Venus and Earth, sister planets
Our sister planet shows what a runaway greenhouse
effect can do to an earth-like world.

The Venus Syndrome:
Alerting humanity to the danger of the ultimate catastrophe

“The Venus syndrome is the greatest threat to the planet, to humanity's continuing existence... In my opinion, if we burn all the coal, there is a good chance we will initiate the runaway greenhouse effect. If we also burn all the tar sands and tar shale (aka oil shale), I think it is a dead certainty.”
-Dr. James Hansen, NASA climatologist

It's been said that if you want to know what the mainstream scientific view on global warming will be a few years down the road, just listen to what James Hansen is saying today. One of the most well-respected climate scientists in the world, Hansen has a history of making assessments about global warming which were considered extreme at the time, but which later were confirmed by the accumulating weight of evidence, to the point that most scientists accepted them.

Dr. Hansen's most recent warnings are not for the faint of heart. New findings on how sensitive the Earth's climate is to carbon dioxide have led him to conclude that the process of runaway climate feedbacks that happened on our sister planet Venus is not only possible on the Earth, but virtually guaranteed if humanity continues its project of transfering our planet's stored carbon to the atmosphere.

Earth's Twin

Venus evening sky
The brightest "star" we see in our Earthly skies is the planet Venus.
                       Photo credit: Mbz1 via Wikimedia

Venus is the second planet from the sun, and the planet that comes the closest distance to the Earth. Shining brilliantly like a beacon in the evening and morning skies, Venus is the brightest object in our sky, after the Sun and Moon. The dazzling beauty of this spectacle inspired the ancient Romans to name it Venus, after their goddess of love.

In many ways, Earth and Venus are twin sister planets. Roughly the same size, the two worlds have approximately the same overall composition. But the second planet from the sun is not a place you'd want to visit.

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The Planet of Love (And Sulfuric Acid Rain)

Conditions on Venus strain our ability to understand how different an Earth-like world can be from our own planet. The average temperature on the surface is 900 degrees Fahrenheit, hot enough to melt lead. The atmospheric pressure is a bone-crushing 90 times the air pressure on our own planet's surface. You'd have to dive a half mile deep in Earth's ocean to experience the same pressure. Standing on the surface of Venus, a human would get simultaneously crushed and roasted.

Venus surface
“With searing heat, crushing pressures, noxious gases and everything suffused in an eerie,
reddish glow, Venus seems less the goddess of love than the incarnation of hell.”

                        -Carl Sagan

As if that wasn't enough to complete the picture of an alien world, on the planet of love, it rains concentrated sulfuric acid and snows metal. Because of the searing temperatures, the rain evaporates before hitting the ground, but on the highest mountain tops, it's "cool" enough that flurries of metal snow fall to the ground and accumulate.

But Venus wan't always the brutal place it is today. It's thought that Venus began its existence with a similar atmosphere to the Earth, and oceans. What happened to turn the planet of love into a planetary hell? The answer is that Venus has suffered a runaway greenhouse effect.

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How It Happened: The Runaway Greenhouse

Venus oceans steam greenhouse
When Venus was young, it probably had an Earth-like atmosphere and
oceans. Those oceans likely played a key role in helping to bring about
a runaway greenhouse effect.
                       Image by Sean O'Flaherty via Wikimedia

Shortly after Venus formed, it was probably much like the Earth, with oceans and a similar atmosphere. A natural property of stars is that they very gradually brighten as they age, so in the early days of the Solar System, the sun was dimmer than it is now. As the sun slowly brightened, at some point the increasing intensity of sunlight tripped the first domino of a cascade of heat-trapping feedbacks on Venus.

The oceans were the first domino. Evaporated water is a powerful greenhouse gas. Once the increasing sunlight evaporated enough water vapor into the air, the steam atmosphere trapped so much heat that it exceeded the ability of any natural cycle to regulate the temperature. That was the point of no return for our sister planet.

It was a classic feedback effect: higher temperatures evaporated water vapor into the air, which trapped more solar heat, raising the temperature further and evaporating more water vapor, in a vicious cycle. The accelerating temperature increase continued until the entire oceans boiled away.

By now, with oceans' worth of water vapor in the atmosphere trapping heat, the pressure cooker-like conditions awakened a new feedback. The largest store of the element carbon on Venus until this time had been in the planet's crust, in the form of carbon-containing rocks, just is it is now on Earth. But the searing temperatures cooked the crustal rocks to the point that the minerals started to break down, releasing that carbon to the atmosphere in the form of carbon dioxide. Carbon dioxide, of course, is another greenhouse gas, so this raised the planet's temperature further still. This feedback cycle continued until most of the planet's stock of carbon had been baked out of its crust and transferred to its atmosphere, where it stays to this day, trapping solar heat and maintaining the planetary furnace.

It's important to understand that the slowly increasing output of sunlight was the trigger that set in motion the runaway greenhouse on Venus, but once the process started, it awakened climate feedback effects, and the process then moved on its own momentum.

The greater amount of sunlight shining on Venus is probably what started the runaway greenhouse, but it is not what maintains it. Once a runaway greenhouse effect has started on a planet, the greenhouse is able to maintain itself.

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Stronger Sunlight Is NOT Why Venus Is So Hot Today

The first thing most people think about Venus is that since it's closer to the sun than Earth, the extra sunlight it gets must be what's fueling the super-greenhouse conditions. That couldn't happen here, people figure, because Earth doesn't get as much sunlight as Venus does. Closer examination suggests we shouldn't breathe so easy.

