Early Friday morning an unidentified man climbed onto the outside of a 16th-floor balcony at 257 Clinton St. and threatened to jump. He spent almost two harrowing hours on the edge, at several times hanging by just one hand and leaning precariously out over the street. After talking with members of the Police Department’s Emergency Services Unit, he climbed back inside and was taken away in an ambulance. It was not immediately known what made the man threaten to jump.