This is just one of dozens of responses to common climate change denial arguments, which can all be found at How to Talk to a Climate Sceptic.
Objection:
Clouds are a very large negative feedback that will stop any drastic warming. The climate models don't even take cloud effects into account.
Answer:
All of the Atmospheric Global Climate Models used for the kind of climate projections reported on by the IPCC take the effects of clouds into account. You can read a discussion about cloud processes and feedbacks in the IPCC TAR.
It is true however that clouds are one of the largest sources of uncertainty in the GCM's. They are very complicated to model because they have both positive feedbacks, preventing surface heat from escaping back into space and negative feedbacks, reflecting incoming sun light before it can even reach the surface. The precise balance of these opposing effects depends on the time of day, the time of year, the cloud's altitude, the size of the water droplets and/or ice particles forming the clouds, the latitude, the current air temperature and the cloud's size and shape. On top of that, different types of clouds will interact, amplifying or mitigating each other's effect as they co-exist in different layers of the atmosphere. There are also latent heat considerations as water vapour condenses during cloud formation and precipitation events and as water droplets evaporate when clouds dissipate.
The ultimate contribution to global temperature trends is very uncertain, but according to the best estimates is likely to be positive over the coming century. There is no indication anywhere that any kind of cloud processes will stop greenhouse gas driven warming, and this includes observations of the past as well as modelling experiments.
This is just one of dozens of responses to common climate change denial arguments, which can all be found at How to Talk to a Climate Sceptic.
"The Models Don't Have Clouds" was first published here, where you can still find the original comment thread. This updated version is also posted on the Grist website, where additional comments can be found, though the author, Coby Beck, does not monitor or respond there.
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This explanation is incoherent. You say,
"The ultimate contribution to global temperature trends is very uncertain, but according to the best estimates is likely to be positive over the coming century."
So is their effect ovet the next century "very uncertain" or is it "likely" to increase temperatures? It can't be both.
[coby: while it is not the precise use of language you will find in the IPCC documents, I think "incoherent" is just a litle harsh! It is uncertain but more likely positive.]
You also say "There is no indication anywhere that any kind of cloud processes will stop greenhouse gas driven warming".
I would point you to your previous paragraph. You say quite clearly that modelling clouds is very difficult and there are potential positive and negative feedbacks, and exactly what will happen is not clear - "The precise balance of these opposing effects depends on...[a number of things]".
So which is it, is it possible that some "cloud processes" could decrease temperature or is it not.
[coby: It is possible clouds could mitigate warming, but there is no evidence anywhere that suggests cloud effects can actually stop temperature rise or that they can cause a net cooling
Posted by: paul | November 21, 2008 5:04 AM
paul, see my replies inline.
Posted by: coby | November 21, 2008 5:42 AM
This is not a topic I know much about, I would like to know more. But I am completely underwhelmed by your answers. You are phrasing it so as to put a positive spin on the unalterable fact no'one really understands clouds or how they will change or be changed by the temperatures and/or climate.
That's ok for me and my stance on AGW, as I just think the debate needs to continue and am happy to accept this. However, for those who wish to claim that the debate is over, not understanding a major player in climate dynamics poses a problem, and trying to brush this away with "likely" is not going to convince anyone.
Posted by: paul | November 22, 2008 4:54 AM
You know, reading over what you wrote and paul's response to it, I wonder if part of the problem is that you've been using a lot of "science-speak" that means one thing to scientists and another to non-scientists.
I think that what you were trying to say, in brief, was, "Yes, there is a whole lot that we don't know about clouds, but we understand them well enough to be able to say that even taking into account the things that we don't know, we are pretty certain that they are not going to cancel out the effect of CO2." As a researcher in a different field, this is certainly what I got from what you wrote.
However, to people who are not used to the practice of quantifying and understanding uncertainties, all that they see is a lot of discussion about how uncertain things are, and then remarkably how nonetheless you think that you understand something well enough to draw a conclusion from it!
Anyway, just my two cents, for what it's worth. :-)
Posted by: Greg | January 25, 2009 9:56 AM
Hi Greg,
You're probably right it could be worded a bit better. Maybe I'll revisit this one in the future, perhaps with a focus on Richard Lindzen's failed "iris" hypothesis.
Thanks for the feedback!
