Is the Earth inherently unstable?

[KenJackson]

Please critique this logic.

1. It's well known from chemistry that cooler water can hold more gasses in solution than warmer water.
2. As ocean temperatures rise (slowly, for any reason, over centuries) dissolved greenhouse gasses will come out of solution and into the atmosphere. Conversely, as ocean temperatures cool, more greenhouse gasses in the atmosphere will be dissolved.
3. This action is positive feedback. That is, it only serves to make the existing trend worse instead of opposing it.
4. Any system with primarily positive feedback is inherently unstable and will end up at one extreme or the other.

This logic seems to suggest that no matter what happens, the Earth is doomed to end up either scorched like Venus or frozen like Mars. And yet, as far as I'm aware, the Earth has been quite stable for eons. So what gives?

 

[phinds]

Please critique this logic.

1. It's well known from chemistry that cooler water can hold more gasses in solution than warmer water.
2. As ocean temperatures rise (slowly, for any reason, over centuries) dissolved greenhouse gasses will come out of solution and into the atmosphere. Conversely, as ocean temperatures cool, more greenhouse gasses in the atmosphere will be dissolved.
3. This action is positive feedback. That is, it only serves to make the existing trend worse instead of opposing it.
4. Any system with primarily positive feedback is inherently unstable and will end up at one extreme or the other.

This logic seems to suggest that no matter what happens, the Earth is doomed to end up either scorched like Venus or frozen like Mars. And yet, as far as I'm aware, the Earth has been quite stable for eons. So what gives?

Earth is a very complex system. You are making projections based on a single factor. Way too simplistic.

 

[KenJackson]

Earth is a very complex system. You are making projections based on a single factor. Way too simplistic.

In the news, scientists present greenhouse gasses--especially CO₂--as the only credible influence in climate change.

 

[phyzguy]

Since there have been forcing functions in the geologic past much larger than what we are currently doing, and since the Earth hasn't run away to either scorched Venus or frozen Mars, I think you have to conclude that the Earth's climate is not inherently unstable.

 

[KenJackson]

..., I think you have to conclude that the Earth's climate is not inherently unstable.

That seems like a very reasonable conclusion. But it implies either something in my four points is incorrect or greenhouse gasses are not the most significant influence in climate change. Am I missing something?

 

[phyzguy]

That seems like a very reasonable conclusion. But it implies either something in my four points is incorrect or greenhouse gasses are not the most significant influence in climate change. Am I missing something?

I think, as phinds said, it is a very complex system with many factors. Some factors act as positive feedback, and some act as negative feedback. The net result is very difficult to predict and model. I like this Nature paper analyzing the factors that contribute to ice ages on the Earth. One of their conclusions is that an important factor is the position of North America on the globe, and the rate at which the North American continent rebounds from the weight of the overlying ice after an ice age ends.
Below is a quote from that paper. Who would have thought that this would be a major variable? Certainly not me.

"A remarkable conclusion from our model results is therefore that
the 100-kyr glacial cycle exists only because of the unique geographic
and climatological setting of the NorthAmerican ice sheet with respect
to received insolation. Only for the North American ice sheet is the
upper hysteresis branch moderately inclined; that is, there is a gradual
change between large and small equilibrium ice-sheet volumes over a
large range of insolation forcings. For this reason, as demonstrated in
Fig. 2b, the amplitude modulation of summer insolation variation in
the precessional cycle, due primarily to eccentricity, is able to generate
the 100-kyr cycles with large amplitude, gradual growth and rapid
terminations."

 

[berkeman]

Thread closed temporarily for Moderation.

 

[berkeman]

Thread is re-opened with a reminder of the rules for discussing global warming at PF. As phyzguy has done above, any discussion needs to be about the science, as published in acceptable sources. Thank you.

