The Earth isn't turning into Venus

[Mijin]

@scotandrsn

You’re generous. Given that the OP is tilting at windmills that haven’t even been built yet, I’d put it in MPSIMS.

“…that haven’t even been built yet” is a corruption of an already strange expression. It doesn’t work when you look at the origins of the phrase.

But anyway, the OP has provided two good cites and a couple of people in this thread have argued the case that the earth could / is going to become like Venus.

[Mangetout]

@Mijin

“…that haven’t even been built yet” is a corruption of an already strange expression. It doesn’t work when you look at the origins of the phrase.

I see what you’re saying, but I quite like it.

[wevets]

The whole question of Venus and tectonic activity seemed pretty interesting, so I dug up a couple quotes related to Venus’ weak tectonics and infrequent or absent subduction.

@USGS

Venus may still be active, though the evidence is questionable. In 1979, the Pioneer-Venus spacecraft measured a high amount of sulfur in the upper atmosphere of the planet; the sulfur amount then decreased over the next few years. This observation suggested that the high sulfur concentration measured in 1979 may have resulted from a catastrophic event, perhaps a volcanic eruption. Beginning in 1990, radar images made by the Magellan spacecraft revealed dramatic volcanic features and long, deep valleys similar in size and shape to oceanic trenches on Earth.

http://pubs.usgs.gov/gip/dynamic/unanswered.html

@Turcotte et al.

One explanation for the catastrophic resurfacing is the episodic subduction hypothesis. We model episodic subduction using a thermal boundary-layer stability analysis. We find that episodic subduction events with intervals of 500 to 700 Myr can transport only 15-25% of the radiogenic heat produced within the planet. We suggest that the remainder of the heat must be lost to the surface during a period of vigorous tectonic activity, following the subduction event but prior to the subsequent stabilization of a global lithosphere.

Catastrophic Resurfacing and Episodic Subduction on Venus

http://www.sciencemag.org/cgi/content/summary/277/5330/1177g
I guess no one really asked a question about Venus tectonics, but there’s not really a question in the OP, either.

Then can I ask my own?

Was Stephen Hawking using hyperbole or joking when he taked about Venus or is he poorly understanding the problem of global warming? Or does the context of the quote reveal what he’s talking about?

[Mangetout]

@wevets

Was Stephen Hawking using hyperbole or joking when he taked about Venus or is he poorly understanding the problem of global warming? Or does the context of the quote reveal what he’s talking about?

It seems reasonable to me that he meant ‘like Venus’, rather than perhaps, ‘exactly like Venus’.

[garygnu]

It may not end up like Venus, but it is certainly possible to completely change to chemical makeup of the Earth’s atmosphere. It’s happened before. A new type of organism[sup]1[/sup] made a waste product[sup]2[/sup] in high quantities. That waste product chemically reacted to existing life forms’ food source[sup]3[/sup] resulting in a massive change in both ocean water and atmospheric chemical composition, climate change, and near-total wipeout of all life.
(Other Articles Here)

1: Cyanobacteria
2: Oxygen
3: Iron

[Captain_Lance_Murdoch]

The Earth is already like Venus in that both planets have greenhouse effects. Without any greenhouse effect the Earth would be a very, very cold place. The issue with warming is turning up the greenhouse effect to the point that it causes damage to the environment and life as we now know it.

As was pointed out, most of the Earth’s greenhouse gases are trapped not in fossil fuels, but in places like the oceans.

Even if the Earth’s atmosphere were magically replaced with Venus’ the Earth would still be a bit cooler than Venus as it is farther from the Sun.

[marshmallow]

@Cosmic Relief

Earth is never going to become like Venus, at least not as a consequence of carbon emissions. That’s the answer to the GQ. Of course we all know that a cataclysm only takes tens of degrees of increase, not hundreds, but OP appears to be immune to this concept.

Post #8. Also a red herring.

@Mangetout

But not all at the same time.

I realise Der Trihs already pointed this out - I’m just agreeing.
That’s the fundamental flaw that the whole argument proceeds from.

So you’re both saying that all the CO2 and methane derived from fossil fuel sources were not in the air at one time in Earth’s past. Can you please explain and cite a source? Look at this chart. Carbon ppm in the atmosphere in Earth’s past were orders of magnitude higher than today. For example, during the Cambrian it was approximately 7,000 ppm. During the Mesozoic it varied anywhere from 1000-2000 ppm.