Posted by: coby | January 25, 2009 4:35 PM
The main article's argument is pretty weak. You state that cloud effects are complex and are likely to be one of the largest sources of uncertainty in the models, but then state that the "best" estimates indicate they are likely to be a positive feedback to global warming. What are those best estimates and what evidence indicates that the effects of clouds are likely to contribute to warming?
The fact of the matter is that clouds have an enormous effect on weather and thus on climate. Through the precipitation cycle, they control the distribution of the most important greenhouse gas (water vapor) in the atmosphere. Furthermore, they have a very large effect on the Earth's albedo and thus on the amount of solar radiation arriving at the earth's surface. If GCMs cannot properly model cloud behavior, they cannot be expected to provide accurate results.
Finally, you state that "There is no indication anywhere that any kind of cloud processes will stop greenhouse gas driven warming". However, in another post you indicate that aerosols contributed to a significant degree to the cooling in the mid-twentieth century. In fact aerosols are known to enhance cloud formation through seeding of water droplets. It is very likely that the global cooling caused by aerosol pollution was largely due to enhanced cloud formation. Therefore, clouds certainly have the potential to counter-act any CO2-induced global warming. Thus, unless we understand how global warming impacts cloud formation, we cannot expect to be able to make long-range predictions of global warming effects.
Posted by: SemiChemE | June 19, 2009 6:07 PM
"What are those best estimates and what evidence indicates that the effects of clouds are likely to contribute to warming?"
The evidence comes from observations of past climate changes, both modern and glacial-interglacial climate. It is hard to get ~10oC warming from GHG, orbital changes and albedo if clouds are a significant negative feedback. I recommend the IPCC report for summaries and citation of the primary literature on this topic.
"The fact of the matter is that clouds have an enormous effect on weather and thus on climate. Through the precipitation cycle, they control the distribution of the most important greenhouse gas (water vapor) in the atmosphere."
I think you have this backwards. The amount of vapour in the atmosphere (partly) controls cloud formation. Regardless, I have no objection to saying clouds are a very important part of weather and climate.
"Furthermore, they have a very large effect on the Earth's albedo and thus on the amount of solar radiation arriving at the earth's surface."
...and the amount of IR escaping.
"It is very likely that the global cooling caused by aerosol pollution was largely due to enhanced cloud formation."
Can you provide some evidence for this?
"Therefore, clouds certainly have the potential to counter-act any CO2-induced global warming."
And yet they aren't now, and didn't seem to in the interclacial climates.
"Thus, unless we understand how global warming impacts cloud formation, we cannot expect to be able to make long-range predictions of global warming effects."
I can't argue with this depending on the precision you are looking for. However arguments about uncertainty cut both ways. The models could well be drastically underestimating future warming as easily as they could be drastically overestimating. For example, sea ice and ice sheet modeling is very incomplete and thus far nature is responding much more dramatically than the models said we should expect.
Posted by: coby | June 19, 2009 6:33 PM
I would like to ask a question, probably against my better judgement. Nothing is ever solved or resolved on these blogs. But here goes.
The key to the entire global warming debate is how much affect Co2 has on global temperatures. Correct? All the historical data and climate models are just used to support ones view, whatever that may be.
To me, all of that is a distraction from the real issue. Exactly how does Co2 influence the climate. I have read articles about the greenhouse effect. It sounds like a pretty simple and reasonable answer. But I have also read quite a few articles completely debunking this view.
Without just trying to discredit those that disagree with the greenhouse effect view, I would love to see a real discussion from people with much more expertise than me, from both sides of the issue, without it denigrating into a bash fest.
Posted by: Steve | June 20, 2009 6:46 AM
Hi Steve,
The greenhouse effect of planetary atmospheres and the radiative physics that it is based on is such basic textbook science that you simply will not find a real discussion between two people with real expertise on whether or not it exists. The best you can do is hear a lecture about it.
If you have a specific "debunking" of the GHE in mind, perhaps I can help show you where it is wrong.
I am very serious though, and not just trying to belittle anyone, this is well established and uncontroversial science for over 100 years. If it were wrong, NASA's probes to other planets would fail because they would be designed for inappropriate temperatures; astronomers would be all wrong about the composition of stars and galaxies and the sizes and temperatures of extra solar bodies and many other things in many fields of science would be complete garbage.
