Pope Leo XIV will be the Catholic Church's 267th leader.
VATICAN CITY -- The temporary chimney atop the Sistine Chapel released a plume of white smoke on Thursday evening local time, signaling that the 133 cardinals working inside had reached a two-thirds majority to elect a new pope for the Catholic Church.
American Cardinal Robert Prevost was shortly thereafter announced as the 267th pontiff. He chose the name Leo XIV, a senior cardinal deacon announced.
The 69-year-old Chicago native is the first American pope and is seen as a diplomat in the church.
"This is the first greeting of the risen Christ. May the peace be with you," Leo said in Italian in his first remarks as pope. "This is the peace of the risen Christ."
(The Associated Press and ABC News contributed to this report.)
Pope Leo XIV - history-making, the first American Pope. Now, David Muir reports from the Vatican in the breaking, new "20/20" special edition. Watch the premiere of "The American Pope | Leo XIV" tonight at 9/8c on ABC. Stream on Hulu and Disney+
White smoke was seen emanating from the chimney of the Sistine Chapel, indicating that a two-thirds vote has been reached to elect the new pope.
Thousands of people cheered in Vatican Square when the smoke appeared.
What is the science behind the smoke signals on the Sistine Chapel to announce if a new pope has been elected?
Dr. Olivia Castellini, senior exhibit strategist at the Griffin Museum of Science, says chemicals are added to the fire to slow down the combustion reaction and create smoke.
"When it is a black fire, they add in potassium perchlorate, anthracene and sulfur," Dr. Castellini said. "So the potassium perchlorate is bringing the oxygen to the party because that is one of the ingredients for our combustion. The anthracite is going to be our fuel, it doesn't like to burn completely so you put some sulfur in there to help things along. So you actually end up using up the oxygen before the fuel, so you get a lot of soot that comes out and the soot is black.
The white smoke is a slightly different chemical composition.
"You have calcium chlorate, which again is going to bring that oxygen, you use lactose, which is just sugar," Dr. Castellini said. "Sugar burns really quickly, very cleanly, so you get a clean smoke coming out. And they also add pine resin, which used to be called pitch, so that has a lot of water. You have a lot of water and particles that come out. You are basically making an artificial cloud."
Black smoke emerged from the chimney of the Sistine Chapel during the conclave.
That meant that no new pope had been elected by the cardinals.
It signified the end of the second round of voting -- and three ballots -- with no consensus.
The cardinals planned to take a break for lunch before beginning their next round of voting.
Eyewitness News Anchor Joe Torres reports from the Vatican.
An estimated 45,000 people gathered in St Peter's Square to await the results of the first conclave vote, which had been expected some time after 7 p.m. but ended up coming in around 9 p.m., according to Vatican News.
After failing to come to a consensus, the College of Cardinals have gathered on Thursday morning for the second day of conclave, with up to four more opportunities for them to select the 267th pope.
-ABC News' Phoebe Natanson
