Germany, which last year generated 23.4 percent of the electricity that it used from renewable sources, is often thought of as a world leader in clean energy. But the nation still filled even more of its energy needs — 25 percent — by burning brown coal,  which is one of the dirtiest fuels around in terms of carbon dioxide emissions that contribute to climate change.

Since the late 1970s, giant earth-moving machines have been digging what German environmentalists decry as “Europe’s biggest hole” at Hambach in the Lower Rhine basin. The massive open-pit mine now sprawls across a more than 50-square-mile area, and the machines each day are digging up 240,000 tons of brown coal — enough to fill a stadium with a 100-foot-high layer of it, according to German energy company RWE, which operates the site — and describes it, oddly, as “a popular tourist destination in the region.”

The coal mine is also home to the world's largest machine, an excavator that's twice the length of a soccer field and 30 stories tall.

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The German environmental group BUND is worried that continued mining in the area will destroy the local forest, which is home to an endangered species of woodpecker and numerous other birds, but RWE counters that it is restoring the area by planting trees there. After the the coal is exhausted around 2040,  the hole will be converted into what might be the biggest man-made lake in Europe.

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Paradoxically, Germany is even more dependent than ever upon brown coal, thanks to the government’s decision to gradually phase out nuclear power in the wake of the 2011 accident at Japan’s Fukushima nuclear complex. German environmentalists are now worried because their nation’s carbon dioxide output, which had been on the decline, is now again rising, according to Deutsche Welle. They’re pushing the European Union to force German utilities to curtail their use of coal.