Climate, stabilty and feedback

[billvon]

Thousands of man-years of work has gone into climate modeling in the past few decades. With all that work we are getting better and better at modeling climate change, and indeed IPCC estimates (which use large interdisciplinary models) are becoming more and more accurate, and are matching observed temperature rises quite accurately. One of the reasons for this is that the basic inputs to the models (insolation, reduction of re-radiation, changes in albedo, changes in gas concentration) are easy to measure. A second reason is that we now have decades of models to compare with predictions, and so we now know what works and what doesn't.

There are, however, two uncertainties that limit how accurate any model can be as the prediction time is extended. One is human behavior. Like the stock market, the future climate is dependent on human behavior. For example, a future where we return to emitting a lot of high altitude aerosols while dramatically cut down on CO2 production will look very different than a future where we avoid high altitude aerosols and decide to abandon renewable energy and efficiency standards in faavor of cheap coal.

The second factors are nonlinear feedbacks. These are feedbacks that change with the temperature. Thus even though we may have an understanding of what they are doing now, we don't have a full understanding of what they will do when the temperatures increase.

Some of these are pretty straightforward, especially on the negative side, For example, re-radiation will increase as temperatures climb. Since blackbody radiation goes up as the fourth power of temperature, there is a strong negative feedback that will, for example, prevent temperatures rising infinitely high. As temperatures climb, the Earth will radiate more heat until we reach a new equilibrium at a higher temperature, Others include chemical weathering (rocks, concrete and other minerals react with CO2 and take it out of the atmosphere) and biological uptake (higher CO2 levels = more plants = less CO2.)

The positive feedbacks are a lot more worrisome. One common one is methane release from frozen sequestration (tundra, clathrates.) As these materials melt methane and CO2 are released, and methane is a strong greenhouse gas. (CO2 is relatively weak in comparison.) Thus more methane = more temperature increase = more melting = more methane. Another is albedo change; as snow and ice melt, darker surfaces are exposed to the Sun and absorb more heat.

A third category of feedbacks are as yet unknown, since they can drive the climate in either direction. Daytime clouds greatly decrease albedo and lead to cooling. Nighttime clouds trap heat and lead to warming. Thus, an increase in cloudiness (likely as the Earth heats up and more water evaporates) can drive climate in either direction, depending on the time of cloud formation - and we don't have a good predictor of that,

That uncertainty, on the surface, is a bad thing because it leads one to believe that we can't predict what will happen in the future. Fortunately, we have some other tools - behavioral observation.

In engineering, we often design structures that must be kept stable with feedback loops (flight controls, electronic amplifiers, hydraulic systems.) The rigorous way to analyze whether a system will be stable is to do a control system analysis - figure out the expression that describes the system, plot the poles and zeros and look for basic indications (poles on the wrong side of the plot) that indicate the system is unstable. In many cases, though, engineers cannot do that, since they do not always know everything about the system. In a hydraulic system, for example, you may not be able to account for the exact amount of air in the system - and that affects compressibility of the fluid and hence overall system response.

Fortunately they have another option - testing the system. Through either accurate simulation or actual testing, they can build the system and see if it's stable. The most useful method of testing is to apply a stimulus - a step or an impulse - and see how it responds. If it stabilizes at a new level it is stable. If it starts increasing and does so without limit, it is completely unstable. If it "rings" (oscillates) it is dynamically unstable. Thus by testing the response of the system, you can learn a a lot about it.

We cannot (or more accurately should not) do that to the Earth. However, we are fortunate in that we have historical proxy records in the form of ice cores, sedimentation, tree growth rings etc that allow us to see what has happened in the past. Thus we can look back in time at other "step changes" in the climate and see how the planet has reacted.

One of the big worries for some is that the climate is inherently unstable. Give it a step change and first all the methane is released from melting permafrost, and that warms us 20 degrees. Then the oceans evaporate, and all that water in the atmosphere traps all our heat and raises it another 50 degrees. Then some of the water turns to steam and that raises the temperature even more. (Same fear for the other direction - it snows, the snow reflects more light, it gets colder, it snows more, the oceans freeze, it gets colder still etc.) In an inherently unstable climate, a large enough step change will cause an irreversible slide in one of these directions as the positive feedbacks outweigh the negative ones.

Fortunately, in our entire 4.5 billion year history, that has never happened - and that is a strong argument for negative feedback dominating over positive feedback in the long run. However, there are good indications that positive feedback is a significant event in the short term. We have seen several rapid warming periods where a step increase (caused by, for example, an increase in insolation) activates some of the above-mentioned positive feedbacks, and for a time the Earth sees a rapid increase in temperature. The biggest one of these, the Paleocene Eocene Thermal Maximum, resulted in a 6 degree C rise in temperature - higher than almost every conceivable scenario that we could drive by 2100. Fortunately, that data shows that those positive feedbacks are eventually swamped by the negative feedbacks. One of the strongest drivers of this is likely blackbody radiation. It is a small negative feedback at first, but since it increases by the fourth power of temperature, it very rapidly becomes significant and slows down further temperature rise - and thus the Earth stabilizes at a new, higher temperature.

So overall the news is pretty good. If anything, we have learned that although we certainly have the power to change the climate by driving modest climate changes (2-3C worldwide), we don't have the power (yet) to send it to either deadly extreme. Whether or not we want to make those 2-3C changes, of course, is still an excellent question.

