Date of this Version
Global warming seems destined to become one of the defining issues of the twenty-first century. Most scientists now agree that measurable increases in average global mean temperatures over the past decades cannot be explained by natural temporal variations in the earth’s climate. Instead, global warming appears to be a fact that can be attributed to human induced changes in the composition of greenhouse gasses in the earth’s atmosphere. Moreover, if the trend toward ever increasing temperatures continues, consequences for the earth’s environment will be dramatic, and perhaps irreversible. Growing concern over the potential for human activities to alter the earth’s climate has precipitated a flurry of proposals designed to address the problem. Most notably, an international agreement to address the issue, the Framework Convention on Climate Change,1 was adopted in 1992. That agreement, and the fact that it has been signed and ratified by most nations on earth, including the United States, is testament to the significance and seriousness of the issue.
The Greenhouse Effect and its Vulnerability to Human Induced Changes
Earth’s climate is warmed and moderated by gases in the atmosphere that trap the sun’s heat, notably water vapor and carbon dioxide. These gases allow radiant energy from the sun in the form of visible light to pass through and reach the earth’s surface where it is converted into heat. Some of this heat is reflected from the earth’s surface in the form of infrared radiation. Certain gasses, including carbon dioxide, absorb a portion of this heat energy and reradiate it back toward the surface of the earth, much as a greenhouse allows sunlight to enter and heat the interior, but where the roof and walls retain the heat. The greenhouse effect is critical to maintaining life on the planet. Absent greenhouse gasses, heat energy would be reflected back into deep space and average planetary temperatures would be some 60 degrees Fahrenheit colder than they are today.