Posted by: coby | June 20, 2009 8:30 AM
Hi Coby,
Do you think there is a distinction between atmospheric composition and atmospheric density in terms of their affect on global temps? Which is more important?
Posted by: Steve | June 20, 2009 8:50 AM
Posted by: Richard Simons | June 20, 2009 9:46 AM
Richard,
Well, I'm a non-scientist. What do you mean? Can you answer my question above (#10)regarding composition and density? Sorry if these are somewhat rudimentary questions.
Thanks.
Posted by: Steve | June 20, 2009 10:26 AM
Steve: the concentration of CO2 (and various other gases) is usually measured by measuring the amount of absorption of infrared radiation at specific wavelengths. The greenhouse gases are effective because they absorb infrared radiation (the energy being turned into heat).
The relative amounts of N2, O2, CO2, water vapour and the other gases have a negligible effect on atmospheric density (as I understand it - I am not an atmospheric scientist). Atmospheric density depends mainly on temperature (hotter = less dense) and air pressure so if anything the relationship is the other way round.
Posted by: Richard Simons | June 20, 2009 7:49 PM
To get back to clouds, in trying to model out cloud effect you have to set the variable of how much the temperature will rise. Greater temperature generally leads to greater atmospheric instability, greater instability leads to greater cloud coverage, and greater cloud coverage has a net cooling effect.
But for use weather forecasters that simply do forecasting and not global climate or modeling we are quite familiar with the effects of local, meso, synoptic, and hemispheric. and that you go from large scale to small scale not the other way around, when trying to write a forecast, if you try and say the local scale will effect the synoptic, you'll get the forecast wrong every time.
Remember, too, to distinguish what is "local weather" from what is "global climate". It's the difference between being able to predict that a tea kettle will blow a "whistle" when certain thermodynamic conditions are met, and NOT being able to predict the space-time-phase diagram of individual water molecules, and yet still being able to predict the overall shape and form of the stream of vapor/steam that emerges from the kettle's mouth.
Posted by: m2moyer | July 5, 2009 9:00 AM
Hi m2moyer,
As I understand it, the net effect of cloud coverage depends on time of day, type of cloud and altitude, as well as the interaction of various layers of cloud cover. For a simple example, cloudy nights are warmer than clear ones (time of day effect).
I like your boiling kettle analogy! Thanks for the visit.
Posted by: coby | July 5, 2009 12:09 PM
Here is a very good explanation of computer models.
h.t.t.p://climaterealists.com/index.php?id=3711
Posted by: crakar14 | July 14, 2009 12:25 AM
The basic explanation of how models work isn't bad. However his conclusion that CO2 doesn't cause warming but rather changes in cloud cover do is based on one statement he makes:
"I believe"
Doesn't get you far in science.
Posted by: dhogaza | July 14, 2009 7:12 AM
Yes agreed the basic explanation is good (for the layman like me anyway). The point he makes is that a small change in cloud cover could account for what is believed to be CO2 induced warming. Cloud cover is poorly understood or catered for in the models so he "believes" this maybe the source of the temp changes and not CO2.
Mind you dhogaza the statements "very likely" or "very unlikely" dont get you too far in science either.
To put it another way, the accuracy of a model is determined by the accuracy with which it simulates each climatic factor and climatic process rather than the closeness of the match between its output and historical data. If the internal processing is correct then so too will be the output, but accurate output does not confer accuracy on the internal process.
For example;
The combination of a number of inaccuracies can produce acceptable outputs if calculations that are too high counterbalance those that are too low.
It all gets back to that statement "if you cant explain it you cant model it".
Posted by: crakar14 | July 14, 2009 4:44 PM
Since crakar14 is making a rare attempt to be reasonable and thoughtful, I'll answer.
"poorly understood" does not mean "no knowledge". In other words, it doesn't mean that the possible physics is unknown and unbounded, and that you can just plug in any value you want that happens to give results that match your political beliefs. Which is essentially what he's claiming.The other problem he and spencer etc face is that if changes in cloud cover are driving climate change, then everything known by physicists about the interaction of CO2 and LW IR in the atmosphere is wrong. It is up to your side to *prove* that known physics is bollocks. You have to be able to reproduce the success of models using known physics in paleoclimate, etc as well. You can't just say "I believe that the underlying physics is wrong" just because you do, and expect anyone in the world of science to pay attention.
