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Clouds - Positive And Negative Feedback Discussion


pottyprof

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Posted
  • Location: Dorset
  • Location: Dorset

    http://www.uah.edu/news/newsread.php?newsID=875

    http://www.drroyspencer.com/

    http://ams.allenpress.com/archive/1520-044...442-22-1-20.pdf

    Jethro's post on the subject.

    "The projected response to increases in CO2 was an increase in heat trapping Cirrus clouds; this is the corner stone to the much vaunted "positive feedback" loop which would enable increased emissions to raise temperatures. This premise has been included in all models which try to add parameters for clouds (some don't, these are even more inaccurate; clouds are hugely important).

    The latest studies (supported by NASA's Aqua satellite) show that in reality, this is not happening. What is actually happening is a DECREASE in Cirrus clouds - a negative feedback allowing heat to escape to outer space. An inherent, in-built safety valve. It is this component which is preventing run away warming.

    If a positive feedback loop exists between CO2 and water vapour, then it is subject to any inherent negative feedback systems. Breaching or reaching new equilibrium points, relies upon over-riding the immensely powerful natural system; there is no evidence to suggest this is possible. We have to remember, CO2 has a logarithmic effect - the more you add, the less effective it is.

    Here are some links about Cirrus clouds/feedbacks etc.

    "

    A paper posted by me which maybe on the subject.

    My belief is that the spencer/christy letter/research has been disputed by various people included the Metoffice see this paper here http://adsabs.harvard.edu/abs/2007GeoRL..3416702T

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    Guest North Sea Snow Convection

    Thanks for opening the thread.

    Will reply more when I have done more reading on this. Hopefully there is more out there to google than blag about author reputations etc

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    Posted
  • Location: Cheddar Valley, 20mtrs asl
  • Weather Preferences: Snow and lots of it or warm and sunny, no mediocre dross
  • Location: Cheddar Valley, 20mtrs asl

    Thanks for this Potty, more from me after dog walking.

    Iceberg: that paper you linked to is about Tropical vertical temperature trends, not clouds.

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    Posted
  • Location: Cheddar Valley, 20mtrs asl
  • Weather Preferences: Snow and lots of it or warm and sunny, no mediocre dross
  • Location: Cheddar Valley, 20mtrs asl

    Just a quickie before I go....

    Here's a couple of papers which define fairly well the uncertainties regarding clouds and their influence upon projected temperatures:

    http://ieeexplore.ieee.org/xpls/abs_all.js...;isnumber=13305

    http://ams.allenpress.com/perlserv/?reques...75%2FJCLI3799.1

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    Posted
  • Location: Cheddar Valley, 20mtrs asl
  • Weather Preferences: Snow and lots of it or warm and sunny, no mediocre dross
  • Location: Cheddar Valley, 20mtrs asl
    http://climatesci.org/2008/05/13/tropical-...-and-tao-zhang/

    Seems to suggest that most climate models have a weak negative feedback.

    ????? Now you've confused me.

    After consulting the authors (to clarify) this point, the article concludes " This study indicates that the IPCC models are over predicting global warming in response to positive radiative forcing."

    In other words most climate models have a positive feedback, predicting greater warming.

    Here are a few more links explaining the uncertainties in cloud/model predictions:

    http://www.sciencedaily.com/releases/2008/...81124163607.htm

    http://www.sciencedaily.com/releases/2008/...81110071245.htm

    http://www.sciencedaily.com/releases/2008/...81021190646.htm

    http://www.sciencedaily.com/releases/2008/...80611184722.htm

    Apologies for them all being press orientated, haven't got much time so did a quick scan through.

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    Guest North Sea Snow Convection
    ????? Now you've confused me.

    After consulting the authors (to clarify) this point, the article concludes " This study indicates that the IPCC models are over predicting global warming in response to positive radiative forcing."

    In other words most climate models have a positive feedback, predicting greater warming.

