Bishop Hill Thoughts on aerosols
Aug 7, 2015 Climate: Models I've been reading a bit about aerosols in recent days. As many BH readers will know, these are one of the great uncertainties in the Earth's climate and so they crop up all the time.
This interest was provoked in part by a conversation I was having with Ed Hawkins about his new paper. I had invoked Bjorn Stevens' study from which it is possible to infer a value of -0.5 Wm-2 for the overall effect of aerosols, around half of the IPCC's best estimate of -0.9 Wm-2. This of course would imply that climate sensitivity would have to be much less than the IPCC suggests it is.
Ed suggested that I was cherrypicking a single paper that gave me the answer I wanted, and I wondered what the range of estimates was. Here is Figure 7.19 from the Fifth Assessment Report (click for a slightly larger version), which shows the observational estimates from satellite measurements and the various GCM estimates ("with physics in") and how these are combined using "expert judgement" to give the best estimate of -0.9 Wm-2.
;)
We are interested in the two grey boxes on the right, which show the total of the direct and indirect effects of aerosols. In the top box, the markers with black borders are the subset selected for the expert judgement. The squares are the satellite estimates, and as you can see they are all packed into a corner, with none of them below -1 Wm-2 and some considerably closer to zero. The GCM estimates - the diamonds and stars - are all over the place, which is not surprising when you realise that the effect of aerosols is intimately bound up with clouds, which are little understood and cannot be properly modelled in a GCM.
So it is similarly unsurprising that by the time you get to the expert judgement subsets in the lower panel, there is a startling lack of overlap between observations and GCMs.
This kind of thing might have led more traditionally minded scientists to question the validity of the GCMs - the observations trumping the hypotheses as in other fields of scientific endeavour. But this being the IPCC, we get instead an "expert judgement" combining the observations with the hypotheses, in a process that seems to neatly mirror what happens on the climate sensitivity side of the equation.
This is particularly worrying in the light of Bjorn Stevens' thinking on these questions. Stevens' headline finding was that aerosol forcing values more negative than -1 Wm-2 were implausible. If he is correct, the majority of the GCM estimates of aerosol forcing would have to be junked. Stevens had several lines of reasoning for this conclusion, but one of his observations was that the temperature history of the past was quite hard to reproduce with a strong aerosol forcing. So in the first decades of the twentieth century, when there were lots of aerosols around but relatively little greenhouse gas forcing, we should not have seen any warming. But in fact that is just what we saw, with the planet warming from 1900 to 1940. In similar vein aerosols, being shortlived, should mainly effect the Northern Hemisphere where they are produced, particularly in the early part of the temperature record when the effect would be most pronounced. Again, this is not what is seen in practice.
Now undoubtedly there are issues with the satellite observations - with several adjustments required to reach a final figure. I haven't yet investigated the uncertainty bounds involved in these studies, which might, if very wide, provide some justification for what the IPCC has done. But with the satellite best estimates so tightly grouped one can't help but pick up something of a stench from Chapter 7 of the Fifth Assessment Report.
Reader Comments (59)
Typo:
"But if fact that is just what we saw, with the planet warming from 1900 to 1940."
Should be,
"But in fact that is just what we saw, with the planet warming from 1900 to 1940.".
The squares are the satellite estimates, and as you can see they are all packed into a corner, with none of them below -1 Wm-2 and some considerably lower. ?
Bloke,
"lower"...the author apparently means "closer to zero", meaning a lower magnitude. English is a little ambiguous in the situation, eh?
Roughly 97% of organ grinders have told their climate scientists to rubbish the ridiculous idea that climate sensitivity is un-catastrophic.
Bloke
I always have trouble with that sort of thing just as I have always had difficulty wrapping my mind round mathematical notation. I mean is there a difference between W/M2 and W/M-2 and if so what is it?
And does no-one else know that in Windows Alt+0176 gives you ° and Alt+0178 is ²?
Andrew -- Question: Why was there relatively little greenhouse gas forcing in the early years of the 20th century? CO2 (sorry, I can't find a subscript!) was at about ¾ the level it is now and I'm sure water vapour wasn't materially different, was it?