 

[Billy T]

... Some of these are pretty straightforward, especially on the negative side, For example, re-radiation will increase as temperatures climb. Since blackbody radiation goes up as the fourth power of temperature, there is a strong negative feedback that will, for example, prevent temperatures rising infinitely high. As temperatures climb, the Earth will radiate more heat until we reach a new equilibrium at a higher temperature, ... Fortunately, that data shows that those positive feedbacks are eventually swamped by the negative feedbacks. One of the strongest drivers of this is likely blackbody radiation. It is a small negative feedback at first, but since it increases by the fourth power of temperature, it very rapidly becomes significant and slows down further temperature rise - and thus the Earth stabilizes at a new, higher temperature. ...

It is not "straight forward" at all but very complex. First point is the Black Body, BB, radiation is an upper limit - Nothing at the same temperature can radiate more. Second point, you should have at least mentioned is the "optical depth," which can be, and usually is, a strong function of the wave length.

For example, in the absorption band wave length where the optical depth is greater than the thickness of the atmosphere - the IR radiation from the surface, which is that of a BB reduced by a less than unity factor (e, the emissivity) will not cool the Earth as you state. It will be absorbed. If that absorption point is in the first layer of the atmosphere, where most of the gases are, the troposphere, then the absorbing layers are colder than the surface and are BB radiation limited to a much lower rate than the surface rate, again by the ratio (t/T)^4, where t is the temperature at the elevated point in the atmosphere approximately one optical depth from outer space (not from the surface) and T is the surface temperature. (In the troposphere the temperature decreases with altitude adiabatically - a warm mass of air rises and expands cooling as it does so.)

The strongest absorber (of the three main ones: H20, CH4 & CO2, in that order per molecule or per Kg) is H2O. There is essentially unlimired H2O on Earth and the amount in the atmosphere increases (on average) by 7% for every degree C of temperature rise. Thus it is well know, but not easy to demonstrate mathematically (but has been done several times)* that no matter how hot the Earth surface becomes there is a maximium rate at which IR can escape to space in the many and wide H2O absorption bands. - Exactly the opposite of your assertion.

What you say about BB cooling the surface is true ONLY for wave lengths where the atmosphere is "optically thin." Because of "pressure broadening" of spectral lines as more H20 is added to the atmosphere these optically thin "windows" narrow. (Doppler broadening is less important but also helps to close these windows in the IR.) Visible light will still heat the surface, if not reflected by clouds, but GW is increasing the amount of carbon soot put into the clouds by large fires, reducing their effectiveness.

Although the math showing this is complex, understanding approximately how this comes to be is easy: As the surface temperature increases, the H2O in the atmosphere increases, and the layer, one optical depth from space, from which the H2O radiation can escape moves to higher altitude, where the air is colder.

... So overall the news is pretty good. If anything, we have learned that although we certainly have the power to change the climate by driving modest climate changes (2-3C worldwide), we don't have the power (yet) to send it to either deadly extreme. ...

We certainly do have the power to make life on much of the Earth impossible, and if present rate of GHG continues that is certain where every the wet bulb temperature reaches 35C for all warm blooded creatures, except the very tiny ones, like miniature mice. Just sitting in a chair, humans generate ~100W, which they must transfer to their environment or die in less than an hour. Most of the transfer, when not in cold water but thermally stressed (sweating) is by evaporation of water from the skin (and moister leaving in your breath). Your 37C body can not cool adequately in 35C wet bulb temperature - you will die. Civilization will collapse and as it does so, the release of aerosols will dramatically decrease. That leads to at least a 2degree C step increase in air temperature (On the same time scale as the collapse, which can be weeks with no power or drinking water coming from your water faucet. More than 10 million bodies will be unburied in the first month post collapse, climbing to more than 100 million in less than a year, creating global plagues that kill most, if not all who live closer to the Poles where 35C will not occur for decades.

SUMMARY: A little knowledge (about IR transfer, in this case) is a dangerous thing.

* I'll try to return by edit to give a least one such math demonstration, but until I do, consider Venus. Its surface is very hot (may have lakes of liquid lead) but it only send back to space as IR a tiny part of what the surface is radiating.

 

[billvon]

The strongest absorber (of the three main ones: H20, CH4 & CO2, in that order per molecule or per Kg) is H2O. There is essentially unlimired H2O on Earth and the amount in the atmosphere increases (on average) by 7% for every degree C of temperature rise. Thus it is well know, but not easy to demonstrate mathematically (but has been done several times)* that no matter how hot the Earth surface becomes there is a maximium rate at which IR can escape to space in the many and wide H2O absorption bands. - Exactly the opposite of your assertion.

Again, if that were true, and this feedback was capable of sending us into a "steam Venus" - then past pertubations, even stronger than our current forcing, would have done so. Fortunately, they do not.

We certainly do have the power to make life on much of the Earth impossible, and if present rate of GHG continues that is certain where every the wet bulb temperature reaches 35C for all warm blooded creatures, except the very tiny ones, like miniature mice.

Yes, if that happened everywhere, we'd wipe out most life on the planet. Fortunately no sane scenario posits that.

 

[Billy T]

(1) Again, if that were true, and this feedback was capable of sending us into a "steam Venus" - then past pertubations, even stronger than our current forcing, would have done so. Fortunately, they do not. (2) Yes, if that happened everywhere, we'd wipe out most life on the planet. Fortunately no sane scenario posits that.

On (1):
No need to make steam atmosphere to kill all - 35C wet bulb comes along and does that - You are knocking down an unimportant straw man.
On(2):
No true: 35C wet bulb is certain if present trends continue - just when is uncertain.

