Could Earth's 'evil twin' Venus carry a dire warning about climate change?

A blue, white and green sphere next to a slightly smaller golden orange sphere

An image depicting Earth next to Venus. Does the hellish planet harbor a grim climate warning for us? (Image credit: Robert Lea (created with Canva)/NASA)

There is very little doubt that Earth is getting warmer, and that this warming is a result of human-driven gases in the atmosphere that store heat and redirect it toward our planet's surface. And Earth isn't the only planet to have experienced this so-called "greenhouse effect."

Venus is the hottest planet in the solar system and is often referred to as Earth's "evil twin." The two planets are similar in size and mass, with Venus only slightly more diminutive than Earth. They are also comparatively similar in their distances from the sun, and even started off looking remarkably similar to each other. Venus also has volcanoes like Earth, though it isn't clear if they are still active.

Yet something seems to have gone drastically wrong in the development of Venus, leaving it quite hellish and inhospitable. There is a good chance that "something" is an extreme runaway greenhouse effect, the consequence of an overabundance of atmospheric greenhouse gases.

Since the 1970s, satellites stationed in space have been vital in gathering a picture of how Earth is being impacted by global warming — and this warming is caused by the greenhouse effect. Humans are pumping increasing amounts of greenhouse gases into the atmosphere due to the burning of fossil fuels and, in turn, are forcing the planet to heat up far faster than it should.

What makes Venus so extreme?

The major differences between Earth and Venus mostly come down to the planets' differing atmospheres. Venus' atmosphere at the surface is 90 bars, which means that it is 90 times as thick as Earth's atmosphere. This means that, at the surface of Venus, there is a pressure similar to what's found in the ocean at a depth of around 2,550 feet (777 meters).

As you might imagine, for a planet experiencing a runaway greenhouse effect, Venus is also far hotter than Earth. The hottest temperature ever recorded on the surface of our planet was 134.1 degrees Fahrenheit (56.7 degrees Celsius) at the aptly named Furnace Creek Ranch in Death Valley, California on July 10, 1913.

Venus makes this seem like a winter walk in the park.

Temperatures on Earth's evil twin are estimated to reach around 870 degrees Fahrenheit (465 degrees Celsius), which is hot enough to melt lead. You could find similar temperatures here on Earth — but only if you were to climb into a pizza oven.

"This hot, thick atmosphere means Venus can't have any liquid water on the surface today, unlike Earth. But we have evidence that Venus has lost huge amounts of water over its history enough to suggest that ancient Venus might have had a similar amount of water as Earth does today," Cangi said. "However, we don't know if that water was ever in the liquid form — it may have only existed as steam in the atmosphere."

a pale yellow planet in the night sky — Don't be fooled by this relatively placid looking image of Venus, Earth's neighbor is a hellscape. (Image credit: Starry Night Software)

The second planet from the sun, Venus, is closer to our star than Earth is, so it is natural to expect it to be hotter. But Venus orbits the sun at a distance of around 70% of that between Earth and the sun, which isn't that much closer. Mercury is actually much closer to the sun than Venus, orbiting at a distance equivalent to around 33% of the distance between our planet and the sun — yet temperatures on the closest planet to the sun reach 800 degrees Fahrenheit (465 degrees Celsius).

So, there must be some reason behind Venus' heat other than its proximity to the sun. And, well, it turns out that the mystery of why Venus diverged from Earth in its early history, and the puzzle of how it can be hotter than the closest planet to the sun, both have the same solution: a runaway greenhouse effect.

A greenhouse in hell

Earth and Venus receive heat from solar radiation, but some of that radiation gets radiated back into space when sunlight is reflected back by clouds or ice. The planet's surface absorbs the heat that is not radiated back from space.

Certain gases in a planet's atmosphere can trap heat, affecting how much energy that planet loses back to space. They're called greenhouse gases.

Greenhouse gases can bounce the heat around in all directions, meaning some of the heat inevitably gets directed back to the surface of the planet, thereby raising the planet's overall temperature. The main greenhouse gases are water vapor, methane, nitrous oxide and carbon dioxide, which are released by the burning of fossil fuels.

