A bicyclist rides down the street during this year's Bike to Work Day in San Francisco. Events such as this promote biking as a viable form of commuting, but tensions between cyclists and drivers persist.
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Coal-fueled power stations like this one in Warrington, United Kingdom, are said to be contributing to global warming. But e-mail messages stolen from a group of climate scientists recently are fodder for skeptics who say global warming is a plot, not a real problem.
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