 

[Aqueous Id]

Consider this partial description of what Global Climate Modeling entails:

At their core, all GCMs employ a specific set of primitive dynamic equations, which allow the atmosphere to move in three dimensions, warm up and cool down, and transport moisture, etc. These equations are solved over and over again at specified locations in the model's three-dimensional space. There are two main methods for establishing the horizontal domain of a model. The simplest is to establish a grid along lines of latitude and longitude. For example, the CCSM3 can be run on a 2° x 2.5° grid. Another method is to treat atmospheric motion as waves using Fast Fourier Transforms (FFTs) to make the spectral conversion. The resolution then is represented as the number of waves that can be represented around the earth. The CCSM3 uses wave numbers of T31, T42, and T85; where T represents the triangular truncation of the Fourier transform. This resolution can be approximated to longitude/latitude with a resolution of T31 and T85 is 3.75° and 1.41° respectively.​

http://www.csa.com/discoveryguides/models/review3.php

 

[billvon]

No need to make steam atmosphere to kill all - 35C wet bulb comes along and does that - You are knocking down an unimportant straw man.

If by your statement I can take it that you are no longer claiming the "Venus Hell" outcome as realistic - then I will gladly retract that statement. Yes, I agree, that is both unlikely and unnecessary.

Not true: 35C wet bulb is certain if present trends continue - just when is uncertain.

Agreed. However, it would be just as accurate to say that we would certainly all freeze to death if 1970's trends had continued.
So the next question is - when might that begin to happen? Matthew Huber, in his paper "An Adaptability Limit to Climate Change Due to Heat Stress", had this to say:

"We found that a warming of 12 degrees Fahrenheit would cause some areas of the world to surpass the wet-bulb temperature limit, and a 21-degree warming would put half of the world's population in an uninhabitable environment."

Thus when we see global warming of 12 degrees F, we would begin to see this problem. When will we see that? If, as you suggest, we follow present trends (.27F per decade) we are looking at 44 decades, or 440 years. Or in 778 years we might see "half the world's population in an uninhabitable environment." Assuming, of course, that we are still burning coal and oil in 778 years.

Or let's say we go alarmist and go with the worst-case IPCC scenarios - .9F per decade. Now we might see the first such temperatures, per Huber, in 133 years.

Is that something to worry about? Definitely. Will it kill your grandkids? Not even close.

 

[Trippy]

If by your statement I can take it that you are no longer claiming the "Venus Hell" outcome as realistic - then I will gladly retract that statement. Yes, I agree, that is both unlikely and unnecessary.

Agreed. However, it would be just as accurate to say that we would certainly all freeze to death if 1970's trends had continued.
So the next question is - when might that begin to happen? Matthew Huber, in his paper "An Adaptability Limit to Climate Change Due to Heat Stress", had this to say:

"We found that a warming of 12 degrees Fahrenheit would cause some areas of the world to surpass the wet-bulb temperature limit, and a 21-degree warming would put half of the world's population in an uninhabitable environment."

Thus when we see global warming of 12 degrees F, we would begin to see this problem. When will we see that? If, as you suggest, we follow present trends (.27F per decade) we are looking at 44 decades, or 440 years. Or in 778 years we might see "half the world's population in an uninhabitable environment." Assuming, of course, that we are still burning coal and oil in 778 years.

Or let's say we go alarmist and go with the worst-case IPCC scenarios - .9F per decade. Now we might see the first such temperatures, per Huber, in 133 years.

Is that something to worry about? Definitely. Will it kill your grandkids? Not even close.

A change of:
12°F = 6.7°C
21°F = 11.7°C

 

[brucep]

Thousands of man-years of work has gone into climate modeling in the past few decades. With all that work we are getting better and better at modeling climate change, and indeed IPCC estimates (which use large interdisciplinary models) are becoming more and more accurate, and are matching observed temperature rises quite accurately. One of the reasons for this is that the basic inputs to the models (insolation, reduction of re-radiation, changes in albedo, changes in gas concentration) are easy to measure. A second reason is that we now have decades of models to compare with predictions, and so we now know what works and what doesn't.

There are, however, two uncertainties that limit how accurate any model can be as the prediction time is extended. One is human behavior. Like the stock market, the future climate is dependent on human behavior. For example, a future where we return to emitting a lot of high altitude aerosols while dramatically cut down on CO2 production will look very different than a future where we avoid high altitude aerosols and decide to abandon renewable energy and efficiency standards in faavor of cheap coal.

The second factors are nonlinear feedbacks. These are feedbacks that change with the temperature. Thus even though we may have an understanding of what they are doing now, we don't have a full understanding of what they will do when the temperatures increase.

Some of these are pretty straightforward, especially on the negative side, For example, re-radiation will increase as temperatures climb. Since blackbody radiation goes up as the fourth power of temperature, there is a strong negative feedback that will, for example, prevent temperatures rising infinitely high. As temperatures climb, the Earth will radiate more heat until we reach a new equilibrium at a higher temperature, Others include chemical weathering (rocks, concrete and other minerals react with CO2 and take it out of the atmosphere) and biological uptake (higher CO2 levels = more plants = less CO2.)

The positive feedbacks are a lot more worrisome. One common one is methane release from frozen sequestration (tundra, clathrates.) As these materials melt methane and CO2 are released, and methane is a strong greenhouse gas. (CO2 is relatively weak in comparison.) Thus more methane = more temperature increase = more melting = more methane. Another is albedo change; as snow and ice melt, darker surfaces are exposed to the Sun and absorb more heat.