Without this greenhouse effect, it is estimated that Earth's surface temperature would be tens of degrees lower. Without the greenhouse effect on Venus, the temperature on the second planet from the sun would be an estimated 700 degrees (390 degrees C) cooler.

Earth and the sun are seen in this diagram. The greenhouse effect is depicted. — Diagram depicting how the greenhouse effect works on Earth. (Image credit: Siberian Art/Shutterstock)

Scientists aren't exactly sure when this greenhouse effect grabbed Venus in a stranglehold, with estimates ranging from 3 billion years ago to 250 million years ago. Quite how this "Great Climate Transition" took Venus from potentially habitable to a hellish wasteland is also debated, but one possibility is that a massive bout of volcanism greater than anything ever seen on Earth ripped open the crust of Venus and released vast amounts of greenhouse gases, particularly carbon dioxide.

As temperatures on Venus soared, liquid water would have boiled away, with water vapor joining other vast amounts of greenhouse gases in the Venusian atmosphere, causing more and more heat to be trapped, further driving up temperatures. This would have caused a feedback loop of more and more water evaporating, and more heat being trapped, creating a "runaway greenhouse effect."

Artist’s impression of an active volcano on Venus. — The hellish landscape of Venus. Not a crystal ball predicting Earth's future but still a stark warning about the power of climate change. (Image credit: ESA/AOES)

Though Venus is a striking example of the greenhouse effect, it shouldn't serve as a "crystal ball" to predict the future of the Earth. The situation on our neighboring planet is different from that on Earth.

"I think it's pretty unlikely that Earth would end up the same as Venus, which has 90 Earth atmospheres worth of carbon dioxide. On Earth, carbon dioxide is only 0.04% of the atmosphere, and the orbital mechanics also play into the difference," Cangi explained. "That doesn't mean we shouldn't worry about climate change on Earth. Many societal and energy system changes that can help mitigate anthropogenic [human-caused] climate change are also good for the health of ourselves, our societies and our economies."

A fiery orange sky with a spherical silver spacecraft descending through it — An artist's depiction of the DAVINCI probe nearing the surface of Venus. (Image credit: NASA's Goddard Space Flight Center)

The unlikeliness of Earth in following Venus down the highway to climate hell also doesn't mean we can't learn anything about the climate dilemma facing our planet by investigating Venus. Several upcoming missions will visit Venus in an attempt to unlock the secrets of its violent conditions and its transformation into the solar system's most fearsome world.

NASA's Deep Atmosphere Venus Investigation of Noble Gases, Chemistry and Imaging (DAVINCI) spacecraft will be of particular interest. Set to reach Venus in the late 2030s, DAVINCI will be the first spacecraft to drop a probe through the dense atmosphere of this hellish world, gathering data about its structure and composition. Though this probe isn't predicted to survive its fall, scientists are prepared for the possibility that it could briefly survive the crushing atmospheric pressures of Venus to gather data directly from the Venusian surface for humanity.

"I'm interested in anything we don't understand, so other planets are perfect! Venus is especially fascinating because there's still so much we don't know. I'm very excited to learn more about the surface of Venus from upcoming missions, especially the extent of present-day volcanism," Cangi concluded. "Below the clouds, we know so little about the lower atmosphere. I'm very interested in what makes planets habitable or not and how that can change over time, so Venus is a great case study and example of a planet that could have once been habitable but isn't today."

— If Venus had Earth-like plate tectonics in its distant past, did it have life too?

— The Magellanic Clouds must be renamed, astronomers say

Though this could reveal more about the greenhouse effect on Venus, for us to learn really learn more about climate change and the greenhouse effect's impact on our own planet, we depend on space monitoring and the kind of technology World Space Week will highlight over the next few days.

This article is part of a special series by Space.com in honor of World Space Week 2024, which ran from Oct. 4 to Oct. 10 and explored how space technology can help fill the toolboxes of climate scientists.

Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: community@space.com.

