Playing Devil's advocate on climate

[Saul]

That is a very elementary misunderstanding of the greenhouse effect, you know. When CO2 absorbs, it also emits thermal radiation. It is unfortunate that the popular explanation of the greenhouse effect concentrates on "absorption" by greenhouse gasses. They absorb, and they re-radiate. However, they re-radiate according to the temperature of the air where they are. A layer of CO2 that is at the same temperature than the surface has strictly no effect on the thermal radiation emanating from that surface, as it will emit exactly as much as it will absorb. It is only because the "last layer" is at a lower temperature than the "emitting surface" that there *seems to be* a net absorption.

Indeed, but what counts is what is re-emitted, and hence, at what altitude (and hence at what temperature) that "last emitting layer" is. As such, the fact that there is total absorption (several times over) of certain lines doesn't matter, because it also means that there is re-emission. More (evenly distributed) absorption gas simply means that the "last emitting layer" is higher up, and hence colder.

If you would have a thick layer of totally black gas, 50 meters thick, hovering over the Earth's surface, that wouldn't cause any greenhouse effect at all, because that layer of gas (at the same temperature as the surface) would absorb all of the surface's radiation, but would also emit exactly the same radiation upward.

My point is that CO2 only absorbs and emits specific frequencies. If the photons are frequency shifted off of those frequencies CO2 no longer is a factor. Do you understand that point?

Does any in the forum disagree with that assertion?

This is a good paper that describes the basic physics of greenhouse gases.http://www.warwickhughes.com/papers/barrett_ee05.pdfGreenhouse molecules, their spectra and function in the atmosphere by Jack Barrett

Comment:
In the above you state something about absorption and emission which appears to not be relavent to my point.

 

[Saul]

There is in paleo record abrupt cyclic cooling events that correlate with solar magnetic cycle changes. Humanity has not in recorded history experience an abrupt cooling event.

As the sun is moving rapidly to an unusual minimum it appears we will be able to observe which hypothesis is correct. Assuming the planet does as it did in the past abruptly cool, I am curious as to how long and what process the scientific change occur.

Based on the solar mechanism there should be an observable difference this winter.

To sylas or skyhunter: Is there any evidence that could disprove the AWG hypothesis?http://www.sciencemag.org/cgi/content/abstract/292/5520/1367?ck=nck

Solar Forcing of Drought Frequency in the Maya Lowlands
David A. Hodell, Mark Brenner,1 Jason H. Curtis,1 Thomas Guilderson

http://www.essc.psu.edu/essc_web/seminars/spring2006/Mar1/Bond et al 2001.pdfPersistent Solar Influence on North Atlantic Climate During the Holocene

Gerard Bond, Bernd Kromer, Juerg Beer, Raimund Muscheler, Michael N. Evans, William Showers, Sharon Hoffmann,Rusty Lotti-Bond,1 Irka Hajdas, Georges Bonani
http://geology.geoscienceworld.org/cgi/content/abstract/30/5/455

Widespread evidence of 1500 yr climate variability in North America during the past 14 000 yr

I see one response to this comment by vanesch. Vansesch did not understand my point. sylas ignored my posting as it does not support his premise.

The point is if the planet is about to abruptly cool, CO2 sequestration, CO2 caps, and CO2 trading have no scientific purpose.

The sun was at its highest activity level in 10,000 years during the later half of the 20th century. This has happened before. Following the very high solar activity the sun goes into a peculiar minimum. Planetary temperature then abruptly drops. During the 8200 year cooling event planetary temperature dropped 2C.

The global warming premise is that the planet will due to a doubling of CO2 increase in temperature by 3C to 5C. CO2 has increased 30% and the planet is now starting to cool. Something is obvious incorrect with either the prediction or the models.

The key issue is the magnitude of the warming. All else being equal (i.e. If the sun was not currently moving toward the peculiar minimum.) it appears the actual warming due to doubling of CO2 would have been around 0.75C not 3C to 5C. Now of course 0.75C is not catastrophic.

 

[sylas]

My point is that CO2 only absorbs and emits specific frequencies. If the photons are frequency shifted off of those frequency CO2 no longer is a factor. Do you understand that point?

Does any in the forum disagree with that assertion?

This is a subject on which you were mistaken in past discussions, and it seems you still don't understand it. CO₂ is ALWAYS a factor at any conceivable concentration up to many many times more than we are ever likely to see. There are always still frequencies of light that are on the shoulder of the main saturated absorption band. As CO₂ concentrations increase, the width of the saturated band increases. There is more absorption, because there are more frequencies that move from being weakly absorbed in the atmosphere to being strongly absorbed. The approximately logarithmic relation between concentrations and forcing continues smoothly up to very high densities of CO₂ within the atmosphere.

I first explained this for you back in April, in [post=2165483]msg #3[/post] of thread "Estimating the impact of CO2 on global mean temperature".

I have subsequently given another account of the relevant physics, with reference to an easily accessible textbook on "Principles of Planetary Climate", in [post=2323067]msg #15[/post] of thread "Rising Carbon Dioxide Levels Don’t Increase Earth’s Temperature". Note especially the diagram in that post showing the spectrum of emitted radiation for different CO₂ concentrations. Note that the width of the band of absorbed frequencies is increasing, and that increasing CO₂ continues to be a factor even up past an atmosphere of 1% CO₂, at which point some additional bands start to take hold and enhance the impact even more.

This is the aspect of the underlying and well established physics of light absorption in a gas which is not understood by those who think that there is some level of concentration beyond which additional CO₂ has negligible further effect. The fact of the matter is that the absorption of light at a given frequency is not a simple case of yes/no, but varies continuously in strength, so that as concentrations increase, there is more and more of the spectrum that becomes strongly absorbed.

Sylas

PS. I continue to find it ridiculous that in this thread, of all threads, we end up going over the same tired old topics, refuting the same misconceptions as before. I feel a bit guilty participating in this way, but given the direct question, I succumbed to temptation and gave the explanation.

Saul: don't make up self serving statements about why I might ignore a posting. Speak for yourself; do not try to speak for me or my choices. You do not know why I might respond to one post or another, and in this case you are flatly wrong about why I am ignoring most of your posts here.

I'll continue to try and avoid using this thread to just debate climate with everyone taking the same perspective as they have ever done. The topic, as I understand it, was about being able to argue for the OTHER person's perspective. I'm not sure that this is all that useful, frankly, but certainly it is very useful to actually understand the arguments being made on their own merits. Being able to repeat the argument is a rather futile exercise if the argument takes for granted some premise that is incorrect.

The greatest benefits of being able to repeat the argument for a position you don't hold yourself is (IMO) when the argument is sufficiently sensible. The restriction of the guidelines to consider arguments that have been made in peer reviewed literature is a good way to help getting to such arguments.

 

[vanesch]

My point is that CO2 only absorbs and emits specific frequencies. If the photons are frequency shifted off of those frequencies CO2 no longer is a factor. Do you understand that point?

First of all, CO2 doesn't absorb and emit at just specific frequencies, because there is Doppler and collision broadening, which is dependent on temperature and pressure, so we have finite absorption bands. I don't know if this is part of what you consider "specific frequencies".

Next, there are very few "wavelength-shifting" phenomena in the atmosphere, which operate between specific levels (like people sometimes try to do in scintillators). What you have is that absorbed radiation goes into the "heat bath" of the specific layer of gas (just as any other heat, like that brought by convection, latent heat transport, or even conduction), and the heat bath induces the gas to radiate black body radiation modulated with its overall emissivity.

What counts is the "final radiator" which can put its radiation into space. Not what happens with essentially isothermal low-lying layers.

 

[vanesch]

The point is if the planet is about to abruptly cool, CO2 sequestration, CO2 caps, and CO2 trading have no scientific purpose.

