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A Warm Global Issue

In 1986, a panel of 150 scientists from eleven countries issued a report warning that human activities such as automobile use, the production of energy from burning fossil fuels, and deforestation could cause global temperatures to rise by intensifying the earth’s greenhouse effect.

An essential component of the earth’s climate, the greenhouse effect is the warming process that results from the atmospheric presence of heat-trapping gases such as water vapor, carbon dioxide, and nitrous oxide. Much of the solar energy that reaches the planet is absorbed by oceans and land masses, which in turn radiate the energy back into space. However, small concentrations of water vapor and other “greenhouse gases” convert some of this energy to heat and either retain it or reflect it back to the earth’s surface. This “trapped” energy creates a blanket of warm air around the earth that moderates global temperatures and climate patterns. Without greenhouse gases, the earth would exist in a perpetual ice age.

The scientists who maintained in the 1980s that human activities could amplify the greenhouse effect were elaborating on a nineteenthcentury theory proposed by Swedish chemist Svante Arrhenius. In 1896, Arrhenius hypothesized that the carbon dioxide produced from the burning of coal and other fossil fuels would cause global temperatures to rise by trapping excess heat in the earth’s atmosphere. But the global warming theory did not capture the world’s attention until 1988, when James Hansen, an atmospheric scientist and director of the Goddard Institute for Space Studies at NASA, testified before a U.S. Senate committee that the “evidence is strong” that human-made pollutants were raising world temperatures. If temperatures continued to rise, he warned, the earth would face catastrophic climate changes that would adversely affect the environment and human health.

Initially, most climate researchers were skeptical about Hansen’s warning. It was true that carbon...