Robert Lea is a science journalist in the U.K. whose articles have been published in Physics World, New Scientist, Astronomy Magazine, All About Space, Newsweek and ZME Science. He also writes about science communication for Elsevier and the European Journal of Physics. Rob holds a bachelor of science degree in physics and astronomy from the U.K.’s Open University. Follow him on Twitter @sciencef1rst.

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10 Comments Comment from the forums

Unclear Engineer

At least this article does say that Earth is unlikely to be turned into Venus by humans.

But, it seems to really short-shrift the discussion about why Venus' atmosphere is so different from Earth's, mentioning only that the various theories range from millions to billions of years ago when the greenhouse gas effect "ran away" to create the high temperatures we measure there now.

I would like to see more about those theories, mainly to know what to think about various exoplanet discoveries.

The article talks about Venus "only" being at about 70% of Earth's distance from the Sun. But, that results in Venus getting about twice as much solar energy hitting its atmosphere. That is a big difference to begin with.

And, speaking of the beginning of both planets as they condensed from the gas and dust cloud surrounding the Sun, why would we expect the initial atmospheric compositions to be much different? The article even says something about nitrous oxide and CO2 "which are released by the burning of fossil fuels". But, that is really irrelevant, because there may never have been any "fossil" fuels on Venus, much less a technological civilization to burn them.

The differences seem to be that Venus lost its water to space, or at least into its atmosphere, but did not lose its CO2. In contrast, Earth seems to have had its CO2 removed from its atmosphere and stored in the solid parts of the planet, by life forms. that also oxygenated the atmosphere, largely by removing the carbon into the ground.

So, it seems unlikely that this all happened by some process where Venus was much like Earth, with abundant life that created an atmosphere like Earth's, only to have had massive volcanic eruptions on Venus release CO2 from under ground in sufficient quantity to kick of the greenhouse effect only "millions" of years ago.

It would not surprise me if Venus simply had an initially dense atmosphere that promptly created sufficient greenhouse effect to have always made the planet too hot for liquid water or the hydrocarbon chemicals that are the basis for life on Earth. With twice the solar energy input, Venus would have an "advantage" to go in that direction, compared to Earth.

So, at least for me, what I think is important to learn from Venus about Earth is more about how Earth could have gone from a dense, heavy atmosphere to what we have today, instead of turning out like Venus. Is the 50% less solar energy input the only determinant?
Reply
einsteinium253

Unclear Engineer said:
At least this article does say that Earth is unlikely to be turned into Venus by humans.

But, it seems to really short-shrift the discussion about why Venus' atmosphere is so different from Earth's, mentioning only that the various theories range from millions to billions of years ago when the greenhouse gas effect "ran away" to create the high temperatures we measure there not.

I would like to see more about those theories, mainly to know what to think about various exoplanet discoveries.

The article talks about Venus "only" being at about 70% if Earth's distance from the Sun. But, that results in Venus getting about twice as much solar energy hitting its atmosphere. That is a big difference to begin with.

And, speaking of the beginning of both planets as they condensed from the gas and dust cloud surrounding the Sun, why would we expect the initial atmospheric compositions to be much different? The article even says something about nitrous oxide and CO2 "which are released by the burning of fossil fuels". But, that is really irrelevant, because there may never have been any "fossil" fuels on Venus, much less a technological civilization to burn them.

The differences seem to be that Venus lost its water to space, or at least into its atmosphere, but did not lose its CO2. In contrast, Earth seems to have had its CO2 removed from its atmosphere and stored in the solid parts of the planet, by life forms. that also oxygenated the atmosphere, largely by removing the carbon into the ground.

So, it seems unlikely that this all happened by some process where Venus was much like Earth, with abundant life that created an atmosphere like Earth's, only to have had massive volcanic eruptions on Venus release CO2 from under ground in sufficient quantity to kick of the greenhouse effect only "millions" of years ago.

It would not surprise me if Venus simply had an initially dense atmosphere that promptly created sufficient greenhouse effect to have always made the planet too hot for liquid water or the hydrocarbon chemicals that are the basis for life on Earth. With twice the solar energy input, Venus would have an "advantage" to go in that direction, compared to Earth.

