This year, the summer months have brought record high temperatures, fires, floods and other climate extremes.  A U.N. climate change report has sounded a "red alert" for humanity.  We're joined by one of the contributors to that report, Kevin Gurney of Northern Arizona University's school of Informatics, Computing and Cyber Systems.  Also joining us, Ron Cohen from the University of California, Berkeley, professor of chemistry who studies air quality and climate, and Amy Mueller from Northeastern University's College of engineering, who develops new instruments for studying the environment.  Hosts Judy Muller and George Lewis lead our panel in a discussion of this unfortunately "hot" topic and the role that cities can play in solving the problem.