All the carbon for two trillion barrels of oil, trillions of tons of oil shale, and trillions of tons of coal were in the environment at some point. Right? So before biological processes were able to lay it down in the ground, it was in the air (for coal) or oceans (for oil), right? But you say no. Why not?

Or maybe that’s not quite right. As Manda JO showed, there’s a lot more carbon locked up via geologic processes than in fossil fuels. Maybe in the past, for whatever reasons, all this (or some large percent of it) was in the air. I don’t know what carbon ppm figure would be expected if we could literally burn all the fossil fuels today. Would it even get close to 1000 ppm? Would there be too many complicated moderating effects to even guess?

Are jshore and/or intention in the house?

My basic question is, if the carbon concentration during the Cambrian was 7,000 ppm, why didn’t the Earth suffer a catastrophic runaway greenhouse effect and turn into an oven then? Or during the upper Jurassic when it was an order of magnitude higher than today? We are in a period of historically low carbon ppm concentrations. Why will going from ~350 to 500 or even 1000 set Earth down the path of becoming an oven?

@Chronos

This thread would be a lot more interesting if you could find an example of anyone, anywhere, with any shred of credibility, who claims that Earth is going to get just as bad as Venus.

Given your tone, I take it you think such a scenario is impossible.

Aside from the already cited sources, I found this interesting albeit old (1992) article here about a poll of climate scientists asking their views on the severity of global warming.

‘Climate scientists have a long track record of underestimating threats to the planet - like their forecasts of ozone depletion,’ said Leggett. ‘If these climate models turn out to be significant underestimates, we are potentially in terminal trouble.’

In the worst of all cases, the positive feedback mechanisms might combine to trigger an unstoppable warming. ‘The survey shows that more than 1 in 10 of our best climate scientists think the worst-case analysis is probable. The point is not that it will happen but that it could happen - and that is to be feared,’ said Leggett.

I’d be interested in seeing such a poll conducted today. One in ten seems surprising to me, honestly. I didn’t actually expect experts to think such a thing. I was mostly hearing it from people who didn’t seem to know much beyond what they see on TV or via the latest scaremongering magazine article.

[wevets]

@marshmallow

Aside from the already cited sources, I found this interesting albeit old (1992) article here about a poll of climate scientists asking their views on the severity of global warming.
I’d be interested in seeing such a poll conducted today. One in ten seems surprising to me, honestly. I didn’t actually expect experts to think such a thing. I was mostly hearing it from people who didn’t seem to know much beyond what they see on TV or via the latest scaremongering magazine article.

You seem to be putting words in the mouths of the poll-takers here. Nowhere in the article linked to does it mention Venus, or 96% of the atmosphere composed of CO[sub]2[/sub]. What the poll-takers apparently asked was whether the warming could be stopped (you yourself even quoted the word “unstoppable”) and whether the worst-case scenario is probable. You seem to have leapt to the conclusion that the worst-case scenario was turning the Earth into Venus, but the only scenario mentioned in the article is:

The models predict that the world will warm by 3 °C by the year 2100, but none of them takes into account any possible feedback mechanisms. Some of these mechanisms are positive and would accelerate warming; others are negative and would slow the process down.

Same source as your quote above. It seems in this context the worst case scenario might be 3 degrees C before 2100, not 850 degress C by 2100.
If I can borrow Scotandrsn’s metaphor blender for a bit - you seem to be building windmills out of molehills for you to tilt at. It’s not a very convincing strategem for discussion.

[sub]Thanks for the loan of the blender, Scotandrsn. :)[/sub]

[marshmallow]

@wevets

It seems in this context the worst case scenario might be 3 degrees C before 2100, not 850 degress C by 2100.

The 3 degrees C before 2100 was the mainstream scenario as understood by “most widely accepted estimates of global warming.” That would not be the view of 13% who said a “runaway greenhouse effect” was probable and as criticized by Leggett, who said if the model was wrong we could be in “terminal trouble.”

If I can borrow Scotandrsn’s metaphor blender for a bit - you seem to be building windmills out of molehills for you to tilt at. It’s not a very convincing strategem for discussion.

Whether or not anyone in the history of the world ever claimed global warming could end life on earth isn’t germane to this discussion. It’s wholly immaterial to whether it is possible or not. But as a matter of fact, it does happen with some frequency and I find it annoying because it vastly overblows the issue. As I said, it tends to be among those who are easily startled, especially after reading scaremongering magazine articles and watching bizarre television specials. You see it pop up here and there in almost any global warming discussion on the internet, including on these boards in certain instances.