A third category of feedbacks are as yet unknown, since they can drive the climate in either direction. Daytime clouds greatly decrease albedo and lead to cooling. Nighttime clouds trap heat and lead to warming. Thus, an increase in cloudiness (likely as the Earth heats up and more water evaporates) can drive climate in either direction, depending on the time of cloud formation - and we don't have a good predictor of that,

That uncertainty, on the surface, is a bad thing because it leads one to believe that we can't predict what will happen in the future. Fortunately, we have some other tools - behavioral observation.

In engineering, we often design structures that must be kept stable with feedback loops (flight controls, electronic amplifiers, hydraulic systems.) The rigorous way to analyze whether a system will be stable is to do a control system analysis - figure out the expression that describes the system, plot the poles and zeros and look for basic indications (poles on the wrong side of the plot) that indicate the system is unstable. In many cases, though, engineers cannot do that, since they do not always know everything about the system. In a hydraulic system, for example, you may not be able to account for the exact amount of air in the system - and that affects compressibility of the fluid and hence overall system response.

Fortunately they have another option - testing the system. Through either accurate simulation or actual testing, they can build the system and see if it's stable. The most useful method of testing is to apply a stimulus - a step or an impulse - and see how it responds. If it stabilizes at a new level it is stable. If it starts increasing and does so without limit, it is completely unstable. If it "rings" (oscillates) it is dynamically unstable. Thus by testing the response of the system, you can learn a a lot about it.

We cannot (or more accurately should not) do that to the Earth. However, we are fortunate in that we have historical proxy records in the form of ice cores, sedimentation, tree growth rings etc that allow us to see what has happened in the past. Thus we can look back in time at other "step changes" in the climate and see how the planet has reacted.

One of the big worries for some is that the climate is inherently unstable. Give it a step change and first all the methane is released from melting permafrost, and that warms us 20 degrees. Then the oceans evaporate, and all that water in the atmosphere traps all our heat and raises it another 50 degrees. Then some of the water turns to steam and that raises the temperature even more. (Same fear for the other direction - it snows, the snow reflects more light, it gets colder, it snows more, the oceans freeze, it gets colder still etc.) In an inherently unstable climate, a large enough step change will cause an irreversible slide in one of these directions as the positive feedbacks outweigh the negative ones.

Fortunately, in our entire 4.5 billion year history, that has never happened - and that is a strong argument for negative feedback dominating over positive feedback in the long run. However, there are good indications that positive feedback is a significant event in the short term. We have seen several rapid warming periods where a step increase (caused by, for example, an increase in insolation) activates some of the above-mentioned positive feedbacks, and for a time the Earth sees a rapid increase in temperature. The biggest one of these, the Paleocene Eocene Thermal Maximum, resulted in a 6 degree C rise in temperature - higher than almost every conceivable scenario that we could drive by 2100. Fortunately, that data shows that those positive feedbacks are eventually swamped by the negative feedbacks. One of the strongest drivers of this is likely blackbody radiation. It is a small negative feedback at first, but since it increases by the fourth power of temperature, it very rapidly becomes significant and slows down further temperature rise - and thus the Earth stabilizes at a new, higher temperature.

So overall the news is pretty good. If anything, we have learned that although we certainly have the power to change the climate by driving modest climate changes (2-3C worldwide), we don't have the power (yet) to send it to either deadly extreme. Whether or not we want to make those 2-3C changes, of course, is still an excellent question.

That's been your theme all the way through this. That we're incapable of causing any real damage. Where have I heard that argument before? You're painting the minimalist picture. It may not be nice but I can't help painting you a denier. Who else is for the minimalist response? Alarmist/minimalist same thing to me.

 

[billvon]

That's been your theme all the way through this. That we're incapable of causing any real damage.

?? I've never claimed that. How the heck do you get that?

 

[brucep]

?? I've never claimed that. How the heck do you get that?

On a very basic level you've been painting Billy T as an alarmist. When he asked you to do some science you refused. Your assertion is it didn't happen in the past so it won't happen in the future. The very same argument you made in your opening post. Not the first time you made that argument and not the first time Billy T had to explain why it was bogus. Sorry if I'm wrong but I don't think your assertion, in the final paragraph of your opening comments, has any scientific merit. I'm not an expert on this science but it would be interesting for you to explain why Billy T is wrong when he says your analysis is backwards?

 

[billvon]

On a very basic level you've been painting Billy T as an alarmist.

Correct. There is a difference between thinking climate change is a bad thing, to be avoided, and thinking that the human race will become extinct between 2016 and 2060. The former can lead to some serious discussion on how to reduce our impact on the planet; the latter is easily disproved by simply waiting, and makes climate scientists laughingstocks. James Hansen has described this very problem in a recent editorial, and it would be wise to heed his experience.

I'm not an expert on this science but it would be interesting for you to explain why Billy T is wrong when he says your analysis is backwards?

Rather than going through all this again I will instead reference a few other authors.

Raymond Pierrehumbert, University of Chicago - "I think you can say we're still safe against the Venus syndrome."

Colin Goldblatt, University of Victoria - you would need the equivalent of 30,000 parts per million CO2 and that "is far beyond what humans are capable of contributing. Indeed, that’s about 10 times what CO2 levels would be even if we quickly burned through all the remaining fossil fuels. There’s no evidence that human action could cause this."

More details if you want them, from Goldblatt's paper in Nature:
============
At 280 K, the surface emits directly to space through the water vapour window (Fig. 3). For surface temperatures above 310 K the temperature of the emitting level remains between 250 and 300 K, regardless of the surface temperature. If greenhouse gases other than water are more abundant, τλ = 1 is higher in the absorption bands of these gases and less radiation is emitted overall. However, the relative magnitude of this effect decreases in hotter atmospheres with more water. In flux terms (Fig. 4), for the endmember case of a saturated, cloud-free atmosphere with contemporary surface albedo, the net absorbed solar radiation exceeds thermal emission in all scenarios except that with no greenhouse gases other than water, implying that a runaway greenhouse should occur. As this has manifestly not happened to Earth, we are led to the conclusion that a combination of atmospheric subsaturation and an excess of cloud albedo forcing over cloud greenhouse forcing prevents a runaway greenhouse on Earth today. . . .

