BICEP2

I had considered writing about BICEP2 a little while ago, but wasn’t sure how much of what I knew was in the public domain; so thought I would wait a little while. It all seems to be out in the open now, so I thought I might write a brief post. To be clear, though, I’m not a cosmologist, so may not get this quite right. Also, I’m going to write this at a level that I think will be understandable. However, anyone who thinks something needs correcting, feel free to do so through the comments.

The background to this issue is that there are a number of cosmological conundrums. For example, the universe appears homogeneous. It looks the same in all directions. However, different parts of the sky are not causally connected, so how can they have the same basic properties? Similarly, the universe appears to be flat, but that’s a tricky concept to explain, so I won’t (to be clear, it’s not because I don’t think my readers could understand this; it’s because I don’t think I can explain it properly 🙂 ). A solution to these conundrums is that the universe – when very young – underwent a very short period of very rapid expansion : called inflation. Prior to this, everything was connected. Afterwards, different regions were no longer causally connected, but now had the same basic properties.

A signature of this inflation is primordial gravitational waves (for those interested in climate science, these are not the same as gravity waves) that would be imprinted on the cosmic microwave background (CMB) radiation – the remnant radiation from the Big Bang. To detect these gravitational waves requires detecting a polarization signal in the CMB. This is what the BICEP2 team announced that they had done a few months ago. To determine this, however, they had to remove the influence of gravitation lensing (as the CMB radiation travels through the universe, mass can introduce polarization) and they have to remove the polarization from foreground – i.e., from dust in our own galaxy. They did this and presented a result that suggested that they had detected (at very high significance) polarization in the CMB and, hence, the first evidence for primordial gravitational waves (indicative of an early period of inflation).

This result was hailed by everyone I knew who worked in this area – including those who were associated with competing teams. It was seen as a remarkable discovery; possibly the discovery of the century (apart from maybe the Higgs Boson). Noone I knew wanted this to be wrong. I even asked a seminar speaker whether or not they thought the foreground contamination could be an issue, and their response was that the signal was so strong that all it could do was reduce the significance a little.

Well, it now seems that that was wrong. It appears that the BICEP2 team may have done their foreground correction using a figure from a conference presentation given by someone on a competing team. They didn’t – it seems – realise that the data in the figure had been smoothed so as to reduce the apparent foreground in the relevant region. It now seems that there is a good chance that their signal is simply polarization from material in our own galaxy, and not a signature of primordial gravitational waves. I don’t think this is yet certain, but it is a little disappointing if true.

There are, however, a number of interesting aspects to this issue. Firstly, noone I know of is – publicly at least – suggesting that the BICEP team did anything nefarious. They were maybe a little sloppy. Took a bit of a risk; maybe they should have waited to be more certain. However, everyone recognises that this was an extremely exciting discovery. Career defining. Furthermore, it’s a great illustration – in my view – of how science works. Despite everyone being extremely excited by this announcement, there were still people delving into the details and checking what was being presented. Within a matter of weeks, there were already hints that there might be a problem. I don’t think that the BICEP team have yet conceded that the measurement is purely foreground, but I’m sure they will if that is what the additional analysis suggests. It’s still possible, of course, that they will still have a small signal of primordial gravitational waves. So, it could still end up being an exciting discovery; just not quite as significant/robust as – at first – thought.

In a sense, this is why I get frustrated by suggestions that scientists (climate scientists in particular) are involved in some kind of conspiracy or suffering from groupthink. It’s very difficult for incorrect results to persist. Anything interesting is going to be checked by clever people who will almost certainly find a problem, if there is something to be found. I appreciate that the BICEP2 issue is only one example and we don’t yet know the final outcome, but I think it is still an illustration of the scientific process in action. There may be negative aspects to this whole issue but – from a scientific perspective – the BICEP2 announcement has done no damage. Even if we don’t actually have evidence for inflation, we’ve learned something and, presumably, understand aspects of this topic more now than we did before.

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69 Responses to BICEP2

  1. leonretief says:

    Sorry if I’m being stupid, but is there a difference between gravitational waves and gravity waves?

  2. OPatrick says:

    Would that be cosmic microwave background (CMB) radiation? If not, the mind boggles at the possibilities.