It would appear I am correct in viewing it as foolishness and my reasoning is correct. No one in this thread seems to think otherwise. Of course, if someone can demonstrate a process in which all surface life could be extinguished I would certainly be interested and scale back my view.

Reading the background of this does raise other questions for me though, although maybe another thread is appropriate. But I’m certainly curious about:

1. How much of the drop in carbon ppm through history is due to fossil fuel formation? That is to say, if we were able to burn all known reserves, what would be the expected ppm? 1000ish?

2. Why do we live in such a low carbon ppm environment?

3. In general, what causes huge amounts of carbon dioxide to be released/stored? I was reading some timelines and summaries of carbon ppm on earth and I’d see the carbon ppm measurement swing wildly in a short amount of time, like from 5,000 here to 1,000 tere in only a couple million years. That’s a lot of carbon moving around! But I should probably just research that on my own.

[wevets]

@marshmallow

The 3 degrees C before 2100 was the mainstream scenario as understood by “most widely accepted estimates of global warming.” That would not be the view of 13% who said a “runaway greenhouse effect” was probable and as criticized by Leggett, who said if the model was wrong we could be in “terminal trouble.”

It was the only scenario in the article you quoted!

I don’t know where you get the idea that 13% think the Earth would have an atmosphere like Venus. As far as I can tell, you’re making it up out of whole cloth and the article you cite does not provide any evidence for your viewpoint. The article you linked to does say:

Of the 113 scientists who returned their questionnaires, almost half thought a runaway greenhouse effect is possible, and 13 per cent thought it probable.

The models predict that the world will warm by 3 °C by the year 2100, but none of them takes into account any possible feedback mechanisms. Some of these mechanisms are positive and would accelerate warming; others are negative and would slow the process down.

(Emphasis mine)

Using the actual text in the article, I believe the “runaway” being referred to here is warming accelerated faster than 3 °C by the year 2100. The bolding refers to text I read in the article. I have not found any mention of Venus in the article you linked to.

If you can provide textual support for your “like Venus” notion in the survey these scientists took, please provide it.

@marshmellow

But as a matter of fact, it does happen with some frequency and I find it annoying because it vastly overblows the issue.

“Many people are silly and overreact” would be a fine Pit thread. But this is GQ, and you have stated that 13% of the 113 scientists who took the survey mentioned here: Runaway greenhouse warming 'cannot be rule out': The American Association for the Advancement of Science met this week for its annual jamboree in Chicago. Topics ranged from Patriot missiles to Neanderthals and pawpaws with peculiar names | New Scientist are overreacting in a silly way (yes, it is silly to say the Earth’s atmosphere would become like that of Venus due to human carbon emissions.)

That is a different and, AFAICS, an unsupported, claim.

@marshmellow

1. How much of the drop in carbon ppm through history is due to fossil fuel formation? That is to say, if we were able to burn all known reserves, what would be the expected ppm? 1000ish?

You might be interested in this graph from a recent issue of National Geographic, which implies a concentration of over 800 ppm by 2057 in a “business as usual” situation without efforts to reduce greenhouse gases.

@marshmellow

2. Why do we live in such a low carbon ppm environment?

Low carbon relative to what? Venus? If so, the processes that lock carbon up in the biosphere have a major impact on the atmospheric proportion of carbon. If you look here and scroll down to “Addition of O2 to the Atmosphere,” there’s a list of several ways oxygen has come to be common in our atmosphere, and you’ll note that the carbon and oxygen cycles are linked because much of that oxygen was released from carbon dioxide.