The so-called ‘hothouse’ climate of the Eocene is the most useful constraint for anthropogenic change. With the solar constant 1% less than today and a few thousand ppmv CO2, the mean temperature was ~ 10 K warmer than today With CO2 and temperature both higher then than we expect in the foreseeable future, this implies that an anthropogenic runaway greenhouse is unlikely. Deglaciaton from Neoproterozoic snowball Earth events probably required that ~ 10% of the atmosphere was carbon dioxide. The solar constant was 6% less than today, so net solar radiation absorbed would have been 12 W m−2 less and climate not yet bistable.
============
(This is what I base my "examine the system's response to transients to learn what it is capable of" position on. Does that mean it will never happen? No. As solar output climbs it becomes more likely in the far future
===========
As the solar constant increases with time, Earth’s future is analogous to Venus’s past. We expect a runaway greenhouse on Earth 1.5 billion years hence if water is the only greenhouse gas, or sooner if there are others.
==========

Thus we are far away from conditions that could trigger the sort of rapid and deadly feedbacks BillyT is talking about.

Claiming we will all be dead in 2 to 46 years is irresponsible. Sure, it's fun. It gets you attention and generates the excitement that any prediction of apocalypse does. But in terms of actually fighting climate change, it gives ammunition to the deniers, who will be happy to point out in 47 years that we are not all dead and thus climate scientists were wrong again, just like they were wrong in the 1970's about the next ice age.

 

[Billy T]

... Rather than going through all this again I will instead reference a few other authors.

Raymond Pierrehumbert, University of Chicago - "I think you can say we're still safe against the Venus syndrome."

Colin Goldblatt, University of Victoria - you would need the equivalent of 30,000 parts per million CO2 and that "is far beyond what humans are capable of contributing. Indeed, that’s about 10 times what CO2 levels would be even if we quickly burned through all the remaining fossil fuels. There’s no evidence that human action could cause this." ... The so-called ‘hothouse’ climate of the Eocene is the most useful constraint for anthropogenic change. With the solar constant 1% less than today and a few thousand ppmv CO2, the mean temperature was ~ 10 K warmer than today With CO2 and temperature both higher then than we expect in the foreseeable future, this implies that an anthropogenic runaway greenhouse is unlikely. ... Thus we are far away from conditions that could trigger the sort of rapid and deadly feedbacks BillyT is talking about. ...

Like other deniers of the seriousness of GW, you cheery pick what to discuss and beat dead horses. I. e. resurrect my earlier, now abandoned, concerns. The first being run-a-way to Venus like state – which was then Hansen's concern also, but both of us have been persuaded that is not likely until Sun is a few percent hotter. I have totally dropped interest in the question as Human extinction will come long before that from any one of several faster acting processes as this, posted this long ago, stated:

{http://www.sciforums.com/showthread.php?97892-Climate-gate/page25, post 996, in part}... I have never suggest that transition to a Venus like hot thermal states would happen - was a certain fact. I have explained how it might be possible, with CO2's very rapid release causing the release of much more powerful GHG methane to be released faster than OH radical could destroy it, as is fact now, with their combined acceleration of water accumulation in the atmosphere (7% more for each degree of ocean surface temperature rise.)* and many times asked if any one had a solid proof that run away to Earth's hot stable state (IR opaque atmosphere with high pressure steam atmosphere at the surface) was impossible. My interest in this question ending at least a year ago when I realized that exposure to 35C wet bulb conditions kill humans (and all but the smallest of warm blooded animals - tiny mice might be able to survive 35C WBT) in less than hour. ...

Even my concern about CH4 has greatly diminished:

{post 1106 after agreeing with reference that massive release of CH4 was not a near term threat, although certainly possible later - after 35C wet bulb had killed most mammals} ... Thus, I am not as concern about methane as I once was - especially as now realizing much more rapid and likely processes can lead to extinction first. I.e. Amazon (and other rain forests) drying - becoming major CO2 sources and possibly burning with Hadley cells pumping the soot into high clouds, effectively making same global heating effect as about a 10% step up in solar intensity until the clouds become clean again (Years?). Thermal run-a-ways is interesting physics to consider - but of no import to man as 35C wet bulb temperature kills all land mammals but the tiny mice first.

Please address my more recent concerns, like albedo of currently high clouds being greatly reduced by large fires, effectively increasing the solar heating of Earth. Or the multi-pronged threat to life in the oceans.

{post 1088, in part, but still long below:} ... In this post I provide numerical analysis showing how that “abolishing of the safety margin” can occur; but first ... There exist a natural process, quite plausible in my opinion, if not highly probable assuming present drought conditions continue, that the current 60W/m^2 safety margin might be totally abolished. I. e. the absorption of solar energy might be significantly increased by an increasingly common natural process – forest fires.

