The global-warming theory argues that carbon dioxide emissions from the burning of fossil fuels (e. g., in electrical generation plants) will eventually lead to significant increases in the earth's average global temperature, with catastrophic consequences. Based solely on computer models from which many poorly understood factors have been excluded, the theory lacks any valid empirical basis; on the contrary, the most reliable evidence indicates that average global temperatures have been decreasing slightly since about 1979. Because land-based temperature gauges are typically located in or near urban areas, widely recognized as unrepresentative "heat islands," they provide relatively inaccurate measurements of average temperatures. The most reliable data, provided by satellites and weather balloons, show a slight downward average temperature trend over the last two decades. Over longer periods, the earth is subject to significant natural temperature fluctuations, unrelated to human activities. Since the end of the Little Ice Age around 150 years ago, average global temperatures are believed to have risen about 1.5º F. The vast majority of this increase, however, was realized prior to 1940, when fossil fuel consumption remained far below that of recent years (source).