Bishop Hill Climatologists respond
Feb 1, 2012 "Travesty" Trenberth et al are in the Wall Street Journal today, taking issue with last week's letter suggesting that panic over global warming is not required. Presumably, the message from the scientific establishment is that panic is a necessity.
It's pretty dull stuff - "97% of climatologists whose funders expressed a preference" - that kind of thing. But I was struck by this:
Climate experts know that the long-term warming trend has not abated in the past decade. In fact, it was the warmest decade on record.
I do wish people would make it clear where the differences lie. Otherwise we will get nowhere. Sceptics note that the temperature has flatlined since the turn of the millennium. Upholders say this means nothing, it's just a pause, and the long-term trend remains upward. Fine. Maybe we should talk about model falsification or something.
But take a look at that sentence again. I don't see how the long-term trend (normally assessed over 30 years) can not have been abated to some extent by a 10-year flatlining. Is the maths they use in climatology a bit different?
Reader Comments (160)
The CRU claims to be "... widely recognised as one of the world's leading institutions concerned with the study of natural and anthropogenic climate change."
Why have no representatives from the CRU at the University of East Anglia signed on? Did director Phil Jones and assistant director Keith Briffa refuse to sign on? Or weren't they even asked?
Martin A: I have spent much time looking at the physics of radiant heat transfer in metallurgical plants so I suppose I am rather more of an expert on this than most.
What you must understand is that Prevost Exchange Energy, IR radiation from the colder to the hotter body, 'DLR', cannot be converted at equilibrium to heat energy in the hotter body. Its function is to act as a thermal valve thereby regulating energy flow.
You explain it by a thought experiment. Suddenly decrease the temperature of the air, DLR decreases and the IR density of states at the solid surface has more empty states than Local Thermodynamic Equilibrium requires. Those empty states are immediately filled by energy from the general kinetic energy of the solid so the total radiated flux is that defined by S-B. However, less of it is cancelled out by the lower DLR from the air. If you were to raise the temperature of the air, the reverse would happen.
At radiative equilibrium, no net heat transfer, the number per unit area of the IR density of states in line of sight of the two bodies has to be the same at any IR quantum energy so there can be no net heat transfer.
IR quanta once absorbed have no directional information, are indistinguishable so what then happens due to Local Thermodynamic Equilibrium, cannot be linked to a second body.
So, DLR is solely a measure of the impedance of transmission of IR energy to space. At equilibrium, the DLR from the cooler body is cancelled out by exactly the same photonic flux in the reverse direction. The excess from the hotter body is the only photonic energy converted to molecular velocity = heat.
Hence there can be no positive feedback as claimed in the models, in effect the iterative accumulation of more and more energy in the atmosphere via the totally imaginary 'hot spot'.
Sorry: 'At radiative equilibrium, no net heat transfer, the number per unit area of the IR density of states in line of sight of the two bodies convolved with the probability of emission of an IR quantum at that energy has to be the same at any IR quantum energy so there can be no net heat transfer.'
This physics has been forgotten for 40 years!
I bet the experts also charge more, can't have non-climate scientists under cutting the climate ones now can we.
This man realised years ago when the heat was missing from the water that he had lost the argument, it's now about saving his career.
Second hand smoking is rapidly becoming the new Nazi argument in debating. Once employed it is obvious that the argument has no foundation.
MDGNN
Thank you. I'll need to pore over what you have said.
"Hence there can be no positive feedback as claimed in the models, in effect the iterative accumulation of more and more energy in the atmosphere via the totally imaginary 'hot spot'."
I think we may be looking at different greenhouse explanations. The ones I have looked at do not (so far as I can see) explicitly or implicitly claim any +ve feedback mechanism.
They explain that a proportion (around 50%) of the long wavelength power radiated from the ground arrives back, having been intercepted and then re-radiated in all directions by the greenhouse layer, and so has to be radiated again by the ground. Of this re-radiated 50%, 50% returns and has to be re-radiated again, and so on. So the total power being radiated from the ground is 1 + 1/2 + 1/4 + 1/8 + ... = 2 times the total power arriving from the sun as visible and short wavelength IR.
Some of the energy bounces around a bit before finally going off to the far corners of the universe but this does not amount to what I would term "positive feedback", any more than my car's bouncing after I have hit a pothole constitutes positive feedback.