So, at least for me, what I think is important to learn from Venus about Earth is more about how Earth could have gone from a dense, heavy atmosphere to what we have today, instead of turning out like Venus. Is the 50% less solar energy input the only determinant?
As stated in the article, we as yet have no way of knowing exactly what led to the runaway greenhouse effect that is believed to have occurred on Venus.

"...something seems to have gone drastically wrong in the development of Venus... There is a good chance that "something" is an extreme runaway greenhouse effect, the consequence of an overabundance of atmospheric greenhouse gases."

The article also does not go into detail about why "we" "believe" that a runaway greenhouse effect occurred on Venus, focusing instead on the approximate timeframe and hypothetical causes of this theoretical process.

"The causes of this greenhouse effect on Venus and Earth are different, to be clear. On Venus, the effect was natural and likely the result of excessive volcanism millions or billions of years ago — on Earth, it is the result of humankind's burning of fossil fuels."

Why should we suppose that it is impossible for advanced life, even technologically "advanced" (as we see it) life to have existed on Venus at some point in its past?

For the author to claim outright as a "fact" that the runaway greenhouse effect on Venus is a result of natural causes is unscientific. To be clear, I am not aware of any evidence to suggest that there was advanced life on Venus at any point in its past, but I have also not seen any evidence to the contrary. How would I have?

It is often forgotten (particularly in the modern media landscape) that the true function of science is to help us make the most informed possible speculations (whenever it is necessary) from a practical perspective.

Science also exists as the best known human framework for engaging in the perpetual practice of raising new questions about the phenomena we encounter in our so-called "observable universe", and their relationship to each other.

In other words, in this brief article, the author was not able to explore the reasons why many in the scientific community presumably speculate that our neighboring planet experienced a runaway greenhouse effect at some point in its history. I would assume that, based on empirical evidence gathered over time, there have been theoretical (e.g. speculative) discussions, simulations, and research papers on the subject which have led many in the scientific community to reach the conclusion that this speculation is the "most likely" (in light of the fact of uncertainty, which is a permanent condition of human existence) to be "true" (although I have not extensively researched this subject).

The author also did not have the space to go at length into detail about the theoretical causes of the theoretical runaway greenhouse effect on Venus, but again, I would assume that scientists have their reasons for speculating as they do.

Now, to quote a portion of your own response:
"The differences seem to be that Venus lost its water to space, or at least into its atmosphere, but did not lose its CO2. In contrast, Earth seems to have had its CO2 removed from its atmosphere and stored in the solid parts of the planet, by life forms. that also oxygenated the atmosphere, largely by removing the carbon into the ground."

This is a very valid point, and it speaks to the heart of the issue at hand. According to theory (which, not to belabor the point, is nothing more and nothing less than scientific speculation aiming, hopefully, in the direction of the truth) extraordinary amounts of the carbon you speak of that was once stored in plants, was eventually turned through the processes of nature into what we call "fossil fuels".

When we recover those fossil fuels from the Earth and burn them for fuel, all that carbon that has been locked away in the Earth for countless generations is released back into our atmosphere in the form of gaseous carbon dioxide.

It would be reductive to say that this alone is the cause of anthropogenic climate change, however, it is an extremely important part of the picture.

Much like the theoretical runaway greenhouse effect on Venus, the greenhouse effect on Earth has a way of compounding itself.

For example, as the Earth continues to warm in part due to the CO2 released by our primitive form of energy generation, one consequence is the melting of permafrost across the arctic regions. As permafrost melts, methane (another greenhouse gas) that has also been trapped in the soil is released into the atmosphere in massive amounts, adding a correlated layer of cause into the constellation of problems that we reduce to the phrase "anthropogenic climate change".

For human beings, what we call a "problem" is essentially a result (specifically a negative consequence) of causes (plural, because nothing is ever the result of one cause) that we don't understand or are simply unable to rectify.

The lesson that we should learn, when it comes to the theoretical runaway greenhouse effect of Venus, is that sometimes problems have a way of creating new causes that lead to worse problems.