Note that where warm air is rising even this diagram shows high altitude clouds form. If the since 2005 drought in the Amazon continues, for a few years more, not only will the Amazon be a net source (not sink) for CO2, and thus accelerate the surface temperature increase, but it could burn - making a huge "burp" of CO2 but even worse: high clouds with fine soot – I. e. a great increase in solar heating - throwing Earth into the start of a thermal run-a-way process in about 10 days! {mathematical analysis that is here, is not copied} ... Note however, a cloud, especially a high altitude one, is not a simple surface. Almost all of a clean cloud's reflectivity is the result of MANY small angle scattering as “forward scattering cross section” (Scattering angle small compared to 90 degrees.) is much greater than “backward scattering cross section.” Thus, the reflection by a clean cloud is a "biased random walk" * thru angle space with many small angle scatterings. Each of which could absorb the photo if it is incident on the surface of a soot particle. I. e. a very tiny fraction of soot content will make the albedo of the cloud essentially zero!

My main point being that large part of the Amazon burning could drastically reduce or totally abolish Earth's current (by the link below's calculation) “safety margin” in a very short period. Also, other fires are already lowering the albedo of high albedo surface, like Greenland's ice cover. See photo of this in post here: http://www.sciforums.com/showthread.php?97892-Climate-gate&p=3217548&viewfull=1#post3217548 ...
----------------
* The bias is for the typical scattering to send the photon deeper into the cloud, but if it is not absorbed and the cloud is thick, it will get out of the top eventually - prehaps after 50 or so scatterings. I have worked with commercial Sodium Iodide scintillation crystals to detect and gamma rays. Typically they are cylindrical with single photomultiplier tube bonded to one end of the cylinder, but when the gamma ray passing thru the crystal scatters and produces visible light,most of the light does not go directly to that detector. Instead it leaves thur some other surface of the crystal and must be very efficiently diffusely reflected back many times until it does enter the photomultiplier tube. The best metallic mirror is vastly inferior as a reflector to less than half a cm think layer of very clean small crystals surrounding the scintillation crystal - I. e. the reflection is just like that a clean cloud, but of course perfectly clean clouds do not exist. The higher ones are cleaner than the lower ones and can reflect even 2/3 of sun light away from Earth but the photon that eventually escapes may have been dozens of meters deep inside the cloud before doing so - scattering more than 90 degrees. {text that was here showing this is due to conservation of momentum also omitted.} ...
6. Conclusion {of Jan 2012 paper with nothing deleted or changed from http://arxiv.org/pdf/1201.1593v1.pdf }
The runaway greenhouse is well defined in theory: As the surface warms, the atmosphere becomes optically thick with water vapour, which limits the amount of thermal radiation which can be emitted to space. If the planet absorbs more solar energy than this limit, runaway warming ensues. The practical limit on outgoing thermal radiation occurs when the atmospheric structure tends towards the saturation vapour pressure curve of water as the atmospheric composition tends towards pure water vapour, giving a limit of around 300Wm−2. Earth presently absorbs around 240Wm−2 of solar radiation.

Increasing carbon dioxide concentration will make surface warmer with the same outgoing thermal flux. Following this theory, we are not near the threshold of a runaway greenhouse. However, the behaviour of hot, water vapour rich, atmospheres is poorly understood and much more study of these is necessary. In the event that our analysis is wrong, we would be left with the situation in which only geoengineering could save us. The only useful methods would be those which would reduce the amount of solar energy that the Earth absorbs.

BTW this link is the one promised in post 2, - the math showing that no matter how hot Earth's surface get, IR escaping is not more than the limit of ~300W/m^2. - Why your OP is very wrong.

I am still concerned about collapse of the food chain in the ocean due to CO2 adsorption / acidification, lack of nutrient rich upwelling of bottom water and also, seldom mentioned, possibility it will lack oxygen except in surface layers:

… disruption of the meridional overturning circulation can have far-reaching consequences. Models and paleoclimate data suggest that as less warm water flows north across the equator, the southern oceans will warm. The thermal equator (band of highest temperatures) would therefore likely shift south. The tropical rain belts would follow, altering rainfall patterns. Decreased downwelling would deliver less oxygen to the deep ocean,* and decreased upwelling would carry fewer nutrients up from the bottom, potentially devastating ocean ecosystems.

Also for same facts see: https://scripps.ucsd.edu/programs/keelingcurve/2013/07/03/how-much-co2-can-the-oceans-take-up/

* It is very simple physic: Oxygen, enters surface waters from the air or is made there by phytoplankton, 1/3 of which acidification has already killed (via oxidation of their essential and limiting free iron). If the major ocean currents don't fall down, the bottom becomes anaerobic as many processes consume oxygen that was down there. More important for sustaining life, is fact that if masses of water stop sinking then masses of bottom water stop rising and without those nutrients steadily being recovered from the bottom, most fish we eat die as their food chain was also hit by acidification as well. We see this already when ever El Nino fails – Peru's fish industry collapses as nutrient rich bottom water stops upwelling off its coast. No sinking of the Gulf Stream (and its Pacific case counter part, the Japanese current) will be a global, not local event.

Stop denier cheery picking: beating my old, abandoned concerns and address my facts and current concerns.

I have told you many times that I agree CO2 was much higher in the past with animals on earth, but never did it rise even 5% as fast as it is now. As I have said at least half dozen times, This time is different due to the RATE of rise not the level of CO2. Please stop posting that there is no serious problem as CO2 has been much higher in the distant past, as if that had any significance for the present GW threat. You know better – why join the ignorant deniers? Why ignore (or try to deny with irrelevant posts) the facts I post?

In the past the concentration of CH4 was ALWAYS much lower than now as released at such a slow rate, even when temperature were equal or greater than now, that the reaction with UV created OH radical destroyed it as fast as it was released with essentially a low concentration (<750 ppb) in dymanic equlibrium with the production on OH radical, but man has more than doubled the CH4 concentration.