  3. leonretief,
    There is (I did have to check myself). Gravity waves are essentially waves in a fluid where the restoring force is gravity. You see them in our atmosphere. Gravitational waves are waves in the gravitational field (in the universe) driven by the movement of masses. For example, black holes can exist in a binary (i.e., two black holes in orbit about each other). This system will send out gravitational waves. This is what projects like LIGO and LISA are – or will be – trying to measure. They’ve never been directly detected. They have, however, been inferred. I think that we have observations of neutron star binary systems (two very dense remnant cores of massive stars) that show that the orbit decays with time, and the only way to explain this is through the loss of energy by the radiation of gravitational waves.

  4. OPatrick,
    Indeed, thanks. Good thing the font I’m using isn’t cosmic sans 🙂

  5. Pingback: Announced discovery of Gravitational Waves may be an error.

  6. Bobby says:

    Good post. I was one of the ones excited by the initial announcement. I loved the cleverness of looking for gravity waves in the polarization of CMB. I don’t have an experimental background so never would’ve been able to have found their error. Interested to see where the whole thing lands.

  7. I regularly read theoretical physicist Matt Strassler’s Of Particular Significance blog. Regarding BICEP2 he first wrote on March 17:

    “Talking to and listening to experts, I’d describe the mood as cautiously optimistic; some people are worried about certain weird features of the data, while others seem less concerned about them… typical when a new discovery is claimed. I’m disturbed that the media is declaring victory before the scientific community is ready to.”

    He has followed up with several more posts you may find interesting.

    April 30th, Did BICEP2 Detect Gravitational Waves Directly or Indirectly?

    May 19th, Will BICEP2 Lose Some of Its Muscle?

    May 30th, The BICEP2 Dust-Up Continues

    If you’ve not visited his site I highly recommend it.

  8. Bobby,
    Thanks.

    Kevin,
    I did read some of the early posts, but hadn’t read the more recent ones. Very good site, thanks.

  9. clivebest says:

    Do you think that the model based natural variation corrections applied in chapter 10 of AR5 WG1 to determine Attribution are any different? There is a similar bult in assumption that any such multi-deccadel AMO/PDO variations are irrelevant. A different assumption would yield a smaller net anthropogenic forcing. Sometimes we see things we want to see!

  10. clivebest,
    I don’t understand what you’re implying. How is that related to what’s being discussed here?

    However, since you mention it, maybe you can explain how unforced variability since 1950 can produce a significant fraction of the warming we’ve observed. You’re a physicist, maybe you can explain how a system with as little heat content as our atmosphere could retain the energy that it’s received, and not simply radiate it back into space in a matter of months.

  11. clivebest says:

    I think you misunderstand. When subtracting backgrounds to measure a physical signal one must ensure that all uncertainties are included. Of course anthropogenic warming is real but that doesn’t mean that possible oceanic cycles should be discarded prematurely. http://clivebest.com/blog/?p=2353. I think that fig 10.5 will be the contentious result in the future because the error on ‘ANT’ is smaller than both internal variability and combined GHG + OA.

  12. clivebest,
    I don’t think you quite get what I’m getting at either then. If you’re arguing that some of the warming over the last 50 years is natural variability and that it has lead to a faster warming trend that anthropogenic would have produced alone, then you’re suggesting – I presume – that the next 50 years could see a much slower warming trend. Given the potential increase in radiative forcing, how plausible do you really think that is? On the other hand, if you’re simply suggesting that we can associate some of the variation in surface warming with natural cycles, I don’t think anyone would dispute that. I also don’t think it necessarily has any real significance with respect to climate sensitivity though.

    Also, please tell me that you understand the errors on that figure. I know some who should know better don’t seem to, but I really think you should be able to get this. It’s not that hard. I’ve tried to explain it here.

  13. clivebest says:

    There is a clear 60 year natural cycle of magnitude about 0.15C of origin as yet unknown superimposed on a general anthropogenic warming trend which fits to a transient temperature response proportional to 2.5 ln (C/C0). So yes temperatures will remain essentially flat till ~2030 and then increase more rapidly thereafter. I will check out your argument regarding fig 10.5 but so far I remain unconvinced by those made on real climate because they are simply based on models which assume natural variability is insignificant.

  14. clivebest,
    A few basic questions then.

    Remain flat? They’re not even remaining flat now. Mean warming trend is probably around 0.1 degrees per decade. Yes, I know there’s uncertainty, but that is the mean.

    Flat till 2030? At current emission rates, we could increase anthropogenic forcings by 0.6 Wm-2 by 2030 (maybe more). Do you really think it plausible that we could have no surface warming while increasing our energy imbalance by in excess of 0.5 Wm-2?

