Alain Robert, a French stuntman known for climbing tall buildings, scaled the north face of the New York Times building on Thursday, ascending 52 stories to the roof and clutching a bright green banner, before police officers arrested him around 12:22 p.m.

Police and security officials cordoned off the sidewalk below, on West 41st Street, as a crowd assembled. The words on the banner were illegible from the sidewalk, but from office windows inside the tower the slogan on the banner could be clearly read: “Global warming kills more people than 9/11 every week.”