Just a reminder from the Earth forum rules:

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This topic is under probation. It will be banned again if discussion isn't civil and well intentioned.
​

 

[rootone]

Geology and climate of Earth is essentially chaotic, which is good for life.
However greenhouse gases do exist, and there are other considerations, like solar emissions.
Yes the Earth could be tipped into a stable but uninhabitable condition like Mars or Venus.
Woody Allen: 'I'm not afraid of death; I just don't want to be there when it happens.',

 

[Bandersnatch]

Please critique this logic.

1. It's well known from chemistry that cooler water can hold more gasses in solution than warmer water.
2. As ocean temperatures rise (slowly, for any reason, over centuries) dissolved greenhouse gasses will come out of solution and into the atmosphere. Conversely, as ocean temperatures cool, more greenhouse gasses in the atmosphere will be dissolved.
3. This action is positive feedback. That is, it only serves to make the existing trend worse instead of opposing it.
4. Any system with primarily positive feedback is inherently unstable and will end up at one extreme or the other.

This logic seems to suggest that no matter what happens, the Earth is doomed to end up either scorched like Venus or frozen like Mars. And yet, as far as I'm aware, the Earth has been quite stable for eons. So what gives?

First, a correction - oceans currently at as a sink for CO2. This is because you're not only increasing the water temperature, but also partial pressure of atmospheric CO2, plus, the CO2 already in the oceans is removed by formation and sedimentation of carbonates, which reduces oceanic partial pressure of CO2.
A third, up to half of the anthropogenic CO2 emissions ends up in the oceans. (https://www.gfdl.noaa.gov/bibliography/related_files/us9301.pdf)
It is feasible that at some point in the future, when ocean temperatures will have risen enough as compared to CO2 concentrations, so as to reach saturation, they will start to release their stored CO2.
So, currently, they don't act as positive feedback in this way (but they do act as one in the sense of being the source of water vapour).Anyway, even using some other positive feedback as an example - it doesn't mean that the system is inherently unstable, because there are also negative feedbacks. Forcings, and both types of feedbacks interact to produce new equilibrium point.
For one, the hotter you make the planet, the faster it re-radiates energy into space (as per the Stefan-Boltzman law), so at some point a new equilibrium point is reached. For a runaway destabilisation you'd need positive feedbacks to overcome all negative feedbacks, an stay there. This isn't true even on Venus or Mars, as neither has 0 K temperature, nor infinite temperature - their climates have stabilised at whatever the corresponding equilibrium temperature is.

As a rule of thumb, feedbacks can't be the driver of climate change. They need something else to force the change, to which they then respond.
That's why when referring to the causes of climate change, people talk only about the forcings (drivers).

Let's take the aforementioned water vapour as an example. It is a greenhouse gas much stronger than CO2. However, in the environment of Earth, water condenses, while CO2 doesn't. So, if we add extra water vapour emissions, they will not stay in the atmosphere, and drive the long-term temperature changes, but will instead precipitate within hours to days. Hence water vapour is not a climate forcing.
On the other hand, you can pump CO2 into the atmosphere practically without limit, which then causes temperature to rise, which causes more evaporation and more water vapour to stay in the atmosphere, which in turn causes more temperature increase - i.e., water vapour acts as positive feedback to CO2 forcing.

Since there have been forcing functions in the geologic past much larger than what we are currently doing, and since the Earth hasn't run away to either scorched Venus or frozen Mars,

To be fair, it is possible there were periods when Earth was frozen over (the snowball Earth hypothesis).

 

[KenJackson]

Just a reminder from the Earth forum rules:

Yeah, I read that. I know there's a lot of emotion on this topic, but I have a real science question and I'm trying to pursue it delicately. There's an inconsistency between my understanding of science and what scientists say in the news. As a responsible citizen, I'm trying to make sense of it all.

I like this Nature paper analyzing the factors that contribute to ice ages on the Earth.

But there hasn't been an ice age in millennia. I'm sure there were lots of other factors (and diminishing accuracy of information) the further back we go. But I'm interested in today and maybe the last several centuries.

This is the tricky part. I need to ask a key question on this science topic without stirring up emotion. We're led to believe that the number one, most significant influence on climate today is greenhouse gas, especially CO₂. I'm trying to piece together how that and the four original points can all be true.