There is not a single instance in which CO2 sequestration, CO2 caps, and CO2 trading would have any scientific purpose, in any case, except in the case where we want to experiment with first rising, and then lowering, CO2 levels, to see how the Earth reacts.

As I said already several times, whether AGW is "good" or "bad", whether one "should do something about it or not", and the like, are no part in the scientific debate about whether AGW exists, and if it exists, how strong it is.

You wouldn't react that way if the scientific debate were to know whether volcanic eruptions on Titan change the surface temperature, and by how much, would you ? Well, the scientific AGW debate is the same. It is totally distinct from any political, societal, or economical consideration in itself. It just asks a question: by how much, if any, will the Earth be warmer when there are CO2 emissions of such and such a kind, as compared to when this is not the case, all else equal. The attempt to an answer to that question, and the argumentation for it, is what the scientific AGW debate is about. And that's it.

 

[vanesch]

The topic, as I understand it, was about being able to argue for the OTHER person's perspective. I'm not sure that this is all that useful, frankly, but certainly it is very useful to actually understand the arguments being made on their own merits. Being able to repeat the argument is a rather futile exercise if the argument takes for granted some premise that is incorrect.

I think it is inspired by Feynman's statement, that one should try by all means to prove oneself wrong, if one is doing science. The highest form of skepticism should be towards one's own ideas.

 

[Saul]

This is a subject on which you were mistaken in past discussions, and it seems you still don't understand it. CO₂ is ALWAYS a factor at any conceivable concentration up to many many times more than we are ever likely to see. There are always still frequencies of light that are on the shoulder of the main saturated absorption band. As CO₂ concentrations increase, the width of the saturated band increases. There is more absorption, because there are more frequencies that move from being weakly absorbed in the atmosphere to being strongly absorbed. The approximately logarithmic relation between concentrations and forcing continues smoothly up to very high densities of CO₂ within the atmosphere.

I first explained this for you back in April, in [post=2165483]msg #3[/post] of thread "Estimating the impact of CO2 on global mean temperature".

I have subsequently given another account of the relevant physics, with reference to an easily accessible textbook on "Principles of Planetary Climate", in [post=2323067]msg #15[/post] of thread "Rising Carbon Dioxide Levels Don’t Increase Earth’s Temperature". Note especially the diagram in that post showing the spectrum of emitted radiation for different CO₂ concentrations. Note that the width of the band of absorbed frequencies is increasing, and that increasing CO₂ continues to be a factor even up past an atmosphere of 1% CO₂, at which point some additional bands start to take hold and enhance the impact even more.

This is the aspect of the underlying and well established physics of light absorption in a gas which is not understood by those who think that there is some level of concentration beyond which additional CO₂ has negligible further effect. The fact of the matter is that the absorption of light at a given frequency is not a simple case of yes/no, but varies continuously in strength, so that as concentrations increase, there is more and more of the spectrum that becomes strongly absorbed.

Sylas

PS. I continue to find it ridiculous that in this thread, of all threads, we end up going over the same tired old topics, refuting the same misconceptions as before. I feel a bit guilty participating in this way, but given the direct question, I succumbed to temptation and gave the explanation.

Saul: don't make up self serving statements about why I might ignore a posting. Speak for yourself; do not try to speak for me or my choices. You do not know why I might respond to one post or another, and in this case you are flatly wrong about why I am ignoring most of your posts here.

I'll continue to try and avoid using this thread to just debate climate with everyone taking the same perspective as they have ever done. The topic, as I understand it, was about being able to argue for the OTHER person's perspective. I'm not sure that this is all that useful, frankly, but certainly it is very useful to actually understand the arguments being made on their own merits. Being able to repeat the argument is a rather futile exercise if the argument takes for granted some premise that is incorrect.

The greatest benefits of being able to repeat the argument for a position you don't hold yourself is (IMO) when the argument is sufficiently sensible. The restriction of the guidelines to consider arguments that have been made in peer reviewed literature is a good way to help getting to such arguments.

sylas,

I am saying the first CO2 added has the greatest impact on global warming. Additional CO2 added has less impact. The physical reason why that statement is correct is that CO2 only absorbs and emits specific band widths.

http://www.warwickhughes.com/papers/barrett_ee05.pdf

The effect of adding additional CO2 to the atmosphere is logarithmic. The first 30% added has a significantly greater affect on planetary temperature than the last 30% added. (280 ppm to 560 ppm.)

Do you disagree with that statement? Do you have a paper that disputes that statement? Do you have a paper that refutes this paper?

Greenhouse molecules, their spectra and function in the atmosphere by Jack Barrett

http://www.warwickhughes.com/papers/barrett_ee05.pdf

Please do not use ad hominem. It serves no purpose. This is a scientific forum not a debating forum. Compare the two different scientific positions rather than trying to win a debate. In a debate, ad hominem is acceptable if one can get away with ad hominem. In a debate the objective is to win the debate rather than to understand a scientific problem.

A scientific discussion/debate must handle uncertainty. It is not absolutes.The process of science is the creation and comparison of hypotheses. For science to progress hypotheses must be challenged and discussed. The title of this thread is devil's advocate.

I have provided papers and logic to support a scientific position. I have provided data from papers concerning cyclic abrupt climate change. In the past cyclic abrupt climate change has correlated with cosmogenic isotope changes. I presented a paper that shows planetary clouds have decreased in the 20th century. I provided a paper that shows planetary temperature is directly correlated with solar wind bursts in the 20th century. I have provided papers that explain electroscavenging which is the hypothesized mechanism by which the solar wind burst modulate planetary cloud cover.

The question which we are discussing is the magnitude of the 20th century warming that was due to CO2 as opposed to changes in planetary cloud cover. Your ad hominem is that I have not provided papers to support a position. Or that I do not understand the physics. Or that all scientists agree with your position.

Note I am presenting a scientific hypothesis. I do not own it. It is not my baby, my child, and so forth on. I have no emotional attachment to it. Note it is a scientific position.

Try to think of the two scientific positions in a hypothetical manner. What are the implications of the two hypotheses? If this were true than that what would we expect to happen in the future. Does new observational data support or refute the position? Do new papers support or refute the scientific position?

Please note also that I have found and presented new papers that support the cloud hypothesis. The archeomagnetic jerk paper. The paper that shows anomalously high solar wind bursts during this solar cycle minimum. I am not simply stating the same thing over again. I come back to the forum with new information.

I find this subject interesting because the scientific issues are not resolved. Scientists do not know what causes abrupt climate change and the glacial/interglacial cycle. I find this discussion interesting also because the sun is moving abruptly to a peculiar solar minimum. Solar physicists do not understand what is happening to sun currently and do not know what will happen next. Solar physicists do not know what is limits of solar CME magnitude.

 

[sylas]

The effect of adding additional CO2 to the atmosphere is logarithmic. The first 30% added has a significantly greater affect on planetary temperature than the last 30% added. (280 ppm to 560 ppm.)

Yes. The forcing is about 3.7 W/m² for each doubling of concentration.

This is much better than the previous statement you gave, which spoke of "CO2 is no longer a factor". The full sentence which you used in the previous post was "If the photons are frequency shifted off of those frequencies CO2 no longer is a factor."

That's incoherent, so it was impossible to agree or disagree with the sentence as you phrased it in the earlier post. "the photons are frequency shifted off those frequencies"? Who knows what this might mean? What I do know is that a few months ago you were saying:

It is not a fact that a doubling of CO2 will increase forcing by 3.71 W/m^2. Why do you make that statement?

The consensus is the lower atmosphere is saturated from the standpoint of direct heating effects of CO2. Adding more CO2 to the lower atmosphere will not result in higher surface temperatures.

