Global Warming: An Introduction
by Robert J. Ruhf
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This paper was written in 1999 and focuses on research done in the early to mid 1990's. I have not yet had the time to update this paper to include research conducted more recently. The reader may wish to look elsewhere for a summary of more recent research.
[About the author: Robert J. Ruhf received his Ph.D. in Science Education from the Mallinson Institute for Science Education at Western Michigan University in 2006. He also received a Communications degree from Cornerstone University in 1990, a Meteorology degree from Central Michigan University in 1998 and a master in Geography from Western Michigan University in 2000. He currently works as a program evaluator with the center for Science and Mathematics Program Improvement (SAMPI) at Western Michigan University.]
Global Warming: An Introduction
Many researchers, scientists, and environmentalists are expressing concerns about changes in the overall climate of the earth. Some believe that a dramatically dangerous warming is taking place in the overall global climate, a problem that is referred to as "global warming." This paper will attempt to explore this very issue.
Climate is defined as the analysis of accumulated weather data for long term patterns and trends. The Oxford Reference Dictionary defines change as, "To make or become different." Climate change is therefore defined as "long-term weather patterns and trends becoming different over an extended period of time." For example, if the average temperature in Kalamazoo, Michigan over the 20th century is significantly higher or lower than the average temperature in Kalamazoo, Michigan over the 19th century, this would be an example of climate change.
Changes in climate can result from both natural events and human activities. Examples of natural causes of climate change are volcanic eruptions, variations in the earth's orbit around the sun, and variations in solar output (Ahrens, 485-491). Examples of human-induced causes of climate change include industrial pollutants and fossil fuels (Rhodes, 116), warming of average annual temperatures due to urbanization (Eichenlaub, 163), and changes in the earth's albedo due to deforestation of tropical rainforests (Geiger, 320). Climate change in the context of this paper refers to changes that result from human activities, especially as these changes relate to the issue of global warming. Of special importance is the "greenhouse gas" effect which is defined as, "The trapping of thermal emissions from the earth's surface by human-induced greenhouse gases" (He). If global warming is indeed happening, it is the greenhouse gas effect that is believed to be the most responsible.
There are some scientists who do not believe that there is enough evidence to support the idea of global warming. They assert that concerns about global warming have been blown well out of proportion by the media. At the same time, other scientists assert that there is sufficient evidence to suggest that industrial activities, automobile emissions, and technological pollutants may eventually result in dangerous (and even deadly) trends in the overall global climate. This paper will attempt to address this concern by analyzing some of the scientific studies that have been published in major meteorology journals.
Our atmosphere consists of many gases. Some of these gases, such as carbon dioxide and water vapor, naturally absorb long-wave radiation that is emitted from the earth's surface. Short-wave solar radiation enters the earth's atmosphere and is absorbed by the earth's surface. This radiation is then recycled and emitted as long wave terrestrial radiation. Gases such as water vapor and carbon dioxide absorb this radiation, hold it in the atmosphere, and keep the temperature of the earth warmer than it would otherwise be if there wasn't an atmosphere. This is what meteorologists refer to as the "natural greenhouse effect" (Mower).
Problems could potentially arise, however, when human activities add additional trace gases into the atmosphere that also absorb out-going long-wave radiation. These additional trace gases include methane, chlorofloro carbons, nitrous oxide, aerosols, ozone, and carbon dioxide. The result is an increase in the amount of long-wave radiation that is being trapped by the atmosphere. It is believed that this could eventually increase the average overall global temperature.
Carbon dioxide "...is considered the trace gas of greatest importance because of the substantial increase in its atmospheric concentration as well as its probable continued rise due to global consumption of fossil fuels" (Rhodes, 116). It is clear from looking at the evidence that carbon dioxide concentrations are increasing dramatically in the atmosphere. Observations of carbon dioxide concentrations are available for several locations. Over the period of 1973 to 1982, the atmospheric concentrations of carbon dioxide in Barrow, Alaska rose steadily from 332.6 parts per million (ppm) to 342.8 parts per million (Geiger, 110-111).
