Bishop Hill The missing tropical hotspot
Aug 19, 2013 Climate: Models Climate Dialogue has another of its learned coffee mornings up and running, this time examining the missing tropical hotspot in the troposphere. In it we learn from Carl Mears that
...the tropospheric hotspot is often presented as some sort of lynchpin of global warming theory. It is not. It is just a feature of a close-to-unstable moist atmosphere.
Now this is pretty surprising to me. If I recall correctly, the tropospheric hotspot was behind the big story of the IPCC's Second Assessment Report, the "discernable influence" of mankind on the climate; his fingerprints left all over the scene of the crime.
This is all rather reminscent of the Hockey Stick, which everyone now agrees is peripheral to the global warming hypothesis, but was nevertheless promoted by the IPCC as if it meant something.
Reader Comments (67)
The tropical hotspot is not the fingerprint of AGW, but of water vapour feedback. It would still occur if the heating was due to increased sunlight instead of greenhouse gases, but it's relevant to the AGW claims because most of the predicted warming is due to feedbacks like water vapour, and if this is wrong, or if as Lindzen suggests the surface temperature is wrong, it means climate sensitivity is lower than the 3 C/2xCO2 the models exhibit.
The greenhouse effect is due to the average altitude of emission of radiation to space being about 5 km up, due to greenhouse gases (H2O and CO2 mainly) in the air, working in combination with the adiabatic lapse rate which is the result of the simple physics of gases under compression. The surface temperature is the temperature at which the Earth as a whole radiates as much energy to space as it absorbs (which depends on insolation, cloudiness, etc.) plus the average altitude of emission of this infrared radiation to space (which depends on GHGs) times the adiabatic lapse rate (which depends on humidity).
In the models, increasing GHGs increases the altitude of emission to space, which translates the entire atmospheric temperature profile up. This causes more water to evaporate, decreasing the lapse rate, and this causes the slope of the temperature profile to tilt. If you plot temperature horizontally and height vertically, the profile near the surface is a fairly straight \-shaped line. The higher you go, the colder it gets. The greenhouse effect lifts the line vertically (the GHG effect), and at the same time tilts it about its centre so it is more vertical (the lapse rate effect). The net effect of the two motions is that it only gets slightly warmer at the surface, where the two motions nearly cancel (i.e. this is actually a negative feedback), but a lot warmer at the top, where the two motions reinforce one another.
There are plenty of observations to confirm that a moister atmosphere does have a lower lapse rate (besides being basic lab physics), and it's hard to see how the ocean surface could be warmer without evaporating more water. It has been suggested that it may be due to the way the water vapour is distributed (e.g. if the moister bits are concentrated in the narrow columns of thunderstorms and the excess rains out before mixing with the rest of the atmosphere,) or there may be another counter-acting feedback, or it might be a measurement problem. Remember, we don't believe the surface record, anyway.
The real answer is "we don't know".
Whatever the case, while it's not specifically an AGW fingerprint, it is very much still relevant to the AGW debate.
Not sure if anybody has linked yet to this analysis by Lucia: http://rankexploits.com/musings/2008/who-expects-a-tropical-tropospheric-hot-spot-from-any-and-all-sources-of-warming/
The authors of section 9.2.2.1 in AR4-WG1 evidently did not know that "the tropical hotspot is not the fingerprint of AGW, but of water vapour feedback", unless this feedback magically materialises only when "well-mixed greenhouse gases" are available, and never for solar heating, volcanoes, aerosol changes, ozone, etc.
I think this is the closest evidence yet that the RC guys knew AR4 replete with rubbish already in Dec 2007.
omnologos,
The AR4 figure is somewhat misleading in this context, in that it is not showing what the temperature distribution that would occur if *all* the warming was due to each mechanism. It's showing the contribution of each mechanism according to the models. Since the models posit only a tiny solar contribution, the effect illustrated is likewise tiny.
The diagram does not actually demonstrate what some people interpret it as saying. It doesn't say "This particular pattern is unique to CO2 and is what is observed, therefore CO2 is the likely mechanism for the observations." What it's saying is that "the model-projected warming is primarily from the CO2 contribution - the models model the other factors as only minor contributors." The pattern shown gives no assurance that another model couldn't be constructed in which it was the solar contribution that gave rise to that pattern, instead. And as we've noted, anything powerful enough to increase humidity assuredly would.
It's a subtle bit of misdirection, putting the diagram in a chapter about "fingerprints". In this case, everyone has near enough the *same* fingerprint, but according to the prosecution, only one of the suspects has pressed hard enough to actually leave one.
NiV - if that's the standard quality of AR4's explanatory prose, the report is even less useful than I suspected ;)
Depends what you're using it for. :-)
Nullius
You seem well up to date with theory but you write in a way which suggests that you understand everything that is happening and you do not. I have no idea how much of the true understanding of climate you currently have but I would guess not much more than 15%. You are part of the problem we have today where scientists speak as if they know all the answers when in reality they know hardly any. Were you to write with a little humility and intersperse your facts with "our current understanding is" or "what we have discovered so far is", it might be possible to take you seriously.