This was, of course, completely incorrect. When you said just now "CO2 is no longer a factor", I confess that I had thought you were still thinking that there is a condition of "saturation" which means adding more CO2 does not raise temperatures any further. There's nothing in the older discussion to suggest you had come to understand why you do get continuing increases in temperature with continuing increases in concentration, with a logarithmic relation of a certain impact per doubling. I am sincerely glad to hear we are now on the same page with this, and that you no longer hold to the view you had four months ago. You deserve full credit for that -- it shows that you ARE learning new things, and that is good. Truly.

It is a bit amusing, however, to see you demand whether I can refute your position when it is what I had to explain to you four months ago.

Please do not use ad hominem.

I did not use any ad hominem in that post at all.

PS. I do know you have come back to the forum with new material, and you're engaging that in some other threads. Good for you, really. I won't join in all those threads, because it's not all my main interest. And I don't want to take up climate debates here. This thread is for a meta-discussion on the nature of discussion methods for engaging conflicting views. It's not for going straight into another round of climate debates. I am now returning to that proper focus for this thread.

Over and out -- sylas

 

[sylas]

I think it is inspired by Feynman's statement, that one should try by all means to prove oneself wrong, if one is doing science. The highest form of skepticism should be towards one's own ideas.

I agree.

Doing science vs learning science

In physicsforums, a lot of what we do is basic education. People come with questions about some tricky subject, be it cosmology, relativity, climate, quantum mechanics, whatever, and discussion tries to answer those questions.

This is a worthwhile endeavor, but in most cases it has nothing much to do with trying to prove oneself wrong.

In my opinion, a large part of the confusion over climate is simply outright error about what is really quite basic physics or statistics or whatever. One of the things I would like to see at physicsforums is some basic educational threads on background details or concepts that people may be confused about, so that those who are interested are on more solid ground for starting to look at the harder and open questions. I've tried to put up some.

But that project has nothing much to do with the laudable exercise of self-criticism. It is rather about the also laudable exercise of science education, with a transfer of knowledge from people who have more background understanding to others who have less.

Most of us here are able to give useful instruction in some topics, and have other topics where we are seeking to learn. Doing science is a good way to learn science; but in most cases we are exploring a well beaten trail blazed by those who did the same science before us.

Open questions vs popular misconceptions

The quality of arguments relating to climate and AGW varies enormously.

We swiftly get straight into deep water, however, because people don't agree about which questions are actually those that are genuinely open; and there's no general recognition of an acceptable authority. Many people seem to be quite sure that the whole idea of global warming is some kind of hoax. We get into all kinds of secondary matters of why people argue for something or other, or what their history or funding is, or how important it is, and so on; this (as you point out) just distracts from the business of learning about the science.

We are not doing cutting edge science here. There are members at physicsforums who are actively involved in cutting edge science, but most of the discussion here is trying to learn about the science being done by others.

In the process of learning, we also learn about open questions. We aren't going to resolve those questions here in physicsforums! But we can learn about them. In particular, we can get a better idea of what questions really are wide open, and what is reasonably solid and used by working scientists as a foundation for exploring into the unknown.

The physicsforums context: physics as practiced by the scientific community

The https://www.physicsforums.com/showthread.php?t=5374" for physicsforums single out as a focus "the current status of physics as practiced by the scientific community". I think climate is primarily a field within physics; dealing with thermodynamics, atmospheric physics, fluid dynamics, energy and temperature, and so on.

Physicsforums also deals with open questions. From the https://www.physicsforums.com/showthread.php?t=5374" again:

There are many open questions in physics, and we welcome discussion on those subjects provided the discussion remains intellectually sound. It is against our Posting Guidelines to discuss, in most of the PF forums or in blogs, new or non-mainstream theories or ideas that have not been published in professional peer-reviewed journals or are not part of current professional mainstream scientific discussion.​

In climate, there are many open questions, relating to sensitivity, cloud effects, paleoclimate, approximations in modeling, the carbon cycle, and on, and on. We aren't going to resolve them, but understanding the credible alternatives is well worthwhile.

There are also a lot of questions which are not actually intellectually sound open questions at all, but simply misunderstandings or even outright crackpottery. There's a lot that is said outside the professional mainstream which has been enthusiastically passed around in the public domain as being of equal standing to genuine science. In some respects, a lot of this public debate (not all of it!) bears a significant similarity to the whole "intelligent design" movement.

Physicsforums guidelines give a convenient way to strip out most of the rubbish, and they have special force in the Earth subforum. We simply stick to claims that have been published in the peer reviewed scientific literature. (And, like it or not, the journal "Energy and Environment" does not qualify. See [post=2142377]this post[/post] from an Earth subforum mentor.)

There are sometimes good papers published outside the peer reviewed literature. But if the claims made are at all credible, then you should be able to find them in the peer reviewed literature as well. Apart from that, there is a Independent Research subforum, with its own [post=679686]Rules for submission in Independent Research[/post].

Don't let's fall into the mistake of "journalistic balance", in which we simply presume all voices are equally worthwhile for study and serious consideration. Understanding all sides of an open question is good; but not all the questions or challenges being raised are actually open questions with two sides of comparable standing.

Cheers -- sylas

 

[Saul]

This is a fascinating forum, and these climate discussions are very interesting and educational. I couldn't help but notice however that it seems posters tend to line up along sides on the issue of AGW (or perhaps the degree to which they are skeptical of the consensus). I think it would be interesting to see people play devil's advocate and argue for the other position, or rather acknoweldge data that does not support their view (on both sides).

Galtheeth,

Climate discussion for some strange reason seems to be an emotional subject.

I agree that scientific discussions should compare one hypothesis to another. What does the hypotheses predict? What do the observations indicate? It should be noted that papers are still begin written and published concerning planetary temperature change.

This topic is it not settled scientifically. There is good quality data and published papers that challenge the base AWG hypothesis that doubling CO2 will result in planetary warming of 3C to 5C.

There has been a recent paper published warning of a decade or two of cooling which seems odd. Typically when there is disagreement between observations and theory, something is incorrect with the base assumptions.

It is extraordinary the sun is currently moving toward a peculiar minimum. As I have noted there have been a series of abrupt cooling events that correlate with cosmogenic isotope changes. Everyone has heard of the "Little Ice Age". There is in the paleo climatic record a cyclic series of abrupt cooling events.

 

[Skyhunter]

It is extraordinary the sun is currently moving toward a peculiar minimum. As I have noted there have been a series of abrupt cooling events that correlate with cosmogenic isotope changes. Everyone has heard of the "Little Ice Ages". There is in the paleo climatic record a cyclic series of abrupt cooling events.

What do you consider an abrupt cooling?

You posted a graphic of the Antarctic ice cores that show the glacial/interglacial cycles that are correlated to the Milankovic cycles. These cooling and warming events occur over centuries and indicate strong feedbacks to long term forcings. The solar constant does not vary enough to account for the difference in temperature from a glacial to interglacial period.

The Sun is currently at a minimum as cycle 23 ends and cycle 24 begins. Expect higher solar intensity for the next five years.

 

[Saul]

What do you consider an abrupt cooling?

You posted a graphic of the Antarctic ice cores that show the glacial/interglacial cycles that are correlated to the Milankovic cycles. These cooling and warming events occur over centuries and indicate strong feedbacks to long term forcings. The solar constant does not vary enough to account for the difference in temperature from a glacial to interglacial period.

The Sun is currently at a minimum as cycle 23 ends and cycle 24 begins. Expect higher solar intensity for the next five years.

The 8200 BP present event was a 2C degree cooling event in the Northern Hemisphere.

There is evidence of an abrupt change of cosmogenic isotopes that occurs concurrently with each of the past abrupt cooling events. The mechanism is not as you note a reduction in TSI. The sun does not get warmer or colder, so the explanation for abrupt planetary cooling is not a reduction in TSI.

One possible explanation is an increase in GCR due to a reduction in the heliosphere which in turn causes an increase in planetary clouds. That is a possible explanation for some of the cooling events.

