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Home > Climate Change Science > Time Scale for Water Utilities
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First, it is important to understand that climate change is already happening. Over the past century, global average surface temperature increased by approximately 0.6°C (Figure 1). Warming is expected to accelerate during the current century. The modest warming to date has not been evenly distributed over the surface of the globe. In particular, arctic areas have warmed more rapidly than other areas. Climate model simulations also suggest that future warming will tend to be most pronounced in the higher northern latitudes (Figure 2). That picture might change if there is a significant slowing of the oceanic thermohaline circulation, because that would reduce the poleward transport of heat through the ocean.
Figure 1. Variations of the Earth’s surface temperature for the past 140 years (1860 to 2000). Source: IPCC, 2001: Climate Change 2001: The Scientific Basis. Contribution of Working Group I to the Third Assessment Report of the IPCC. Cambridge, UK: Cambridge University Press.
Figure 2, page 26.
Figure 2. The multiple model ensemble map for the end of the 21st century projects that most warming will occur over the Arctic and land areas, when compared with the 1960–1990 Normals. Image created by Robert A. Rohde / Global Warming Art http://www.globalwarmingart.com/wiki/Image:Global_Warming_Predictions_Map_jpg
As for impacts on water resources, warming over the past half-century appears to be associated with reduced spring snowpacks in some of the mountainous areas of the western United States. In California’s Sacramento River Basin, for example, spring runoff has been peaking earlier, and there has been a century-long downward trend in late spring and early summer flow as a proportion of total annual flow (Dettinger and Cayan 1995). In addition, higher sea levels have caused saltwater intrusion problems in some areas. Over the past century, warmer temperatures contributed to rising sea levels through thermal expansion of the World’s oceans and glacial melt (U.S. Geological Survey 2000). Measured increases vary at different locations as a result of local processes, such as subsidence. Miami-Dade County, for example, has experienced a twelve-inch increase in sea level since 1848.
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