Projecting the climatic effects of increasing carbon dioxide: Volume summary

For almost a century, it has been recognized that changes in the atmospheric carbon dioxide (CO2) concentration could alter the Earth's climate. Preliminary compilations of measurements indicated a CO2 increase starting in the 19th century. More definitive measurements made since the International Geophysical Year (IGY) in 1957-1958 have confirmed about a 25% increase in CO2 concentration since about 1850, caused in its initial stages by deforestation and now primarily by fossil fuel combustion. Initial studies of the potential climatic consequences of increasing CO2 concentration indicated that substantial warming would occur, but important approximations and simplification in the early studies introduced many uncertainties. The need to resolve these uncertainties and to carry out more accurate and complete assessments prompted the initiation of a carbon dioxide research program by the US Department of Energy. Over the past 10 years, significant progress has been made in our understanding of the various processes that make up the climate system. These processes include physical, chemical, radiative, and dynamical processes that affect the atmosphere, the hydrosphere (the oceans and water distributed on the land), the cryosphere (the snow and ice on, at, or beneath the Earth's surface), and the biosphere. Improvements have been made in our ability to model these processes through a combination of theoretical research and the collection and interpretation of observational data. This chapter summarizes the significant progress that is reported in more detail and with complete references in the earlier chapters of this volume