It seems the sun is involved with what ever the forcing mechanism is. As I noted there have been a recent set of papers published noting a reduction in the geomagnetic field at the same time as the abrupt cooling.

Comment:
I have been following this solar minimum. It appears to be a interruption to the solar magnetic cycle rather than the cycle slow down. The magnetic field of new sunspots that are produced has been decreasing linearly with time. The typical magnetic field strength of a sun spot was around 3000 gauss before this change. It is calculated the sunspot requires a minimum field strength of 2000 gauss to survive the trip from the bottom of solar convection zone through the convection zone. The sunspots that are produce are smaller and last only a day or two as compared to up to a week for a normal sunspot. The last sunspot only survived a few hours.

As this phenomena has never been observed before it is not clear what specifically is happening. It is also not clear how the solar cycle restarts after an interruption.

http://www.ingentaconnect.com/content/klu/367/2008/00000028/00000003/00000095

Evidence for the 8,200 a b.p. cooling event in the middle Okinawa Trough

Based on new and existing data on oxygen isotopes, alkenone-surface seawater temperature trends, planktonic foraminifers, lithology, and clay mineral composition of piston cores, a distinct cooling event has been identified around 8,200 cal a b.p. in the middle Okinawa Trough, northwest Pacific. This corresponds to the 8,200 a b.p. cooling event recorded in many places of the Northern Hemisphere. During this event, the local temperature decreased by 1°C, and the δ18O value increased by 0.6‰. A strengthened Asian winter monsoon is the most probable cause for this event, which thus adds further credibility to the contention that we are dealing here with a global phenomenon.

http://adsabs.harvard.edu/abs/2005Natur.434..975RCentennial-scale climate cooling with a sudden cold event around 8,200 years ago

The extent of climate variability during the current interglacial period, the Holocene, is still debated. Temperature records derived from central Greenland ice cores show one significant temperature anomaly between 8,200 and 8,100 years ago, which is often attributed to a meltwater outflow into the North Atlantic Ocean and a slowdown of North Atlantic Deep Water formation--this anomaly provides an opportunity to study such processes with relevance to present-day freshening of the North Atlantic. Anomalies in climate proxy records from locations around the globe are often correlated with this sharp event in Greenland. But the anomalies in many of these records span 400 to 600 years, start from about 8,600 years ago and form part of a repeating pattern within the Holocene. More sudden climate changes around 8,200 years ago appear superimposed on this longer-term cooling. The compounded nature of the signals implies that far-field climate anomalies around 8,200 years ago cannot be used in a straightforward manner to assess the impact of a slowdown of North Atlantic Deep Water formation, and the geographical extent of the rapid cooling event 8,200 years ago remains to be determined.

http://www.essc.psu.edu/essc_web/seminars/spring2006/Mar1/Bond et al 2001.pdf


Persistent Solar Influence on North Atlantic Climate During the Holocene

Gerard Bond, Bernd Kromer, Juerg Beer, Raimund Muscheler, Michael N. Evans, William Showers, Sharon Hoffmann,Rusty Lotti-Bond,1 Irka Hajdas, Georges Bonani

Surface winds and surface ocean hydrography in the subpolar North Atlantic appear to have been influenced by variations in solar output through the entire Holocene. The evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon-14 and beryllium-10 and centennial to millennial time scale changes in proxies of drift ice measured in deep-sea sediment cores. A solar forcing mechanism therefore may underlie at least the Holocene segment of the North Atlantic 1500-year cycle. The surface hydrographic changes may have affected production of North Atlantic Deep Water, potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally.

http://geology.geoscienceworld.org/cgi/content/abstract/30/5/455Widespread evidence of 1500 yr climate variability in North America during the past 14,000 yr

There is debate concerning the spatial extent and magnitude of the recently identified 1500 yr climate oscillation. Existing evidence is largely restricted to the North Atlantic and adjacent landmasses. The spatial extent, magnitude, and effects of these climate variations within the terrestrial environment during the Holocene have not been established. We show that millennial-scale climate variability caused changes in vegetation communities across all of North America with a periodicity of 1650 ± 500 yr during the past 14 000 calendar years (cal yr). Times of major transitions identified in pollen records occurred at 600, 1650, 2850, 4030, 6700, 8100, 10 190, 12 900, and 13 800 cal yr B.P., consistent with ice and marine records. We suggest that North Atlantic millennial-scale climate variability is associated with rearrangements of the atmospheric circulation with far-reaching influences on the climate.

 

[Saul]

This is solar data the indicates something unusual is occurring with the sun.

http://science.nasa.gov/headlines/y2009/03sep_sunspots.htm

Penn's colleague Bill Livingston of the NSO has been measuring the magnetic fields of sunspots for the past 17 years, and he has found a remarkable trend. Sunspot magnetism is on the decline:

"Sunspot magnetic fields are dropping by about 50 gauss per year," says Penn. "If we extrapolate this trend into the future, sunspots could completely vanish around the year 2015."

"According to our measurements, sunspots seem to form only if the magnetic field is stronger than about 1500 gauss," says Livingston. "If the current trend continues, we'll hit that threshold in the near future, and solar magnetic fields would become too weak to form sunspots."

(my comment: Eugene Parker’s calculation was that a minimum field strength of 2000 gauss is required for a sunspot to survive the turbulence in the convection zone. This data however shows sunspots with a field of strength minimum of 1500 gauss. Base on Penn and Livingstone’s data, there will be no more sunspots sometime late 2012. They state 2015 in the article but the graph seems to indicate around 2012.)

"This work has caused a sensation in the field of solar physics," comments NASA sunspot expert David Hathaway, who is not directly involved in the research. "It's controversial stuff."

Penn himself wonders about these points. "Our technique is relatively new and the data stretches back in time only 17 years. We could be observing a temporary downturn that will reverse itself."

Are Sunspots Different During This Solar Minimum?

http://www.leif.org/EOS/2009EO300001.pdf

 

[Saul]

This is further from the solar paper and a link to a sunspot summary.

As that solar wind paper noted solar wind bursts increased anomalously by a factor of three during the end of cycle 24, as compared to past solar cycles. The solar wind bursts have now started to abate. Based on the mechanisms it is expected this winter should be unusually cold.

But something is unusual about the current sunspot cycle. The current solar minimum has been unusually long, and with more than 670 days without sunspots through June 2009, the number of spotless days has not been equaled since 1933 (see ) The solar wind is http://users.telenet.be/j.janssens/Spotless/Spotless.html reported to be in a uniquely low energy state since space measurements began nearly 40 years ago [Fisk and Zhao, 2009].

Yet although the Sun’s magnetic polarity has reversed and the new solar cycle has been detected, most of the new cycle’s spots have been tiny “pores” without penumbrae (see Figure 1); in fact, nearly all of these features are seen only on flux magnetograms and are difficult to detect on whitelight images.

What could be happening? Clues can be found in the McMath- Pierce’s infrared magnetic measurements, which are able to calculate the total magnetic field strength directly (not the flux) in the umbrae. These measurements also have the advantage of observing the sunspots in the infrared spectrum, which guarantees the reduction ...

 

[Xnn]

What sun spots?

The current minimum is the greatest minimum since about 1911, which globally was a very cool period unlike our current situation.

 

[Skyhunter]

Climate until recently is closely correlated with solar activity. No surprise since aside from orbital and volcanic forcings, it has been the strongest variable. That fact has no bearing on the radiative forcing of CO₂.

Also, the highest resolution of the proxies in the links you provided is 20 years, and generally 30 to 50 years. If the Sun is entering another Dalton or Maunder minimum then it is a good thing. It means we will have more time to stabilize atmospheric CO₂.

 

[Saul]

What sun spots?

The current minimum is the greatest minimum since about 1911, which globally was a very cool period unlike our current situation.

There is a reason why the planet has not cooled due to the increase GCR. GCR has increased 18%.