    Here are a few more links explaining the uncertainties in cloud/model predictions:

    http://www.sciencedaily.com/releases/2008/...81124163607.htm

    http://www.sciencedaily.com/releases/2008/...81110071245.htm

    http://www.sciencedaily.com/releases/2008/...81021190646.htm

    http://www.sciencedaily.com/releases/2008/...80611184722.htm

    Apologies for them all being press orientated, haven't got much time so did a quick scan through.

    Yes, my take on this is that the IPCC related models have the weak negative feedbacks. In other words the over sensitivity of these models to the various feedbacks involved may well have overcooked the positive feedbacks and underplayed the negative one's :)

    This is important because a lot of the radiation loss of warmth through less cloud (negative feedback) accounts for quite a wedge of AGW theory

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    Posted
  • Location: Mytholmroyd, West Yorks.......
  • Weather Preferences: Hot & Sunny, Cold & Snowy
  • Location: Mytholmroyd, West Yorks.......

    I thought the contrarians were imploring adherents to turn up the 'missing heat' that current levels of CO2 should be providing and now the mechanism for explaining such a shortfall is also a prop to attack AGW with??????

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    Posted
  • Location: Cheddar Valley, 20mtrs asl
  • Weather Preferences: Snow and lots of it or warm and sunny, no mediocre dross
  • Location: Cheddar Valley, 20mtrs asl
    I thought the contrarians were imploring adherents to turn up the 'missing heat' that current levels of CO2 should be providing and now the mechanism for explaining such a shortfall is also a prop to attack AGW with??????

    Who said anything about attacking anything? Why so combative all the time? Could have sworn this thread was to discuss clouds and the uncertainty in the models regarding this aspect.

    Every climate scientist in the world agrees clouds are one of the greatest, if not THE greatest unknowns in all this; if you know better, please do post the links and explain why.

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    Posted
  • Location: Beccles, Suffolk.
  • Weather Preferences: Thunder, snow, heat, sunshine...
  • Location: Beccles, Suffolk.
    I thought the contrarians were imploring adherents to turn up the 'missing heat' that current levels of CO2 should be providing and now the mechanism for explaining such a shortfall is also a prop to attack AGW with??????

    Come one, G-W...That's hardly a good way to start a discussion?

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    Posted
  • Location: Mytholmroyd, West Yorks.......
  • Weather Preferences: Hot & Sunny, Cold & Snowy
  • Location: Mytholmroyd, West Yorks.......

    Sorry guys ,I'll tone it down a tad. It is a bit of a bug bear of mine that and augmentation of our current warming is seen by some as either proof that AGW is wrong or that 'it' (whatever 'it' is ,be it clouds,magnetism,cool phase oscillation) superseded it as a better take on current observations.

    'Clouds' and their impacts/formation/propagation seem to be as complex as system as global warming itself and ,as with AGW, lots more study is needed to help us understand the processes better.

    I can see in a world without excess CO2/greenhouse gasses that cloud cover (be it high level or low level) impacts upon surface temps but when the planet is able to take onboard any excess heat radiating back it could only go to 'modify' the impacts of AGW and neither negate nor replace it as a reason for our warming (IMHO).

    Sorry again for the gripe.

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    Posted
  • Location: Cheddar Valley, 20mtrs asl
  • Weather Preferences: Snow and lots of it or warm and sunny, no mediocre dross
  • Location: Cheddar Valley, 20mtrs asl

    Ian, I think you've mis-understood both the purpose of this thread and the impacts of the uncertainty regarding clouds. No one is saying clouds are causing warming, no one is looking at them as a possible reason to negate or replace CO2 as a cause.

    One of the cornerstones of the IPCC theory upon AGW is that CO2 will warm the oceans, creating more evaporation and thus more clouds. It is this positive feedback which is supposed to cause the largest degree of warming. The idea being that clouds will trap the heat, leading to more warming, leading to more clouds, trapping more heat. CO2 alone is not capable of causing the warming, it relies heavily upon water vapour to amplify it's effects, thus the models used to project future climate change have an in-built positive feedback bias built into them.