Everything is connected, and when we burn fossil fuels for energy, we are not merely releasing excess carbon dioxide into the atmosphere to no affect. We are creating a feedback loop of problems leading to causes leading to problems, and this process has the potential to spiral completely out of our control if it hasn't already.

If Earth ends up like Venus, it will take a long time relative to the individual human lifespan. That doesn't mean we can't or won't see catastrophic impacts resulting from climate change in our lifetimes, especially when you start factoring in related problems like mass migration, economic and geopolitical instability, and the human propensity for war.

Famines, droughts, monster storms, plagues... all of these things lead to a dearth of resources and massive increases to collective stress and tension, which are primary causes of war.

It would take extraordinary leadership to force us to face the most significant problems that challenge us as a society, all of which are connected and just one of which is climate change.

If we don't face these challenges head on, and soon, it will take even more extraordinary leadership to keep humanity from destroying itself entirely. The problems of our time, like the dynamics of the climate of Venus that lead theoretically to the runaway greenhouse effect, have a chance to feed off of each other and run away from us.
Reply
Ken Fabian

I'm not convinced studying Venus will tell us anything about Earth's climate that we couldn't deduce by other means, but I am not certain of that and other planets to compare to will have some value, if only in showing the uniqueness of Earth. Earth has it's own potential for significant climate changes as well as humans to be a source of climate change and be vulnerable to it.
Reply
einsteinium253

Ken Fabian said:
I'm not convinced studying Venus will tell us anything about Earth's climate that we couldn't deduce by other means, but I am not certain of that and other planets to compare to will have some value, if only in showing the uniqueness of Earth. Earth has it's own potential for significant climate changes as well as humans to be a source of climate change and be vulnerable to it.
"I'm not convinced studying Venus will tell us anything about Earth's climate that we couldn't deduce by other means... other planets to compare to will have some value, if only in showing the uniqueness of Earth."

Copernicus authored a similarly anthropocentric (e.g. egotistical) point of view (so to speak).

Copernicus broke the mould. How could a man, after all these centuries of "brand new insight" dare to suggest that the Sun, and not the Earth, is the center of the Universe?
Reply
Helio

Unclear Engineer said:
The article talks about Venus "only" being at about 70% of Earth's distance from the Sun. But, that results in Venus getting about twice as much solar energy hitting its atmosphere. That is a big difference to begin with.
Yes, though a = 0.723AU for Venus, so it receives 90% more solar radiation. No small matter.

Unclear Engineer said:
In contrast, Earth seems to have had its CO2 removed from its atmosphere and stored in the solid parts of the planet, by life forms. that also oxygenated the atmosphere, largely by removing the carbon into the ground.
Right. Did I miss plate tectonics mentioned in the article? Venus may have had some tectonics, according to a 2023 article, but this seems to have ended perhaps 4 billion years ago. If so, advanced life would seem very unlikely to have had time to come along.

Perhaps, though, both the biological and non-biological processes worked to make limestone, and other carbonates, during that period, but then failed with the lack of tectonic activity.

Unclear Engineer said:
So, at least for me, what I think is important to learn from Venus about Earth is more about how Earth could have gone from a dense, heavy atmosphere to what we have today, instead of turning out like Venus. Is the 50% less solar energy input the only determinant?
No doubt there is a lot more to learn about Venus. How did it lose it’s rotational ang. momentum? An impact? Or was it tidally locked in a closer orbit then moved out when Saturn and Jupiter went into resonance? There is also, apparently, a lack of temperature gradient at the cloud tops as the poles are about the same temperature as the equatorial region. Lots of questions but the phosphine story, though diminished, may be helping to get a probe over there.
Reply
einsteinium253

Helio said:
Yes, though a = 0.723AU for Venus, so it receives 90% more solar radiation. No small matter.

Right. Did I miss plate tectonics mentioned in the article? Venus may have had some tectonics, according to a 2023 article, but this seems to have ended perhaps 4 billion years ago. If so, advanced life would seem very unlikely to have had time to come along.