    Here’s a question to ponder. Do you think that there could be a multi-decade natural, unforced warming cycle without any change in radiative forcing (i.e., in the absence of anthropogenic emissions)?

    I must admit that I am surprised by how certain you seem to be about temperatures remaining flat till 2030.

  15. Mike Fayette says:

    I simply love this post and the incredibly rational attitude that you and others have on this exciting – but uncertain – new discovery. This is the way that science is SUPPOSED to work. We all WANT it to be true, but maybe it isn’t…..

    Those of us on the skeptical side of CAGW (or AGW or whatever) are simply desperate for the same level of skeptical analysis on Climate Change. Our skepticism may eventually prove to be wrong, but we simply have to avoid saying that the “Science is Settled” on the climate issue, any more than the science is settled on what the BICEP 2 team reported.

    Thank you for a great post.

  16. Magma says:

    Another example of a groundbreaking discovery that wasn’t was the apparent measurement of faster-than-light neutrinos by CERN’s OPERA in late 2011. But in that case the discovery team made it perfectly and repeatedly clear that the potential (and even expectation) of an experimental error was very possible.

  17. Those FTL neutrino results had already been prebunked to much higher precision by neutrinos from SN1987a. But if inflation is wrong, we need another explanation(s) for the homogeneity and flatness of the universe.

    Also, we’d need to find another explanation for the apparent lack of heavy exotic particles predicted by most grand unified theories, such as magnetic monopoles. Griffiths 3rd ed page 327 shows how symmetric Maxwell’s equations appear in the presence of magnetic monopoles, and Griffiths opines that they “beg for magnetic charge to exist.” See problem 8.12 on page 362, along with footnotes 11 and 12 on the same page. Griffiths guides the reader through a proof that quantization of electric charge can be deduced (rather than assumed a priori) if the universe contains just one magnetic monopole.

    A period of rapid inflation after the universe becomes too cold (i.e. not energetic enough) to create magnetic monopoles would greatly reduce their initial density, which in turn would explain why they’re so hard to find (Kolb p239,266).

  18. Mike,

    Those of us on the skeptical side of CAGW (or AGW or whatever) are simply desperate for the same level of skeptical analysis on Climate Change. Our skepticism may eventually prove to be wrong, but we simply have to avoid saying that the “Science is Settled” on the climate issue, any more than the science is settled on what the BICEP 2 team reported.

    I think you should at least consider that the reason that you’re seeing what you want to see in climate science is that it is very difficult to find something that is wrong with the fundamentals. Doesn’t mean there isn’t something, but just because you aren’t seeing scientists being skeptical doesn’t mean that they aren’t thoroughly checking the evidence.

    Magma,
    The FTL neutrinos was an interesting issue, but I don’t think anyone was at all surprised (as DumbSci) says that it turned out to be wrong.

    DumbSci,
    One of the unfortunate outcomes of this issue may well be that detecting CMB polarization may be quite difficult, which would be unfortunate. I don’t know if Planck will find something, but I think they won’t be announcing anything for another year or so.

  19. izen says:

    @- Mike Fayette
    “… but we simply have to avoid saying that the “Science is Settled” on the climate issue, any more than the science is settled on what the BICEP 2 team reported.”

    BICEP2 is an attempt to measure/detect an aspect of the present best theory of cosmology, the big bang.
    I suspect 97% of cosmologists think the science is settled on the big bang, but research uncertain or difficult areas of the theory. Like the existence and magnitude of gravitational waves.

    A comparison would be with attempts to derive climate sensitivity from paleoclimate data. a group could claim that their method of analysis gives a particular figure. others may then point out that assumptions in the method may have distorted the result.

    This would not mean that because a particular effort to determine ECS has problems the science of climate is suddenly ALL uncertain. Any more than the big bang is thrown into significant doubt by problems determining the magnitude of gravitational waves.

    There is a caveat on this.
    I have a suspicion that the big bang theory could be a significantly incomplete explanation of physics.
    But with dark matter/energy, unifying quantum fields and gravity and a number of other ‘perihelion of Mercury’ type problems in the observations I keep thinking that there is another shoe to drop in basic physics/cosmology.
    In many ways the physics underlying the big bang is much less certain than climate science, a heat engine constrained by the 2nd LoT.