Now however, CH4 rate of release is faster than it can be destroyed. In the air in 2003, the half life of a molecule of CH4 againist OH radical oxidation was only 9.6 years. Now that CH4 has been destroying OH radical faster than the UV flux can produce it, the half life is 10.6 years (2013 data). This time is different as you can see below (referenced data – not like your assertions only):

NOAA's graph at: http://www.esrl.noaa.gov/research/themes/forcing/Methane.pdf will not copy, but 7th power point chart shows that the man made increase in CH4's radiative forcing is already 0.5W/m^2, however, the rate of CH4 release seems to have been slower for last few years (See last part of right graph above.). Perhaps this is due to GW having “picked the low hanging fruit.” - I. e. the shallow water methane ice and shallow tundra has given up the easy to release CH4. Now it will come in larger but less frequent “burps” See one of the first from deep tundra here: http://earthsky.org/earth/second-mysterious-crater-reported-from-yamal where title of the 31 July2014 article is:
"Methane release likely caused mystery crater on Yamal peninsula" and tells (by measurement) than CH4 concentration inside crater is 50,000 times higher than normal in the air.

See this "non-posting" pie chart and 8.4 years data at: http://en.wikipedia.org/wiki/Atmospheric_methane
The other CH4 sinks reduce the over all half life to only 8.4 years. However the “soil” (especially the tundra) is now a huge net source of CH4. So not only is each molecule lasting longer, there are many, many more being added to the air each year than are removed; but I think CH4 will lose the race to be the first to make most mammals extinct. - Sorry, methane, there is no prize for second or third place.

 

[brucep]

Correct. There is a difference between thinking climate change is a bad thing, to be avoided, and thinking that the human race will become extinct between 2016 and 2060. The former can lead to some serious discussion on how to reduce our impact on the planet; the latter is easily disproved by simply waiting, and makes climate scientists laughingstocks. James Hansen has described this very problem in a recent editorial, and it would be wise to heed his experience.



Rather than going through all this again I will instead reference a few other authors.

Raymond Pierrehumbert, University of Chicago - "I think you can say we're still safe against the Venus syndrome."

Colin Goldblatt, University of Victoria - you would need the equivalent of 30,000 parts per million CO2 and that "is far beyond what humans are capable of contributing. Indeed, that’s about 10 times what CO2 levels would be even if we quickly burned through all the remaining fossil fuels. There’s no evidence that human action could cause this."

More details if you want them, from Goldblatt's paper in Nature:
============
At 280 K, the surface emits directly to space through the water vapour window (Fig. 3). For surface temperatures above 310 K the temperature of the emitting level remains between 250 and 300 K, regardless of the surface temperature. If greenhouse gases other than water are more abundant, τλ = 1 is higher in the absorption bands of these gases and less radiation is emitted overall. However, the relative magnitude of this effect decreases in hotter atmospheres with more water. In flux terms (Fig. 4), for the endmember case of a saturated, cloud-free atmosphere with contemporary surface albedo, the net absorbed solar radiation exceeds thermal emission in all scenarios except that with no greenhouse gases other than water, implying that a runaway greenhouse should occur. As this has manifestly not happened to Earth, we are led to the conclusion that a combination of atmospheric subsaturation and an excess of cloud albedo forcing over cloud greenhouse forcing prevents a runaway greenhouse on Earth today. . . .

The so-called ‘hothouse’ climate of the Eocene is the most useful constraint for anthropogenic change. With the solar constant 1% less than today and a few thousand ppmv CO2, the mean temperature was ~ 10 K warmer than today With CO2 and temperature both higher then than we expect in the foreseeable future, this implies that an anthropogenic runaway greenhouse is unlikely. Deglaciaton from Neoproterozoic snowball Earth events probably required that ~ 10% of the atmosphere was carbon dioxide. The solar constant was 6% less than today, so net solar radiation absorbed would have been 12 W m−2 less and climate not yet bistable.
============
(This is what I base my "examine the system's response to transients to learn what it is capable of" position on. Does that mean it will never happen? No. As solar output climbs it becomes more likely in the far future
===========
As the solar constant increases with time, Earth’s future is analogous to Venus’s past. We expect a runaway greenhouse on Earth 1.5 billion years hence if water is the only greenhouse gas, or sooner if there are others.
==========

Thus we are far away from conditions that could trigger the sort of rapid and deadly feedbacks BillyT is talking about.

Claiming we will all be dead in 2 to 46 years is irresponsible. Sure, it's fun. It gets you attention and generates the excitement that any prediction of apocalypse does. But in terms of actually fighting climate change, it gives ammunition to the deniers, who will be happy to point out in 47 years that we are not all dead and thus climate scientists were wrong again, just like they were wrong in the 1970's about the next ice age.

The theme of your assertion is we really don't need to do anything. That's the theme of the originating post for this thread. Your assertion is the human contribution has a limit of 2-3C and we could just as we'll do nothing. I'm suspect of your motivation for making comments which are frequently scoffed at for lack of scholarship. What is the purpose of this new thread? We could probably get away without any painful changes in the way we interact with our home planet? Who makes those arguments? Not climate scientists. What gives ammunition to deniers is the bunk you've been saying.

 

[billvon]

The theme of your assertion is we really don't need to do anything.

Again, no, it's not. That's a strawman; a statement that you invent in order to have an easier opposing argument to argue against. Just because we will not all be extinct by 2060 does NOT mean we "really don't need to do anything." We should do something - not because we will all be dead in ~40 years, but because we can save ourselves a whole lot of misery by taking action sooner rather than later.

Your assertion is the human contribution has a limit of 2-3C and we could just as we'll do nothing.