    This thread is to examine the new information filtering through that is not only questioning the validity of that bias, but looking at observational evidence which is showing in reality what is happening. The latest information suggests that the opposite is happening and fewer heat trapping clouds are forming, thus allowing extra heat to escape to the atmosphere.

    It would appear Mother Nature may have an in-built thermostat preventing the build up of too much heat. If this is the case, it throws the future projections into complete disarray and we may well have peeked in temperature already.

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    Guest North Sea Snow Convection

    This extract below is taken from Journal of Climate paper - and is a summary of the extensive discussion from within the link provided at the bottom of this post. There is a lot to plough through, but by reading at least some of the discussion, and, from the extract provided, my interpretation is how the gun may be being jumped in terms of the projected CO2 positive feedback (assumed by IPCC) and the potential understating and lack of understanding/awareness of the feedback processes that this paper clearly states are interdependant, and not directed one way (ie just positive). I think that the global observations may well reflect the unexpected extent of the negative feedbacks that Spencer, for eg, has discussed. I would also say that this paper is written without any inherent bias to one side of the argument or another - just a thorough look at the facts and uncertainties involved.:-

    Feedbacks in the climate system associated with clouds continue to be considered as a major source of uncertainty in model projections of global warming. This paper offers a critical discussion of the topic of cloud–climate feedbacks and exposes some of the underlying reasons for the inherent lack of understanding of these feedbacks. Despite the complexity of the cloud feedback problem, it is argued that the basis for understanding such feedbacks, in part, lies in developing a clearer understanding of the association between atmospheric circulation regimes and the cloudiness that characterizes these "weather" regimes.

    One of the factors that has limited progress on the topic specifically concerns the problem of the parameterization of cloud processes in global models and the limited evaluation of these representations. While GCM climate and NWP models represent the most complete description of all the interactions between the processes that establish the main cloud feedbacks, the weak link in the use of these models lies in the cloud parameterization imbedded in them. Aspects of these parameterizations remain worrisome containing levels of empiricism and assumptions that are hard to evaluate with current global observation

    For example, the relationship between convection, cirrus anvil clouds, and SST is a recurring theme in many feedback hypotheses (section 5) yet the connections between convection and cirrus in parameterization schemes is highly uncertain, in many cases empirical, and difficult to evaluate with observations. This is one area where observations are needed to evaluate

    cloud parameterization processes and feedbacks derived from these processes. A second factor that has limited progress concerns the methods developed and used to define and then quantify feedbacks in models. These methods are invariably based on a system's perspective, the implementation of which has been most problematic

    <a href="http://www.gfdl.gov/~ih/jerusalem_papers/S..._JClim_2005.pdf" target="_blank">http://www.gfdl.gov/~ih/jerusalem_papers/S..._JClim_2005.pdf</a>

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    Posted
  • Location: Dorset
  • Location: Dorset

    A bit of info on Cirrus might be helpful for anybody that is trying to understand this (It should be given on a weather forum, but I know that I needed to re-read up on them ! ).

    Taken from Wiki.

    "Cirrus clouds are characterized by thin, wisplike strands, often accompanied by tufts, leading to their common (non-standard) name of mare's tail.[1] Sometimes these clouds are so extensive that they are virtually indistinguishable from one another, forming a sheet of Cirrus called cirrostratus. Sometimes convection at high altitudes produces another form of cirrus called cirrocumulus, a pattern of small cloud tufts which include droplets of supercooled water.

    Many cirrus clouds produce hair like filaments made of the heavier ice crystals that precipitate from them. These "fall streaks", a form of virga, often indicate the difference in the motion of air (wind shear) between the upper part of the cirrus cloud and the air below it. Sometimes the top of the cirrus cloud is moving rapidly above a slower layer of air, or the streak is falling into a faster moving lower layer. The directions of these winds can also vary."

