NBC: A new report from a panel of former Pentagon leaders calls climate change a direct threat to national security and the U.S. economy, as extreme weather stands to stretch troops thin, spark unrest in unstable regions, and unravel global networks of trade and resources. The authors - 16 retired three- and four-star generals and admirals who compose the CNA Corporations Military Advisory Board (MAB) -- blame a warming planet for, in part, aggravating tensions among some nations. Their study, released...