This is not isolated to Barrow, Alaska. Records from other locations, such as Mauna Loa in Hawaii, are confirming that carbon dioxide concentrations are increasing in the atmosphere at a dramatic rate. Continuous instrument records for atmospheric carbon dioxide concentrations date back to the 1950's at the Mauna Loa observatory (Michaels, 1564). In 1958, the average atmospheric concentration of carbon dioxide was only 316 parts per million (ppm). Preindustrial carbon dioxide concentrations are believed to be 279 parts per million (Michaels, 1564), and the atmospheric carbon dioxide concentration in 1990 was 353 parts per million (Rhodes, 116). However, as one author points out, the fact that we are dealing with significant changes in carbon dioxide does not automatically mean that we are looking at a serious problem (Lindzen, 288). This author points out that carbon dioxide is a " ...minor atmospheric constituent and as such, its variations might not be notably important." He goes on to say that there are a number of things that increasing levels of carbon dioxide could effect and influence, including in ways that are beneficial. For example, " ...at altitudes of 25 km to 90 km, the atmosphere is cooled primarily by thermal radiation emitted to space by carbon dioxide. Increasing carbon dioxide should cool these regions, and this, in turn, should lead to increasing concentrations of ozone at these levels. Increasing carbon dioxide might also stimulate the growth of vegetation..." (Lindzen, 288-289).
While there are indeed some possible benefits to increased atmospheric carbon dioxide concentrations, "...the main concerns have focused on the possibility that increasing carbon dioxide might significantly warm our climate" (Lindzen, 289). One author wrote that there is "...general agreement that increasing carbon dioxide will produce warming due to its ability to absorb in the infrared radiation" (Lindzen, 289).
There are studies that have indicated that no significant change in the overall global climate has yet taken place. For example, a study that was done by P. W. Spencer and J. R. Christy, using temperature records from the period of 1979 through 1990, showed a global trend of only +0.04 degrees Celsius per decade (Michaels, 1566). Other studies showed that the Northern Hemisphere has had no significant warming, while the Southern Hemisphere has had a slight temperature increase in the order of 0.2 degrees Celsius since the 1950's (Michaels, 1566). Patrick J. Michaels speculates that the reason that we have not seen a significant increase in temperatures in the Northern Hemisphere is because of the balancing effect of anthropogenerated sulfates going into the atmosphere as a result of industrial pollution. Anthropogenerated sulfates have a cooling effect on the atmosphere because of their ability to reflect incoming solar radiation back to space. Michaels explains this in more detail when he writes, "Because anthropogenerated sulfates are primarily produced and reside in the Northern Hemisphere, we may therefore be equaling the current enhanced greenhouse forcing ... with actual negative forcing in the hemisphere that contains most of the world's population" (Michaels, 1573).
This lead to the obvious question of whether or not the lack of a significant increase in global temperature should be taken as evidence that we should not be concerned about the issue. William W. Kellog of the National Center for Atmospheric Research in Boulder, Colorado has written an article called "Response to Skeptics of Global Warming" in which he responds to many of the objections that have been raised against global warming. Kellog points out that "...five or so of the most advanced climate models, developed over a period of many years by top notch teams, have all come to essentially the same conclusion: The global average surface temperature would probably rise by about 2 to 5 K if the greenhouse gas concentration were maintained at double the pre-industrial revolution level" (Kellog, 500). Kellog suggests that the reason that we have not seen a change as of yet in the overall warming is because of a temperature lag of several decades "...due in large part to the large heat capacity of the oceans of the world" (Kellog, 500). He asserts that the evidence is still in favor of the fact that, sooner or later, a serious warming of the climate will occur.
Ahrens, C. Donald. Meteorology Today: An Introduction to Weather, Climate, and the Environment, 5th Edition. New York: West Publishing Company, 1995.
Eichenlaub, Val L., Jay R. Haman, Fred V. Nurnberger, and Hans J. Stolle. The Climatic Atlas of Michigan. University of Notre Dame Press: Notre Dame, Indiana, 1990.
Geiger, Rudolf, Robert H. Aron, Paul Todhunter. The Climate Near the Ground, 5th Edition. Braunschweig, Germany: Friedr, Veiweg & Sohn Verlagsgesellschaft, 1995.
He, Chansheng. Classroom notes presented verbally in Natural Resource Management, GEOG 555. Western Michigan University, winter 1999.
Kellog, William W. "Response to Skeptics of Global Warming." Bulletin American Meteorology Society. Volume 74, Number 4 (April 1991), pp. 499-511.
Oxford American Dictionary. Oxford University Press: New York, 1980.
Lindzen, Richard S. "Some Coolness Concerning Global Warming." Bulletin American Meteorology Society. Volume 71, Number 3 (March 1990), pp. 288-299.
Michaels, Patrick J. "Global Warming: A Reduced Threat?" Bulletin American Meteorology Society. Volume 73, Number 10 (October 1992), pp. 1563-1577.
Mower, R. Neil. Classroom notes presented verbally in Physical Meteorology, ESC 530. Central Michigan University, autumn 1996.
Rhodes, Steven L. "Climate and Environmental Degradation of the Great Lakes." Journal of Environmental Systems. Volume 22, Number 2, pp. 105-122.
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