A key part of the question is about positive feedback. Wikipedia says:

Positive feedback is a process that occurs in a feedback loop in which the effects of a small disturbance on a system include an increase in the magnitude of the perturbation. That is, A produces more of B which in turn produces more of A. ...

Positive feedback tends to cause system instability.

 

[KenJackson]

Grief. Interruptions delayed my post so long that another answer slipped in unnoticed. Let me take a quick look.

First, a correction - oceans currently at as a sink for CO2. This is because you're not only increasing the water temperature, but also partial pressure of atmospheric CO2, plus, the CO2 already in the oceans is removed by formation and sedimentation of carbonates, which reduces oceanic partial pressure of CO2.

Interesting. That deserves some thought.

As a rule of thumb, feedbacks can't be the driver of climate change. They need something else to force the change, to which they then respond.
That's why when referring to the causes of climate change, people talk only about the forcings (drivers).

Sure, there are well publicized sources of CO₂, but the question concerned an increase in gas causing an increase in temperature causing an eventual increase in ocean temperature releasing more CO₂ which would be positive feedback. The note about partial pressure is interesting though.

 

[Bystander]

This is the tricky part. I need to ask a key question on this science topic without stirring up emotion.

If it CAN be answered within the bounds of what is considered appropriate, it will be; ask it, and take your lumps up front rather than sneaking around like "ban hammer" bait.

 

[Astronuc]

• It's well known from chemistry that cooler water can hold more gasses in solution than warmer water.

• As ocean temperatures rise (slowly, for any reason, over centuries) dissolved greenhouse gasses will come out of solution and into the atmosphere. Conversely, as ocean temperatures cool, more greenhouse gasses in the atmosphere will be dissolved.

• This action is positive feedback. That is, it only serves to make the existing trend worse instead of opposing it.

• Any system with primarily positive feedback is inherently unstable and will end up at one extreme or the other.

That's not a complete picture, and there is faulty logic.

This logic seems to suggest that no matter what happens, the Earth is doomed to end up either scorched like Venus or frozen like Mars. And yet, as far as I'm aware, the Earth has been quite stable for eons. So what gives?

I believe Venus and Mars have been relatively stable over the same period as the earth.

With respect to Venus and Mars, one must realize that Venus is much closer to the Sun, while Mars is further away, so the heat input from the Sun is very different. The atmosphere of Venus is 0.965 CO₂ and 0.035 N₂ with traces of SO₂, and the surface pressure is approximately 92 atm (93 bar); so very different from earth's.

Regarding point 2, one refers to both positive and negative feedback, but in point 3, one addresses positive feedback and ignores the negative feedback. Ocean temperature is but one input. Other inputs include land temperature, which is affected by vegetation or lack thereof, and atmospheric temperature. Vegetation is also a sink for CO₂ and water. Ice reflects light, which would otherwise be absorbed by rocks, minerals or vegetation.

As for positive vs negative feedback, as atmosphere temperature increases, it will radiate more energy, thus providing a negative feedback. Rather than runaway and become like Venus, the Earth may warm and reach a new equilibrium at a greater average surface temperature.

Climate can be chaotic but relatively stable in a macroscopic sense, but certainly, there may be local instabilities or transients that produce winds or storms, which is part of the weather.

 

[Baluncore]

Ice keeps a drink cool until all the ice has melted. Temperature can then rise more rapidly. The next stabilising phase change is when the water evaporates or boils. Cloud coverage might play a part in stabilisation.

 

[DrClaude]

In the news, scientists present greenhouse gasses--especially CO₂--as the only credible influence in climate change.

The increase of atmospheric CO₂ from fossil sources is the main driver of climate change. What the final steady state will be will not depend on CO₂ only.