    "Cirrus clouds are formed when water vapor freezes into ice crystals at altitudes above 8000 meters (26,000 ft).[2] Due to the sparse moisture at a high altitude, they tend to be very thin. [1]. At this altitude, aircraft leave condensation trails that can turn into cirrus clouds.[3] This happens when hot exhaust, mostly water, freezes, leaving a visible trail. Streaks may appear straight when wind shear is absent, giving the clouds the appearance of a comma (cirrus uncinus), or tangle, an indication of high-level turbulence. The falling ice crystals evaporate before reaching the ground.

    Cirrus clouds trap and reflect infrared radiation (heat) beneath them (greenhouse effect), but also reflect sunlight to some extent (albedo). It has not yet been determined whether the net effect of cirrus clouds is to warm or cool the earth. Much of the difficulty lies in modeling the albedo effect of clouds composed of various size and shape crystals. Older models tend to underestimate the albedo effect of cirrus. Refinements of these models will improve climate predictions"

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    Posted
  • Location: Dorset
  • Location: Dorset

    Is it worth trying to decided whether an increase in Cirrus has a positive or negative effect on Global temperatures.?. Maybe then going on to the debate of how this fits into AGW.(This way we leave the contentious stuff till last !.

    Reading about it.

    Spencer seems to agree that they have a postive effect on temps.

    ""While low clouds have a predominantly cooling effect due to their shading of sunlight, most cirrus clouds have a net warming effect on the Earth," Spencer said. With high altitude ice clouds their infrared heat trapping exceeds their solar shading effect. "

    This is also the view of the IPCC in AR4.

    Does anybody disagree with this ?.

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    Posted
  • Location: Mytholmroyd, West Yorks.......
  • Weather Preferences: Hot & Sunny, Cold & Snowy
  • Location: Mytholmroyd, West Yorks.......

    The other 'factor' , to me at least, is the post 9/11 grounding of aircraft across the U.S. and it's immediate effect on the temps below. If we are noticing less high cirrus around the equator then what of the increase in con trails globally and their inevitable impacts?

    As far as I can gauge a con trail is much the same as high cirrus, apart from the fact that we seed them of course, and maybe the Post 9/11 'experience' gives us a better insight as to the impact of high level ice crystals and their impacts on temps below.

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    Guest North Sea Snow Convection
    Is it worth trying to decided whether an increase in Cirrus has a positive or negative effect on Global temperatures.?. Maybe then going on to the debate of how this fits into AGW.(This way we leave the contentious stuff till last !.

    Reading about it.

    Spencer seems to agree that they have a postive effect on temps.

    ""While low clouds have a predominantly cooling effect due to their shading of sunlight, most cirrus clouds have a net warming effect on the Earth," Spencer said. With high altitude ice clouds their infrared heat trapping exceeds their solar shading effect. "

    This is also the view of the IPCC in AR4.

    Does anybody disagree with this ?.

    In terms of assuming just the positive feedback in isolation, I would say that is true enough.

    But, and it is a big but, the parameterization of clouds as I highligted in my extract above, and the interplay between the various feedbacks is not well understood and Spencer is demonstrating this by arguing that the assumed increase in cirrus clouds as part of a positive feeback is not an observed process under study.

    Aspects of these parameterizations remain worrisome containing levels of empiricism and assumptions that are hard to evaluate with current global observation.

    Above italicised as highlighted by the Journal paper to mirror these concerns and inconsistencies of thought.

    Those global observations, Spencer declares, show the opposite happening, with less cirrus clouds and therefore a negative feedback that highlight the 'worrisome levels of empiricism and assumptions'

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    Posted
  • Location: Worthing West Sussex
  • Location: Worthing West Sussex
    Is it worth trying to decided whether an increase in Cirrus has a positive or negative effect on Global temperatures.?. Maybe then going on to the debate of how this fits into AGW.(This way we leave the contentious stuff till last !.

