India's capital is among the most polluted cities in the world, thanks in large part to the growing number of vehicles on its roads. In its just-announced climate change plan, India does not commit to an absolute reduction of its emissions. Instead, it will slow the release of greenhouse gases. DIBYANGSHU SARKAR/AFP/Getty Images hide caption

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Using an instrument they've named the HOLODEC, for Holographic Detector for Clouds, scientists can now see in fine detail the way air and water droplets mix at a cloud's wispiest edge. iStockphoto hide caption

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David Whitcomb of Waynesboro, Va., says he paid a premium for the diesel engine on his 2015 Passat TDI because he thought it would mean fewer emissions. Courtesy of David Whitcomb hide caption

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Residents of Flint, Mich. (shown here in January), have been protesting the quality and cost of the city's tap water for more than a year. Steve Carmody/Michigan Radio hide caption

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Dry conditions in California have limited the amount of pollen and nectar bees can collect. Ezra David Romero/Valley Public Radio hide caption

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A worker pours a bucket of pesticide into a machine to be sprayed on almond trees at Del Bosque Farms Inc. in Firebaugh, Calif., on April 6, 2015. California and Washington already have adopted, through state regulation, many of the rules that the EPA now wants to put in place nationwide. David Paul Morris/Bloomberg/Getty Images hide caption

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ShellNo flotilla participants float near the Polar Pioneer oil drilling rig during demonstrations in May against the presence of the first of two Royal Dutch Shell oil rigs in the Port of Seattle. David Ryder/Getty Images hide caption

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