- What happens if you just keep adding CO2 to a planet's atmosphere?

Is there a tipping point that will basically break the climate?

Well, you actually don't have to look far to find out.

If you plotted the surface temperature of every planet in our solar system.

You'd probably expect to see something roughly like this with the temperature gradually going down, the further you get from the sun, which is pretty much what we see with one notable exception.

Venus is a huge outlier, but it hasn't always been.

Scientists think Venus may once have been a lot like Earth with water oceans, a much milder climate, but something pushed it past a tipping point.

The greenhouse effect ran away, the oceans evaporated, and today it's nearly 900 degrees Fahrenheit on the surface while Earth its next door neighbor became the only known place in the universe with life.

Weird, right?

So what was that tipping point?

And are there any similar tipping points like that on planet Earth?

Let's find out.

But before we go any further, I just wanna thank everyone who's joined our Patreon or purchased merch.

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For a long time, scientists thought Venus might be the most earth-like planet rivaling Mars even.

But then in 1962, after scientists scanned Venus' surface, the vision of Venus as a potentially life holding planet was shattered.

Scientists now estimate that Venus is 470 degrees Celsius on the surface with an atmosphere composed almost entirely of CO2 and a pressure of 92 times that of Earth's surface.

But there's evidence that Venus was a lot like Earth, here fold and thrust mountain belts like the Himalayas form when two continents collide and the crust crumples folds and stacks up along massive thrust faults building mountains over millions of years.

But strangely, there is a place on Venus that meets this description.

- There is a place in the northern hemisphere of Venus called Ishtar Terra.

It's a thickened crust.

It's a high flat plateau of with a crumpled up structure that looks very much like the tectonics that you create in the Andes or the Himalayas.

And in fact, if I showed a picture of the structure, somebody who knows about the Himalayas would say, that sounds a lot like the Himalayas.

And it does.

- To create that kind of movement and slip, you have to have one crucial ingredient that is not present on Venus today... water.

It weakens rock and helps fault slip, acting like a lubricant that makes big pieces of the crust more likely to move.

So when scientists see a Venusian region like Ishtar Terra, that's Himalayan and scale and structure, it suggests Venus likely once had significant amounts of water.

And there's another clue that Venus used to be a lot more like Earth.

- We know that Venus lost a lot of water at some point in time.

- That's because when a planet loses water, it leaves something else behind a special kind of hydrogen that's heavier called deuterium.

- The heavier version, because it has more mass, doesn't escape as easily as the lighter version.

As you lose hydrogen generically, that ratio of D to H goes up with time and the value that we measure at Venus is significantly higher than the value we see at Earth.

It tells us that Venus, it's lost hydrogen, but really the the, the reservoir for that is water.

- So Venus once had water, but then something changed.

It crossed a threshold where liquid water couldn't survive and once the water is gone, the planet may have lost one of its most long-term ways to stabilize the climate.

So what exactly was Venus's tipping point?

Well, on Earth, the last true hot house period was the Eocene.

And one of the big drivers scientists point to is a massive volcanic pulse called a LIP or a large igneous province.

- We like acronyms if you haven't figured that out.

- We actually made a whole episode about LIPs and their connection to mass extinction events, and we've got an extended interview with the scientists who help make that link on our Patreon.

But here's the short version.

If normal volcanism is a steady leak of greenhouse gases, like CO2, A LIP is a fire hose of CO2 running for tens of thousands or even millions of years, - They produce a lot of vulcanism.

The deckhand traps was a million cubic kilometers of lava in a million years.

That's a lot of material coming out all at once and coming from a deeper part of the planet than the mid ocean ridge volcanism that occurs all the time.

- So when we get one of these LIP events, a huge amount of CO2 enters the atmosphere and the climate system has to respond.

But here's the key difference between Earth and Venus.

On earth, even when CO2 spikes from a massive natural event, the planet has ways to slowly correct: oceans that absorb carbon, rain, that weathers rocks, and long-term geologic processes that can eventually pull CO2 back out of the air and lock it away.

And that's why we can have these ancient hot house periods like the Eocene without turning into Venus.

But Venus wasn't so lucky.

First of all, it's a lot closer to the sun than Earth, so it was already a lot hotter.