Does any understanding of any aerosols mask the stench from Mann's rotting Hockey Stick?
Isn't this upside-down?
I thought Stevens expected number closer to 0 than -1, as in the estimate of -0.5, and values below -1 (i.e. more negative) were implausible. The satellites values are less negative, so how does this mean they need to be 'junked'?
I agree with the previous comments. The "lower" should be changed to "smaller" if you are talking magnitudes. Absolutely, it should be "higher" than the opinions of self interest.
Thanks Andrew
See also this comment of Stevens on the Carslaw paper:
http://www.mpimet.mpg.de/nc/en/communication/news/single-news/article/aerosol-effects-on-climate-uncertain-then-irrelevant-now.html
This graph http://www.nature.com/nature/journal/v503/n7474/images/503047a-f1.jpg is enlightening, being almost flat after 1950. This seems to be how at least Stevens' thinking is evolving. If aerosols are "irrelevant" after 1950, they can't explain the "pause" between 1945-1975 either, let alone of course the current pause.
Interesting times
Marcel
So here are the Nasa GISS forcings showing increasing direct and indirect aerosol since 1900:
http://data.giss.nasa.gov/modelforce/RadF.gif
While Stevens in his Nature comment - following Carslaw - shows this figure:
http://www.nature.com/nature/journal/v503/n7474/images/503047a-f1.jpg
suggesting aerosols had an effect when the atmosphere was still "pristine" but after 1900 the extra aerosols had little effect.
Ed Hawkins used GISS forcings and it would be interesting to see what would happen if he used "Stevens' forcings".
Marcel
"If he is correct, the majority of the satellite estimates of aerosol forcing would have to be junked." I believe it should be "majority of non-satellite estimates" here.
[Thanks - fixed]
"Now undoubtedly there are issues with the satellite observations"
If you can't trust a satellite, who can you trust, as my old mother used to say ?
This is Batman meets Donald Trump. Comic book science.
Deleted as O/T. BH
I am not doubting the validity of the detailed, scientific arguments, but you can't use that level of uncertainty and disagreement to forecast the future of the climate.
97% of Climate Scientists are aerosols....:o)
http://www.bing.com/videos/search?q=not+the+nine+oclcock+news+aerosols&FORM=HDRSC3#view=detail&mid=EF2F069324F0166DD030EF2F069324F0166DD030
Discounting the hiding heat theory, sensitivity is low or we have started a natural cycle cooling trend which high sensitivity is masking (exactly). Therefore, if you are a warmist, the optimum quantity of CO2 emissions is that which we are currently producing if your theory is correct. On the other hand, if you are a sceptic then low sensitivity fits the observations.
So what is the panic and why no celebrations?
Mike Jackson
Not really What I meant is that I am not questioning the basic equations used. I am however sceptical about everything that can be 'interpreted'.
@NCC
now that was funny :-)
Mike Jackson:
On your question about the units:
There are a variety of ways units such as "watts per square meter" can be abbreviated, and with different levels of formality.
First, on superscripts, I for one, and I know many others, have long since given up on trying to create subscripts or superscripts in blog posts, given the variety of "source" computers (I use Windows, Macs, and Linux myself) and of target blog software. Personally, I use the "^" character in these cases to indicate that what follows is a superscript. But it is typically obvious from context even without that.
As to this particular example, the Bish used the formal style found in technical papers of Wm-2 (with -2 as superscript). Note that there is no "/" here. A less formal way of expressing the same units, and one that is probably clearer to less technical people, is W/m2 (with the 2 as superscript).
The key point is that the m^-2 unit is equivalent to 1/m^2 unit, just as the 10^-2 value is equivalent to 1/(10^2). (Both equal 0.01.)
As to your final question, virtually all measurements/estimates of CO2 concentrations in the atmosphere show a much slower rate of increase in the first part of the 20th century than later. The rate of increase went up several times after WW2. So the interesting question is why there was a significant temperature increase from 1910-1940 when CO2 levels did not increase much, and flat to decreasing temperatures from 1940-1975 when CO2 levels were increasing rapidly.
