A cousin, Rochelle “Rocky” Lieberman, confirmed the death and said she did not know the precise cause.

Dr. Singer was a Princeton-trained physicist who held a number of prestigious academic posts throughout his career, including as a longtime professor of environmental sciences at the University of Virginia.

He conducted some of the first experiments with high-altitude rockets and satellites, measuring cosmic rays and other components in the upper atmosphere. He was a consultant during the start-up of the U.S. space program in the 1950s and later, while working for what is now the National Oceanic and Atmospheric Administration, participated in early efforts to use satellites in weather forecasting.

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Dr. Singer was a professor at the University of Maryland in the 1950s, then in 1964 became the first dean of a school of environmental and planetary studies at the University of Miami. He held high-ranking positions at the Interior Department and the Environmental Protection Agency before joining the faculty of the University of Virginia in 1971.

During those years, Dr. Singer wrote dozens if not hundreds of research papers and contributed articles to the popular press, including a 1967 essay in The Washington Post, written as a retrospective view from the year 2007.

Among his activities, he foresaw an “increased reliance on the electronic computer and data processor” and “increased understanding of our environment” that included climate-modifying “planetary engineering.” The melting of ice caps and the redirecting of rivers could help irrigate the arid Southwest and produce “a general improvement to the climate of the North American Arctic,” he wrote.

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Warning of the dangers of overpopulation in 1971, Dr. Singer noted, “Environmental quality is not a luxury; it is an absolute necessity of life.”

At that time, he advocated the “conservation of resources” and “above all . . . choosing life styles which permit ‘growth’ of a type that makes a minimum impact on the ecology of the earth’s biosphere.”

As some of his predictions came into focus and others faded from view over the next half-century, Dr. Singer came to occupy a different place in the scientific world. Somewhere along the line, Dr. Singer’s views of science became entwined with a libertarian, anti-communist political viewpoint that made him increasingly outspoken and contrarian.

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He found a new purpose as a scourge who sought to denigrate other scientists who warned the public about secondhand smoke, greenhouse gas emissions, acid rain and the dangers of a steadily warming climate.

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“It’s all bunk,” he often said.

“Stop worrying, don’t worry,” he told a gathering at Colorado State University in 2011. “Nothing you do will have any effect on the carbon dioxide level in the atmosphere. Even if it did have an effect, it won’t affect the planet.”

In 1990, Dr. Singer founded the Virginia-based Science and Environmental Policy Project “to challenge government environmental policies based on poor science.” The group’s mission statement notes that “omitting critical data violates the scientific method” — precisely what Dr. Singer’s critics accused him of doing.

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In 2007, he helped launch the Non-governmental International Panel on Climate Change (NIPCC) — a climate-skeptical counterpart to the United Nations Intergovernmental Panel on Climate Change (IPCC).

From climate change to tobacco to air pollution, Dr. Singer held firm to the belief that government regulations were wrong in principle and too costly in practice. Over time, he focused his attention mostly on climate change, becoming perhaps the most prominent scientist speaking out in opposition to a growing body of evidence that rising global temperatures could have a catastrophic effect on the planet.

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“There is no debate among any statured scientists of what is happening,” Harvard University earth scientist James McCarthy said in 1997. “The only debate is the rate at which it’s happening.”

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Genial and glib, Dr. Singer spoke in a British accent and was eager to spread his views in speeches, articles and interviews.

“There is nothing remotely like scientific consensus that global warming is occurring, or if it is, that it will have disastrous consequences,” he wrote in 1991 in his regular column in the Washington Times. “A respectable body of opinion in the international scientific community holds that any climate warming is as likely to be beneficial as harmful, acting as a hedge against global cooling.”

He dismissed many studies about the dangers of secondhand tobacco smoke and rising temperatures as “junk science.” In 1995, he denounced the Royal Swedish Academy of Sciences for making a “political statement” by awarding the Nobel Prize in chemistry to three scientists who demonstrated that chlorofluorocarbon emissions were depleting the ozone layer.

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He had a long association with the Heartland Institute, a libertarian think tank that published some of his books. including “Nature, Not Human Activity, Rules the Climate” (2008).

Among mainstream scientists, Dr. Singer came to be regarded as a charlatan and a crank. He was no longer published in peer-reviewed journals. At least 97 percent of scientists studying the climate, reports indicated, believed that human actions had played a central role in climate change.

“He’s not doing firsthand research, and he does not have regular communication with the rest of the climate research community,” University of Texas climate science professor Rong Fu said in 2009. “I’m not sure he’s even on the fringe.”

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Dubbed the “grandfather of climate denial” in Britain’s Guardian newspaper, Dr. Singer was singled out for his obstructionism in several books, including “Merchants of Doubt,” by science historians Naomi Oreskes and Erik M. Conway. When a documentary was made based on “Merchants of Doubt” in 2014, Dr. Singer sent a letter to director Robert Kenner, noting, “I have some experience with libel suits.”

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Yet, as Dr. Singer found himself speaking to an ever-shrinking room, his shouts continued to be heard by some lawmakers and officials who called for the United States to withdraw from international agreements on the climate and environment.

To his supporters, he was a hero.

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“Where others stayed silent out of fear of retaliation by activists in government and in universities,” Heartland Institute co-founder Joseph Bast wrote in an online appreciation, “Fred was utterly fearless, willing to take the slings and arrows of critics in order to defend real (not political) science.”

Siegfried Frederick Singer was born Sept. 27, 1924, in Vienna. His father was a jeweler, his mother a homemaker.

After the Nazi invasion of Austria, Dr. Singer went to England as part of the “Kindertransport” program that resettled Jewish children. He came to the United States in the 1940s and served in the Navy during World War II, working on weapons programs.

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He received a bachelor’s degree in electrical engineering from Ohio State University in 1943 and master’s and doctoral degrees in physics from Princeton University in 1944 and 1948, respectively.

In addition to his academic posts at Maryland, Miami and U-Va., Dr. Singer was chief scientist at the U.S. Transportation Department in the late 1980s and a research professor at George Mason University in the 1990s.

His two marriages ended in divorce, and he had no immediate survivors.

In a 2008 interview with ABC News, Dr. Singer was asked whether he was concerned that his assertions about climate change had been largely discredited by scientists from the National Academy of Sciences, the American Association for the Advancement of Science, NASA and NOAA.

“What can I say?” he replied. “They’re wrong.”

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“You never wake up in the middle of the night,” ABC’s Dan Harris asked, “and think what if I’m wrong about all this?”

“Never,” Dr. Singer said. “Never.”