This chapter examines the increasingly serious impacts on people as the world warms. Climate change is a serious and urgent issue. The Earth has already warmed by 0.7°C since around 1900 and is committed to further warming over coming decades simply due to past emissions. On current trends, average global temperatures could rise by 2–3°C within the next fifty years or so, with several degrees more in the pipeline by the end of the century if emissions continue to grow. This chapter examines how the physical changes in climate . . . affect the essential components of lives and livelihoods of people around the world — water supply, food production, human health, availability of land, and ecosystems. It looks in particular at how these impacts intensify with increasing amounts of warming. The latest science suggests that the Earth’s average temperature will rise by even more than 5 or 6°C if feedbacks amplify the warming effect of greenhouse gases through the release of carbon dioxide from soils or methane from permafrost. . . . Throughout the chapter, changes in global mean temperature are expressed relative to pre-industrial levels (1750–1850). The chapter builds up a comprehensive picture of impacts by incorporating two effects that are not usually included in existing studies (extreme events and threshold effects at higher temperatures). In general, impact studies have focused predominantly on changes in average conditions and rarely examine the consequences of increased variability and more extreme weather. In addition, almost all impact studies have only considered global temperature rises up to 4 or 5°C and therefore do not take account of threshold effects that could be triggered by temperatures higher than 5 or 6°C.



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