Which ... is why people don't.
Posted by: dhogaza | July 14, 2009 5:18 PM
While true, if you're going to claim this is true in regard to current GCMs, YOUR SIDE NEEDS TO SHOW IT. Spreading FUD isn't doing science. Saying "I believe" isn't doing science.
Posted by: dhogaza | July 14, 2009 5:21 PM
dhogaza,
First post,
poorly understood means poorly understood
Which is what you have just shown on this topic, they are not saying that clouds drive the climate they are saying that clouds act as both heat trapping and sunlight reflecting objects which can either add to or reduce the temps. As we have a poor understanding of cloud formation and very little data on cloud increase or decrease over the years the models cannot simulate this very important part of the climate.
This has nothing to do with the physics of atmospheric CO2 or political beliefs, i hope you understand this now.
Second post,
I am not claiming anything just stating fact, the internal processes of a computer model need to be correct for the output to be correct, this can be applied to any model not just ones used for climate.
As you agree my statement was true then you must also agree that, cloud formation and precipitation are poorly understood as this is part of the internal process of a model the output should not be viewed as the be all and end all of climate science. This is not about proving the GCM's wrong and winning some petty debate on a website it is about using their results as another tool available in attempting to predict furture climate. As our understanding of the climate process improves so will the models results.
Until then models will assist us in our ever growing understand of Earths climate.
By the way I did not know there were sides in science, differing of opinion yes but sides? It is a shame that only one of us is attempting to be reasonable and thoughtful whilst the other just continues with same old diatribe.
Posted by: crakar14 | July 14, 2009 6:10 PM
Crakar, your "side" is not doing science.
Posted by: Ian Forrester | July 14, 2009 6:31 PM
And what side might that be Ian?
Posted by: crakar14 | July 14, 2009 7:00 PM
Your "side" consists of a bunch of whackos who are misinformed, dishonest and don't know squat about science or how it works. They are only posting to confuse those people who are not up on the science of climate change.
They have differing motives for this obfuscation but one thing they never do is read or quote a real paper let alone write one.
Posted by: Ian Forrester | July 14, 2009 7:11 PM
What are their differing motives Ian?
Posted by: crakar14 | July 14, 2009 7:37 PM
However, as I tried to explain above, despite it being poorly understood, as much as it *is* understood, points to the net effect being positive, not negative. There's plenty of research that makes that almost certain.
In fact, there's building evidence that the positive feedback from clouds and other sources will be higher than even the highest current model result.
For a good time, go to WUWT and watch those who would overturn climate science - including the host, Watts - totally misunderstand another paper, thinking it means that current model results are too high rather than possibly 30% too low.
Posted by: dhogaza | July 15, 2009 6:26 AM
Crakar14 is right that clouds are not only poorly understood, they are even worse modeled. The GCM's treat clouds as an "average tunable cloudiness parameter" based on radiative heat transfer. The best example I can give is with structural statics: if you have a supporting structure to whatever you’re analyzing, it is fair to represent it as a spring, with an equivalent spring stiffness of the actual supporting structure. Notice that the spring stiffness of sup. structure can be measured/calculated, so this is just a simplification and can be called "parametrization" (as done with radiation in some models according to RC). "Tunable parameter", would be if we didn’t know (or couldn’t measure) the spring stiffness, and attempted to calculate it back (hindcasting) to an observed force-displacement (historical reconstructed records). As far as I see it, this is where the clouds fall in. And clouds being much smaller than the spatial scale of the most state-of-the-art models, they must be averaged to at least one grid size (which is still a couple of orders of magnitude larger), hence the "tunable average cloudiness parameter". The danger in this, is that you’re already assuming some kind of a response mechanism, and are working back to get a parameter to fit a potentially flawed assumption (like convective heat transport /w water, which is not radiation based at all!)
That's why a statement like "All of the Atmospheric Global Climate Models (...) take the effects of clouds into account" should not be comforting to anyone. They are essentially reduced to radiative shields or traps. I haven't seen any discussions on how convective heat transport with water is accounted for in clouds, perhaps someone might point me in the right direction
Posted by: ThomasC | July 15, 2009 7:24 AM
Crakar, here is a link to a list of the reasons people like you are anti-science, especially anti-AGW.
