Venus is NOT a "Runaway" Greenhouse Effect!

thanks to squarespace for helping support this episode hey crazies life as we know it requires liquid water and that's only possible on the surface of a planet if that planet is in the habitable zone of its system earth is right in the middle of ours but at the inner edge you'll find venus and at the outer edge you'll find mars of course neither of them is habitable for the same reason their atmospheres venus's thick atmosphere retains too much heat mars's thin atmosphere doesn't retain enough but what if in some alternate universe venus formed in mars orbit would it be habitable then [Music] this episode was made possible by the generous support of our patrons and youtube members i think it'll be best if we start with what venus is like now it's about the same size as earth so it can hold on to more atmosphere than mars and boy does it ever venus atmosphere is mostly carbon dioxide or co2 and it's super thick the pressure is 92 times what we have on earth yeah you heard that right 92 times venus will crush you like a pancake it's really hot on the surface too but not because it's closer to the sun almost no light reaches the surface that super thick atmosphere and these shiny clouds reflect a bunch of it back into space the reason it's so hot on the surface is because the co2 in the atmosphere absorbs infrared light holding in the heat the surface temperature is a steady fahrenheit that's 470 celsius even crazier venus atmosphere is so dense that it doesn't even matter if it's day or night it's 870 fahrenheit all the time imagine being covered with thousands of blankets you'd get crushed and you'd burn up from your own body heat if somehow you survived that you'd still have to deal with the rain these clouds aren't made of water like earth clouds they're sulfuric acid it literally rains sulfuric acid on venus is that an actual picture oh yeah it is does that mean we landed there yeah it does these pictures were taken by one of the soviet venera probes during the 1970s the russians built a venus lander and it lasted almost an hour humans rock anyway venus got that way because it's a runaway greenhouse actually venus is not in a runaway greenhouse effect what the term runaway greenhouse effect it's kind of reserved for something different than just a very strong greenhouse effect really wait who are you chris close dr chris kolhaus from the nasa goddard institute for space studies yeah cool uh what exactly do you do there it's primarily an earth climate modeling center but there's a few people that have done modeling of planetary atmospheres and exoplanet interests and such i'm part of that exoplanet modeling group ah so this is definitely in your wheelhouse okay so if venus isn't a runaway greenhouse then what is it it's fair to call it strong or supercharged or whatever but it's it's reached in equilibrium it's it's right right it's an equilibrium and it's just it's just a very hot equilibrium so what's a runaway greenhouse it actually refers to a very specific process in which the outgoing radiation cannot reach the absorbed solar radiation oh so venus had a runaway greenhouse in the past but has since stopped what is thought to maybe have occurred on early venus okay so i just learned so much that my brain hurts but i'm gonna try to summarize say you've got some random planet it doesn't matter which one its average surface temperature can be determined by a relatively simple equation incoming light from the sun minus outgoing light from the planet which is mostly infrared that's it the trick is knowing what happens with those numbers under different circumstances and that's what we're going to need to know if we plan on moving venus around naturally there will be less incoming light if the planet is further from the sun light leaving a source gets spread out over a larger and larger area as it moves away it's called an inverse square law because the intensity drops with the square of the distance we measure area in square units square miles square feet square meters you get the idea mars's orbit is a little over twice as far from the sun as venus if venus formed there instead it would receive less than a quarter of the light which is pretty significant does that mean it would be one quarter of the temperature actually no if you put an ice cube on the counter it'll seek an equilibrium with its warmer surroundings for this ice cube that means it'll eventually melt but that ice cube is in contact with a counter and surrounded by air a planet like venus is floating in the vacuum of space it's not in contact with anything except the light from the sun the intensity of that light is not proportional to temperature though it's proportional to the fourth power of temperature something we call the stefan boltzmann law if we want to think of venus as being enveloped in light we're gonna need to factor that in by the time the light gets to this alternate venus the intensity would be less than a quarter of what it is for our venus but the effective temperature of that light would be the fourth root of that or about 69 so not as cold as you might think however the amount of light that arrives at a planet is not necessarily the amount that arrives at the surface remember when i said this that super thick atmosphere and these shiny clouds reflect a bunch of it back into space venus is the most reflective of any of the eight planets very little light actually reaches the surface from space it's not pitch black but it is dark think just after dusk on a cloudy day what venus's atmosphere does with the outgoing infrared light is what keeps it so hot since planets like venus are surrounded by empty space the only way they can exchange heat with that space is through light while the incoming light from the sun tries to warm the planet up the planet also tries to cool off by emitting light mostly in the infrared range but you know how we have these things called greenhouses they're really useful for growing plants because they let light in but don't let the hot air out it's a temperature regulation system planets do a similar thing to retain heat it's called the greenhouse effect but the mechanism is a little different than an actual greenhouse for one if a greenhouse gets too hot they just open a vent you can't do that on a planet also planets aren't surrounded by glass but they are surrounded by gas i'm such a dork some of those gases absorb infrared light and send it back to the surface they're called greenhouse gases because they help the planet hold in heat kind of like a greenhouse any planet will find a balance between incoming and outgoing light eventually remember the simple equation incoming light minus outgoing light when those two factors are balanced the planet is said to be in equilibrium it's not heating up or cooling down uncontrollably a weak greenhouse lets more infrared light leak into space that'll give you a cold desert like we find on mars with a strong greenhouse there's less infrared light leaking into space that'll give you something like the hellscape we see on venus now we don't actually know that much about venus's past resurfacing events have kind of wiped the slate clean but this equation does tell us a little bit it tells us that at some point in venus's past it was receiving far more light than it could emit venus could have easily started with a large shallow ocean the increasing heat on the surface just evaporated it but what if we caught that before it even began if we were to move venus to mars orbit now nothing would change the damage has already been done it's a hellscape and likely will be for a very long time but if in some alternate universe venus just formed there instead of mars it actually stands a chance it's more massive than mars so its higher gravity would help it hold on to more atmosphere which includes more human-friendly gases like oxygen and nitrogen by the inverse square law venus would receive less light in its new orbit less than a quarter of the light which means about 69 of the incoming heat but doesn't it still have the carbon dioxide yes but not as much of it in its younger days the habitable zone around a star is defined by the limits of the greenhouse effect for various reasons there are limits to how warm greenhouse gases can keep a planet's surface beyond this point they just suck at it at least the heavier ones that rocky planets like venus can hold onto if venus formed out there it could have found equilibrium before the climate got carried away it could have been earth 2.0 just kept warm with a little less light and a little more co2 mind you this is all a bit speculative as dr colas mentioned in our conversation plate tectonics is sort of a complex variable in this story geologic activity in the distant past can have wild effects on the present the point is we don't know if venus would have been habitable in this alternate universe but it would definitely have less incoming light and more outgoing light which would have at least made it possible for venus to be habitable and if you ask me that's pretty cool so would you move to venus if it formed in mars orbit let us know in the comments if you want to listen to the entire conversation with dr chris kolos i posted it to the second channel huge thanks to chris for taking the time to talk to me thanks for liking and sharing this video don't forget to subscribe if you'd like to keep up with us and until next time remember it's okay to be a little crazy this episode was sponsored by squarespace the all-in-one platform to build a beautiful online presence and run your business there are lots of reasons you might want a website if you don't have a coding background or good design instincts though you're gonna have a rough time with squarespace making a website is easy and quick they have tons of design templates that look professional on all devices do you need your website to accept payments 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Channel: The Science Asylum