    Reading about it.

    Spencer seems to agree that they have a postive effect on temps.

    ""While low clouds have a predominantly cooling effect due to their shading of sunlight, most cirrus clouds have a net warming effect on the Earth," Spencer said. With high altitude ice clouds their infrared heat trapping exceeds their solar shading effect. "

    This is also the view of the IPCC in AR4.

    Does anybody disagree with this ?.

    Going from this summer's experience in the UK, where daily mean temperatures were high, and above average with long periods of wet overcast, subjectively cool summer weather, this would suggest that low cloud cover is also capable of warming, although I cannot say how much cirrus was above the low cloud we experienced, :D , we couldn't see it.

    Surely cloud bases, high or low, reradiate heat differently depending on their temperature - cirrus at -60 deg C or less, cumulus at -4 deg C or more. At infrared wavelengths, don't clouds behave like black bodies, whereas at shorter, visible wavelengths, they either reflect, diffuse or scatter light.

    It is in the visible part of the spectrum that the majority of solar energy is emitted from the sun, and the same part of the spectrum which reaches the surface of the earth, heating surface and ocean, before the heat emitted from the surface or oceans can warm the lower atmosphere, mostly due to the presence of greenhouse gases absorbing the infrared and then transmitting the heat by standard gas thermodynamics to the non-greenhouse gas moieties in the atmosphere. Thence to convection, adiabatic expansion and, under the right conditions, cloud formation.

    Also the transparency of the cloud in the visible spectrum would proportionately let through to the surface, more solar radiation in the form of light, i.e. greater for dry icy cirrus clouds, than for lower level wet droplet-based opaque clouds like cumulus.

    Again, where do you get 100% cover by cirrus clouds, completely obscuring the sun, as is common with lower troposphere cloud cover.

    Finally, are radiation frosts more likely with cirrus clouds than with a similar whole-sky proportion of cumulus clouds in mid winter?

    So for temperate UK, Cirrus warm during the day, neutral at night in summer, cool during the winter. Low cloud warm during the night, cool during the day in summer, warm during winter.

    In duvet terms Cirrus TOG 2.5, Cumulus TOG 5.5. :rolleyes:

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    Posted
  • Location: Dorset
  • Location: Dorset

    I agree with All, that different clouds have different effects, which was why I trying to concentrate on Cirrus, as it was Jethro's original paper.

    I am not saying yet whether the cirrus is increasing or decreasing with AGW.

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    Posted
  • Location: Cheddar Valley, 20mtrs asl
  • Weather Preferences: Snow and lots of it or warm and sunny, no mediocre dross
  • Location: Cheddar Valley, 20mtrs asl

    Here's the latest information; curiouser and curiouser .......

    http://www.terradaily.com/reports/NJIT_Sol...Temps_Rise.html

    Doesn't the period of decreased cloud cover 1985-2000 coincide with the rapid climb in temperatures? We've had increased cloud cover since 2000 but temperatures haven't fallen (?????), they've certainly stopped climbing and I'd hazard a guess the difference in albedo due to less Arctic ice would account for the discrepancy.

    Wonder how this ties in with the Cosmic Ray levels?

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    Posted
  • Location: Worthing West Sussex
  • Location: Worthing West Sussex
    Here's the latest information; curiouser and curiouser .......

    http://www.terradaily.com/reports/NJIT_Sol...Temps_Rise.html

    Doesn't the period of decreased cloud cover 1985-2000 coincide with the rapid climb in temperatures? We've had increased cloud cover since 2000 but temperatures haven't fallen (?????), they've certainly stopped climbing and I'd hazard a guess the difference in albedo due to less Arctic ice would account for the discrepancy.

    Wonder how this ties in with the Cosmic Ray levels?

    The scientists, who monitor the Earth's reflectance by measuring what is known as the moon's earthshine, have observed that the amount of light reflected by Earth - its albedo - has increased since 2000. The result has been less sunlight reaching the Earth's surface.