Please read it and tell us where you think you fit in, or would you rather we did it for you?
ht-tp://scienceblogs.com/deltoid/2008/12/the_australians_war_on_science_28.php#comment-1272743
(remove the hyphen)
Posted by: Ian Forrester | July 15, 2009 7:47 AM
Are you sure you want to hang your hat on that hook?
Posted by: dhogaza | July 15, 2009 9:30 AM
No, dhogaza, I'm saying that assigning an average radiative parameter to clouds is a flawed assumption, because there are a lot of interactions which are not radiation based
I never said that convective heat transport (with water) has no underlying physics, only that it should not be modeled with radiation heat-transfer equations.
This is akin to me modeling a resistor with an inductor.
Posted by: ThomasC | July 15, 2009 12:01 PM
If I had to guess, they don't just assign one average radiative parameter to model the effects of clouds.
Posted by: dhogaza | July 15, 2009 1:13 PM
More on the "flawed assumption" that leads to the "assigning an average radiative parameter to clouds" in GISS Model E:
Oh, wait, looks like they do much, much more than "assign an average radiative parameter to clouds"
Posted by: dhogaza | July 15, 2009 1:25 PM
ThomasC, before pontificating more on "how GCMs work", you might want to spend some time studying how they actually do work rather than rely on third-hand descriptions.
Here's the main documentation for GISS Model E
You can browse the model source online. A good place to start looking to understand how clouds are actully modeled would appear to be in these modules:
CLOUDS.f, CLOUDS_COM.f, CLOUDS_DRV.f: Column model, common variables and driver routines for moist convection and large scale condensation
I suspect the model's not as primitive as you've been led to believe ...
Posted by: dhogaza | July 15, 2009 1:33 PM
dhogaza -
pshhht. We know that entire document is a lie written by the lying liars at GISS who COOK THE BOOKS and hand-wave away any VERY SERIOUS problems with models the anyway. That's only the fake documentation they put on their website to trick fanatical environmentalists into believing the models aren't just guys sitting around an etch-a-sketch drawing increasing temperature lines on a graph.
What's next, are you going to quote the IPCC report as some sort of scientific consensus instead of the personal opinion of Al Gore who just wants other people to use less energy so there's more for him to use?????
Posted by: Adam | July 15, 2009 2:24 PM
First off, I never said that they assign "one average radiative parameter" for the whole global finite element model, let's not build a strawman here. Averaged out over an element size, yes (which is still very large).
From the HadCM3:
"The large-scale precipitation and cloud scheme is
formulated in terms of an explicit cloud water variable following Smith (1990)." I couldn't dig up the paper, but the abstract follows "the cloud amount and water content are generated by a scheme which assumes a distribution of thermodynamic and water content variables about their grid-box-mean values." That's where the average parameter comes in, average, because the equatorial grid size in that finite-volume grid is 417 km x 278 km (orders upon orders of magnitude larger than clouds).
Thanks for the link to GISS ModelE. I'm glad they have some kind of a moist convection scheme. I take back the radiation part, it seems they are handling the moist heat transport in the energy balance which may be ok. Still, the ModelE has an even greater element size, and when you've got energy or inertia transport from element to element, you're averaging. A way to capture this behavior across boundaries is to use mesh refinement, higher-degree shape function or use adaptive meshing, none of which are mentioned in ModelE (though some do show promise)
Adam gets an A+ for sarcasm, we all know that GCM's are serious business
Posted by: ThomasC | July 16, 2009 5:01 PM
No, I didn't think you did. I assumed you meant PER GRID CELL, which is a false statement.
In software, a parameter and variable are very different. So when you said "parameter" I understood you to mean something very different than is implied by the quote above.
My guess is that Model E does something similar but as a result of the somewhat detailed convection-based cloud model, which chases plumes up multiple layers until it stabilizes, appears to have different parameterization for anvil clouds. Hmm actually IIRC from my quick read of the comments in the code they do some horizontal transfer stuff when modeling plumes so maybe it's not as simple as the quote implies is true for HadCM3 (there's already a HadCM4 BTW).
Thank you. I almost posted Adam to say that his sarcastic response was undeserved, because you do seem to be trying to understand and learn, as opposed to certain other people who post here.
Nothing wrong with honest skepticism.
They're working on a new version in preparation for doing new runs for the next round of IPCC stuff (as I understand it).
