up. According to the United States Environmental Protection Agency, the best estimates are that Earth's temperature has increased by 0.5°C (1.0°F) in the last century, precipitation has increased by 1 percent, and sea level has risen by 2 to 5 centimeters (1.0 to 2.0 inches). This is strong evidence for a small but significant increase in global average temperature. Almost all scientists agree with these facts. However, scientists cannot agree on what causes global warming. Many researchers are convinced the data show unequivocally that global warming is directly related to the increase in greenhouse gases such as carbon dioxide. Others feel the data simply indicate a short-term climatic phenomenon.

The "greenhouse" effect is somewhat misnamed. A greenhouse gets warm on a sunny winter day because the sunlight passes through the glass, warming the plants and other surfaces in the greenhouse. The plants warm the air, but the warm air cannot escape, so the temperature in the greenhouse rises. The planetary greenhouse effect operates a little differently. Infrared radiation from the sun passes through the atmosphere and warms the surface of Earth. As the surface warms, it also radiates infrared. However, since the temperature of Earth is much lower than the temperature of the surface of the sun, the infrared radiation emitted by the ground, building, rocks, and plants has a much longer wavelength. Radiation of this longer wavelength cannot pass through the atmosphere, and is absorbed by the air or reflected back to the ground.

A little greenhouse effect is a good thing. If it were not for the greenhouse effect, Earth's average surface temperature would be well below the freezing point of water and life could not exist. The question is, can we have too much of a good thing? Is it possible that rising temperatures on Earth are due to increased levels of greenhouse gases in the atmosphere?

Greenhouse Gases

There are several greenhouse gases. Naturally occurring greenhouse gases include water vapor, carbon dioxide, methane (from plant decay and other sources), nitrous oxide (from volcanoes), and ozone. All these gases can also result from human activity. Carbon dioxide is released when fossil fuels are burned. Methane is emitted from livestock operations and the decomposition of organic waste. Nitrous oxide is emitted by internal combustion engines and by the burning of solid waste. Several synthetic materials are powerful greenhouse gases, including hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride.

Of all the greenhouse gases, carbon dioxide causes the most concern and is therefore closely monitored. Scientists know that carbon dioxide levels in the atmosphere have increased steadily since the beginning of the Industrial Revolution. Most scientists also agree that the average surface temperature of Earth has increased by about 0.5°C (1°F) over the last 100 years. In addition, most scientists now think there is a direct correlation between the increase of carbon dioxide in the atmosphere and the increase in the global average temperature. What remains uncertain is what will happen in the future and what should be done about it. Although the consensus among scientists is that Earth's temperature will continue to increase over the next 100 years, there is no consensus on the size of the increase. Estimates range from 1°C (2°F) to over 5°C (9°F). A 10°C rise will have little effect and is no cause for alarm. However, a 5°C rise could have disastrous consequences. Sea level could rise by 100 meters (330 feet), deserts could expand dramatically, and precipitation patterns would change in unpredictable ways.

Controversy Over Global Warming

Discussions about global warming have become intensely political, with "conservatives" and "liberals" taking contradictory positions. Two questions related to global warming should be discussed and debated. The first question is whether global warming is occurring and whether humans are causing it. The second question is this—if global warming is occurring and humans are causing it, what should be done about it? This second question is clearly a matter of public policy and political process. Public media, Congress, and other public forums are the appropriate arenas for the debate about this question.

Many national governments and international organizations continue to raise concerns about global warming and the possible link to carbon dioxide emissions. Most countries are firmly committed to strengthening international response to risks of adverse climate change. Since gases emitted into the atmosphere do not recognize political boundaries, this is a legitimate question of international concern. The United Nations Framework Convention on Climate Change currently provides a vehicle for discussion and continuing scientific research into this difficult problem.

SEE ALSO FOSSIL FUELS.

Elliot Richmond

Bibliography

Barnes-Svarney, Patricia. New York Public Library Desk Reference. New York: Macmillan, 1995.

Berger, John J. Beating the Heat: Why & How We Must Combat Global Warming. Berkeley, CA: Berkeley Hills Books, 2000.

Gelbspan, Ross. The Heat Is On: The Climate Crisis, the Cover-Up, the Prescription. Cambridge, MA: Perseus Publishing Company, Inc., 1998.

Goodstein, Eban. The Trade-Off Myth: Fact and Fiction About Jobs and the Environment. Washington, D.C.: Island Press, 1999.