Now that everyone is looking for ways to generate carbon-free electricity, at least one ancient method is coming back in vogue—the hydroelectric dam. Dams are clean, relatively cheap, and, best of all, there's no glitzy technology required. The first electricity-generating waterwheel, after all, appeared in Appleton, Wisconsin in 1882—just two years after Edison had shown the world incandescent lighting. If Wisconsin can do it, anyone can!

And there's been a real uptick in recent years: The World Bank plans to spend about $1.3 billion funding dam projects in 2011, up from $800 million last year. Environmental groups like Greenpeace China are also embracing hydropower with a newfound fervor. Already, some 48,000 dams taller than 50 feet have been built around the world, and plenty more are on the way in places like Brazil, India, and Laos—countries looking to unhitch themselves from fossil fuels. China alone is backing some 200 projects in developing countries (though many analysts say they're doing this in exchange for access to resources, not because they're worried about the climate).

So the future's looking bright, yeah? Well, sort of. As David Biello points out in a terrific Yale e360 piece, there are more than a few problems with the dam craze. Back before the world started fretting about greenhouse-gas emissions and climate change, recall, many environmental groups actually opposed large-scale dam projects, and not without reason—the dams usually displace people and can wreak havoc on the local ecosystems. China's Three Gorges Dam, which produces as much electricity as 50 to 100 small coal-fired plants, has already displaced some 1.2 million people, and isn't done yet. Many Brazilian dam projects threaten to flood sensitive rainforest areas and, potentially, alter parts of the Amazon River that it would affect the migration patterns of some 750 species of fish. None of those concerns have gone away. But while environmental groups still protest some especially egregious projects, it's hard to oppose renewable power these days.

Still, it's hard to imagine that hydropower frenzy in China—or elsewhere around the globe—will abate anytime soon. A few Chinese analysts think hydropower could one day supplant coal as the country's chief energy source. Yet Biello notes that dam planning in China is often less-than-stellar—many subsidiary dams are being erected for the sole purpose of preventing silt buildup behind the giant Three Gorges, while other dams are poorly planned and end up depriving each other of water. Redundancies are everywhere. And the surplus dams are causing mudslides, relocations, and devastating the water quality in some areas. Worst of all, Chinese companies often receive carbon credits for these projects under the Kyoto Protocol—despite the fact that many of these dams would get built with or without the credits. (One more reason the carbon-offset system is badly flawed.)

Oh yes, and the final irony? Given that the Earth is still warming, it's possible that many of the glaciers in the Himalayas and the Tibetan plateau will shrink dramatically in the coming century. Not only will that affect the supply of freshwater for some 1 billion people, but reduced glacial melt could also dry up the Yangtze and Yellow rivers—precisely where most of China's hydroelectric dams sit. Whoops. Indeed, it's another reason why Beijing should worry about global warming—one of their major power sources (and drivers of economic development) increasingly depends on limiting future temperature rises.

--Bradford Plumer