[jshore]

Here’s a good piece on Venus’s greenhouse effect and comparisons to earth on RealClimate.org. I’ll quote the most relevant section:

Although the atmospheres and climates of Venus and Earth differ very greatly today, it is generally believed that the two planets started out in a rather similar state, but subsequently evolved along divergent paths. Venus succumbed early to a “runaway water vapor greenhouse,” in which the increased water vapor content arising from increased temperature reached an end state with much of the ocean evaporated into the atmosphere. Once this happens, it is easy for the water vapor to decompose in the upper atmosphere, whereafter the light hydrogen escapes and oxygen either escapes or reacts with rocks. One hypothesis is that the weak magnetic field at Venus, which otherwise would protect the planet from the solar wind, is one reason for why the oxygen and hydrogen escaped faster into space. Once water is lost, the reaction that turns carbon dioxide into limestone can no longer take place, so CO2 outgassing from volcanoes accumulates in the atmosphere instead of staying bound up in the rocks. The end state of this process is the current atmosphere of Venus, with essentially no water in the atmosphere and essentially the planet’s whole inventory of carbon in the form of atmospheric CO2. Earth, in contrast, kept its water, which allowed the planet to keep most of its carbon inventory safely bound up in the crust. The amount of CO2 in the atmosphere of Venus is approximately the same as the amount of CO2 bound up in the form of carbonate rocks on Earth today.

The runaway greenhouse that presumably led to the present Venus is an extreme form of the water vapor feedback that amplifies the effect of CO2 increases on Earth. Is there a risk that anthropogenic global warming could kick the Earth into a runaway greenhouse state? Almost certainly not. For an atmosphere saturated with water vapor, but with no CO2 in it, the threshold absorbed solar radiation for triggering a runaway greenhouse is about 350 Watts/m2 (see Kasting Icarus 74 (1988)). The addition of up to 8 times present CO2 might bring this threshold down to around 325 Watts/m2 , but the fact that the Earth’s atmosphere is substantially undersaturated with respect to water vapor probably brings the threshold back up to the neighborhood of 375 Watts/m2. Allowing for a 20% albedo (considerably less than the actual albedo of Earth), our present absorbed solar radiation is only about 275 Watts/m2, comfortably below the threshold. The Earth may well succumb to a runaway greenhouse as the Sun continues to brighten over the next billion years or so, but the amount of CO2 we could add to the atmosphere by burning all available fossil fuel reserves would not move us significantly closer to the runaway greenhouse threshold. There are plenty of nightmares lurking in anthropogenic global warming, but the runaway greenhouse is not among them.

So, there you have it. We do have enough carbon bound up in rocks to mimic the atmosphere of Venus but it appears that at the moment (i.e., for the next few billion years) we do not have sufficient solar radiation to trigger a runaway greenhouse effect.

I think part of the confusion about runaway greenhouse effects, tipping points, and the like is that they are used to describe lots of different things. I.e., while it is true that a true runaway greenhouse effect like occurred on Venus is viewed as extremely unlikely, there are concerns about various positive feedbacks kicking in that cause some land or ocean sinks of CO2 or methane to start releasing them in large enough quantities that it causes further warming. These sorts of surprises could result in the climate changing more dramatically than we would otherwise expect. However, it would stop well short of Venus, which should provide some…but not a hell of a lot…of comfort.

[jshore]

By the way, it is also worth reading raypierre’s response to Comment #8 in that RealClimate piece that I linked to.

[jshore]

@marshmallow

1. How much of the drop in carbon ppm through history is due to fossil fuel formation? That is to say, if we were able to burn all known reserves, what would be the expected ppm? 1000ish?

The estimates in this paper are that if we burn all fossil fuels in the next few hundred years, atmospheric CO2 levels will rise to somewhere between 1200ppm (if we burn only “conventional resources”) and 4000ppm (if we burn “conventional plus exotic resource”). Unfortunately, they don’t seem to elaborate on where these estimates come from, what exactly they mean by “conventional” and “exotic” (although I assume things like the Canadian tar sands would be "exotic), and what their assumptions are for the fraction of emissions that would be taken up by the oceans and biosphere. (Right now, only about half our emissions are staying in the atmosphere, with the rest being taken up by these two sinks that are, however, eventually expected to start to saturate.)

2. Why do we live in such a low carbon ppm environment?

3. In general, what causes huge amounts of carbon dioxide to be released/stored? I was reading some timelines and summaries of carbon ppm on earth and I’d see the carbon ppm measurement swing wildly in a short amount of time, like from 5,000 here to 1,000 tere in only a couple million years. That’s a lot of carbon moving around! But I should probably just research that on my own.

I am not really up on this but, as you can see, it is a complicated problem, as a lot of carbon can be stored not only as fossil fuels but also in the oceans, in the biosphere, and (on geological timescales) in rocks (e.g., as limestone). And, while a fair bit about this is known (and there are even models that simulate the rise and fall of atmospheric CO2 over ancient times), there also seem to be outstanding mysteries, such as this.