There is direct correlation of planetary temperature change with solar wind bursts (see the attached paper). The solar wind bursts remove the cloud forming ions that are created by galactic cosmic rays (GCR) by a process called electroscavenging. (The solar wind burst create a space charge differential in the ionosphere which creates a potential difference from the ionosphere and the surface of the earth.)

Although the sun is mostly spotless this year there has continued to be solar wind bursts produced which is masking the affects of the weak solar heliosphere. The heliosphere blocks GCR from striking the earth. The solar wind bursts are still occurring but are starting to weaken.

An observed change that accompanied the reducing of the solar wind bursts is a curious sudden weakening of the super El Nino. This winter should be anomalously cold.

http://wattsupwiththat.com/2009/09/...of-long-range-forecasters-and-climatologists/

http://www.agu.org/pubs/crossref/2009/2009JA014342.shtml

If the Sun is so quiet, why is the Earth ringing? A comparison of two solar minimum intervals.

Observations from the recent Whole Heliosphere Interval (WHI) solar minimum campaign are compared to last cycle's Whole Sun Month (WSM) to demonstrate that sunspot numbers, while providing a good measure of solar activity, do not provide sufficient information to gauge solar and heliospheric magnetic complexity and its effect at the Earth. The present solar minimum is exceptionally quiet, with sunspot numbers at their lowest in 75 years and solar wind magnetic field strength lower than ever observed. Despite, or perhaps because of, a global weakness in the heliospheric magnetic field, large near-equatorial coronal holes lingered even as the sunspots disappeared. Consequently, for the months surrounding the WHI campaign, strong, long, and recurring high-speed streams in the solar wind intercepted the Earth in contrast to the weaker and more sporadic streams that occurred around the time of last cycle's WSM campaign.

http://sait.oat.ts.astro.it/MSAIt760405/PDF/2005MmSAI..76..969G.pdf

Once again about global warming and solar activity K. Georgieva, C. Bianchi, and B. Kirov

We show that the index commonly used for quantifying long-term changes in solar activity, the sunspot number, accounts for only one part of solar activity and using this index leads to the underestimation of the role of solar activity in the global warming in the recent decades. A more suitable index is the geomagnetic activity which reflects all solar activity, and it is highly correlated to global temperature variations in the whole period for which we have data.

In Figure 6 the long-term variations in global temperature are compared to the long-term variations in geomagnetic activity as expressed by the ak-index (Nevanlinna and Kataja 2003). The correlation between the two quantities is 0.85 with p<0.01 for the whole period studied.It could therefore be concluded that both the decreasing correlation between sunspot number and geomagnetic activity, and the deviation of the global temperature long-term trend from solar activity as expressed by sunspot index are due to the increased number of high-speed streams of solar wind on the declining phase and in the minimum of sunspot cycle in the last decades

 

[vanesch]

Don't let's fall into the mistake of "journalistic balance", in which we simply presume all voices are equally worthwhile for study and serious consideration. Understanding all sides of an open question is good; but not all the questions or challenges being raised are actually open questions with two sides of comparable standing.

Well, we tend to try to establish indeed some kind of "journalistic balance", but to get it "biased" towards the scientifically sound, we are rather strict (much more so than anywhere else) on the "peer review of sources" side.

The reason for that is simple and down-to-earth: the staff at PF doesn't feel qualified enough to do so in an unanimous way. This is much less of a problem in most other forums of PF: we have quite some very knowledgeable people on board in physics, engineering, mathematics and so on. If something obviously wrong is posted there, there is very soon a consensus by "those who know" amongst staff and regular posters, and appropriate action is taken. If you know a field rather well, it is not too difficult to make the distinction between "an open question" and a "basic error".

But in Earth sciences we haven't such a set of staff members, especially for the topic of AGW. So we had a few options:
- leave the Earth sciences forum evolve by itself (but that's against the basic philosophy of PF)
- close it down
- impose the current policy which is a kind of "coward's moderation": discuss what you want, but have peer-reviewed sources.

This debate comes up regularly.

 

[sylas]

Well, we tend to try to establish indeed some kind of "journalistic balance", but to get it "biased" towards the scientifically sound, we are rather strict (much more so than anywhere else) on the "peer review of sources" side.

This is an excellent solution, and a perfectly good resolution of the problem. It still leaves the field wide open to all the genuinely open questions on climate.

The reason for that is simple and down-to-earth: the staff at PF doesn't feel qualified enough to do so in an unanimous way. This is much less of a problem in most other forums of PF: we have quite some very knowledgeable people on board in physics, engineering, mathematics and so on. If something obviously wrong is posted there, there is very soon a consensus by "those who know" amongst staff and regular posters, and appropriate action is taken. If you know a field rather well, it is not too difficult to make the distinction between "an open question" and a "basic error".

I've heard the problem mentioned already, of a lack of a staff member with a particular expertise in climate.

It seems to me that this shouldn't be that much of a problem... and that you've collectively hit upon an ideal solution.

As you say, the reason it would be nice to have an expert available is that they would be well placed to identify straight away what arguments are disconnected from scientifically sound engagements. But you might find that the application of such expertise in this way is more trouble than it is worth. It works okay with relativity and maths and engineering, because there isn't a huge popular support for the few cranks that we get. That's not the case with climate. I am quite sure you will find that even if you had a climate expert available, even the staff would be divided on whether they were "balanced".

(And it doesn't matter which side you think has most of the cranks. Whether you accept AGW, or reject it, or are on the fence; it is still not hard to see that there is a particular problem here with unscientific argument -- whether you think it is in the IPCC or in the ranks of their critics.)

I think it is much better to have a simple clear guideline, which is a natural extension of the overall physicsforums guidelines. It is expressed without any reference to the particular claims that may not be argued.

Even if you had an expert on staff, you are still best to enforce this rule in the Earth forum, simply because there is so much more material being passed around on the subject which is not scientifically sensible, and because there are such widely divergent views amongst people interested in the subject.

On being a mentor, and being a debator

Even if you had such an expert on staff, my own suggestion (for what it is worth) is that they would be better as a participant in the Earth forum than as a mentor. I've been a moderator in other forums (evcforms.com), and a general rule was that moderators don't moderate threads in which they are involved as participants. It runs into problems with conflict of interest. If an issue turns up in a thread where a moderator is participating, then a new staff member must be called into deal with it.

A moderator is not there to give the answers to questions, but to manage the way discussion is engaged. Having someone to give answers is great; but you don't need special moderator powers for that. The mentors here do often seem to have excellent knowledge in their own major fields of interest, and their input as experts is very welcome. But that input is distinct from acting as a moderator of the debate,

And by the way; I love the fact that you speak of "mentors" here rather than "moderators". It's a great way to look at this special role.

A mentor role in general does include giving guidance on substance, as well as conduct or rules of debate. Unfortunately, that is not going to work in a debate unless the mentor is recognized as an expert by participants; and that is going to be a particular problem in climate discussions.

Therefore you're going to have to give some enforced rulings to people who don't want them; and for that we are back to being a moderator and having a clear guideline that does not require special expertise to apply, and which someone can understand without having to accept your expertise.

But in Earth sciences we haven't such a set of staff members, especially for the topic of AGW. So we had a few options:
- leave the Earth sciences forum evolve by itself (but that's against the basic philosophy of PF)
- close it down
- impose the current policy which is a kind of "coward's moderation": discuss what you want, but have peer-reviewed sources.

This debate comes up regularly.

I think you've got this one nailed. The first solution is obviously wrong, and would make this forum no different to a thousand other venues. It is the second solution that is the one which is a coward's moderation.

The third is not cowardice at all. It is recognition not only of a lack of a particular expert, but of the problem that you will NEVER get anyone who is recognized as a legitimate expert by the people who want to discuss this topic. There's a huge need for improved understanding of the physical science behind climate disputes -- and again, this is a point that would be recognized by both sides, even if they might differ on who it is that needs to improve their understanding!