The highly negative aerosol forcing values in most global climate models (averaging ~ -1.2 W/m2 for CMIP5 models) are mainly due to the indirect 'cloud albedo' effect: aerosols make clouds more reflective. A key point is that this indirect forcing has a logarithmic relationship to total aerosol concentration. So the higher the natural background level of aerosols, the smaller the change in indirect forcing resulting from adding any given level of anthropogenic aerosol emissions. And it seems that the level of natural aerosols that produce the relevant 'cloud condensation nuclei' is much high than generally assumed up till now. That is probably the main reason why anthropogenic aerosol forcing is (it seems) substantially too strong in most GCMs.
Like aerosols clouds are also incorporated as a fudge factor, used to make the result you wish for.
It is amazing that so many models is used, and they all give very different results. How can that be when they are all based on the same basic physics as we are told.
Some excuses are lack of knowledge of the begining state, but what should that matter after ten years. It is not even close to predict the weather more than a week or two.
Now undoubtedly there are issues with the satellite observations - with several adjustments required to reach a final figure
Isn't that the point - the moment they start making adjustments the truth goes out the window.
If the engineers didn't build the instruments correctly then the satellites are useless and the readings worthless. The thing is I have more faith in the engineers than I do in climate scientists that make 'value judgements' as to what the readings should be.
aTTP still binds himself to IPCC reports as though they are sacred tablets of stone.
Fortunately for us all, sea level is not rising in accordance with IPCC reports.
@Svend Ferdinandsen,
I'd find it hard to disagree with you that both aerosols and clouds are the fudge-factors that can be brought into play whenever Climate Models are brought into question.
All beliefs, the shakier they are, the more obfuscatory conflations conferred by fudge-factors are necessitated to maintain the illusion of absolute (>=0.97) certainty.
Twenty-first century climate science still has many years to run before it slips into the historic irrelevant obscurity enjoyed by Norse and Grecian mythology (to mention but two) but its malignant, lingering political, societal and financial implications will continue to ruin many an individuals existence before it's finally consigned to the dustbin marked 'FUBAR' with the legend 'WTF' in bold and doubly-underlined stamped beneath it.
Deleting Aerosol Forcing, and inserting Approximation Factor, makes more sense of the climate science
'Fortunately for us all, sea level is not rising in accordance with IPCC reports'
Give a sucker a break, GC.
Both' warmists' and large number of 'sceptics' agree that strapping a pair of narrow, steel bladed heels to one's shoes and expecting to walk on that body of water called the Thames in a broadly horizontal direction for any meaningful stretch of time has a much lower expectation for a successful outcome than would have been the case a century and a half ago.
Yes, warmistadors and scepticialists, without mutually agreeing about how much their lives have been extended and enriched by fossil-fuels, do share some particles of empiricism even if only because it's much trickier to photo-shop a 19th Century picture than a 20th Century temperature log..
If climate ideology was Krikkit, the former would be all-out shortly after one of them actually looked out of the pavilion window and noted that someone at the Met-office had screwed up, yet again.
Give them, at least for pities sake GC, that sea-levels are still rising. Resist the temptation to point out that the bible of Climate Wisden records that the rate of rise has been unchanged for centuries - these guys need a break, mate.
There's no point in having just one team on the field. We need two even if it's just to beat the a** of them every time.
That's not Krikkit, GC, play the game!
RoyFOMR, the sea level is rising, just, but not in accordance with IPCC reports, or ChiefWizard Hansen's wailing.
'Forcing' the climate and evidence to match the models, really is Voodoo Science.
I think the Parisian climate jamboree should include some Morris Dancers, to appease Gaia. On the basis of evidence gathered, there is no reason why this should not work, and Slartibartfast's fjord design will be preserved.
Very informative
Of course, all this is on the assumption that there actually IS a “greenhouse effect”, and there actually IS “climate sensitivity” for aerosols to affect. It might be that we are talking about modern-day equivalent of gravity waves or phlogiston or how many angels can dance on the head of a pin.
