What makes the climate of Venus so hot?

The planet’s searing temperatures are sustained by a thick atmosphere full of carbon dioxide.

January 5, 2026

If you’ve had the pleasure of spotting Venus, one of the brightest objects in the sky, you’ve gazed at a planet that is in some ways quite similar to our own.

Earth and its shiny celestial neighbor “were born in the same family” and are similar in size and mass, says Sara Seager, an astrophysicist and planetary scientist at MIT. Into the twentieth century, some scientists thought Venus’s atmosphere was also much like Earth’s: rich with water vapor and home to water clouds.^{1, 2} The chemist Svante Arrhenius, who helped shape our understanding of our own planet’s climate, envisioned Venus as a drenched world teeming with plants—a lush image that also showed up in science fiction.²

After closer inspection, we now know that Venus is… not that. Instead of abundant water clouds to feed a planetary forest, says Seager, “it’s got very unfriendly clouds” made of sulfuric acid,³ which never go away. Its massive atmosphere creates a surface pressure more than 90 times as high as what we experience on Earth. And its average surface temperature blazes above 450 degrees Celsius, or roughly 840 degrees Fahrenheit.² (Venus’s surface temperature, it has been pointed out,⁴ is like the inside of an oven in self-cleaning mode. Delightful.)

What is it about our feverish friend next door—which shares with Earth what Seager calls some “very basic planet parameters”—that makes it so unbearably hot?

You might think it’s because Venus, which is closer to the Sun, absorbs more solar energy. But here we see a “really interesting” difference between Venus and Earth, says Julien de Wit, a planetary scientist at MIT. Thanks in large part to its permanent clouds, reflective Venus bounces more than 70% of its incoming sunlight right back to space.⁵ Earth, which has patchier cloud cover, actually absorbs much more solar energy, de Wit says.^{2, 6} If the only thing controlling a planet’s surface temperature were how much sunlight it absorbed, he adds, you’d expect both Earth and Venus to be below freezing, with Venus the colder of the two.

Ultimately, “you have to ask yourself what happens to the energy that is getting absorbed,” says Seager. Earth’s atmosphere holds in enough heat to keep us comfortably thawed out, thanks to the greenhouse effect. Certain trace gases, like carbon dioxide (CO₂), let sunlight into our planet, but interfere with the infrared radiation that Earth releases back out. These gases absorb that radiation and release it again, both towards space and back towards the ground. It’s like having a blanket wrapped around Earth, warming it up. And the more infrared-absorbing CO₂ we add to our atmosphere, the toastier that blanket becomes.

So what about Venus? It’s baked by a far stronger greenhouse effect than Earth is. On Venus, CO₂ is no trace gas: It’s a whopping 96.5% of the atmosphere by volume.² (Compare that to a little more than 0.04% for Earth.)

In addition, Venus’s atmosphere is staggeringly thick. This, too, drives up temperatures on the ground, in a couple of ways.

The first has to do with how heat moves through a planet’s atmosphere. We know planets have to send enough infrared radiation back to space to balance out the energy they absorb from the Sun. But on planets like Earth and Venus with greenhouse gases hanging around, the radiation can only escape where the atmosphere becomes thin enough. This layer is called the “tropopause.”

Below the tropopause, infrared radiation hits so many roadblocks that another kind of heat transport takes over: convection. Here, masses of air cycle up to the tropopause and back down again, shuttling heat to the level where radiation can escape.

Physics tells us that air will expand and cool as it rises, and compress and warm as it falls. That means closer to the surface, where pressures are higher, the air is hotter, Seager says. How much hotter? Well, Venus's massive atmosphere creates truly crushing pressures on the ground. By the time you reach the surface—where pressures are hundreds of times greater than at the thin tropopause—the intensely compressed gas is scorching.

This pressure effect is crucial, de Wit says. To illustrate, imagine an Earth with an atmosphere as pressurized as Venus’s, but without Venus’s ultra-high CO₂ concentrations. He says this Earth’s surface temperature would soar to hundreds of degrees Fahrenheit.

Another wrinkle of Venus’s dense atmosphere: At such high pressures, molecules collide more often. These collisions allow CO₂ to absorb wavelengths of infrared radiation that it normally doesn’t interact with, so the planet’s greenhouse effect is even stronger.⁷

Scientists are still working to figure out how Venus got to its current state. It’s possible the planet used to be a lot more Earth-like, and it may have had a water ocean for some period of its life, Seager says.

In one version of Venus’s biography, a once-habitable planet is parched by a “runaway greenhouse” process. The temperate landscape heats up (say, from volcanism that belches heaps of CO₂ into the atmosphere) and the oceans begin to evaporate. Water vapor is itself a greenhouse gas, so temperatures increase further. What’s more, the shrinking seas, which once sponged up much of the atmosphere’s CO₂, can no longer absorb as much—and thus begins a cycle that feeds on itself. Eventually, the oceans dry up, and the water vapor that’s traveled high into the atmosphere is broken down by sunlight, never to re-condense.⁸ A new generation of missions to Venus will help scientists gather clues as to whether this story is the right one.⁹

Venus’s runaway greenhouse is not an immediate cautionary tale about Earth’s climate. When scientists talk about the risks posed by climate-warming CO₂ here on our home planet, they’re not warning of an oceanless, Venus-like future. But Earth doesn’t need to approach anything like our foul-weather friend for rising temperatures to seriously affect people’s lives; after all, people are already feeling the impacts. There’s plenty of reason to work urgently to address rising surface temperatures—even if they’re not Venusian.

We are grateful to Raymond Pierrehumbert, Professor of Planetary Physics at the University of Oxford, and to Timothy Cronin, Associate Professor of Atmospheric Science at MIT, for additional assistance with this article.

Thank you to Andrew Mercer of Annandale, Virginia, for the question.

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