 

[zbikraw]

Solubility of gases in water is a fast way to regulate climate, but there exist some other ways. The fastest is change in air opacity which changes amount of solar radiation and "greenhouse" IR radiation achieving Earh surface (note 2 different processes). Very powerful is change of Earth albedo (reflection coefficient, also highly dependent of wavelength), velocity of this change is comparable to "greenhouse" changes. Somewhat slower are changes related to CO2 assimilation by green organisms and greenhouse gases release after their death.
CO2 dissolution in seawater is the first step of complex processes of transport, absorption, desorption, inorganic chemical reactions, salt (and living organisms skeleteons/shells) petrification and dissolution, visible in years to kiloyears timescale. Carbon transport/deposition in these processes is on trillion tonnes scale (annual CO2 transport to and from atmosfere is larger than 200 bln tonnes). All these processes are nonlinearly dependent on water phase acidity and CO2 is an "anhydride" of very weak carbonic acid. All these processes are reversible (but kinetics of forward/reverse carbon transport is different, sometimes drastically), so these are analyzed as equilibria". Of course all are feedback prone. There is possibility of drawing general formulas for these processes and feedbacks, but from practice point of view it is useless as combining the concentrations of the same individua in the same place masks errors in their measurement/estimation, which are very different for all processes yielding the substance.
Of course, greenhouse effect only moderates the main equilibria determining Earth climate. After light absorption/emission there is heat transfer associated with water phase changes, which stabilizes all entire climate. As for climate change: there are limitations for Earth surface availability of most substances critical to climate feedbacks, although we are generally far from these limitations.
For better understanding the problem, please try to differentiate positive/negative feedbacks in all the processes mentioned above.

 

[D-11]

I did not notice anybody listing biosphere itself as a separate factor(of comparable scale of magnitude to geological processes) of climate state.

So, i will just leave this here:
https://en.wikipedia.org/wiki/Medea_hypothesis

 

[jim mcnamara]

@D-11 Please see: http://astrobiologysociety.org/the-medea-hypothesis-by-peter-ward/

The gist of the review is that it is a neat idea, with weak scientific support. If you were to search on PF you would see that the alternative Gaia hypothesis has become much more mainstream. Lots of supporting research. To be fair, the Gaia was initially received as an idea with weak support, just as Peter Ward's concept now stands.

Anyway - to anyone reading this thread: the Medea Hypothesis as things now stand is largely unaccepted.

 

[jim hardy]

Am I missing something?

As ocean temperatures rise (slowly, for any reason, over centuries) dissolved greenhouse gasses will come out of solution and into the atmosphere

Vapor pressure of said water rises so evaporation increases.
Light moist air rises , water vapor condenses into clouds reflecting heat .

That's a negative feedback.

Can you put numbers on the effects ? That's the start of understanding.

Here's a controversial article about the matter: Just food for thought, it's as i said caused controversy.. Definitely worth reading though.
https://wattsupwiththat.com/2009/06/14/the-thermostat-hypothesis/

Anyhow - atmosphere is busily moving heat from the tropics toward the poles where it can radiate away.
Hurricanes move a LOT of heat up above most of the greenhouse gases - they're another stabilizing mechanism.

Point being - water vapor is an important player that's hardly mentioned in the everyday news.

You might enjoy this discussion about ocean heat
http://www.realclimate.org/index.php/archives/2006/08/ocean-heat-content-latest-numbers/#comments
see response #96 on page 2

old jim

 

[D-11]

@D-11 Please see: http://astrobiologysociety.org/the-medea-hypothesis-by-peter-ward/

The gist of the review is that it is a neat idea, with weak scientific support. If you were to search on PF you would see that the alternative Gaia hypothesis has become much more mainstream. Lots of supporting research. To be fair, the Gaia was initially received as an idea with weak support, just as Peter Ward's concept now stands.

Anyway - to anyone reading this thread: the Medea Hypothesis as things now stand is largely unaccepted.

I definitely don't argue that.
I mention it because i think parts of Ward's book are relevant to this discussion.

Short how - existing biosphere affects planet's atmosphere composition and albedo to a non-trivial degree, and biosphere is not inherently stable(=cyclic?), all that with evolution and stuff (:
So, to discuss feedback loops in crust/hydrosphere/atmosphere you must make a simplification that biosphere is static over geologically significant amount of time.