Troll comment and follow-up removed
Curt
Many thanks for that explanation which does in fact confirm what I believed. There is a danger in using the '-' sign in place of [^] because dumbos like me are likely to confuse ^2 and ^-2 since we don't necessarily know that one of them probably doesn't make sense in context. It's a blind spot of mine, I'm afraid!
@Nic Lewis: the claim that aerosols, by reducing mean droplet size, make clouds more reflective, is only correct for clouds with a narrow droplet size distribution AND maximum hemispherical albedo is 0.5; standard Mie Theory.
You easily show that the Sagan-origin aerosol optical physics, introduced to Atmospheric Science by Lacis and Hansen in 1974 without the absorption terms, is wrong by simple observation. As cloud droplets coarsen prior to raining, albedo increases, as proved by undersides darkening. You have to observe this for a few hours, but it's the real effect and I have see it on numerous occasions.
In 2010 G L Stephens observed from satellite data that low level clouds with 'drizzle' had on average 0.1 higher albedo than the Sagan theory predicted. The second process is a form of percolation physics which I submitted for publication but is impossible to place because it shows the real sign of the AIE is the opposite of that claimed by the IPCC models. Stephens apparently can't publish his observations either. This second process explains Milankovitch amplification and recent AGW; aerosols from Asian industrialisation reducing cloud albedo. Real CO2-AGW is near zero.
But isn't it the case that we have no direct observational measurements for aerosols prior to about 1970?
Everything is just an estimate, often an estimate based upon a model projection, and we all know the value of that!
We know a little about past volcanic eruptions, but the nature of the aerosols ejected, the height etc are simply not known and there appears to be a significant difference depending on a number of different variables including latitude.
It is just reading tea leaves,
Curt
"So the interesting question is why there was a significant temperature increase from 1910-1940 when CO2 levels did not increase much, and flat to decreasing temperatures from 1940-1975 when CO2 levels were increasing rapidly."
Thanks. I saw that at the very beginning of studying this. It's sufficient in itself to make any honest person a sceptic. Today we have another massive anomaly.
Conclusion: It is highly that human beings do not significantly affect global temperature.
Mike Jackson.
Mike, I always use the notation W/m^2 which means the same as Wm-2 but appears to be a little old-fashioned nowadays.
The edits made to the original post make talking point much clearer. Thank you.
In a calculation certainly use Wm-2. That's notation. In a sentence you need to use W/m^2 because that reads as Watts per square metre, it doesn't require the lay reader to pause and translate the term. Or write it out in full and remove all doubt.
geronimo/rhoda
Or, if you have the facility - W/m², which everyone understands. Don't they?
Curt/esmiff
I didn't come back on the early 20th century stuff because the whole thing is becoming increasingly tedious and it appears we can argue from the facts until we are blue in the face.
Nobody denies that there was a moderate warming at some time post-mid 19th century (ending ~1880) and again from ~1910-1940 and again ~1970 (1975 maybe)-2000.
In order to have their government-funded cake the Climateers have constructed a house of cards which claims that the first two periods were "nuffink to do wiv me, guv" as far as CO2 was concerned even though during the second of those two periods atmospheric CO2 was on the increase (as I'm sure it was in the first but without the evidence) but all of a sudden when the eco-activists (like Ehrlich and Hansen and Strong and the useful idiots in the NGOs) need some anthropogenic "peg" to hang their anti-humanity hat on it's all down to CO2.
Their argument has more holes in it than a piece of prime Leerdammer but they are so slippery with it no-one seems able to get a grip on them. They make eels look leathery!
“... in the first decades of the twentieth century, when there were lots of aerosols around but relatively little greenhouse gas forcing …”.
=====================
Particularly so since most of the temperature data was collected from growing industrial and population centres.
I am not sure where all this aerosol talk will lead. To me they are too irregular as well as weak to control any climate features. There are of course situations where the greenhouse warming hypothesis does not explain what happens to global temperature. Probably in most if not all cases.