The language "warmest decade on record" is terribly misleading because they are referring to the modern temperature record that reaches back barely 100 years. The average reader of these articles isn't aware of this and assumes that they mean forever. Lots of meaningless hype.
The 20th century increase was basically the same as the 19th century increase. Nothing to see here...move along.
The following is my post on this topic from WUWT:
How long must we be abused by the False Analogy between climate scientists and physicians? Kevin Trenberth states his version of the fallacious argument as follows:
"Do you consult your dentist about your heart condition? In science, as in any area, reputations are based on knowledge and expertise in a field and on published, peer-reviewed work. If you need surgery, you want a highly experienced expert in the field who has done a large number of the proposed operations."
Physicians practice healing of patients. Scientists create understanding of the universe. The two fields do not have the same goals and cannot be measured by the same standards. Does anyone believe that the surgeon who decided to cut a hole in his patient's leg so that he could access an artery and thread a tube into the patient's heart so that he could inflate a balloon on the end of the tube was practicing science? Of course not. Does anyone believe that the surgeon was justified in his novel actions because he had presented evidence of its likely success? Of course not. Does anyone believe that the surgeon was justified because he had done a large number of this kind of operation? Of course not. The surgeon was justified because all known means of treating the patient's condition had failed and the surgeon's unproven technique offered the only hope of relieving the patient's suffering.
No doubt the reason that people like Trenberth continue to compare themselves to physicians is that they believe that they deserve the respect that physicians receive from patients. But the comparison is made in vain because the respect that physicians receive is based on a record of success in relieving the suffering of patients. By that standard, climate scientists deserve no respect whatsoever. They have failed completely in their efforts to produce scientific theories which explain the behavior of our climate, which rest on empirical evidence, and which can be understood by the highly educated among the masses of humanity. They have failed just as completely in their efforts to offer reasonable paths to healing for what they see as the planet's sickness.
Some have suggested that Trenberth and friends are wedded to the fallacious comparison because they view themselves as physicians to the planet and to humanity. If there is any truth to this suggestion then Trenberth and friends are truly dangerous.
The goal of scientists and the chief duty of scientists is to produce understanding of their piece of the universe. Climate scientists have failed to offer something beyond unvalidated computer simulations and nonempirical claims about proxies such as tree rings. On all the standard measures of scientific success, they have failed. The most telling failure is in their inability to present well confirmed physical hypotheses which explain the connections between rising concentrations of CO2 in the atmosphere and the so-called "feedbacks" such as cloud behavior. Even Arrhenius knew that the effect of CO2 on Earth's temperature could not be determined without the knowledge provided by such well confirmed physical hypotheses.
Finally, climate scientists commit the fallacy of False Analogy because they want the trust that patients have for physicians who have a record of healing people like them. They do not want to be held to a standard of clarity and evidence. They do not want to explain their own science in a way that the prospective "patients," consumers of science, can understand. To that attitude, I say "Scientist, explicate yourself."
The reason why Trenberth imagines himself as a physician is because his knowledge of physics is too bad for him to be considered a physicist....:o)
Martin A: except in the particular case of a temperature inversion, none of the DLR from the atmosphere is [and cannot] be re-radiated. I explained to you that the DLR is solely a measure of temperature and emissivity of the gas, a proxy for the impedance to the transmission of the IR from the ground, the only energy source, to space.
In the absence of a temperature inversion, the DLR is exactly offset by part of the radiated flux from the heat source so the only energy transfer.is the radiation from the hotter body minus the DLR.
This is one of the most fundamental Laws of Physics. The ONLY discipline which claims differently is 'Climate Science', and it's because Arrhenius made a BIG MISTAKE in thinking you could treat the S-B equation for a body on its own, the Earth to space. In reality, you must consider the S-B equation for the cosmic background at 2.7 K!.
Ask any professional engineer and he/she will say the same. We have a problem with physics; there is a lack of intellect in the poorer institutions because of its unpopularity in schools, and unlike engineers like me, few of these people actually have to make process plant work to specification so can get away with being numbskulls [not that you are one, of course]!
So, some have been swayed to the dark side by the Climate Science propaganda!
Indur Goklany has a post at WUWT nailing Trenberth's false analogy. We trust dentists because we and many people we know have been to the dentist before and got problems fixed. No analogy whatsoever with climate scientists. It's a travesty.