The surface of Venus is hotter than the surface of Mercury, despite the fact that Venus is twice as far from the sun, and the sunlight shining on it is only a quarter as intense as the sunlight shining on Mercury. That's because of the greenhouse effect. Venus is like a car sitting out in a parking lot on a sunny day with all the windows and doors closed: it very effectively traps the sunlight, maintaining a much higher temperature than it would if it weren't sealed up.

What about compared to the Earth? It's true that since Venus is closer to the sun, more powerful sunlight shines onto it than onto our own planet. But Venus is really, really bright. The upper cloud layers of Venus are nearly snow-white, and they reflect back off into space most of the sunlight that shines on the planet. (That's why Venus appears such a lovely bright object in our own skies). Earth, on the other hand, is much darker, and it absorbs most of the sunlight shining on it.

Venus absorbed sunlight
The cloud tops of Venus are so reflective that the amount of sunlight Venus absorbs
is actually less than what Earth absorbs.                              

Because those cloud tops are so reflective, even though Venus receives stronger sunlight, the amount of solar energy Venus absorbs is actually LESS than the the amount of solar energy the Earth absorbs.

The greenhouse effect on Venus is so powerful at trapping heat that it's able to take that smaller input of absorbed sunlight, and maintain a surface temperature hot enough to melt lead.

This is a critical point that few people appreciate. The amount of solar energy which Earth absorbs is more than enough to fuel Venus-like temperatures, if Earth had a Venus-like atmosphere. And Earth has enough carbon to create a Venus-like atmosphere.

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Could It Happen Here?

Could a full-fledged runaway greenhouse happen here on our own planet? Until recently, scientists thought we were safe from the Venus syndrome, because the Earth has had much higher CO2 levels at times in its geological history without triggering a runaway greenhouse. There are three reasons why there may not be as much safety margin as we thought.

First, the sun was cooler when CO2 levels were higher hundreds of millions of years ago, so an equivalent level of carbon dioxide would produce higher temperatures today.

Second, new research indicates those ancient levels of carbon dioxide may not have been as high as we thought, so it might take less CO2 to produce a given temperature rise.

And third, the speed at which you add greenhouse gases to the air is as important as the amount, because at a higher speed there's less opportunity for that carbon to get pulled from the air by carbon cycle mechanisms. We're now increasing greenhouse gases in Earth's atmosphere about ten times faster than the fastest natural increase that's ever occured in Earth's geological record.

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How To Trigger The Ultimate Catastrophe

Here's a brief summary how it could happen here. Most elements are from Hansen's book 'Storms of My Grandchildren: The Truth About The Coming Climate Catastrophe And Our Last Chance To Save Humanity'.

In this scenario, humanity continues to transfer the Earth's remaining stored carbon into the atmosphere. That means we build more coal-fired power plants, and we build factories to turn coal into liquid fuels. As we burn the remaining "conventional oil", we develop the vast carbon reserves in the tar sands and oil shales to fuel our vehicles.

Climate feedback loops
Climate feedbacks: The warming from our greenhouse gases threatens to unleash an array
of vicious cycles, creating new sources of warming we won't be able to stop.

Over the course of the twenty first century, this boosts greenhouse gases in the atmosphere to levels rivaling the highest they have ever been. Compared to any other greenhouse gas increase over Earth's history, it all happens in an instant.

The rapidly rising temperatures trigger one feedback effect after another: the melting of the Arctic Ocean's sea ice, the uncontrolled thawing of the Arctic tundra, and the release of methane hydrates from the deep sea. The ice sheets of Antarctica and Greenland go into terminal decline, breaking up and flowing out to the rising sea as they melt.

Even on the fast track, with multiple feedbacks heating the planet, it may take centuries for the ice sheets to entirely melt. During this period, the torrents of melt water pouring off the ice sheets will keep polar oceans relatively cooler, as the rest of the planet relentlessly heats up. The multiple plagues of the twenty-first century's "Hell and High Water", the devastating combined effects of heat waves, drought, crop failure, superstorms, rising sea levels, and ocean acidification, get steadily worse and worse, decade by decade. By the twenty-second to twenty-third centuries, most of the planet is subject at times to heat and humidity extremes that are lethal to humans.

During this period of ice sheet disintegration, much of the extra heat being trapped by the massive load of greenhouse gases in the air will be going into melting the ice. Once the last of the ice sheets melts away, the planet's energy imbalance will be vast and unstoppable. The extra heat will drive more water vapor into the atmosphere, which will trap more heat, which will evaporate more water vapor. This feedback loop accelerates, and planet Earth will proceed to the Venus syndrome.

Keep in mind, this is not a fringe doomsday scenario. This is a science-based projection from one of the world's leading climate scientists - who also happens to be an expert on the atmosphere of Venus.

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Choosing a better way

We can't let this happen. We don't yet know how close we are to triggering the Venus syndrome, but it is clear that continuing on our present course means catastrophic impacts for our children and future generations. Messing with the composition of the Earth's atmosphere is a very dangerous thing to do.

We can choose a bright future for our children and their children, and generations after.

Venus evening sky
Depending on what we do now, for our grandkids the sight of Venus in the evening sky will
either be a terrifying portent of our own planet's near future, or reminder of how we
succeeded in preserving our planet for all future generations.
                    Photo credit: Jorge Diaz via Wikimedia
It all starts with spreading the word about the danger and the solution, and demanding that our governments treat the climate crisis like the life-and-death emergency that it is.

By switching the world rapidly to a post-carbon economy, we can make sure that for our children and those after, the sight of Venus in the evening sky will be a reminder of how we woke up from the nightmare, a reminder of how we succeeded at preserving the precious heritage of our bountiful planet for all future generations.

Next: On to the solution! Building our clean energy supply, Part 1 - Electricity