Secondly, people should pay attention to what the temperature curve actually tells us. To say that the planet is warming from 1900 to 1940 is sloppy and non-sensical. The planet is not warming from 1900 to 1940 for the simple reason that for the first ten years it was cooling, not warming. Warming started suddenly and lasted thirty years. And then it came to a sudden end in 1940 with the start of the World War Two cold spell. Despite some temperature curves showing warming in the forties global temperature dropped precipitously in early 1940. The battle of Suomissalmi in the Finnish winter war was fought in January1940 at minus forty degrees Celsius and one meter of snow. The Russians had sent ten divisions with tanks to cut Finland in half. The Finns destroyed their tanks with Molotov cocktails (a Finnish invention) and chased back the infantry who lost 9000 men in this ill-fated battle. The cold lasted throughout the war and the postwar period was just recovery from this huge cooling. Global temperature did not reach the level of 1940 again until 1980 or so.
We are propagandized today to think that greenhouse warming has been going on since the the mid-1880-s when the industrial age began. That is quite impossible because greenhouse warming can not be the cause of the early century warming. If you subscribe to the greenhouse belief you should know that in order to start any greenhouse warming from scratch you must add carbon dioxide to the atmosphere at the same time. It is easy to find out what CO2 has been doing from the Keeling curve and its extension. If you have bothered to look you should know by now that there was no addition of carbon dioxide to air coincident with the start of that warming. Hence, this warming half century after the start of the industrial age cannot possibly be greenhouse warming. This observation immediately invalidates the claim of warming since the start of the industrial age.
Related question is why did it stop in 1940. To stop greenhouse warming you must somehow remove all carbon dioxide molecules from the air. This never happens in nature, hence the reason this warming stopped cannot be in any way related to the greenhouse effect. You may have noticed that IPCC reports recently claim that human-caused global warming becomes noticeable about 1950. Nothing further is said about warming from the start of the industrial age from which I conclude that they know now that this claim is untenable and needs to be forgotten. If the fifties is all they dare claim for start of warming this represents going back one hundred years from their original claim. Someone should ask them a direct question if opportunity becomes available.
Arno Arrak: am I right in my reading of your comment that you, too, doubt the greenhouse effect?
Perhaps we should accept CO2 as being a greenhouse gas, but only because it is used in greenhouses to stimulate plant growth and increase crop production. It could be argued that the injection of CO2 into greenhouses could give a realistic test of its effect as a “greenhouse gas”: are the temperatures in a CO2-enriched greenhouse noticeably higher than those with a standard (could one call it “control”?) atmosphere? Surely, the implications of the effects of CO2 should be that, with the gas “trapping” more heat within the atmosphere of the greenhouse, then there is less heat to impinge upon the glass, thus less heat is actually being lost, so the temperatures within a CO2-enriched greenhouse should be higher. Or is that too simple a test of the principle?
The trouble is that your average un-informed person/politician thinks they have been told by "scientists" that CO2 acts as a sort of magic blanket high above us that "traps" heat. Thus your greenhouse experiment would not be perceived as relevant. So much fuzzy thinking about!
Tony.
RR
Water vapour, carbon dioxide etc make a non-radiant atmosphere into a radiant one. You have to accept that as indisputable fact. That change is an effect on the distribution of the received energy from the sun before it leaves for space. To argue with that would be ridiculous. The change in distribution of energy results in changes in temperatures via various mechanisms and one of those changes has been named Greenhouse Effect. It does exist. You can't wish it not to be so.
Does additional carbon dioxide increase the GE? Climate science says it does, significantly.
Is there a secondary amplification effect from that increase? Climate science says there is, dangerously.
There are coherent arguments against both those statements. But not about the existence of GE.
Without looking this up, isn't the issue the height at which radiation is absorbed then re-radiated back to earth that causes differences in surface temperature.:?
Aug 8, 2015 at 4:03 PM | Registered CommenterMike Jackson
and again ~1970 (1975 maybe)-2000.