That's your invention, and I have not claimed any such thing. If you want to claim that, then by all means, claim it and we can discuss whether or not it's valid.

So do you claim that?

 

[iceaura]

The so-called ‘hothouse’ climate of the Eocene is the most useful constraint for anthropogenic change.

The main factor overlooked in this approach is the effects of the unprecedented rate of increase of the forcing signal - the CO2 boost. The Eocene stability, and all other non-disasters, was achieved via a much more gradual approach.

Also, there are two different conceptions of "runaway" that concern us: the surface sterilizing Venusian runaway may be unlikely - although a more secure understanding of the actual probabilities involved would be nice - but a short term and self-limited feedback powered runup of any significant scale would be disastrous to human civilization as we know it. There would be small comfort in knowing it was self-limiting to three or four degrees C, possibly even temporary on a scale of hundreds or thousands of years, and survivable for some remaining population fortunately located. That's not reassuring. We should not take any serious risk of touching off something like that.

What gives ammunition to deniers is the bunk you've been saying.

It is not possible to discuss serious scientific issues of import to Exxon's profit margin without "giving ammunition" to such people. They need very little, if any, basis in fact for their inventions and propaganda efforts. Label them, but do not intrude into discussions of reality and physical analysis with imaginations of how they are going to be lying about whatever is said. That paralyzes - and paralysis is their goal.

 

[brucep]

Again, no, it's not. That's a strawman; a statement that you invent in order to have an easier opposing argument to argue against. Just because we will not all be extinct by 2060 does NOT mean we "really don't need to do anything." We should do something - not because we will all be dead in ~40 years, but because we can save ourselves a whole lot of misery by taking action sooner rather than later.

That's your invention, and I have not claimed any such thing. If you want to claim that, then by all means, claim it and we can discuss whether or not it's valid.

So do you claim that?

Read the last paragraph in your opening post for this thread. You tell me how I misinterpret what you said. Your entire theme is to minimize a response by saying everything is hunky dory with a limit you claim is 2-3C. The fact you feel you need to start a new thread based on this analysis tells me a bit about your motivation. You're familiar with feedback control loops. You're an engineer. What energy company do you work for? Why did you start a new thread to make that claim?

 

[billvon]

Read the last paragraph in your opening post for this thread. You tell me how I misinterpret what you said.

You are referring to this I assume:

"we certainly have the power to change the climate by driving modest climate changes (2-3C worldwide), we don't have the power (yet) to send it to either deadly extreme. Whether or not we want to make those 2-3C changes, of course, is still an excellent question. "

Translation - we have the power to do bad things to our climate. We don't have the power to turn it into a Venus or a Pluto. However, despite that fact, we should decide whether or not we want to do bad things to our climate AT ALL.

Your entire theme is to minimize a response by saying everything is hunky dory with a limit you claim is 2-3C. The fact you feel you need to start a new thread based on this analysis tells me a bit about your motivation. You're familiar with feedback control loops. You're an engineer. What energy company do you work for?

None; I work for a communications company and have patents filed in energy efficiency and renewable energy technology.

 

[brucep]

The main factor overlooked in this approach is the effects of the unprecedented rate of increase of the forcing signal - the CO2 boost. The Eocene stability, and all other non-disasters, was achieved via a much more gradual approach.

Also, there are two different conceptions of "runaway" that concern us: the surface sterilizing Venusian runaway may be unlikely - although a more secure understanding of the actual probabilities involved would be nice - but a short term and self-limited feedback powered runup of any significant scale would be disastrous to human civilization as we know it. There would be small comfort in knowing it was self-limiting to three or four degrees C, possibly even temporary on a scale of hundreds or thousands of years, and survivable for some remaining population fortunately located. That's not reassuring. We should not take any serious risk of touching off something like that.

It is not possible to discuss serious scientific issues of import to Exxon's profit margin without "giving ammunition" to such people. They need very little, if any, basis in fact for their inventions and propaganda efforts. Label them, but do not intrude into discussions of reality and physical analysis with imaginations of how they are going to be lying about whatever is said. That paralyzes - and paralysis is their goal.

What do you think of the limit 2-3C for the maximum human contribution? I worked in the oil industry for 40 years and was coerced into joining a PAC whose main purpose was to spread nonsense, in the guise of fact, with respect to anything perceived as a threat to the industries bottom line.

 

[Billy T]

...Translation - we have the power to do bad things to our climate. We don't have the power to turn it into a Venus or a Pluto. However, despite that fact, we should decide whether or not we want to do bad things to our climate AT ALL. ...

There may be an argument about how disastrous only 2C man- made temperature rise would be, but most certainly consider +3C a very bad thing.

Just releasing enough CO2 at current rate to make +3C increase will probably acidify oceans killing most life in them - may cause the Gulf Stream not to flow as higher latitudes are warming more and faster. Certainly +3C will increase the jet stream wander with much greater extremes in weather even in Southern US states, frost killing mid west sprout in the spring some years, if not all, etc. making food production decline in some years when this happens at the wrong time, more floods, and stronger storms, etc. - at least 100 million dollars GW damage in just the US on average every year. Thus I would consider even only +2C "bad thing" as the models have errors - risk too big to take.

+3C will make 35C wet bulb much more probable in regions where more than 100 million people were trying not to die from that.

IMO only a vicious sadist, living in latitude north of Mason-Dixion line, would not want to try to avoid +3C.

Certainly no need to speak of or worry about a Venus like state - all are dead long before that could happen.

 

[Mr. G]

I always advocate for the opposite of what greens want.

They'd never have a real purpose otherwise.