The current state of knowledge onclimate change and water points to predominantly negativeeffects. This paper reviews the literature on these effectsby geographical region and notes the differences as well asthe uncertainties. An important feature is the fact that theclimate effects will occur on top of water scarcity thatcurrently prevails in many parts of the world. The impact ofclimate change on scarcity is present but generally smallcompared to the impact of the socioeconomic factors. Changesin efficiency of water use could make a big contribution towater problems, including those caused by climate change.In-depth estimates of damages from climate change related towater have been made to 2060 and, less accurately, to 2100.The 2060 estimates indicate that the impacts from watersupply changes or changes in water-related extreme eventsand marine flows add up to about 1.5 of GDP in 2060 in theabsence 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 areeven more uncertain but there are strong reasons to believethey will be greater as a percentage of GDP, perhaps around10 globally and possibly even higher. Adaptation can make amajor contribution to reducing damages from climate changefor all mitigation scenarios, and more so when mitigation isabsent or limited. Adaptation will require both private andpublic actions.
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