  20. clivebest says:

    In both High Energy physics and Cosmology it is very important to understand any background data in order to isolate new physics signals. For both the Higgs and Inflation there is a general expectation (consensus) that both must exist. If the Higgs didn’t exist the standard theory of particle physics would be wrong. If inflation did not happen then causality breaks down. Intriguingly the Higgs boson could be the driver of inflation at the Big Bang. So expectations are very high and it is very easy to get misled unless background processes are understood properly. This is one reason why the announcement of the discovery of the Higgs was delayed for over 6 months until 2 independent groups reached the same conclusion at overwhelming statistical significance.

    Climate science is based on well understood physics, but the complexity of interactions between systems is enormous. Out of this complexity we ask the question “Are man made emissions of CO2 and other GHGs warming the planet ? If so how large will be the warming effect in the future ?

    The answer to the first question is yes. To answer the second question however one must understand whether there are natural variations in climate which may give a background signal from which the anthropogenic signal must be measured. We know that such processes can occur on a multi-year basis – ENSO which effect the measured global temperature. We also know that multi-decadel oceanic temperature changes occur AMO/PDO. Do these too effect global temperatures at some level ? Within the limited time period of observations there indeed seems to be a small oscillation in temperatures with a period of ~60 years – see this graph for example

    CMIP5 models on the other hand appear to assume that natural variability is random in nature, and that all observed temperature rise is anthropogenic. However the largest warming has occurred since 1970 which also happens to coincide with an apparent upturn in this natural cycle. By using a natural background simulation based on random natural variation AR5 attribution analysis enhances the anthropogenic signal above the previously assumed small natural background.

    Now your questions
    – If you do a linear fit to the HADCRUT4 monthly data from 1997 to now you get a trend of 0.03 ± 0.02 C/decade .

    – I fit the H4 data back to 1850 to the Keeling CO2 data and a 60y natural cycle. So this includes the anthropogenic signal (TCR=1.7C) and the observed 60y oscillation. Then you can extrapolate forwards based on different emission scenarios. I get the following graph As you see there is little or no warming expected before 2030. Even with the high end emissions curve we would expect just 0.3C warming by 2030.

    So yes the evidence is convincing that there is a naturally forced multi-decadel oscillation independent of any anthropogenic forcing, and that this may be the cause of the current hiatus in warming.

    At the Royal Society meeting to review AR5 WG1in 2013 Julia Slingo made this remark:

    “……you’ve argued very convincingly and I say (said) it’s a great presentation about 15 years being irrelevant, but I think, some of us might say if you look at the Pacific Decadal Oscillation and it’s timescale that it appears to work, it could be be 30 years, not out of the woods yet, on this one”

  21. clivebest,

    If you do a linear fit to the HADCRUT4 monthly data from 1997 to now you get a trend of 0.03 ± 0.02 C/decade .

    Do you? I get 0.05 +- 0.112 degrees per decade. We also now HadCRUT4 under samples in the poles. The Cowtan & Way correction gives 0.11 +- 0.14 degrees per decade

    I fit the H4 data back to 1850 to the Keeling CO2 data and a 60y natural cycle. So this includes the anthropogenic signal (TCR=1.7C) and the observed 60y oscillation. Then you can extrapolate forwards based on different emission scenarios. I get the following graph As you see there is little or no warming expected before 2030. Even with the high end emissions curve we would expect just 0.3C warming by 2030.

    So, you’ve fitted some oscillation that you claim to be indicative of natural variability to the anthropogenic signal. That in itself is a little concerning. You also haven’t really explained how you got the 60 year oscillation. Did you properly correct for the eternal forcings? I’ve run a simple model where I include all the external forcings and it produces a pretty good fit to the observed temperatures. Didn’t seem much of a residual left over that would have much of an effect.

    You also haven’t really answered my question as to whether or not you could explain a multi-decade, unforced, natural warming cycle.

  22. clivebest says:

    ATTP,

    If you use H3 you actually get a slightly negative slope. Regarding H4 under-sampling at the poles – I find that is not the case. The under-sampling is concentrated in Africa and South America which have a vastly larger area. There is a simple (lat,lon) bias involved with over-sampling the poles because the number of cells on their 5×5 degree grid increase with latitude. see: here. To be logical one should also require more samples from Antarctica to compensate.

    Your reply shows a rather model centric view of the world, so let me ask you a question.
    – Is aerosol forcing actually derived from real atmospheric measurements say after earthquakes or is it instead estimated so that the models can agree with hindcasts to observed data ?

    I would put it the other way round. There is observational evidence of a 60 year cycle in global temperature data. A separate issue is the challenge to explain it. There are actually some proposals as to what may be the natural forcing. For example the 18.6 year precession of the moon’s orbit changes the latitudinal positioning of tidal bulges which increase tidal forces in northern/southern oceans especially when coincident with earth’s perihelion. So there are natural effects which may or may not be relevant.