I have no idea whether the growth in computing power that I assume they can tap into vs. the runs done a few years ago for the last TAR is going to be invested in a smaller grid size or better physics modeling per cell (which implies more computation per cell).
As I'm sure you know, the computational requirements for modeling on this scale are immense, so I'm sure they're constantly weighing trade-offs between better physics modeling with cells, better ways of computing the behavior across cell boundaries, and grid size (which as you mentioned a couple of posts ago limits the size of features that can be resolved directly by the model).
And, of course, how long you're willing to watch the lights blink and the computer center lights go dim while it's running. :) Oh yes, and how many runs you need for averaging to give you reasonable results.
So I'd be surprised if they were unaware of such techniques...
Posted by: dhogaza | July 16, 2009 6:01 PM
Let me clarify a bit, I assumed you meant they picked one parameter per grid cell from a set of global parameters, based say on temp, rel humidity, etc etc.
I hope you'll look at the videos coby has posted, they're interesting.
Posted by: dhogaza | July 16, 2009 6:03 PM
Well hello! I'm back again.
I realise that I am out of my depth scientifically in this forum.
I will no longer pose any questions on various posters opinions on any other aspect of the subject of AGW.
I realise, Coby that you've closed the thread on Prof. Ian Plimer, but I'd just like to ask one more question of all readers: Can I get a show of hands as to who has read his book and who hasn't?
Isn't it healthy to read both sides of an argument and form an opinion based on all the information available?
Rather than base your opinion on the "reviews" why not read it for yourself?
I'm sure the book is available on Amazon.
Here is a link to an interview with the man himself.
I understand that he has ties to Capitalism, but honestly, his explanation of Climate Science makes sense to me.
I have absolutely no ties to big business, science, mining, media, politics or anything that would cause my opinion to be biased. I just want to do the right thing for our earth.
I hope that you, dear reader, will read his book, watch this interview, and then form/keep/change your opinion.
Cheers,
Michael
http://abnnewswire.net/multimedia/en/60659/AUDIO-Professor-Ian-Plimer
Posted by: Michael | July 16, 2009 6:47 PM
You'll be out of your depth on Watts Up With That.
False premise: Plimer's book includes objective information (well, it does accidently include the meta-information that he's a damned liar).
I see no reason to read books by those who claim the earth is only 6,000 years, either, because there's no information there, other than the obvious bit of information that the author's a liar.
Why should I waste my time on lying sacks of nightsoil?
Posted by: dhogaza | July 16, 2009 8:46 PM
Also, the fact that you're scientifically illiterate (which is the only way his explanation could make sense to you) is not our problem.
The problem is that you're allowed to vote.
I'm glad you are, but in the US, at least, our founding fathers recognized that the right to vote leads to the state having an obligation to make sure that all who can, can become as educated as they want (never implemented perfectly, but the Land Grant system of financing education in the 1860s came close to it - and Europe became closer to it yet, by far, after WW II).
Now, with the web, there's really no excuse for you to be an IGNORANT voter.
If you want to vote based on science - LEARN THE SCIENCE. The climate science stuff's not that hard. The denialist case is, for the most part, so trivially false that real scientists largely ignored it until a few years ago (when it became clear that politically-motivated people like you were being propagandized by RWnight lying assholes).
Posted by: dhogaza | July 16, 2009 8:50 PM
Gee whiz dhogaza, you really are quite nasty.
Are you nasty like that to people in real life?
Are you a college professor? A Lecturer? Teacher?
You must be quite knowledgable to be justified in speaking to people like that. I'll bet all your students and colleagues are afraid of you, and resent you for your intellect. I imagine you as a tall, fit, handsome man, a bit like the Indiana Jones of climate science.
What are you talking about with the books that claim the earth is only 6000 years old?
What type of book is that? Are you saying that about Prof. Plimer's book? (sorry, it's my utter stupidity again)
What does "voting" have to do with what I wrote?
What did you think of the video interview? Did the link work ok?
You did of course WATCH at least SOME of it. Because you are a fair minded, free thinking person.
I look forward to your kind words of reply.
Posted by: Michael | July 16, 2009 11:09 PM
On the subject of clouds, I would like to raise the phenomenon of noctilucent clouds, which I don't believe has been discussed here (although it is possible I missed it).
