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CLIMATE CHANGE: STATE OF KNOWLEDGE
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This State of Knowledge document presents an introduction to human effects that during the past 100 years have led to increased atmospheric levels of greenhouse gases and corresponding increases in global temperatures. The world's leading climate scientists have concluded that Earth has already warmed about 1 F over the last century. There is mounting evidence that this will lead to global changes and potentially major climatic disruptions. The document introduces the Greenhouse Effect and explains historical emissions of greenhouse gases. A wide variety of human activities contribute to greenhouse emissions, and the overall emissions of greenhouse gases are growing at about 1 percent per year. Subsequent sections of the document discuss climate change over the last 100 years, based on measurements of global surface temperature using ground-, ocean- and satellite-based sites, and predictions about climate change over the next 100 years, based on state-of-the-art climate models. The document concludes with a discussion of vulnerabilities and potential consequences of climate change based on scenarios of doubling current levels of carbon dioxide by 2100. Areas of probable concern are worsening health effects, rising sea level, disruption of the water cycle, changing forests and natural areas, and challenges to agriculture and the food supply. Slowing the rate of change is recommended as a prudent course of action to allow more time for ecological and socioeconomic systems to adapt.