Views: 578,264

Keywords:

Id: Mgw-hMZi5eA

Length: 11min 49sec (709 seconds)

Published: Fri Feb 26 2021

Reddit Comments

[u/Zealousideal-Box-297]

I thought it was astronomy 101 that Venus has no magnetosphere because it's day is almost as long as it's year. That must also create some interesting atmospheric circulation patterns as well.

[u/pr-mth-s]

Oh they have dropped the 'runaway' thing (which began with James Hansen's thesis in 1967), it's no longer on the list of factsthatcannotbedenied like tundra methane, atolls going underwater and so on. once they got pushback from reality and/or experts alarmists just pretend they never thought or said that. if anything every time this happens they feel even cleverer than before.

[u/publius_lxxii]

Oof, at 1:30 this guy starts spouting the 'CO2 causes all warming' narrative.

He says:

The reason it's so hot on the surface is because the CO2 in the atmosphere aborbs infrared light holding in the heat.

which is only kinda sorta true.

In 2010, Lubos Motl and Tony Heller kicked off a kerfluffle in the blogosphere when they (rightly) noted that less than 100 degrees C of Venus surface temps could be attributed to the high CO2 level, - and bulk of the 470C surface temp was due to the 92 atmospheres of pressure.

See:

https://motls.blogspot.com/2010/05/hyperventilating-on-venus.html

https://motls.blogspot.com/2010/05/venus-chris-colose-vs-steve-goddard.html

Interestingly enough, this video's 'Dr. Colose' was the then-grad student running around the blogosphere 'defending the consensus'.

It took a couple years for the alarmists to silently concede the point, but since then you've seen far fewer technically-minded alarmists try to use Venus as scare-mongering tool.

[u/Kim147]

The greenhouse effect requires a transparent atmosphere. If the atmosphere acts like hard ground then the IR just hits the atmosphere and is turned into heat. If the lower layers become hot and the upper layers insulate the lower layers from space the heat is retained. It's no different than the effect of clouds on Earth. Clear sky during the day, Ground heats up. Cloudy night. Heat retained.