I think our warmist trofims are creating urban heat islands on the ocean bottom floor now
Theo Goodwin's point about the difference between scientists and medical practitioners is very important. Note the word 'practitioners'. Doctors are primarily pragmatists, they do what seems to work (but no guarantees) and it is surprising how much of medical practice is based on results but not on understanding.
For example, almost anything they do that relates to the functions of the brain is not understood - whether it be prescribing psychoactive drugs or the crude attempts to modify brain functioning through surgery that have so far yielded such poor results. There are hypotheses about these things, but pretty much none of it passes the test required of scientific proof.
They are on better ground with the more 'mechanical' aspects of their craft like setting broken bones and clearing gunk out of arteries - but in fact it is remarkable how much is not known about even these relatively straightforward procedures in terms of what is actually happening in the human body.
As has been pointed out, the elevated status of doctors comes from the fact that we are almost all scared of being sick and dying - so those who can help us to forestall these events are trusted and lionised. Fair enough.
But much of what they do is not 'science' in the pure sense at all. And the notion of Trenberth et al setting themselves up as doctors to the planet is both scary and remarkably revealing.
Theo Goodwin (and johanna):
To be fair to the letter's authors, I don't think they're trying to compare themselves to physicians. What I suggest they're saying is that, just as you wouldn't go to a dentist if you needed cardiac surgery, so you shouldn't pay attention to the authors of the original letter when it's the views of the relevant experts (i.e."climate scientists") that matter (forgetting, it seems, the specialty of Richard Lindzen).
Of course, their analogy is absurd. If I thought I had a heart problem, I would first consult a general practitioner (analogous to many of the original letter's authors) for an examination and initial opinion - based, I would ensure, on wide real world experience. He/she might then refer me to a specialist (more specifically experienced with the real world) for a more detailed review. Then it might be necessary to see a surgeon. And I'd wish my advisors to ensure that that surgeon's practice was based on a wide knowledge of general medicine, on the best empirical cardiac data and a history of practical success with real patients in the real world - i.e. not remotely analogous to these climate "scientists" with their computer models, unverified hypotheses and failed predictions.
@Robin Guenier - to extend your metaphor slightly:
At which point your GP might diagnose indigestion from last night's curry and send you home.
;-)
To some extent it's true. The 1990s got its trend from a growth through the decade with a high 1998 and also 1999. A flatline then has 2000 substantially warmer than 1990, 2001 vs 1991 and so forth, so the trend is still roughly the same. Extend the logic, and you can't say global warming has stopped until temperatures drop to the long term mean, otherwise you still have a positive trend.
Also, your point is similar to a bet between Tom Fuller and Joe Romm, that the 2010s will be at least .15 warmer than the 2000s. If you are a skeptic who thinks there is no trend, then Fuller is winning as maintaining current temperature would mean Fuller wins easily. If you are a warmist who thinks temperatures are increasing then current results have Romm winning as 2010 was warmer by .3 over 2000, and 2011 by .04 over 2001.
Martin A, I'm not sure how familiar you are with the posting from "mydogsgotnonose", so I think it only fair to warn you that the majority of science literate posters on this and other sites think he's full of it, to use a slightly rude euphemism.
The Trenberth at al letter missed an opportunity to identify areas of agreement with the original WSJ article which stated:
"If elected officials feel compelled to "do something" about climate, we recommend supporting the excellent scientists who are increasing our understanding of climate with well-designed instruments on satellites, in the oceans and on land, and in the analysis of observational data."
In the recent response it was claimed that the "Travesty" quote meant:
"Mr. Trenberth was lamenting the inadequacy of observing systems to fully monitor warming trends in the deep ocean and other aspects of the short-term variations that always occur, together with the long-term human-induced warming trend."
I find it astonishing that so much is being spent on computer modelling while our observation systems are inadequate. It reminds me of the attitude of some in Environment Canada a few years ago who claimed we could discontinue streamflow measurements because computer models could generate the "data".
steveta_uk;looks like I'm getting you rattled!
If you dispute what I have written, please tell me where I have gone wrong. To accuse me of being 'full of it' may be true and sometimes I do sail close to the wind, but if you can't prove it, the retort backfires,
I can assure you, I have researched the whole subject of climate science for 2 years now, and intend systematically to correct the major mistakes. Two of them are elementary no professional should have made, Two are more subtle and I have solved one of those with new physics, to be published.
