Introduction to Part 1

For nearly 100 years following 1897, when Svante Arrhenius first made a quantitative estimate of how human-caused emissions of carbon dioxide (CO₂) would affect the climate, the presumption was that changes in the climate would occur slowly and that, therefore, society would have decades to develop the policies to slow and then stop climate change. When the President’s Science Advisory Council advised President Lyndon Johnson in 1965 that climate change was an important emerging issue, there was no urgency expressed to deal with it. Similarly, assessments by the US National Academy of Sciences and various US government agencies summarized scientific understanding in the 1970s and 1980s, changes in climate that could make a difference to the environment and society seemed many decades off, especially in that observations were not convincingly showing any climatic response to the increasing concentrations of CO₂ and other greenhouse gases.