  23. clivebest says:

    sorry forgot to close the hyperlink ! whoops!

  24. clivebest,

    If you use H3 you actually get a slightly negative slope.

    So? H4 replaces H3 and it may be that Cowtan & Way replaces H4. Also GISS.

    Regarding H4 under-sampling at the poles – I find that is not the case. The under-sampling is concentrated in Africa and South America which have a vastly larger area.

    But this isn’t about undersampling as such. it’s about polar amplification. If you’ve found that the result in Cowtan & Way is wrong, I think you should publish it.

    Your reply shows a rather model centric view of the world

    I don’t think that’s true. I think I have a physics centric view of the world – but it’s not really for me to judge.

    so let me ask you a question.
    – Is aerosol forcing actually derived from real atmospheric measurements say after earthquakes or is it instead estimated so that the models can agree with hindcasts to observed data ?

    As I understand it the aerosol forcing has been determined both from satellite measurements (which are obviously recent) and from models. I can’t speak to the intent behind the models, though. There are some who sometimes comment here (Karsten, PaulS) who understand the details of aerosol forcing estimates better than I do. Suggesting that the intent of their work is simply to produce a fit to past data, however, may not go down terribly well.

    I would put it the other way round. There is observational evidence of a 60 year cycle in global temperature data. A separate issue is the challenge to explain it. There are actually some proposals as to what may be the natural forcing. For example the 18.6 year precession of the moon’s orbit changes the latitudinal positioning of tidal bulges which increase tidal forces in northern/southern oceans especially when coincident with earth’s perihelion. So there are natural effects which may or may not be relevant.

    Okay, and I’m making the point that simply finding a signal in some data is what some called mathturbation. If all you’ve done is find such a signal then it is highly likely that some of that signal is forced (both naturally and anthropogenically). Therefore you haven’t really found a signature of internal variability. Therefore, when you combine this with future estimates of warming due to anthropogenic emissions, you’re likely double counting to a certain extent.

    There’s a similar issue with the AMO (which Michael Mann tried to work on recently). The AMO is simply defined as a detrended sea surface temperature. Since the anthropogenic influence may not be purely linear, the AMO is likely not entirely non-anthropogenic and likely still has a forced component.

  25. clivebest,
    You also still haven’t answered my questions as to whether or not there called be a multi-decade, unforced warming cycle (with a magnitude of about 0.15 degrees) if there was no change in radiative forcing over the relevant time interval (i.e., in the absence of anthropogenic emissions, for example).

  26. clivebest says:

    One obvious contender for natural changes in radiative forcing are small changes in global cloud cover. Here is a paper I wrote on that subject.

    Do clouds control climate?

  27. clivebest,
    Except I’m specifically asking about unforced natural variability. Your “cloud mechanism” is still a natural forcing mechanism. Do I take it that you agree that a multi-decade unforced (i.e., no change in radiative forcing) warming/cooling process is physically implausible. I may have got my terminology slightly wrong, though.

    Also, the majority of scientists who work in the field currently estimate that clouds produce a very small positive forcing. I haven’t had a chance to work through your link, but I would encourage you to try and get it published.

    An issue, though, with a strongly negative cloud feedback is that it then becomes difficult to explain past climate variability.

  28. As far as I can see, present science doesn’t tell, how much multidecadal oscillations contribute to the observed warming. It doesn’t tell in either direction.

    What scientists have tried to determine are TCR and ECS. For this discussion TCR is more relevant. AR5 says on that

    With high confidence the transient climate response (TCR) is positive, likely in the range 1°C to 2.5ºC and extremely unlikely greater than 3°C, based on observed climate change and climate models

    The lower limit of that attributes about half of the warming since 1950s to something else than GHGs, the upper limit tells that other factors have had an opposite effect.

    Not everybody is fully happy with what IPCC tells, but I have not found any of the arguments against the IPCC range convincing. The additional arguments seem also to balance each other to a reasonable degree.

  29. Pekka,

    As far as I can see, present science doesn’t tell, how much multidecadal oscillations contribute to the observed warming. It doesn’t tell in either direction.

    Yes, this is possibly true, but there is a difference between multi-decade oscillations influencing the warming trend and multi-decade oscillations that would produce warming/cooling in the absence of a background trend (i.e., in the absence of any change in radiative forcing).

