The academy, the nation’s leading independent scientific body, had been defending its positions on global climate change, stem-cell advances, genetic engineering and evolution when Dr. Cicerone took over. With a reputation for nonpartisan civility, he pursued the activist agenda that he had inherited even more aggressively, gaining the support of President Obama, who visited the academy twice, and working to rally public opinion behind scientific research.

Under Dr. Cicerone, the academy issued reports that advocated reducing greenhouse gas emissions while identifying strategies for adapting to a changing climate. It also renovated its historic headquarters on the National Mall in Washington and established a $500 million Gulf Research Program after the disastrous Deepwater Horizon oil spill in 2010.

Rush D. Holt, the chief executive of the American Association for the Advancement of Science, called Dr. Cicerone “a champion of science who helped scientists understand their obligations to society and helped nonscientists understand the importance of science to their lives, especially with respect to human induced changes of Earth’s climate.”

Ralph John Cicerone was born on May 2, 1943, in New Castle, in rural western Pennsylvania, the grandson of Italian immigrants. His father, Salvatore, was an insurance salesman who left math problems for Ralph to solve on the evenings he was making house calls to clients. His mother was the former Louise Palus.

The first in his family to attend college, Dr. Cicerone was inspired by the space race with the Soviet Union to pursue an engineering career. He graduated with a bachelor of science degree in electrical engineering in 1965 from the Massachusetts Institute of Technology (where he was captain of the baseball team, a sport he later restored to Irvine) and earned a master’s degree and a doctorate from the University of Illinois at Urbana-Champaign.

He is survived by his wife, the former Carol Ogata; their daughter, Sara; two grandchildren; and two sisters, Sylvia Ferrare and Sally Golis.

Dr. Cicerone was an atmospheric chemist on the faculty of the University of Michigan from 1971 to 1978. After conducting research at the Scripps Institute of Oceanography, part of the University of California, San Diego, he was named senior scientist and director of the atmospheric chemistry division of the National Center for Atmospheric Research in Boulder, Colo.