//////////////////////////////////////
It may have warmed throughout the 1970s, or from 1975 to 1979, but was there any warming post 1979? This certainly appears moot to me.
1. The satellite data shows no significant warming trend between 1979 and the onset of the Super El Nino of 1998.
2. Michael Mann/Briffa's tree rings showed no warming between 1970 to early 1990 (and hence the reason that Mann did not use that data in his infamous hockey stick plot).
There is a strong case that the only warming that took place post 1979 is a one off and isolated release of heat from the oceans to the atmosphere creating a step change in temperature in response to the 1998 Super El Nino.
If there was earlier warming in the land based thermometer record than there is a strong case that the 'warming' is simply an artefact of data handling and corruption/pollution by station drop out, inappropriate adjustments/homogenisation , poorly sited stations and UHI.
richard verney
Yes, and numerous examples of older temperature data being reduced in value and newer increased. UHI blindness too.
richard verney
I was merely going along with the received wisdom that the late 20th century warming was deemed to have started circa 1975 thus continuing the approximately 30-year cycles of warm (-1880), cool (-1910), warm (-1940), cool/stasis (-1970), warm (-2000). All dates approximate.
This was what we were being told with the added information that "this time, it's different!". Along with "we can't account for the warming unless we include CO2" For which read "we want it to be CO2 so we haven't bothered looking any further."
I'm inclined to agree with what you write but that wasn't really my point. Perhaps "nobody denies" was over-stating it a bit!
A few comments deserve answers. First, Radical Rodent, whoever you might be. Yes, I, too, doubt the greenhouse effect. It should be self-evident from the fact that during the hiatus carbon dioxide goes up but temperature stays the same. For the last 18 years the Arrhenius greenhouse theory has been predicting warming and getting nothing. A scientific therory that makes wrong predictions belongs in the waste basket of history, and that is where the Arrhenius theory belongs. But IPCC persistently keeps using a defective theory. Just ignore them, they are not real scientists anyway. Belief in a non-working greenhouse theory makes them pseudo-scientists.
And then there is the mysterious sst. He opines that we must accept as indisputable fact that water vapor, carbon dioxide etc make a non-radiant atmosphere into a radiant one. That is a very strange opinion considering that water vapor and carbon dioxide are normal constituents of the atmosphere. I personally have never noticed that atmospheric radiation he speaks of. Is it possible that he has been misled by IPCC who claims that water vapor in the atmosphere doubles the warming power of carbon dioxide in the air? They do that because they desperately want to bring carbon dioxide greenhouse effect up high enough to put global temperature over the 2 degree limit so that it would trigger a new pile of mitigation moneys to them. This urgency comes from the fact that according to scientists today carbon dioxide alone has a sensitivity of only one degree Celsius. That entire talk of water vapor helping carbon dioxide warm the world is just more of the pseudo-science crap from IPCC. The truth is that carbon dioxide and water vapor in the atmosphere do cooperate with each other but in exactly the opposite direction. Now that we dumped Arrhenius greenhouse theory the only greenhouse theory that correctly explains the actions of both carbon dioxide and waster vapor is MGT, the Miskolczi greenhouse theory.
According to MGT, carbon dioxide and water vapor watablish a joint optimal absorption window in the infrared whose optical thickness is 1.87. That value was determined from radiosonde measurements. If you now add carbon dioxide to the atmosphere it will start to absorb in the IR, just as the Arrhenius theory predicts. But this will increase the optical thickness. And as soon as it happens water vapor will start to diminish, rain out, and the original optical thickness is restored. The added carbon dioxide will of course keep absorbing but the reduction of carbon dioxide will have reduced total absorption enough to block any warming Arrhenius would predict. The MST prediction of future temperature will now be that addition of carbon dioxide to the atmosphere does not cause any warming, precisely what we have been experiencing for the kast 18 years. There is no other theory that can explain why the hiatus behaves this way.
There are of course anti-hiatus aithors who have produced several dozen scholarly articles about it, all to no avail. Wait till they hear that there was another hiatus in the eighties and nineties they will also have to explain.