And second, Venus has a lot of volcanic features more than any other planet in our solar system, giving it a huge potential to release CO2 - On Venus at some point we crossed over that threshold of a hundred degrees Celsius, and now liquid water at the surface doesn't work.

- And without liquid water, Venus lost one of its most important climate stabilizers.

No oceans, no rain, no efficient long-term way to pull CO2 back out of the atmosphere and lock it away.

Once it crossed that line, the planet couldn't cool itself back down.

Now bringing it back to earth, the total warming we've caused so far is still far less than what the planet experienced during some of these ancient volcanic hot house periods.

But our human cause warming today is far faster.

So it's worth asking, are there tipping points here on earth, thresholds that could knock out our stabilizers and make warming much harder to stop or reverse?

- 60 million years ago, we know that earth was very warm crocodiles living in the Arctic and, it's a bit of a mystery how earth was that warm.

- You heard 'em right crocodiles in the Arctic.

So the Eocene was hot, very hot.

But when scientists try to model Earth's climate during that time, something weird - happens.

This has been kind of a puzzle of of the climate community.

And when we try to simulate this with our global models, we're just unable to reproduce how warm it was during this period.

We need to add a lot more CO2 in our models then we think that there was reasonably - So where did the extra warmth come from?

Scientists estimate there were somewhere between 1200 and 2000 parts per million in the atmosphere.

But to recreate a frost-free, crocodile friendly arctic, they have to add around 4,000 parts per million to their models, which had some scientists scratching their heads, but then climate models revealed something shocking.

If you add around 1200 parts per million of CO2, an important type of cloud just disappears, which could explain a lot of that excess warming.

Without clouds, - our earth would be really super hot.

But there's one kind of cloud in particular that will cause the most of this warming, and you're probably familiar with it, especially if you live on the west coast.

- It's what the people call the marine layer out here, right?

It's relatively low, pretty uniform white blankets.

They're they're year round covering large large ocean regions.

- These are stratocumulus clouds, bright, low and unbelievably important because they act like Earth's sunscreen reflecting sunlight back into space and keeping the surface cooler.

In fact, we'd be looking at 14 degrees Fahrenheit of global warming just from losing that one cloud system.

So how could greenhouse gases mess with clouds that much?

It comes down to something weird about stratocumulus.

They're kind of upside down.

- They were in some ways driven by cooling at the top rather than heating at the bottom.

- Stratocumulus clouds survive because the top of the cloud that can radiate heat out to space.

But these models showed that when enough CO2 was added to the atmosphere, these clouds are no longer able to cool at the top.

- You might reach a point where these clouds simply can't exist.

This cooling won't work anymore.

- And remember losing our stratocumulus clouds would add something like 14 degrees Fahrenheit.

Today in 2026, we're already at about 430 parts per million.

So 1200 to 2000 parts per million sounds unattainable.

But when you consider that atmospheric carbon dioxide is now 50% higher than what it was before the industrial revolution, that number starts to sound less crazy and possibly even scarier is that under an extreme but not impossible future scenario, we could approach 1200 parts per million by the year 2100, which would be really, really bad.

We're talking about an unrecognizable planet.

Major ice sheets disappearing over time.

Sea levels ultimately rising by hundreds of feet and a world where many of Earth's big climate systems are pushed far past critical thresholds.

So, when you ask, 'Could Earth become Venus?

', clouds might be one of the biggest wildcards.

But the real answer to that question is a bit more complicated.

In the very long run, Earth does have a Venus like future.

The sun is slowly getting brighter and billions of years from now, that extra energy will make it harder for Earth to hang on to liquid water.

But right now, a Venus like runaway greenhouse effect is not possible on Earth.

So the sun isn't pushing us towards tipping points.

We are.

And the lesson from Venus isn't that it just hit a temperature tipping point.

It's that the planet lost its breaks.

And the more that we push Earth's climate, the more we test the systems that act as our own breaks.

Oceans, ice, forests and yes clouds.

So although we won't turn into Venus, we can tip into a world that's pretty much impossible to reverse on human timescales.

And the best way to make sure Earth doesn't cross major tipping points is to stop adding CO2 into the atmosphere.

But we already know that.

We always say that on this show.

But what do you think about this episode?

Let us know in the comments and we'll see you next time on Weathered.