Ralph John Cicerone (May 2, 1943 – November 5, 2016) was an American atmospheric scientist and administrator. From 1998 to 2005, he was the chancellor of the University of California, Irvine. From 2005 to 2016, he was the president of the National Academy of Sciences (NAS). He was a "renowned authority" on climate change and atmospheric chemistry, and issued an early warning about the grave potential risks of climate change.