starting in the 1960s, scientists recognized long-range problems, concentrating at first on sea-level rise and a threat to food supplies. New items were gradually added to the list, ranging from the degradation of ecosystems to threats to human health. Experts in fields from forestry to economics, even national security experts, pitched in to assess the range of possible consequences. It was impossible to make solid predictions given the complexity of the global system, the differences from one region to another, and the ways human society itself might try to adapt to the changes. But by the start of the 21st century, it was clear that climate change would bring serious harm to many regions — some more than others. Indeed many kinds of damage were already beginning to appear. (This essay does not try to cover the entire history of impact studies, but sketches some examples. Current scientific understanding of impacts is summarized at the end). Through the first half of the 20th century, when global warming from the greenhouse effect was only a speculation, the handful of scientists who thought about it supposed any warming would be for the good. Svante Arrhenius, who published the first calculations, claimed that nations like his native Sweden "may hope to enjoy ages with more equable and better climates."(1) Most people assumed that a "balance of nature" made catastrophic consequences impossible, and if any change did result from the "progress" of human industry, it would be all to the good. In any case nobody worried about the impacts of a climate change that scientists expected would only affect their remote descendents, several centuries in the future, if it happened at all.
| - LINKS - for more on this see <=Public opinion
A few scientists took a closer look in the late 1950s when they realized that the level of carbon dioxide gas (CO2) in the atmosphere might be rising, suggesting that the average global temperature might climb a few degrees Celsius before the end of the 21st century. Roger Revelle, the most senior of these researchers, publicly speculated that in the 21st century the greenhouse effect might exert "a violent effect on the earth's climate" (as Time magazine put it). He thought the temperature rise might eventually melt the Greenland and Antarctic icecaps, raising sea level enough to flood coastlines. Noting that climate had changed abruptly in the past, perhaps bringing the downfall of entire civilizations in the ancient world, in 1957 Revelle told a Congressional committee that the greenhouse effect might someday turn Southern California and Texas into "real deserts." He also remarked that the Arctic Ocean might become ice-free, to Russia's advantage. Everyone understood this was all speculation, more science fiction than scientific prediction. Another senior scientist, more cautious, told his colleagues that they should take seriously the possibility of "warming, and possible changes in rainfall and cloudiness" by the early 21st century. Meanwhile a pair of graduate students reported that the CO2 greenhouse effect "could raise such problems as coastal flooding due to rise in sea level and increased aridity in certain areas."
| <=>Revelle's result
| More scientists began to look at the matter after 1960, when observations showed the level of CO2 in the atmosphere was indeed rising rapidly. In 1963 a path-breaking meeting on "Implications of Rising Carbon Dioxide Content of the Atmosphere" was convened by the private Conservation Foundation. "Conservation" was the traditional term for a movement that was developing into "environmentalism," centered on the growing realization that human activities had expanded to the point where they could damage vital ecosystems on a global scale. Participants in the meeting began to frame greenhouse warming as an environmental problem — something "potentially dangerous" to biological systems as well as to humans.(2)
| The meeting set the pattern...
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