People had long speculated that human activities might affect a region's climate. But a developed conjecture that humanity might change the climate of the entire planet first appeared in 1896: a calculation that carbon dioxide from fossil fuel combustion could gradually warm the globe. Scientists soon rejected the idea. Most people thought it incredible that climate could change globally except on a geological timescale, pushed by forces far stronger than human activity. In midcentury, a few scientists revived the hypothesis of global warming. Meanwhile, the exponential growth of human activity, especially chemical pollution and nuclear armaments, was showing that humanity really could affect the entire atmosphere. Moreover, during the 1960s research suggested that small perturbations might lead to an abrupt change in the climate system. Although nobody expected serious impacts until the distant 21st century, some began to frame global warming not just as a scientific puzzle but as an environmental risk, a security risk, a practical policy question, an international relations issue, and even a moral problem. In the late 1970s a scientific consensus began to take shape, culminating around the end of the century in unanimous agreement among government representatives on essential points, although many uncertainties remained. Meanwhile, increasing media warnings of peril made most of the literate world public aware of the issue, which had deep implications for the human relationship with nature. Skepticism persisted, correlated with aversion to regulation. The majority of the world public were now concerned, but disinclined to take action Copyright © 2010 John Wiley & Sons, Inc.

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