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The current state of knowledge on climate change and water points to predominantly negative effects. This paper reviews the literature on these effects by geographical region and notes the differences as well as the uncertainties. An important feature is the fact that the climate effects will occur on top of water scarcity that currently prevails in many parts of the world. The impact of climate change on scarcity is present but generally small compared to the impact of the socioeconomic factors. Changes in efficiency of water use could make a big contribution to water problems, including those caused by climate change. In-depth estimates of damages from climate change related to water have been made to 2060 and, less accurately, to 2100. The 2060 estimates indicate that the impacts from water supply changes or changes in water-related extreme events and marine flows add up to about 1.5 of GDP in 2060 in the absence of mitigation or adaptation. This average figure, however, may be an underestimate of a number of reasons. Estimates to 2100 of potential damages in economic terms are even more uncertain but there are strong reasons to believe they will be greater as a percentage of GDP, perhaps around 10 globally and possibly even higher. Adaptation can make a major contribution to reducing damages from climate change for all mitigation scenarios, and more so when mitigation is absent or limited. Adaptation will require both private and public actions.