    The lower limit of that attributes about half of the warming since 1950s to something else than GHGs, the upper limit tells that other factors have had an opposite effect.

    I don’t think is strictly correct. I think the IPCC statement is that there is a 95-100% chance that more than 50% of the warming since 1950 was anthropogenic. However, if you actually look at the attribution figure it illustrates that anthropogenic influence have a 95% chance of providing between about 85% and 115% of the warming since 1950. I think the chance that it contributed as little as 51% is extremely low.

  30. Anders,
    TCR of 1°C would imply that almost half of warming since 1950s is something else than due to added GHGs, as 100% corresponds to TCR close to 2°C in absence of any other factors.

  31. Pekka,
    Okay, I see what you mean. In that sense, yes I agree. However, I do think my point about the attribution figure is still correct. It may be an example of a situation where what the IPCC presents is not completely internally consistent. Complex document and process 🙂

  32. Pekka,
    Actually I’m still not sure that your analysis is quite right. The lower TCR values are largely I think because of the possibility of a low aerosol forcing and hence a nigh net anthropogenic forcing. Therefore, I think it is still possible for much more than 50% of the warming since 1950 to have been anthropogenic even if the TCR is 1 degree. I’m trying to do some painting so haven’t had a chance to check properly though 🙂

  33. Anders,

    Check my wording. I wrote that by purpose in that way.

    Proper skepticism is two-sided, without bias in the direction you prefer to see the weaknesses in a statement. Bias towards one-sided skepticism is not limited to the “climate skeptics”.

  34. Pekka,

    Proper skepticism is two-sided, without bias in the direction you prefer to see the weaknesses in a statement. Bias towards one-sided skepticism is not limited to the “climate skeptics”.

    Are you having a bad day or something? I’d really rather not have another comment thread where you do your utmost to annoy and insult everyone else. It’s fun once in a while, but maybe you could save it for special occasions.

    You said,

    TCR of 1°C would imply that almost half of warming since 1950s is something else than due to added GHGs, as 100% corresponds to TCR close to 2°C in absence of any other factors.

    I’m suggesting that this isn’t obviously true. That even a TCR of 1 degree could explain most of the warming since 1950. If I’m wrong, feel free to explain why. If I’ve missed some subtlety in what you said, feel free to explain it. Accusing me of a lack of skepticism is not an explanation.

  35. clivebest says:

    ATTP,

    I agree that a natural multi-decade warming/cooling cycle of ~ 0.15C requires external radiative forcing. A likely contender for that are naturally occurring changes in cloud clover.

    You say “Also, the majority of scientists who work in the field currently estimate that clouds produce a very small positive forcing”. That is not true. The net radiative effect of clouds compared to clear skies as measured by CERES is a net radiative cooling of -22W/m2 – see : Richard P. Allan, Combining satellite data and models to estimate cloud radiative effects at the surface and in the atmosphere, RMetS Meteorol. Appl. 18: 324–333, 2011

    What is true is that the majority estimate that the net effect of cloud feedbacks to anthropogenic warming is very slightly positive, but this is a different issue. In other words if there are natural causes for changes to global cloud cover, then this will change radiative forcing.

  36. clivebest says:

    P.S. Please get back to the painting and never take any of my remarks in any way personally ! I am going out now as well. cheers !

  37. clivebest,

    That is not true. The net radiative effect of clouds compared to clear skies as measured by CERES is a net radiative cooling of -22W/m2 – see : Richard P. Allan, Combining satellite data and models to estimate cloud radiative effects at the surface and in the atmosphere, RMetS Meteorol. Appl. 18: 324–333, 2011

    Okay, maybe I wasn’t sufficiently clear. The current position is that clouds have produced a very small net positive change in forcing (since 1750, I think), That’s very different to what you refer ro above. Yes, the net radiative effect of clouds is cooling, but what matters is how this has changed, not the net effect. I’ve had a quick look through the IPCC documents but can’t find the relevent section, but – IIRC – the current position is that clouds produce a small net positive change in radiative forcing.

  38. Anders,

    Just calculate the ratio of the temperature change to the change in GHG forcing over that period. The result is a well defined number close to 2°C for doubling of CO2 concentration, a little below according to a calculation I made soon after AR5 was made public.

    I have defined the setup in the way that aerosol forcing belongs to the other factors. Including aerosol forcing would make the result much less well defined.

  39. Pekka,

    I have defined the setup in the way that aerosol forcing belongs to the other factors. Including aerosol forcing would make the result much less well defined.