Cheers -- sylas

 

[D H]

Well, we tend to try to establish indeed some kind of "journalistic balance", but to get it "biased" towards the scientifically sound, we are rather strict (much more so than anywhere else) on the "peer review of sources" side.

This is an excellent solution, and a perfectly good resolution of the problem. It still leaves the field wide open to all the genuinely open questions on climate.

That would be an excellent solution if the science behind AGW was not suspect. It certainly looks suspect from the outside. More importantly, it looks suspect to some very well-qualified meteorologists and climatologists. Because PF does not have a supply of meteorologists and climatologists onboard, the PF solution is, as vanesch mentioned, a bit of a cowardly solution.

 

[sylas]

That would be an excellent solution if the science behind AGW was not suspect. It certainly looks suspect from the outside. More importantly, it looks suspect to some very well-qualified meteorologists and climatologists. Because PF does not have a supply of meteorologists and climatologists onboard, the PF solution is, as vanesch mentioned, a bit of a cowardly solution.

Bingo. As it happens, I disagree with you... but it doesn't matter.

The whole reason for this solution is that it doesn't matter if you think it is the science behind AGW that is suspect, or the science of the critics that is suspect. In either case, the case can be found in the scientific literature, and moderators don't have to rule on the basis of choosing sides.

There are also well qualified meterologists and climatologists who think the science behind AGW is just fine. Not settled in every respect of course! There are plenty of open questions.

This is precisely why having an expert won't work. Which expert would be acceptable? The experts you are thinking of, who consider science behind AGW to be suspect? Or the ones I am thinking of, who think AGW is a well supported scientific hypothesis, confirmed to good confidence by a large amount of perfectly good scientific research and still subject to open questions in the details?

As I said previously, you will never find an expert who is acceptable to all sides -- even all sides within the staff!

You've said the science behind AGW is suspect. All I am really saying is that almost everyone can agree that there's a lot of suspect science involved... even if we disagree as to which is the suspect science!

The proper thing to do is to allow the various arguments to be considered, on all sides, and on their own merits... as long as those sides are presented in the scientific literature. That strips out a lot of really bad argument, consistent with the general physicsforums guidelines, and allows us to look at the arguments that have at least passed through the first level of check for credible scholarship. We do NOT rule on the basis of "consensus", or by some method of evaluating the "expertise" of authors, or by deciding which side the argument is on and either binning it or lauding it on that basis.

We look at the actual evidence presented, case, by case, by case.

I don't expect this process to resolve all the differences, but it sure as heck will let you learn a lot, if you are serious about looking at the arguments on their own merits. I've benefited enormously in learning about all the background physics as I've been working on this. Not just arguments for or against AGW, but about the underlying physics that let's me start to follow the details of the arguments being presented. And I'm still learning on that.

I especially disagree with you that this is "cowardly".

There's nothing cowardly about it. What would be "courageous"? To open up physicsforums to all arguments of any kind? Of course not. That would be a complete cop out. To step in and rule that one side or the other is disallowed? That would be just as bad.

So what? How do you decide... and WHO decides? You need something that let's you and I work together on this; not a ruling that rejects the experts you are thinking of or rejects the experts I am thinking of.

Cheers -- sylas

 

[Galteeth]

"Physicsforums also deals with open questions. From the guidelines again:
There are many open questions in physics, and we welcome discussion on those subjects provided the discussion remains intellectually sound. It is against our Posting Guidelines to discuss, in most of the PF forums or in blogs, new or non-mainstream theories or ideas that have not been published in professional peer-reviewed journals or are not part of current professional mainstream scientific discussion.
In climate, there are many open questions, relating to sensitivity, cloud effects, paleoclimate, approximations in modeling, the carbon cycle, and on, and on. We aren't going to resolve them, but understanding the credible alternatives is well worthwhile.

There are also a lot of questions which are not actually intellectually sound open questions at all, but simply misunderstandings or even outright crackpottery. There's a lot that is said outside the professional mainstream which has been enthusiastically passed around in the public domain as being of equal standing to genuine science. In some respects, a lot of this public debate (not all of it!) bears a significant similarity to the whole "intelligent design" movement."


Yes! And it would be quite useful for a lay person to be able to distinguish between legitimate questions and crack-pottery. There is so much noise on this issue that's its hard to get to what's substantive. It is so frustrating when you have people convinced with no evidential basis that global warming is a hoax, then you have "scientists" who post things like "global warming is a 100% certainty" (this was a statement I saw posted on the NYT by a suppossed climatologist which made me raise my eyebrow).

A general overview of what is relatively certain, what's generally agreed upon, what's questionable, and what's controversial would be great. Perhaps I should start a new thread for this?

 

[Andre]

well as far as I'm concerned, there may be relative agreement about a BASIC climate sensitivity of about one degree celsius / Kelvin warming for doubling CO2.

So if you want to increase that to IPCC main figures of something like 2-4 degrees per doubling, you need predominance of positive feedback factors. That is questionable to controversial, like it or not.

Two approaches for that. On one hand statistics, investigating actual dynamic random walk temperature variation to be non-persistent, which suggest dominance of negative feedback, (several publications http://www.aai.ee/~olavi/). On the other hand direct measurements as suggested http://www.leif.org/EOS/2009GL039628-pip.pdf.

 

[Skyhunter]

then you have "scientists" who post things like "global warming is a 100% certainty"

Global warming is a fact. The instrumental record proves it to the very limits of scientific certainty.

Why should a scientist lend credibility to the global warming is a hoax crowd by giving a confusing nuanced answer about open questions and probability distribution curves?

 

[sylas]

A general overview of what is relatively certain, what's generally agreed upon, what's questionable, and what's controversial would be great. Perhaps I should start a new thread for this?

Yes, I think you should; but your topic is going to be too general.

We have different ideas about what the problem really is.

What is "generally" agreed upon is not the same as "universally" agreed upon. For someone on the fence, who is confused, and who doesn't want to have to learn a whole pile of background physics, it is a perfectly sensible question to ask about the "consensus", in the sense of what is the view of the majority of scientists working on the subject. And by majority I mean almost overwhelming majority.

If you want to know a wider consensus going beyond the working scientists, then the consensus is weaker, and in the general public it is gone.

Terms like 100% certainty are not useful, and only rarely used by the working scientists. AGW is not a single proposition, but a whole body of propositions, some of which are more certain than others.

• That the planet is warming, significantly, on decadal scales, is a measurement about as certain as you can get. It's ongoing work to measure that more accurately, and also to find how the warming is distributed, and to separate the warming trend from stationary variations.
• That human factors have a major contribution is about as certain as you can get. But it is also certain that they are not the only factor, and there's a lot of ongoing work to identify and measure the various factors involved.
• In particular, that CO2 is rising rapidly and that this is by far mostly from human industrial emissions is a fact about as certain as you can get. That this necessarily has a significant impact on Earth's energy balance is basic physics, about as certain as you can get.
• A big open question is the one identified by Andre. What is the sensitivity of climate... how much does temperature change in response to energy balance forcing? The best we have is a range of possible values, which as Andre notes is about 2-4 degrees per doubling. It is more usually quoted as 2-4.5, or 1.5-4.5, which is the IPCC range in the 4th AR. That's not a 100% certainty range; more like a 90% certainty range. There continues to be work published from time to time which proposes smaller values, and that is legitimately part of the whole scientific project. If you just want the majority view, then 2-4.5 works. If you want to really get into the debate, then you'll have to look at other proposals also, on their own merits. But there are very few.

That's a brief road map of some of the questions associated with AGW, as I see it. The two biggest open questions are the magnitudes of other forcings and sensitivity to forcings.

Other forcings include in particular cloud and aerosol effects -- and identifying causes for them as well. There are significant anthropogenic factors in these other forcings as well, and most of these are much harder to sort out than CO₂, which is comparatively straightforward by comparison.