    This is a non-seqitur - The result is more sunlight reflected, and no indication of how much sunlight has actually reached the surface. We know already that the atmosphere has become much cleaner over the last 20 years - due to fewer major volcanic events and positive effects of removing aerosol-producing sulphur from aviation fuel.

    A clearer atmosphere will lead to an increased albedo, despite the surface receiving exactly the same, or even more radiation than before. Remember reflected sunlight has to pass through the atmosphere twice, and suffer twice the absorption or scattering due to aerosols or haze.

    We know that the earth's atmosphere selectively absorbs some wavelengths from the broad spectrum the sun bathes us in - the earth is blue when viewed from space - we see only the blue sky and multicoloured clouds from the earth's surface, and if we go up in an airplane, from above the clouds the surface looks a hazy blue colour, much the same as those 19th century paintings of the scottish highlands show the distant peaks as blueish shadows.

    Less Arctic ice is also a red herring - the Arctic sea ice only majorly disappears in the last few weeks before the autumn equinox - when the sun is very low in the arctic sky and has very little heating effect on the exposed Arctic Ocean or air, having traveled through a thick slice of Northern hemisphere troposphere before reaching the Arctic Circle. Albedo effects at these latitudes, at this time of year are pretty negligible.

    TOG ratings for clouds would be a good research project - how much does a cirrus compare to a nimbostratus, at different times of the year, varying latitudes etc

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    Posted
  • Location: Cheddar Valley, 20mtrs asl
  • Weather Preferences: Snow and lots of it or warm and sunny, no mediocre dross
  • Location: Cheddar Valley, 20mtrs asl

    I like the TOG rating idea!

    So, what do you reckon then Chris, why the lack of drop in temperatures? Ocean heat content? Questionable temperature records?

    Strange that this is a new paper and yet they only use data up to 2004, I can understand it not being up to 2008 but surely up to 2007 would have been possible.

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    Posted
  • Location: Worthing West Sussex
  • Location: Worthing West Sussex
    I like the TOG rating idea!

    So, what do you reckon then Chris, why the lack of drop in temperatures? Ocean heat content? Questionable temperature records?

    Strange that this is a new paper and yet they only use data up to 2004, I can understand it not being up to 2008 but surely up to 2007 would have been possible.

    I have some doubts about the Earthshine project - so many variables, so many corrections are needed.

    We need to be doing the experiment properly, with a sensor that can reliably measure and constantly monitor the relative spectral magnitude of the whole earth from some point far enough away in space - like pointed earthward on the SOHO satellite for instance. Accurate earth-sun and earth-sensor distances would also be needed, with regular sensor calibrations using stars of known stable magnitudes.

    Heat energy is generated at the surface of the land, and in the first hundred metres or so of the ocean surface, when solar radiation hits it. Any light that is reflected has a chance of being scattered, or going back into space.

    So Ocean heat content, questionable methodologies (and poor practice) and records of temperature measurement must all play their part.

    Cloud formation releases heat into the atmosphere - this is a golden rule with water - due to latent heat of vaporization or condensation and then latent heat of freezing/melting. Carbon dioxide cannot dump large amounts of heat into specific layers of the atmosphere, water can, does. As we get higher in the atmosphere, Carbon dioxide remains well mixed, water is not, having been removed by condensation. Thus Carbon dioxide does not actually contribute so much to warming the atmosphere, as cooling it - since it remains well mixed into the upper troposphere and the lower stratosphere, where its net radiation to space exceeds its net radiation back to earth. This is a bit of a puzzler for the warmers.

    There's one other thing. Clouds several miles thick still don't blot out all the sunlight, and however bright it is from space, the earth's atmosphere still absorbs some of the solar

    input. In other words, clouds are not perfect mirrors. And no doubt clouds also let out some of the heat. It even happens on Venus, apparently!

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