So, where shall we start? The law of Equipartition of Energy with the Gibbs' Paradox proving that there can be no thermalisation of absorbed IR energy? Over to yo......:o)
luckily people work less when it is getting warmer
remember the mexicans having long siestas under their sombreros
this is then a negative feedback
I am in no doubt there is a parameter for it, in your nearest GCM
Do these sound like dentists???
Claude Allegre
William Kininmonth
Richard Lindzen
Nir Shaviv
Henk Tennekes
Panic = Money, funding
Money, funding = Necessity
So yes panic is a necessity.
steveta_uk Feb 1, 2012 at 5:40 PM
I'm eager to understand MDGNN's viewpoint. I have not yet understood it, despite his patient efforts to explain. Some things he says don't seem to me to add up. Once I have worked out exactly what he is saying, I'll be able to see what's what.
Some things he says do not make sense to me. He says (if I have understood right) that low energy photons cannot be absorbed (and thereby heat) a body at a higher temperature than that corresponding to the energy of the photons.
My microwave oven (frequency ~2.5GHz, wavelength ~12cm ) produces radiation corresponding to thermal emission from a body at around 0.025 K. Yet it has no problem persuading objects far above this temperature to be further heated by its radiation. So there is something I have not yet grasped somewhere.
It's certainly a fact that there is plenty of nonsense on both sides of the climate debate. Hence my desire to understand things from first principles, rather than take them on trust. And likewise, not to dismiss things simply because they disagree with my preconceptions.
Robin writes:
"To be fair to the letter's authors, I don't think they're trying to compare themselves to physicians."
I do not mean to be offensive, Robin, but:
"To be fair to the letter's authors, I don't think they do not know what they are trying to say."
They want the respect that physicians receive from their patients and they want the authority that many patients, sadly, allow their physicians to exercise. So, how are they not comparing themselves to physicians? Notice also what role they want the peons such as you and me to play. They want us to be the submissive, uninformed patients.
Not at all offended, Theo: I've no doubt they want respect. But what they've done here is postulate an unwise, self-defeating analogy - read my post (much improved by woodentop's comment).
Robin,
I had no problem with the rest of your post. That is why I apologized "in advance," as some users of the internet say.
Please pardon the typo above. I meant to write:
"To be fair to the letter's authors, I don't think they know what they are trying to say."
Martin A,
Your microwave is producing electromagnetic radiation ( at rather high power content), not thermal radiation. The resulting molecular vibration in any polar molecules in your food is then converted to heat. Note that the air in your microwave does not heat directly. It is heated only by the food.
Ed Caryl Feb 1, 2012 at 8:12 PM
Hi Ed,
Thermal radiation is electromagnetic radiation.
The only difference is one of wavelength.
Quote: The cosmic microwave background (CMB) radiation is an emission of uniform, black body thermal energy coming from all parts of the sky.
The cosmic background radiation was discovered as unexplained noise in sensitive microwave communications receivers.
Thank you Ed Caryl: the idea that microwave radiation is equivalent to 'back radiation' is stupid.
It's because MW energy couples directly with the asymmetric vibration of water molecules whereas thermal radiation involves the direct coupling of thermal emission states between emitter and absorber.
[I have discussed even stranger ideas with an Ozzie who claimed that the IR mirror in the atmosphere was dichroic; a Fabry-Perot Etalon of ordered CO2 molecules. This is debunked here: http://arxiv.org/abs/0707.1161v4 ]
Martin A
Perhaps a simpler model -- You can't boil water by adding ice -- gently. As one wag pointed out, you can if you throw it fast enough. But that is adding energy to the system just as though you are turning the stove on under the pot.
Second, unless focused in some manner with reflection/refraction, energy tends to go in all directions equally. You can manipulate this with such stuff as mirrors, or differential index of refraction (i.e lenses). However in order to do that, you still have to show that there is reflection/refraction.
I do not see any mechanism in anything you proposed that meets these requirements. Just saying it is done isn't good enough. In short, "show me the mirror." That you have failed to do.