The sensitivity of climate is being better constrained as time goes by, but there is still a substantial range of likely values, and a handful of published arguments for radically different values.

The guidelines at physicsforums do not limit us to the majority or consensus view. We are free to consider any work published in the peer reviewed literature. That includes a very wide range of perspectives; and being able to examine those on their own merits is great. This thread speaks of playing "devil's advocate". That means actually knowing and understanding the arguments you don't agree with yourself; both for those who tend to accept the reality of strong anthropogenic effects on climate, and those who are skeptical of strong human effects.

Some of these arguments are very technical. Quite apart from anything else, getting to follow them is going to involve learning more about the background physics, and that's what PF is about.

Cheers -- sylas

postscript.

On the other hand direct measurements as suggested http://www.leif.org/EOS/2009GL039628-pip.pdf.

There's no such thing as a direct measurement of sensitivity; and the paper you cite makes this clear as well. This is one of the legitimate handful of low estimates. It uses ERBE data. There's a fair bit of work been done with the ERBE data and sensitivity, and if you want majority views, then most of the ERBE based estimates are significantly higher than Andre's citation. To actually follow the details of how the estimates are made, either the low estimates in the paper by Linden and Choi, or the more conventional estimates from ERBE made by Wang, or Gregory and Foster, and others, you have to actually pull apart the details on their own merits. Just declaring one paper to solve the whole thing, or be a "direct" measurement, is foolish.

 

[Xnn]

Within climate science, nothing is 100% certain. However, with respect to CO2 influence on the climate, the following can be said:

Equilibrium climate sensitivity is likely to be in the range of 2C to 4.5C with a most likely value of about 3C, based upon multiple observational and modelling constraints. It is very unlikely to be less than 1.5C.

page 88: http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-ts.pdf

Notice:
Likely = 66% probability
Very Unlikely < 10% probability

In other words, it is more than very likely (>>90% probability) that climate sensitivity is > 1C, while the most likely value is about 3C.

So, while some may wish to argue that climate sensitivity is less than 1C, the odds are greatly against them being correct. However, to suggest that climate sensitivity may be less than 2C while an extreme statement is not out of the realm of possibility since the chance of it being correct is about 33%.

Probably the best thing to say is that there is a small, but not negligible, probability that climate sensitivity is less than 1C.

 

[vanesch]

Yes! And it would be quite useful for a lay person to be able to distinguish between legitimate questions and crack-pottery. There is so much noise on this issue that's its hard to get to what's substantive. It is so frustrating when you have people convinced with no evidential basis that global warming is a hoax, then you have "scientists" who post things like "global warming is a 100% certainty" (this was a statement I saw posted on the NYT by a suppossed climatologist which made me raise my eyebrow).

You've got it. That's what makes this forum so hard to moderate. It is what I personally (I'm not talking on behalf of PF here) disliked most in some IPCC discourse and publications at a certain point: a certain lack of the typical self-criticism one usually finds in well-established science. When a supposed scientific discourse starts to sound like a commercial, or the program of a political party, I'm a bit lost.

BUT, but, how to express some reserves towards that, without opening the flood gates of crackpottery and low-level denial of basic established scientific fact ? That's the hard problem to solve here. And, as sylas pointed out, how can you solve it when certain experts have publicly shown not to show some "scientific self-criticism" ? Even a genuine renowed climate scientist wouldn't be recognized as an "objective expert" by "the other camp".

 

[vanesch]

Notice:
Likely = 66% probability
Very Unlikely < 10% probability

In other words, it is more than very likely (>>90% probability) that climate sensitivity is > 1C, while the most likely value is about 3C.

I really wonder how one gets to these "probability" numbers. I know that they are Bayesian estimators, but as we know, Bayesian estimators need a priori probabilities of our "belief", and only work under the hypothesis that our error probability model is assumed correct.

This looks to me like trying to say that "Newtonian mechanics has 95% chance to be correct", no ?

 

[sylas]

I really wonder how one gets to these "probability" numbers. I know that they are Bayesian estimators, but as we know, Bayesian estimators need a priori probabilities of our "belief", and only work under the hypothesis that our error probability model is assumed correct.

This looks to me like trying to say that "Newtonian mechanics has 95% chance to be correct", no ?

That is an excellent question. Such "probabilities" or "likelihoods" are inevitably subjective. Technically, they are obtained using a Bayesian analysis with assumed prior distributions, as you say... and it is the choice of prior distributions where you can't avoid being subjective.

There is a thread about this very point I started just recently. See [thread=334005]A low likelihood for high climate sensitivity[/thread]. This is about a new paper just out by Annan and Hargreaves, who argue that it is reasonable to reject with high confidence the likelihood of sensitivity values above 4.5; higher confidence than suggested in the 4th AR. The whole basis for the paper is not any new data; but a more "reasonable" choice of priors in the analysis.

Annan and Hargreaves do not propose any new "objective" likelihood measure, but face up to the inevitable subjective aspects of quantified likelihood estimates for a certain unknown real world number.

We've mentioned the range 1.5-4.5 which is widely used, on the basis of the IPCC 4th AR. This is obtained using a "uniform" prior, in which unreasonably high sensitivities are given the same prior expectation as any others, in a certain range (0 to 10, for example). A uniform prior is sometimes taken as a way of avoiding results that incorporate information other than the data being applied; Annan and Hargreaves argue that this is dubious. From their abstract:

In this paper, we investigate some of the assumptions underlying these estimates. We show that the popular choice of a uniform prior has unacceptable properties and cannot be reasonably considered to generate meaningful and usable results. When instead reasonable assumptions are made, much greater confidence in a moderate value for S is easily justified, with an upper 95% probability limit for S easily shown to lie close to 4^oC, and certainly well below 6^oC.​

It seems to me that this is a well grounded criticism, and that exceptionally high sensitivities are less likely than you would think from the 4th assessment report.

Note that the choice of priors has more effect on the upper bound than the lower bound; this is a consequence of the "long tail" of sensitivities, explained in the thread.

Felicitations -- sylas

 

[vanesch]

That is an excellent question. Such "probabilities" or "likelihoods" are inevitably subjective. Technically, they are obtained using a Bayesian analysis with assumed prior distributions, as you say... and it is the choice of prior distributions where you can't avoid being subjective.

This is one of the criticisms I naively have, but apparently it can be dealt with.

However, there's a second, more fundamental criticism, and that is the assumed inherent correcctness of the error probability model.

Imagine I have an unknown system of which I have to make a prediction of response for a given input signal. Now, we can take our system as a black box, a grey box, or a white box, which means that for the black box, we only take former input-output relationships and try to fit a "general-purpose" behavioural black box model on it (for instance, a dynamical neural network), or for the white box, we can study the physics of what's in the box, and write down the supposed dynamics of the model, with or without free parameters, or we can be somewhat in between (grey box) where some physical modeling is done, and where some behavioural modeling is done based upon experimental data.

Now, in order to do any Bayesian estimation, I do not only need a correct model of my system, I also need a correct probability estimation of the errors on my model. If I have a biased model, and/or erroneous error estimations of this model, my Bayesian estimator will be totally off, concerning its probability distribution. Its expectation value might be still more or less right, but its probability distribution will be totally off.

In fact, it is much more difficult to have a correct probability distribution for a Bayesian estimator than to have a more or less good estimator expectation value.

This is why I always expressed my reserves towards these probabilities.
Now, maybe this is due to my naivety, but I've been working in system identification, and usually people are much more prudent when they do such things, than what I've seen from the IPCC.

Of course, there is a totally subjective way in which these numbers DO make sense: you can take them as "this is what we think, *to our best knowledge*. In other words, if I *had to bet my money* on the sensitivity, I would use this Bayesian probability distribution because it is "the best I can do with what I know".

