Copenhagen is the greenest city in the world, and its carefully planned green rooftops are helping it reach that spot. The rooftop oases help trap carbon and water, support biodiversity and help the city prepare for the warmer future that's coming thanks to climate change.
The World's Clark Boyd reports from Denmark on a new factory that's making ethanol from straw. If the technology pans out, supporters hope it will help replace both gasoline and biofuels made from food crops.
The latest dump of secret documents from former NSA contractor Edward Snowden shows that the agency spied on participants in the fateful 2009 UN climate change summit in Copenhagen. The question is whether it mattered.