Will major global environmental change take place in the 21st century? How much is known about the change? Can we find out more? Must we take it seriously? Should we do something now, or can we wait a decade or so? This book seeks to answer these questions. Scientists are reaching consensus that rates of change in many of the environmental indicators are already increasing in some cases, and are likely to increase even more rapidly in the 21st century. Although there are still uncertainties, the case is made that the consequences of not taking action are too great to take a chance that the scientists' expectations are wrong. The book leads to the admonition - Think long term, act now! Signs of Change (Chapter 1) Chapter 1 provides a definition of global change and some examples of changes already taking place in the driving forces (demographics, energy consumption, deforestation, 'mining of groundwater', etc. ) and in some of the environmental variables (increasing atmospheric carbon dioxide concentrations, depletion of stratospheric ozone, desert­ ification, decreasing biodiversity, etc. ) The chapter raises some important questions for science and society, and concludes that global environmental change is both a scientific and a political issue.