Another example: planet's thermal equilibrium is considered in a discussion, which reminds that planet is not an isolated system - star supplies energy to the planet.
This forces to make another simplification that local star is static over geologically significant amount of time.
Simplification - 'cause star is a batch process, not a stable or cyclic one(um, "geologically significant amount of time" is not a discrete number but timescales are not well defined here)

If no simplifications are made - complexity of system prediction increases exponentialy with linear addition of components.
If only matter and energy feedback loops in crust/hydrosphere/atmosphere are considered, this may approach "spherical horse in a vaccum" categoryNot to be critical, just fleshing out that

Earth is a very complex system. You are making projections based on a single factor.

part.

 

[faster]

We have here people asking questions, but some sound like they're trying to make their own points, and many people are trying to use science to debunk science. But scientists recognize ploys like that. Science is not "agenda oriented."
Let me mention, as a non-scientist, that even I realize that studying the systems for climate, on both land and sea, are inherently VERY chaotic. Therefore, to conclude, either way, about Earth's inherent ANYTHING is too broad and generalized to be reliable, even to scientists. It's hard to be precise about something chaotic. When they all agree on something, we have to take it seriously.

One person here spoke of CO2 as if it were the only greenhouse gas. But there are others, and the most notable of them is methane. Earth's original atmosphere was essentially methane and ammonia. Not only can't we breathe them, but methane is a much more powerful greenhouse gas than CO2. Our present atmosphere is NOT Earth's original one. Under the icecaps, we're told that gargantuan quantities of methane can be found trapped under ice, and that in various locations where ice melts, it releases the methane. So far, the releases have not been huge, but eventually it will be. Controlling CO2 means we can slow (or stop, hopefully) the melting and minimize the possibility that methane could be released in quantities that would make it possible to revert to Atmosphere 1. If that happened, Earth would become lifeless. I'd call that important.
So even if we might survive melting and warming, we would NOT survive the methane. And a vast release could happen at any time.
I'm open to corrections from scientists, since I am only the "armchair" variety. Maybe it would be advisable for the public to learn about the methane risk? Since it affects every living thing, including them?

 

[Drakkith]

Controlling CO2 means we can slow (or stop, hopefully) the melting and minimize the possibility that methane could be released in quantities that would make it possible to revert to Atmosphere 1. If that happened, Earth would become lifeless. I'd call that important.

I don't think this is possible, as I doubt there is nearly enough trapped methane to drastically alter the atmosphere. Do you have a valid reference supporting this?

 

[mfb]

We had much warmer periods in the past already. Life on Earth will survive. For humans, however, the conditions might become very uncomfortable.

 

[jim hardy]

Science is not "agenda oriented."

It's not supposed to be anyway.
But scientists have opinions and are capable of "groupthink"
and you will find good scientists in both camps.
http://www.nytimes.com/2009/03/29/magazine/29Dyson-t.html?pagewanted=all

“The climate-studies people who work with models always tend to overestimate their models,” Dyson was saying. “They come to believe models are real and forget they are only models.” Dyson speaks in calm, clear tones that carry simultaneous evidence of his English childhood, the move to the United States after completing his university studies at Cambridge and more than 50 years of marriage to the German-born Imme, but his opinions can be barbed, especially when a conversation turns to climate change. Climate models, he says, take into account atmospheric motion and water levels but have no feeling for the chemistry and biology of sky, soil and trees. “The biologists have essentially been pushed aside,” he continues. “Al Gore’s just an opportunist. The person who is really responsible for this overestimate of global warming is Jim Hansen. He consistently exaggerates all the dangers.”

Check Dyson's credentials for yourself. About the last of the Manhattan Project scientists he's still alert and active, we exchanged email just last week.

old jim

 

[jim mcnamara]

We have gotten speculative too many times in this thread. And there have been good posts as well. Time to close up shop and go home.