A midtown Manhattan skyscraper that is home to The New York Times became the site of twin daredevil stunts today, with two men scaling the 52-story office tower just hours apart.

The first man, Alain Robert, unfurled a banner as he climbed that said “Global warming kills more people than a 9/11 every week.” He was promptly arrested by the NYPD when he made it to the top.

Hours later, a second man made his own ascent up the building — a stunt that drew the attention of hundreds of onlookers, along with TV cameras that captured the drama in real-time. Crowds pressed against police barricades to watch the climb, and people clapped and cheered for him while snapping pictures on their cell phone.

He, too, was arrested as he reached the top.

“Only in New York. This is why I live in New York,” said Emily Perschetz, 29-years-old, who watched the second climber for about 20 minutes.

“You’ve gotta respect them for trying,” she added.

The climber making his way up the building this evening could not immediately be identified, police said.

The building’s facade is covered with slats that allowed the men to climb the tower like a ladder.

Mr. Robert pumped his fist as he made it to the top, where police took him into custody. Charges against the 45-year-old Mr. Robert were pending, a police spokesman said.

Mr. Robert’s Web site says he has climbed more than 70 skyscrapers around the world. He was arrested in February after climbing a 42-floor building at Sao Paolo, Brazil.

The stunt was staged at the Renzo Piano-designed Times building, just a block south of the busy intersection at Eighth Avenue and 42nd Street, across the street from the Port Authority bus terminal.

A spokeswoman for the Times, Catherine Mathis, said no one at the newspaper knew of Mr. Robert’s plan in advance.

The Times itself has “a very green building,” Mathis noted. “We wanted to minimize our environmental footprint.” She said the ceramic slats save energy by reducing the amount of heat and light entering the building, where the Times moved last year.

Mr. Robert said in a news release he was climbing to mark World Environment Day and “to create support for far greater and urgent action from world leaders on global warming.”

His Web site says he climbs even though he suffers from vertigo and is “60 percent disabled” from previous accidents. It also says he has been jailed many times but it does not matter because he “would rather stay in a prison than in a hospital.”

One city councilman is hoping that Mr. Robert gets to know what the inside of a New York City jail looks like.

“Regardless of the cause, in this day and age the police department has more important things to worry about then ridiculous stunts like this that endanger the police and public,” said Councilman Peter Vallone Jr. “If he wants to climb something, he can climb the walls inside his jail cell at Rikers.”

Shaznay Jones was more amused than Mr. Vallone as she watched the second climb while smoking a cigarette.

“It looks crazy, like he’s on drugs, like he’s on something,” Ms. Jones said. “I never saw anything like this before.”