Siegfried Fred Singer (September 27, 1924 – April 6, 2020) was an Austrian-born American physicist and emeritus professor of environmental science at the University of Virginia, trained as an atmospheric physicist. He was known for rejecting the scientific consensus on several issues, including climate change, the connection between UV-B exposure and melanoma rates, stratospheric ozone loss being caused by chlorofluoro compounds, often used as refrigerants, and the health risks of passive smoking.

He is the author or editor of several books, including Global Effects of Environmental Pollution (1970), The Ocean in Human Affairs (1989), Global Climate Change (1989), The Greenhouse Debate Continued (1992), and Hot Talk, Cold Science (1997). He also co-authored Unstoppable Global Warming: Every 1,500 Years (2007) with Dennis Avery, and Climate Change Reconsidered (2009) with Craig Idso.

Singer had a varied career, serving in the armed forces, government, and academia. He designed mines for the U.S. Navy during World War II, before obtaining his Ph.D. in physics from Princeton University in 1948 and working as a scientific liaison officer in the U.S. Embassy in London. He became a leading figure in early space research, was involved in the development of earth observation satellites, and in 1962 established the National Weather Bureau's Satellite Service Center. He was the founding dean of the University of Miami School of Environmental and Planetary Sciences in 1964, and held several government positions, including deputy assistant administrator for the Environmental Protection Agency, and chief scientist for the Department of Transportation. He held a professorship with the University of Virginia from 1971 until 1994, and with George Mason University until 2000.

In 1990 Singer founded the Science & Environmental Policy Project, and in 2006 was named by the Canadian Broadcasting Corporation as one of a minority of scientists said to be creating a stand-off on a consensus on climate change. Singer argued, contrary to the scientific consensus on climate change, that there is no evidence that global warming is attributable to human-caused increases in atmospheric carbon dioxide, and that humanity would benefit if temperatures do rise. He was an opponent of the Kyoto Protocol, and claimed that climate models are not based on reality or evidence. Singer was accused of rejecting peer-reviewed and independently confirmed scientific evidence in his claims concerning public health and environmental issues.

Singer was born in Vienna, Austria, to a Jewish family. His father was a jeweler and his mother a homemaker. Following the Anschluss between Nazi Germany and Austria in 1938, the family fled Austria, and Singer departed on a children's transport train with other Jewish children. He ended up in England, where he lived in Northumberland, working for a time as a teenage optician. Several years later he emigrated to Ohio and became an American citizen in 1944. He received a Bachelor of Electrical Engineering (B.E.E.) from Ohio State University in 1943. He taught physics at Princeton while he worked on his masters and his doctorate, obtaining his Ph.D. there in 1948. His doctoral thesis was titled, "The density spectrum and latitude dependence of extensive cosmic ray air showers." His supervisor was John Archibald Wheeler, and his thesis committee included J. Robert Oppenheimer and Niels Bohr.

After his masters, Singer joined the armed forces, working for the United States Navy on mine warfare and countermeasures from 1944 until 1946. While with the Naval Ordnance Laboratory he developed an arithmetic element for an electronic digital calculator that he called an "electronic brain". He was discharged in 1946 and joined the Upper Atmosphere Rocket Program at the Johns Hopkins University Applied Physics Laboratory in Silver Spring, Maryland, working there until 1950. He focused on ozone, cosmic rays, and the ionosphere, all measured using balloons and rockets launched from White Sands, New Mexico, or from ships out at sea. Rachel White Scheuering writes that for one mission to launch a rocket, he sailed with a naval operation to the Arctic, and also conducted rocket launching from ships at the equator.

From 1950 to 1953, he was attached to the U.S. Embassy in London as a scientific liaison officer with the Office of Naval Research, where he studied research programs in Europe into cosmic radiation and nuclear physics. While there, he was one of eight delegates with a background in guided weapons projects to address the Fourth International Congress of Astronautics in Zurich in August 1953, at a time when, as The New York Times reported, most scientists saw space flight as thinly disguised science fiction.

Singer was one of the first scientists to urge the launching of Earth satellites for scientific observation during the 1950s. In 1951 or 1952 he proposed the MOUSE ("Minimal Orbital Unmanned Satellite, Earth"), a 100 pounds (45 kg) satellite that would contain Geiger counters for measuring cosmic rays, photo cells for scanning the Earth, telemetry electronics for sending data back to Earth, a magnetic data storage device, and rudimentary solar energy cells. Although MOUSE never flew, the Baltimore News-Post reported in 1957 that had Singer's arguments about the need for satellites been heeded, the U.S. could have beaten Russia by launching the first Earth satellite. He also proposed (along with R. C. Wentworth) that satellite measurement of ultraviolet backscatter could be used as a method to measure atmospheric ozone profiles. This technique was later used on early weather satellites.