Carl Sagan warned Congress about climate change in 1985

Person: Carl Sagan
Lived: 1934–1996
Field: Astronomy, planetary science
From: American

The story

Carl Sagan's research on Venus in the early 1960s had shown how a thick blanket of carbon dioxide could trap heat and turn a planet into an inferno. While other scientists had imagined a warm, wet world beneath the clouds, he concluded from radio measurements that the surface was around 500 °C, and the Mariner 2 probe confirmed his conclusions in 1962. He saw a warning in that story for Earth.

He came to regard climate change as a growing, human-made danger and compared it to the natural development of Venus into a hot, life-hostile world through a kind of runaway greenhouse effect. He made the connection for the public in his 1980 television series Cosmos, which described the conditions found on Venus by Soviet Venera landers and drew out the implications for Earth's own greenhouse effect.

On December 10, 1985, Sagan testified to the United States Congress that the greenhouse effect would change the Earth's climate system. The hearing was recorded by the C-SPAN network. It was an early, high-profile warning from a scientist the public trusted, delivered at a time when climate change was not yet a major political issue.

The testimony fitted a wider pattern in his work. In the same years he was warning that smoke from a nuclear war could cool the planet, and in both cases he argued that human activity could alter the climate of an entire world. He believed scientists had a duty to explain such risks plainly to lawmakers and to ordinary people.

Sagan kept the message in view. When he recorded updates for later versions of Cosmos, the episode on Venus was revised to highlight the connection to global warming. In his 1994 book Pale Blue Dot he reflected on Earth as the only home humanity has ever known. He used his fame and his gift for explanation to show that the physics of other planets applies to our own, and that humanity has a responsibility to protect it.

Why it matters

Sagan helped bring the science of the greenhouse effect to public and political attention years before climate change became a global priority, using Venus as a vivid warning.

About Carl Sagan

Brooklyn-born astronomer who explained the Venus greenhouse, helped send humanity’s messages on Pioneer and Voyager, and taught Cosmos viewers worldwide to look at the universe with wonder and doubt.

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Carl Sagan

1934–1996 · Astronomy, planetary science

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