    Okay, if only you’d said that at the beginning. My entire point is based on the uncertainty in the aerosol forcing. Do you agree, therefore, that – given the uncertainty in the aerosol forcing – it is possible for most of the warming since 1950 to be anthropogenic even if the TCR is 1 degree?

  40. if only you’d said that at the beginning

    I did.

  41. Pekka,

    TCR of 1°C would imply that almost half of warming since 1950s is something else than due to added GHGs, as 100% corresponds to TCR close to 2°C in absence of any other factors.

    Not as far as I can see and if “something else than due to added GHGs” meant “aerosol forcings belongs to the other factors” then it wasn’t particularly easy to work that out. Just out of interest, do you ever say “fair enough, I could have made that clearer”?

  42. Pekka,
    Similarly, my first foray into this discussion said

    The lower TCR values are largely I think because of the possibility of a low aerosol forcing and hence a nigh net anthropogenic forcing.

    Given that I explicitly mentioned aerosol forcings here, it would have been straightforward for you to point out that you were assuming aerosols belonged to other factors, rather than accusing me of lacking skepticism, or would that have spoiled all your fun?

  43. Anders,

    Aerosols are not gases. I thought that this was clear enough. Further I thought that my next message helped in noticing that, if it wasn’t noticed before.

  44. Yes, I know aerosols are not gases but the previous discussion had been about non-anthropogenic influences so had assumed (wrongly it seems) that you were using GHG are short-hand for anthropogenic. If you think your message after that “helped” then you and I understand the term “helped” in a very different way. “Helped” to annoy me, maybe. “Helped” me to understand what you meant, not a chance and how you can possibly think that it would is beyond me.

    I’m also now rather confused by what you’re suggesting. If you’re only referring to WMGHGs then they have a change in radiative forcing since 1950 of something close to 3Wm-2 – or am I wrong about this? A TCR of 1 degree would then imply that this could still provide almost all the warming since 1950, or have you defined the TCR as something other than the change in surface temperature when the change in radiative forcing is 3.7Wm-2?

  45. According to AR5 the total forcing of WMGHGs is about 3 W/m^2 relative to 1750, not relative to 1950s. Almost half of the increase in CH4 predates 1960, for CO2 and N2O the share is closer to one third. In relative terms the share is still a little higher.

  46. Okay, so what is the actual change in radiative forging since 1950 due to WMGHGs.

  47. I referred to my calculation of last September. The purpose of that calculation was to show that the IPCC statement that more than 50% of the warming since 1950s is extremely likely due to AGW can easily be justified by specific information presented in the full report. Contrary claims had been made by many people including Judith Curry (one place where I presented my comment was Climate Etc). I did the calculation at a level I considered sufficient for that purpose.

    Here I made my comment to emphasize that the issue being discussed is closely related to estimating TCR and that we can find in the literature much more scientific discussion of TCR than estimates about the multidecadal variability. It’s also clear from the literature that the lacking understanding of natural variability is one important contributor to the uncertainty of estimates of TCR.

  48. Pekka,
    I agree with all of that. My only point – which I think you have still to acknowledge (or dispute) – is that it is still possible that a TCR of 1 degree could still be consistent with AGW providing most of the warming since 1950.

    I also think that the term natural variability is either mis-used, mis-understood, or ill-defined, but I plan to sit outside, read my book and enjoy the sunshine, rather than start a lengthy debate on the topic.

  49. Anders,
    I do agree that TCR of 1°C is consistent with AGW more than 50% of warming since 1950s, but It’s also consistent with the opposite, when all contributing factors are taken into account. Being consistent is such a flexible requirement that both are well within the limits.

    Actually I have earlier mentioned 0.9°C as the value of TCR that is closest to the 50% threshold according to my estimate, but the calculations behind that judgment are not accurate enough to differentiate between 1.0 and 0.9.

  50. Pekka,

    I do agree that TCR of 1°C is consistent with AGW more than 50% of warming since 1950s, but It’s also consistent with the opposite, when all contributing factors are taken into account.

    Indeed, and it took how long to get to this point?

  51. BBD says:

    A climate system exhibiting considerable natural variability is a climate system fairly sensitive to radiative perturbation. So no let-out clauses on sensitivity are engaged by pointing to the former.

  52. BBD,
    Yes, there is that.

  53. BBD says:

    It’s a bugger, this physics stuff. So inflexible. It’ll never make a go of a career in politics.

