Narrated and hosted by Matt Damon, the 13th episode of “Journey to Planet Earth” investigates one of the most critical issues of our time: the link between severe weather events, global warming and threats to our national security. Emmy-award winning filmmakers Marilyn and Hal Weiner consult with experts to find out what is happening to our weather. Lester Brown, Carol Browner and Paul Krugman are among those interviewed.