Harold ("Hal") Warren Lewis (born October 1, 1923 – May 26, 2011) was an American Emeritus Professor of Physics and former department chairman at the University of California, Santa Barbara (UCSB). He was chairman of the JASON Defense Advisory Group from 1966 to 1973, and was active in US government investigations into safety of nuclear reactors.
In his 1990 book Technological Risk he warned of the risks of global warming. In 2010, after 67 years of membership, he resigned from the American Physical Society, citing what he saw as "corruption" from "the money flood" of government grants related to global warming.
Lewis entered New York University in 1940 and graduated in physics. He earned a master's degree from the University of California, Berkeley from 1943 to 1944 before joining the Navy, where he served in World War II as an electronics technician. After the war, he returned to the University of California, Berkeley, and earned his Ph.D. in Physics studying under J. Robert Oppenheimer. His focus was high energy physics (cosmic rays and elementary particles). He, along with the other theoretical physics professors at Berkeley, refused to sign the McCarthy era loyalty oath on principle, and in 1950 went to Princeton. Later, when offered reinstatement at Berkeley, he chose instead to accept a position at Bell Labs where he did research on superconducting materials. In 1956 he left Bell Labs to join the University of Wisconsin, Madison to work on solid state physics and plasmas. In 1964, he left to join the University of California, Santa Barbara as a full professor, and later chairman, in their growing physics department. He retired from UCSB in 1991.