Dung,
I actually wrote "the real answer is "we don't know"."
Hard to get much more humble than that! :-)
But seriously, I try to be clear about which bits we know with some certainty, and which bits we don't. We know the Earth has to radiate roughly as much energy as it absorbs. That's conservation of energy. We know GHGs cause it to be emitted from higher up in the atmosphere - we can see it with IR cameras. We know how lapse rates work - they've been standard in meteorology and aviation since long before global warming. And everybody knows that warm water evaporates faster!
These are the only things I've expressed confidence in. On feedbacks, humidity change, the surface record, I think I've been appropriately vague. And of course, I am simplifying everything grossly, but then everybody does! You start with the simple picture, and then fill in more detail when everyone has caught up.
Science *does* actually know some stuff. The trick is to figure out which bits.
Nevertheless, your advice is noted. Thank you.
I'll get this in first.
"An international panel of scientists has found with near certainty that human activity is the cause of most of the temperature increases of recent decades, and warns that sea levels could conceivably rise by more than three feet by the end of the century if emissions continue at a runaway pace.
The scientists, whose findings are reported in a draft summary of the next big United Nations climate report, largely dismiss a recent slowdown in the pace of warming, which is often cited by climate change doubters, attributing it most likely to short-term factors. The report emphasizes that the basic facts about future climate change are more established than ever, justifying the rise in global concern. It also reiterates that the consequences of escalating emissions are likely to be profound."
http://www.nytimes.com/2013/08/20/science/earth/extremely-likely-that-human-activity-is-driving-climate-change-panel-finds.html?smid=tw-share
Oh my ! What can have happened ? Our friends at the GWPF have confirmed the science is sound, but we have discovered that sea will rise by 3 feet and we are all going to die.
Delingpole will be furious to have been swept aside like this. There will demonstrations in the streets demanding that we hear the voice of comedy on global warming. If only Spike Milligan was alive.
As predicted. The traitors sold the jerseys. Cheque is in the post. Ayn Rand for ever.
I noticed the BH-ClimateDialogue Twitter discussion only just now about relating the hotspot to the Santer controversy.
Sorry I have not read through the discussion here, but some quick points in my (antipodean) lunch break....
I am trying to work all this out myself at the moment, and this is my current view...
Actually, the relationship between the hotspot controversy and the SAR Ch 8 controversy is interesting, and both sides are right on two points:
1. The hotspot is important to AGW detection argument.
Yes and No.
It is more that its lack is important to the counter-argument. In the popular discourse Jo Nova has made a big fuss about this over the years.
2. The hotspot was the big story of SAR.
Yes and No.
And this is interesting and perhaps worth expanding...
Refer to this figure:
http://enthusiasmscepticismscience.wordpress.com/2012/07/01/madrid-1995-and-the-quest-for-the-mirror-in-the-sky-part-ii/
They could not find the hotspot (top chart ) but when they modified it with this crude dampener of sulphate aerosol emissions they got this hotspot smugging down towards antarctica (3rd chart). This more or less matched the real data (bottom chart). The real data is Angell's radiosondes data (all of the calibration of sondes data was controversial at the time) ranging from the big freeze (1963) to 1988. It shows asymetrical warming in the south with a minor hotspot over the mid-lats...and Pat Michaels criticised cherry picking for this etc....as per the story on my blog.
Anyway, something I have taken up with Michaels and Chip Knappenberger is the question of where this work by Santer -- that was sooo important at a very precise political moment --- where does it fit into the history of the vertical fingerprint debate? And I don't exactly agree with what Chip tells me by email, that it was an important paper (but I think we would agree if I clarified the question).
I do believe that the answer is that Santer's paper was hardly important at all. This is evident in the nice history article Crok refers to:
Thorne, P. W. et al., 2011, Tropospheric temperature trends: History of an ongoing controversy. WIRES: Climate Change.
In this history of the scientific controversy it hardly even rates a mention. And nor should it.
So, in the first place Mears is right when he says that it was not the big story because it was not the traditional hotspot that Santer claims he found)
And it was not a big story in the history of the controversy over vertical fingerprint detection.
The aersol dampner seems to have been a quick fix that was then disguarded (true? help on that welcome).
Anyways, if the scientific significance of Santer's paper is correct, then it makes it all the more worrying the way Santer's findings were used to get the attribution bottom line up at Asheville (lead authors meeting) and Madrid (inter-gov plenary)...and caused the text of chapter 8 to be changed in such a radical way and well after peer review. Moreover, it was not published until one year after Asheville and 6 months after Madrid. And when it was published, sure it got cited but in reality it dissappeared from the debate that began before and continued after. It disappeared from the history of the scientific controversy over the vertical fingerprint AGW.
