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Workers cover a glacier with oversized plastic sheets on the peak of Germany's highest mountain, Zugspitze (9,700 feet), in southern Germany, on May 10, 2011. The sheets are meant to keep the glacier from melting during the summer months. It's one proposed geoengineering tactic in the fight against climate change: reflecting sunlight back into space or cooling the planet by sucking heat-trapping carbon dioxide from the air. (RNS/AP/Matthias Schrader)