Ralph J. Cicerone, an atmospheric scientist who helped identify the potentially catastrophic threat to the planet’s ozone layer from man-made chemicals, then served as chancellor of the University of California at Irvine and as president of the National Academy of Sciences, died Nov. 5. He was 73.

Dr. Cicerone, who stepped down from his post at the academy this summer after 11 years but retained a busy schedule of speaking engagements, died unexpectedly at his home in Short Hills, N.J., National Academy spokesman William Kearney said. Kearney said Dr. Cicerone’s family has not disclosed a cause of death.

With Dr. Cicerone’s death, the U.S. scientific establishment has lost a leader known for his calm and civil advocacy for science in a time of rancorous debates over climate change, genetically modified foods, the teaching of evolution in schools, and other politically and culturally charged topics.

“Ralph was a very, very steadying presence within the science community, trying to keep scientists on track, saying everything has to be sticking to the facts,” said Marcia McNutt, Dr. Cicerone’s successor as president of the academy. “It was so important to have a leader like that during these very contentious times.”

Dr. Cicerone produced seminal work in the 1970s showing that chlorine atoms and other gases can damage the ozone layer that shields the Earth from lethal radiation. Such research spurred policymakers to action and led to the Montreal Protocol, the global treaty banning chlorofluorocarbons (CFCs) and other chemicals that had been used as aerosol propellants and as coolants.

“We very much recognized his work as an important part of the atmospheric ozone issue,” said his friend and collaborator Mario ­Molina, who, along with two other scientists, received the 1995 Nobel Prize for work on CFCs.

“He was one of the true pioneers in showing how human activities are damaging our air,” said Dr. Cicerone’s friend and colleague Veerabhadran Ramanathan, of the Scripps Institution of Oceanography. He added that Dr. Cicerone didn’t merely identify a hazard: “He did something about it — he worked with policymakers.”

Ralph John Cicerone was born in 1943 in the rural western Pennsylvania town of New Castle. In a 2013 speech at a science center in Pittsburgh, he recalled that, at the age of 5 or 6, his father gave him a horseshoe magnet. He got the notion that he could recharge it by sticking one end into a ceiling light socket. The electric shock knocked him off the table and onto the floor. But it could have been worse: Because he had seen electrical workers wearing insulating rubber gloves, he had put on his mother’s rubber laundry gloves, he said.

In his speech, he had a broader message for science educators: “We do need to provide children with a way to see that science is alive and is not all about just memorizing facts.”

He was the first person in his family to go to college, arriving in 1961 as a freshman at the Massachusetts Institution of Technology fully aware that he wasn’t as prepared as many of his fellow students. But he prospered in and out of the classroom.

By senior year he had become captain of the baseball team — reflecting a passion he would revisit when, as chancellor of the UC-Irvine in 2002, he brought baseball back to the university. (A baseball field there was later named in his honor.)

He received a doctorate from the University of Illinois in 1970. He joined the faculty of the University of Michigan at Ann Arbor, where he intensified his investigation into atmospheric chemistry. Molina, the Nobel laureate, said he and Dr. Cicerone independently found evidence that chlorine atoms can destroy ozone, and that began a long friendship.

“I got involved in a hot, new field where almost anything you would learn was a discovery,” Dr. Cicerone told the MIT Technology Review decades later.

He left Michigan to work at the Scripps Institution and with the National Center for Atmospheric Research in Boulder, Colo. In 1989 he joined the UC-Irvine faculty and became chancellor there in 1998.

While still at UC-Irvine, Dr. ­Cicerone led an influential National Academy-sponsored report on climate change that had been requested in 2001 by President George W. Bush. After being elected president of the National Academy in 2005, Dr. Cicerone oversaw a series of reports, “America’s Climate Choices,” that called for the country to reduce greenhouse gas emissions.

President Obama visited the National Academy — a private, nonprofit organization founded under a congressional charter in 1863 at the behest of President Abraham Lincoln — twice during Dr. Cicerone’s tenure. Dr. Cicerone also oversaw the renovation of the academy’s building on Constitution Avenue and helped establish the $500 million Gulf Research Program after the 2010 oil spill caused by the Deepwater Horizon explosion.

“Ralph Cicerone was a model for all of us of not only doing what counts, but doing it with honesty, integrity, and deep passion,” McNutt said in a statement released by the academy.

Dr. Cicerone is survived by his wife, the former Carol Ogata; a daughter, Sara Cicerone of Short Hills, N.J.; and two grandchildren.

CORRECTION: An earlier version of the obituary incorrectly reported the maiden name of Dr. Cicerone’s wife as Mitsuko. The story has been updated.