Citing no evidence/measurements whatsoever (par for the climate science course I guess), Dung takes Nullus to task for being overconfident about his prognoses, lamenting that without some humility he cannot take Nullus seriously.
Dung, heal thyself. Otherwise noone will be able to take you seriously. Or do I need to take on board the obvious import of your moniker?
Mears propounds the idea of imperfect models whereas they are in reality inadequate. He then goes on to say that policymakers often rely on imperfect models. Well policymakers often rely on inadequate models too and the results are usually that they recommend the wrong course of action. This has happened very often in economics and ecology. So this is the nub; are the models good enough for policy or not? Christy is the most convincing to me because I use and create models all the time and I rate this as far too difficult to model with our current understanding of the physics: It is unquestionable to me that the are unfit for policy. Mears argument is totally unsound and amounts to the old "its the best we have" argument which is always illogical whenever presented and in this case is also wrong.
Sherwood argues that the observational data are too scanty to reject the models as inadequate just yet but he is absolutely fine with the even scantier data that Levitus and Rahmstorf use to back up the unphysical deep ocean warming meme. Typical double standards!
The contributions from non-scientists are unhelpful. Particularly Chris Colose: Neither Dessler nor Soden has identified positive feedback yet. Desslers trend can be reversed by using a different technique or more data but nobody should really put a trend through such a scatterplot and be taken seriously anyway. Notwithstanding that Spencer concludes the opposite with the same data implying that we have assumption-led conclusions once again. Soden seems to argue only that if the models have it there then it must be there because climate science is just wonderfully good with its gut instincts.
And this is another crux: They haven't a clue but they rely on the funding that comes from the scare. As there is just not enough meat in the sandwich to make a convincing meal, they present a false photo of it and sell it to folk with no taste.
Katisha
You appear to miss the point (I will make a note in case it turns out to be a regular occurrence). I had no need to take issue with the facts, figures etc from Nullius since I am sure they are true to our current understanding of the science. The point is that our current understanding is nowhere near total understanding, geddit?
We have a bunch of scientists around the world in the MO, the IPCC and other places who speak as if the science is well understood and settled but it is neither. I get a very bad feeling when anybody talks as if they fully understand the subject, if the aforementioned scientists spoke with humility perhaps the government might realise how shaky their science is.
Good stuff from Nullius in Verba as usual. Essentially there are three possible explanations of the missing tropical tropospheric hot spot: (1) the tropospheric temperature measurements are wrong; (2) the surface temperature measurements are wrong; (3) we've missed out some critical aspect of the water cycle. Of course you can mix and match these three components if you wish, and if you really want to you can add something along the lines of (4) the whole of atmospheric physics is wrong, though I have never found this extreme route particularly tempting.
The most common approach among climatologists is to jump on (1). Personally I have always found (2) more persuasive, with a small helping of (3) on the side. But fundamentally what this shows is just that there is something we don't understand. Climatology is a young science, with plenty of rough bits around the edges. Dung puts it rather well: "our current understanding is nowhere near total understanding".
Thanks JJ for such a concise summary of the options. Young science indeed.
I came back to this thread because I only read the Twitter adjunct today. Here is some important interaction between Richard Betts, Shub Niggurath and our host:
Andrew sets a good example in admitting a mistake and I follow. Having read Richard's "Science moves on" I withdraw my point that the Met man hadn't made his position clear. He didn't on this thread but he did on that one. Tweet and blog as they say.
It's important to clear those points out of the way because it was SAR setting the policy hare running that was and is the central problem. Shouldn't a science in its childhood years have only very limited pocket money to interfere with policy?
We would expect a warmer ocean to produce more evaporation, but of course this does not necessarily mean an increase in water vapour, it depends on how rapidly it rains out. Roger Pielke questions the claim of increasing water vapour.
I would add (5) The simple picture presented by NiV whereby the temperature of the atmosphere and the surface is completely determined by the height of the (fictional) top of the atmosphere and a lapse rate is, well, too simple.
1. Deep in the Earth's crust, conduction rules. Zero convection, zero radiation.
2. Deep in the darkness of space, radiation rules. Zero conduction, zero convection.
3. The atmosphere is where the transition is made between conduction and radiation, by way of convection.
4. Convection dominates in the troposphere (in first approximation, conduction and radiation can be considered having a negligible impact - I believe raypierre makes this very clear in his book on atmospheric physics, and that's why you don't get warm by simply walking under a cloud)
5. The lapse rate is an intrinsic property of all tropospheres.A troposphere ends at the tropopause, where the lapse rate changes sign.
Therefore in first approximation the temperature a few feet above the ground is completely determined by the temperature and height of the tropopause, and lapse rate of the troposphere below.
The rest is detail to be filled by people with a suitable amount of time available to themselves.
--- and so to go back to topic...whatever happened to the tropopause? Has it increased its height as foretold?
Maurizio: Almost poetic.