But estimating "the probability that such event will happen to be 10% to the best of my knowledge", and claiming that the probability of that event IS 10%, is different. The first statement is: "ok, this is what I know, but I can be wrong". The second is "what's true".

 

[sylas]

But estimating "the probability that such event will happen to be 10% to the best of my knowledge", and claiming that the probability of that event IS 10%, is different. The first statement is: "ok, this is what I know, but I can be wrong". The second is "what's true".

These are not probabilities, but indications of confidence. The report is not saying that there is a known probability of an event. It is quantifying their level of confidence in a proposition.

In other words, the IPCC report, as I read it, more than any other scientific report I have ever seen, attempts to be careful about saying "this is what we think", with explicit acknowledgment of limited confidence. That's just my impression.

It doesn't matter all that much. I tend to use the IPCC assessment report as a secondary reference anyway. I nearly always go back to the primary literature to get at the details. The IPCC report is useful to summarize the state of play from many diverse working scientists; but it's not gospel. It's a useful resource. For reference, then, if anyone would like to check against the report itself:

• The Physical Science Basis is the section of the fourth IPCC assessment report that is relevant to physicsforums and the underlying science of climate. It is the report of "working group 1". From the link, you can download the whole report (996 pages) as separate chapters; also the http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-ts.pdf and other materials.

In such a large report, it has been important to have a high level of consistency in how the report expresses its limited confidence in different propositions. A set of guidelines has been worked out for use throughout the report for expressing the level of confidence. These are described in box TS.1 (Technical summary, page 22-23), with additional pointers to other parts of the report that go into details of error and uncertainty handling.

In particular, the estimates of sensitivity are given on page 66 of the technical summary; with a brief overview on page 88 (quoted above by Xnn) and with more detail in the main report. See especially box 10.2, on page 798 (chapter 10). I quote here the tail end of that box:

Since the TAR, the levels of scientific understanding and confidence in quantitative estimates of equilibrium climate sensitivity have increased substantially. Basing our assessment on a combination of several independent lines of evidence, as summarised in Box 10.2 Figures 1 and 2, including observed climate change and the strength of known feedbacks simulated in GCMs, we conclude that the global mean equilibrium warming for doubling CO2, or ‘equilibrium climate sensitivity’, is likely to lie in the range 2°C to 4.5°C, with a most likely value of about 3°C. Equilibrium climate sensitivity is very likely larger than 1.5°C.

For fundamental physical reasons as well as data limitations, values substantially higher than 4.5°C still cannot be excluded, but agreement with observations and proxy data is generally worse for those high values than for values in the 2°C to 4.5°C range.​

You could hardly be more thorough in avoiding a claim of "what's true"! They are explicit on the foundations of the estimate, and about the limits of their confidence. The values given of 2 to 4.5 are not probabilities of an event, but an indication of how confident they are about this range. The level here is "likely". For the "very likely" range, they give a lower bound only, of 1.5. The omission of an upper bound is deliberate, and reflects how hard it is to give a strong upper bound, given the nature of sensitivity and the "long tail".

In brief, they don't know the sensitivity. No-one does. The best they can do, as an assessment of the current state of knowledge, is that is it "very likely" more than 1.5, and "likely" to be in the range 2 to 4.5. You should read those as indications of how confident they are; not that this is a probability for an event.

In fact, the major criticism of the IPCC report, in this instance, is that it is too cautious in drawing conclusions. The paper by Annan and Hargreaves that I discussed is suggesting explicitly that the IPCC report could reasonably put an upper bound of 4.5, or even lower, in the "very likely" confidence level. It looks to me that they make a good case for this.

It doesn't bother me at all that people have different reactions to the IPCC assessment. One possible approach for moderating consistent with the guidelines would be to let the assessment be a guide to the range of views that are "mainstream", and rule out any argument that goes outside those bounds. I don't think that would be a good idea; but if you ever did decide to delimit boundaries for "mainstream" this would be your best option. But I think you have a much better approach already in place; which allows us to consider any view, from any individual, as long as they have taken that first step of getting it published in the peer reviewed literature.

So I don't mind at all that people differ in their reaction to the report. That's neither here nor there, and shouldn't be used to limit what propositions may be considered in the forum.

My own main interest is to help people understand better the physics of climate, and to learn more about it myself. It seems to me that a lot of debate on climate is based on visceral reactions rather than real physical comprehension of the various concepts.

Cheers -- sylas

---

PS. On reflection... I suggest that there is a problem in some quarters about how the IPCC report is used -- or indeed any scientific paper. Some people seem to treat the IPCC report as gospel, and that's dreadful. Same goes for treating any scientific paper as a final definition of what is known. Presenting a single paper as a final proof or disproof of a tricky scientific question is a misunderstanding of the nature of science. I don't personally think this is a fault of the IPCC report itself; which is more than usually careful about explicit recognition of limited confidence. It is rather a failure of understanding of a few people supposedly defending the report.

You may be able to identify in retrospect a major paper that has solved some problem; but that is generally something that is properly recognized some time after the publication, as other working scientists test and review its results. This is also why I would be against using the IPCC report as a limitation to define the mainstream for the purposes of moderation.

 

[Xnn]

Consider the 3C/CO2 doubling most likely value.

CO2 levels are going up about 0.5% per year.
That works out to 0.015C/year of warming.

Now; look at the amount of observed global warming over the last 30 years.

It's about 0.016C/year.

In other words, observations are tending to support the most likely value.

 

[Xnn]

Concerning criticism of the the IPCC; has anybody noticed that peppered throughout their report are the identification of areas that have a low level of understanding?

Ice Sheet dynamics come to mind. A fair number of people are concerned about just how fast they may melt, but the IPCC hasn't made a definiative statement regarding them and for good reason.

 

[sylas]

Consider the 3C/CO2 doubling most likely value.

CO2 levels are going up about 0.5% per year.
That works out to 0.015C/year of warming.

Now; look at the amount of observed global warming over the last 30 years.

It's about 0.016C/year.

In other words, observations are tending to support the most likely value.

That's technically incorrect on many levels.

First, the doubling value of 3 C/2xCO2 is an equilibrium response; not the transient response.

There's a lot more changing than just CO₂. Taken in isolation, CO₂ is the largest forcing, but there are a number of other forcings, both positive and negative, and they make a difference.

An increase of 0.5% per year is log₂(1.005) of a doubling, and this is 0.0072. At 3 degrees per doubling you would have 3*0.0072 = 0.021 C/year.

As it turns out, observations are consistent with the estimates of sensitivity, but the argument is a bit different. It is not sufficient to give a strong constraint on the sensitivity estimate. If you look at the section of the technical summary you quoted previously, the next paragraph deals with "transient response" as opposed to "equilibrium sensitivity". Chapter 10 deals with the difference between these concepts in more detail. Here's the extract (page 88, technical summary)

The transient climate response is better constrained than the equilibrium climate sensitivity. It is very likely larger than 1°C and very unlikely greater than 3°C. {10.5}​

With a transient response 2°C per doubling, and with an increase of 0.5% per year CO₂, and in the absence of all other forcings, you should expect a temperature increase trend of about 2*log₂(1.005) = 0.0144 C/year. Of course, there are other forcings as well; but all told this is why transient response is better constrained. The available data for the immediate present allows you to constrain it, where equilibrium response requires an additional level of indirection to get from observations to a number.

Also relevant is a recent thread with a discussion of the cummulative carbon emissions response (CCR), which tends to reflect transient climate response rather than equilibrium climate response. There were two recent papers on this, which are discussed in [post=2343088]msg #83[/post] and following of thread "Estimating the impact of CO2 on global mean temperature".

Cheers -- sylas

 

[Xnn]

Thanks sylas;

So, doing this in natural logs, the calculation is 0.016/0.0072 = 2.2 C/CO2 doubling; using the last 30 years of global observational data if other forcings are ignored.

Not sure if how significant other forcings are.