For those who have not been following this story, noctilucent clouds are rather mysterious formations that glow after nightfall (hence the name) about which surprisingly little seems to be known, or at any rate agreed. About the only common ground, as far as I can determine, is the following:
Noctilucent clouds form at extremely high altitudes, typically about 70 to 80 km above the earth. They are thought by some to consist of vast number of tiny ice crystals.
Normally, they form at higher and lower latitudes - between 50 and 70 degrees north (and south). However, over the last year or so they have been spreading well beyond these confines. For example, they have been recently been observed for the first time ever over the southern US states.
There is some speculation that they are linked to volcanic activity, or even (in the case of the most recent ones) to launches of the space shuttle. But whatever the cause, they seem to be relatively new: there is no recorded mention of them before the late 19th century.
Some writers have suggested they may be linked to climate change, although no one seems to know quite why or how.
That's about as much as I have been able to discover. Any thoughts?
Posted by: Snowman | July 16, 2009 11:24 PM
Snowman - don't take this the wrong way but ... thanks for posting something interesting!
All I know about them is what I just read after googling for them, thanks to your comment.
The NASA source I've linked to describes them - apparently they're even higher than you suggest, 80-100km above the surface of the earth. That high, of course, they're made of ice particles, as you say.
The connection with global warming is a simple one: GHGs warm the atmosphere by reducing the amount of heat that escapes the troposphere, causing it to warm while causing everything above the tropopause to cool. This is why stratospheric cooling is considered a fingerprint of GHG-forced warming (because if tropospheric warming is caused by more heat entering the atmosphere due to increased solar output, etc, all layers should warm). Anyway, the mesosphere in which these noctilucent clouds, should be cooling as well, making conditions better for forming these clouds.
If you've not read the NASA summary before, you'll find it interesting, though you might not see anything new there because obviously you've read some informed source(s).
Posted by: dhogaza | July 17, 2009 5:50 AM
No offence taken, dhogaza. I am glad I managed to come up with a contribution you found interesting. Thank you, too, for drawing my attention to the NASA source. It contained new information (new to me, anyway).
I guess time will tell whether or not these clouds are important, or just a passing curiosity. The thing that strikes me as odd is that apparently no one saw them, or at any rate thought they were worth mentioning, before 1885.
Posted by: Snowman | July 17, 2009 7:40 AM
Noctilucent clouds may have not existed before because WV is not supposed to be up that high in the atmosphere. I have heard suggested links to air traffic contrails, those being a source of H2O above the tropopause.
Just to clarify, they do not glow per se, they are just so high that they still catch sunlight after everything else has gone dark.
Posted by: coby | July 17, 2009 8:46 AM
I'd imagine that this is where the possible connection to the space shuttle comes in, too, since the liquid fuel engine, at least, pours out large amounts of water vapor.
Posted by: dhogaza | July 17, 2009 9:24 AM
Hi Coby,
Above in your reply to the imponderables regarding the effects of clouds on climate models, you stated:
"The models could well be drastically underestimating future warming as easily as they could be drastically overestimating. For example, sea ice and ice sheet modeling is very incomplete and thus far nature is responding much more dramatically than the models said we should expect."
According to my own research on the apparent consequences of ice sheet melt I would welcome your comments on the findings of Professor Holgate of UK's Proudman's Oceanographic Lab
http://meteo.lcd.lu/globalwarming/Holgate/sealevel_change_poster_holgate.pdf
Proudman, accords with the datasets from Univ of Colorado in finding that tidal guages don't seem to be indicating ANY additional sea level rises beyond what we would expect naturally from the ongoing warming during an Inter-glacial ( ie. the data shows an average rise of 1.74 ± 0.16mm/yr (about 0.07 in/yr, or 7 inches per century).
Holgate states that the observed sea level rises were higher in the first half of the 20th century compared to the second half. Dare I say then that the models are clearly over-estimating the expected warming if there is no apparent divergence (even slow down) from the historical records if we assume a warming climate causes glacial ice melt and thus rising sea levels.
Posted by: John O'Sullivan | October 7, 2009 12:41 PM
John, I'll take NASA:
http://climate.nasa.gov/keyIndicators/
Satellite data shows sea level increase over the last 15 or so years has accelerated to about 3.3 mm/yr.
Posted by: dhogaza | October 7, 2009 4:15 PM