  54. Magma says:

    @ Dumb Scientist and ATTP: regarding the supraluminal neutrinos, no question. At the time, like many others, I had predicted it would turn out to be experimental error of one sort or another based on the complexity of the instrumentation, the neutrino burst from SN1987a, and of course much of modern physics, tried and tested a thousand different ways. So basically a straightforward Bayesian analysis… but it was interesting to watch how it played out with CERN and in the media.

    I think the OPERA group handled it reasonably well, all in all.

  55. About the natural variability, we have two important factors that appear separable from the global temperature data. The volcanic aerosols is straightforward and understandably very unpredictable WRT timing of the events. On the other hand, the ENSO factor looks complicated but may actually be much more predictable than previously assumed.

    I have been looking at the dynamics of ENSO and have been able to pin it down to a non-linear interaction with the QBO — quasi-biennial oscillations.
    http://contextearth.com/2014/05/27/the-soim-differential-equation/

    What makes this very promising is that the QBO is more periodic than the quasi prefix would indicate. The fact that a regular forcing oscillation can create a predictably erratic ENSO time-series is really a stake in the heart of the deniers that are pinning their hopes on natural variability as a crutch.

  56. This is too funny, a comment from a concern troll over at CE , a guy I like to refer to as Egg FOO Young:


    David Young | June 8, 2014 at 5:01 pm |

    In fairness to Pekka, at ATTP, the trolls have become a real problem and barrier to open discussion. I suspect his comments on this were aimed at them. Does anyone remember our old friend, BBD, and that he was completely an impediment rather than an enlightening influence. I think Judith probably and correctly banned him. At ATTP, he is the chief alter boy, even having suggesting the blog name.

    I tried using the descriptor “concern troll” in a CE comment, but it got deleted.

  57. JCH says:

    BBD was easily one of best at CE. He does not know if BBD was banned, and he says it anyway? What’s that called?

  58. clivebest says:

    BBD: “A climate system exhibiting considerable natural variability is a climate system fairly sensitive to radiative perturbation. So no let-out clauses on sensitivity are engaged by pointing to the former.”

    That’s true but I don’t see the relevance. The climate also seems very sensitive to minor changes in the earth’s orbital parameters, yet that is still not properly understood either. The net radiative perturbation change with orbital eccentricity is tiny but still seems able to trigger an interglacial for the last 800,000 years.

  59. clivebest,
    I think the point that BBD is making is that if it is sensitive then that tells us something of how it will respond to increasing anthropogenic forcings.

  60. clivebest says:

    ATTP,
    Surely that should read is responding. I hope climate science is not becoming like the predictions of Nostradamus 😉

  61. It is impossible to get banned at CE, at least in my experience. It’s largely climate science outsiders on one side vs climate science outsiders on the other side, no holds barred. The occasional snipping of comments gives the illusion that there is some sort of control.

    I’m not looking for a new England, just a place to engage in new thinking.

  62. Ian Forrester says:

    Quote from David Young at CE:

    At ATTP, he is the chief alter boy

    Inquiring minds want to know, what was he before he was “‘altered”?

  63. BBD says:

    I stopped bothering at JCs because she moderated against me for being correct while allowing people like Dave Springer to spew abuse unchecked. That told me all I need to know about where JC stands on the climate “debate”.

  64. BBD says:

    It’s amazing how thin-skinned some of the nastier ClimateBallers actually are, isn’t it? Poor David Young is still apparently suffering PTSD.

  65. BBD says:

    clivebest

    The fact that a mere seasonal and spatial reorganisation of TSI by orbital dynamics can trigger deglaciations *and* initiate the slide back into glacials is further, redundant evidence that the climate system is fairly sensitive to radiative perturbation.

  66. Michael 2 says:

    A thoughtful article — meaning, it makes me think — and well written.

    Science works well when it is free to work.

    If hundreds of billions of dollars hinged on one outcome of BICEP but not the other, I suspect that freedom of movement and willingness to challenge the result would be “less”. In communist nations, science serves the state; I suggest it isn’t all that different here.

    I am reminded also of the extreme excitement surrounding cold fusion; Pons and Fleishman if I remember right. No one could replicate their experiment and I think the whole public awareness of, and interest in, cold fusion has dwindled.

    But you see, both of those things (BICEP2, cold fusion) are amenable to replication and experiment. Global Circulation Models are not amenable to replication and experiment.

  67. Pingback: Making Science Public » Big bang, inflation, gravitational waves: A journey through metaphorical space

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