The God Species: How the Planet Can Survive the Age of Humans by Mark Lynas

Author:Mark Lynas [Lynas, Mark]
Language: eng
Format: epub
ISBN: 9780007375226
Google: cWBotwAACAAJ
Publisher: HarperCollins Publishers Limited
Published: 2012-03-26T00:14:45+00:00

BOUNDARY FIVE

FRESHWATER

We have polluted the seas and appropriated land from other competing species—but water we have not so much stolen as imprisoned, behind concrete dam walls, within dark reservoirs, and behind the high levees that hem in once-mighty free-flowing rivers like the Mississippi and the Yangtze. Whole natural drainage basins, which once responded to the grand seasonal cycles of winter flood and summer drought, now react meekly to the whims of water managers seated in the control rooms that govern sluice gates in tens of thousands of large dams. The Colorado River may have gouged out the most spectacular cutting in the world—the Grand Canyon—but today the flow of this powerful torrent is as much a product of human hydrological engineering as it is of any natural force. If you live in Las Vegas, Los Angeles, or Phoenix, Arizona, the Colorado is more part of an enormous plumbing works that ends in your shower or bath, as it does for 30 million other people. Its ecological role has declined in tandem, for in an average year hardly a drop of the precious water in this 1,400-mile (2,200-km) river now succeeds in reaching the sea.

To put this in context: Worldwide, 60 percent of the 227 largest rivers have been fragmented by man-made infrastructure, and the total number of dams blocking the natural flow of the planet’s watercourses is estimated at 800,000.1 These impound approximately 10,000 cubic kilometers of water—a quantity so substantial that it measurably reduces the rate of sea level rise (by about half a millimeter a year for the last half-century2) and even changes the mass distribution of the planet sufficiently to alter its axis and slightly increase the speed of its rotation.3 The sheer scale of human engineering activity on rivers has been extraordinary: On average we have constructed two large dams per day over the last fifty years, half of those in China alone.4 Humans have affected the water cycle in less visible ways too: Deforestation and irrigation are altering water-vapor flows over the planet’s surface;5 changes in land use and climate are increasing total planetary river runoff.6 Human engineering can have large-scale impacts—agriculture in Pakistan’s dry Indus Basin, supported by the largest irrigation network of canals and dams in the world, probably has a direct effect on the region’s monsoon.7

Due to the globe-girdling reach of modern human civilization, these regional and planetary-scale changes are perhaps unsurprising, for humanity has always had an umbilical connection with rivers and fresh water. Imperial capitals throughout history have lined major watercourses, from Nanjing on the Yangtze to London on the Thames. When water became scarce or was misused—as in ancient Mesopotamia or during Central America’s Classic Maya period—great civilizations could come crashing down, leaving little trace behind as their once unconquerable cities were reclaimed by sand or forest. Today we face the danger of overusing water resources on a planetary scale, and the consequences for our advanced civilization may be just as significant in the long run.

TURNING ON THE TAP

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