There seems to be an ever ending game of smoke and mirrors with regard to what all the fuss was about ie. 'we didnt really predict catastrophic warming'
er, we were just pointing out that the end of the century was warmer than the start etc
but this was never about warming in the 20th century it was about the 21st century and so far, the predicted exponential warming is trending towards 0 depending on which metric you use
Climate scientists such as Trenberth continually ask sceptics: “Why will you not accept our authority on matters of climate?”
Sceptics continually answer: “Because you are not honest about your science. You know, as Arrhenius did, that nothing can be inferred about Earth’s temperature from the fact of rising CO2 concentrations in the atmosphere until someone creates and confirms some set of physical hypotheses which explain the effect of rising CO2 concentrations on the so-called “feedbacks” such as cloud behavior. There are no such well confirmed physical hypotheses."
Who must make the next move in this discussion?
Amongst many fatuities in the Trenberth et al letter in the WSJ is their failure to realise that dental infections can cause serious heart problems.
Another is the pathetic failure of KT et al to remember that the national academies of science endorsing the IPCC themselves consitute the IPCC. For example, the Australian Academy of Science's propaganda booklet The Science of Climate Change (2010) at www.science.org.au/policy/climatechange2010.html
did indeed endorse the IPCC's AR4, but at least 7 of its 9 authors were Lead Authors or Review Editors of AR4. Three of those 9 (England, Karoly, Sherwood) co-signed the Trenberth letter. How amazing that they independently endorse their own work! They also stress the role of peer review, but they always see to it that they themselves peer review each other, and if not, Trenberth ensures that editors who do not use him as their peer reviewer get to "resign" or face life without grants dispensed by KT and his pals.
In fact, it was the warmest decade on record.
Whether AGW is significant or not, just where would you expect "the warmest decade on record" to be? A decade close to the LIA or the latest decade in the subsequent warming trend?
Gosh, wouldn't you love to be this guy's stock broker?
"Well, Dr. Trenbleth, what you've got to realize is financial experts know that the long-term investment trend has not abated in the past decade. In fact, stock market indices were at the highest level on record."
What would logically follow would be
"Give me all your money and I will fully invest it to take advantage of this obviously increasing phenomenon (less commissions of course)."
They explain that a proportion (around 50%) of the long wavelength power radiated from the ground arrives back, having been intercepted and then re-radiated in all directions by the greenhouse layer, and so has to be radiated again by the ground. Of this re-radiated 50%, 50% returns and has to be re-radiated again, and so on. So the total power being radiated from the ground is 1 + 1/2 + 1/4 + 1/8 + ... = 2 times the total power arriving from the sun as visible and short wavelength IR.
Some of the energy bounces around a bit before finally going off to the far corners of the universe but this does not amount to what I would term "positive feedback", any more than my car's bouncing after I have hit a pothole constitutes positive feedback.
Feb 1, 2012 at 4:11 PM | Martin A
Think on it.
Your words:- "They explain that a proportion (around 50%) of the long wavelength power radiated from the ground arrives back"
Do you really think that a gas constituting a tiny 400ppm of the total atmosphere can somehow reflect/back radiate 50% of ALL the LW radiation emitted by the Earth's surface back to the ground.
Not bad for a gas with an emissivity of around 0.01 at atmospheric pressure.
Do you consult your climatologist about your stats condition?
Mydogsgotnonose
If you experiment, you will discover that just as panting is a more energetic exercise than tail wagging, CO2 molecules have stretching and vibrational modes differing in frequency, and hence in energy and absoption and emission wavelengths.
I suspect if you packed enough hounds into kennel similar pressure broadening phenomena might be observed as well.
As to Arrhenius, his two Victorian and Edwardian estimates of CO2 sensitivity remain among the largest ever published.
Martin A
Mie scattering theory predicts and direct photometric measurement confirms that 400 ppm of 1 micron air bubbles can backscatter 50% of the suns energy from any water surface.
Not bad for air.
I thought Trenberth's final paragraph was very revealing: "In addition, there is very clear evidence that investing in the transition to a low-carbon economy will not only allow the world to avoid the worst risks of climate change, but could also drive decades of economic growth. Just what the doctor ordered."
There we see the great climate scientist turn into a blatant and unashamed propagandist. The man should be running for public office! -- he'd fit right in.
@ Martin A...
(Note: I'm not a scientist.)
You wrote:
"They explain that a proportion (around 50%) of the long wavelength power radiated from the ground arrives back, having been intercepted and then re-radiated in all directions by the greenhouse layer, and so has to be radiated again by the ground. "
What does the word "radiated" mean; emitted; reflected: both?