Perhaps, though, both the biological and non-biological processes worked to make limestone, and other carbonates, during that period, but then failed with the lack of tectonic activity.

No doubt there is a lot more to learn about Venus. How did it lose it’s rotational ang. momentum? An impact? Or was it tidally locked in a closer orbit then moved out when Saturn and Jupiter went into resonance? There is also, apparently, a lack of temperature gradient at the cloud tops as the poles are about the same temperature as the equatorial region. Lots of questions but the phosphine story, though diminished, may be helping to get a probe over there.
Lots of questions, and all of them imaginary.

What is imaginary is real. What is imagined is really imagined.

What is experienced is real. What is experienced is really experienced.

What is real is real. What is real is real.

All these made up words, suggesting that we know this or know that...
We've forgotten the one thing we are bound to remember. The truth.
Reply
Helio

einsteinium253 said:
Copernicus broke the mould. How could a man, after all these centuries of "brand new insight" dare to suggest that the Sun, and not the Earth, is the center of the Universe?
Yes, that's an important question for science. I think there were a number of factors:

His approx. 12 years of college taught him not only law but Greek and astrology/astronomy. The latter required for medical work.

1) Ptolemy's model was required a lot of work to update the tables.
2) He read about Aristarchus and other early Greeks who postulated the large Sun was the center.
3) He recognized the elegance of the period-distance relationship for the planets.
4) His model easily explained planetary retrogrades.
5) The Sun was much, much bigger.
6) His model, he thought, was simpler. 7) He was encouraged by others, including other clergy like himself, to publish, and he was about as far from Rome as one could be at the time. :)
9) The Almagest was mainly a math model. Ptolemy never argued his epicycles, equants, eccentrics and deferents were physical manifestations. He sought a method to determine the planet's location with time.
Copernicus, however, sought a physical model.

This latter point, 9, is important since we see many metaphysical works that lack a physical model. Friedmann is not credited with the BBT since his work was mathematical only, lacking objective arguments.
Reply
Helio

einsteinium253 said:
Lots of questions, and all of them imaginary.

What is imaginary is real. What is imagined is really imagined.

What is experienced is real. What is experienced is really experienced.

What is real is real. What is real is real.

All these made up words, suggesting that we know this or know that...
We've forgotten the one thing we are bound to remember. The truth.
This is why science plays an important and unique role. Objective-based hypotheses are as good as knowledge can get. This is where tests take place. Truth transcends it so it is a bit too illusive for science, IMO.
Reply
Ken Fabian

No intention of belittling the studying of Venus - and didn't James Hansen apply atmospheric modeling developed for Venus to better understand how changing GHG levels affect Earth's? But we do have a very good understanding of the fundamentals of how Earth's climate system works now, primarily without reference to other planets. We have a good idea of what happens when lots of CO2 and methane get added -; there are enough dire warnings coming out of that without the specter of Venus style runaway greenhouse effect.
Reply
Helio

In "The Secret Life of the Universe", Natalie Cabrol (Dir. of Car Sagan Inst. at SETI) has a chapter on Venus and habitability. She notes that it will take atmospheric probes to help determine the best scenario for the history of Venus.

She addresses three scenarios, but the favored, apparently, is one where Venus was habitable until the last few hundred million years. Since the Sun was 75% less luminous in the distant past, then she claims it would have been in the habitable zone. I disagree since the temperature method I use says otherwise even when I bump the HZ width to include the broader Equilibrium Temp. method, which allows only a 15% luminosity increase. As noted above, the current orbital distance for Venus would exceed this even when the Sun was cooler. Of course, who knows what orbit it had back then.
The scenario suggests that volcanic activity was great pumping CO2 and other products in the atmosphere. Water vapor, too hot to condense, along with CO2, etc. would have disastrous effects. Tectonic plate movements would have ceased without the important lubrication effects of liquid water.

But, there is a chance that life may have been there prior to the catastrophe. The other scenarios seem very unfavorable for life given the planetary temperatures were hot from the start, more or less.
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