Clearly, in the first two uses of "radiate" it means "emit", but what about that last use? If it means "emit" there, then that would require the ground to be a perfect absorber of IR, no?
"Is the maths they use in climatology a bit different?"
There's nothing wrong with their maths. Here is a plot of the NOAA index, 50 year trends from 1880. No abatement. There's a small recent decline in the 30 year trend, basically because the trend 30 years ago was high.
Martin does seem a bit out of his optical depth
MDGNN
OK, so I'm stupid.
Come on you lot. It's all electromagnetic radiation. It warms stuff. Despite having energy per photon which is miniscule compared with the energy per photon of long wavelength IR.
The stuff being warmed may ask the radiation what's its wavelength (equivalently, energy per photon).
But I've never come across a text that explains that the absorbing item asks the em radiation "OK, before I decide to absorb you or not, tell me by what process you were generated", though this seems to be what MDGNN is saying. I've asked for reference to a text that explains it, but have not yet been given such a reference.
Feb 2, 2012 at 7:56 AM | Unregistered CommenterRussell
Yes, very funny.
I'm trying to understand what MDGNN is on about. I've explained my understanding in the hope he'll explain where it's wrong and how his view is correct.
Russell, do you understand what MDGNN is on about?
If you understand his claim that the physics used to explain the greenhouse effect is wrong, why don't you explain it? Or just give a reference to a textbook on radiative heat transfer that explains the quantum mechanics he's going on about?
I
Sleepalot Feb 2, 2012 at 4:48 AM
Just to confirm: radiate = emit.
Yes, that's right.
It seems there is solid evidence from measurements that the ground (the ocean too) is pretty damn close to being a perfect absorber of long wavelength IR. So it's also pretty damn close to being an ideal black body, so far as the relation between power radiated per unit area and temperature are concerned.
References to this on the Science of Doom site.
.
Don Pablo de la Sierra Feb 1, 2012 at 9:32 PM
It's not my theory. I'm not defending it. But I'm trying to understand MDGNN 's view that it's wrong.
I'm just repeating what I understand is the normal explanation of the greenhouse effect. MDGNN said it contains positive feedback. Others say it equates to perpetual motion, generation of energy from nothing and so on. I've explained my understanding of the normal explanation which does not seem to me to have these impossible features.
For what it's worth, I think the model is hopelessly oversimplified - taking the 4th power of an integral, rather than integrating integrating the 4th power etc etc. But although it's oversimplified, I can't see where it contradicts the laws of physics.
Feb 2, 2012 at 12:32 AM | Unregistered CommenterRKS
Don't forget there is a load of water vapour whose effect is no doubt immensely greater than that of CO2 etc.
But please understand I'm not saying what *I* think. I'm re-stating the way the greenhouse effect is normally explained.
I can't see that the explanation involves creation of energy from nothing as sometimes stated or that it involves +ve feedback as MDGNN states. Do you believe the normal explanation involves these features?
Don't forget there is a load of water vapour whose effect is no doubt immensely greater than that of CO2 etc.
Feb 2, 2012 at 8:50 AM | Martin A
But that's the crux of the whole AGW argument.
Is it CO2 or water vapour.
are you implying that if you either halved or doubled CO2 it would still reflect 50% of all outgoing LW radiation?
Is there some magic number for the concentration of CO2 to achieve this condition?
If not CO2, then what's all the fuss about.
f you understand his claim that the physics used to explain the greenhouse effect is wrong, why don't you explain it? Or just give a reference to a textbook on radiative heat transfer that explains the quantum mechanics he's going on about?
I
Feb 2, 2012 at 8:28 AM | Martin A
Take a look at the work of Ned Nikolov, Ph.D. & Karl Zeller, PhD. on the United Theory of Climate thread on this blog, and perhaps also the work of Prof. Harry Huffman in this paper :- http://theendofthemystery.blogspot.com/2010/11/venus-no-greenhouse-effect.html
for examples of the many scientists now refuting AGW.
http://theendofthemystery.blogspot.com/2010/11/venus-no-greenhouse-effect.html
That's a simple elegant explanation of why AGW is a load of bollocks.
I, like Martin A, still don't understand what MDGNN is banging on about, can someone explain
it simply?