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  • 11ºC warming, climate crisis in 10 years? « RealClimate
    us a big favor in this case given that the probability density function most runs predicted about 3 For example 7 Taskforce did not say that climate collapse was 10 years away Although the report does say that achieving a concentration of 400ppm of carbon dioxide by 2100 gives the best chance 80 according to the Baer research see footnote 14 of preventing a 2 degree C rise the Taskforce members are well aware that other emission pathways are possible and that between now and 2100 our understanding of the climate system will improve Of course our chances at leveling out at 400 ppmv CO2 are indistinguishable from zero Finally so how do I say 1 C and get it to format correctly 9 loveall says 31 Jan 2005 at 1 13 AM If it is true that very high the earth will as hot as sun 10 John Finn says 31 Jan 2005 at 7 28 AM Gavin On climate sensitivity As a quick and dirty estimate why can t we use the Stefan Boltzmann equation In particular use the first derviative i e dE dT then calculate the sensitivity from the inverse dT dE which gives 1 4 x Sigma T 3 where Sigma 5 67 x 10 8 T 288k current earth temperature This gives a sensitivity of 0 18 deg C per W m2 which obviously doesn t agree with the 0 75 deg C per W m2 but does agree more with some modern day observations e g Pinatubo Response The Earth is not a blackbody Therefore theories that apply to blackbodies don t work The low sensitivity you quote is just as incredible as the high numbers discussed above think about what it would imply for the glacial climate The notion that the response to Pinatubo can determine equilibrium climate sensitivity is rather odd and is not supported by evidence Models with average sensitivities do a very good job simulating the Pinatubo eruption and aftermath see Soden et al 2002 Shindell et al 2004 gavin 11 John Finn says 31 Jan 2005 at 7 40 AM For instance total forcings since 1850 are around 1 6 1 W m2 the temperature change is around 0 7 0 1 C Gavin As around half the temperature rise took place BEFORE the bulk of the increase in forcing this seems like false logic Response The forcings have been increasing since 1850 see here and taking the longest period possible minimises the influence of intrinsic decadal variability in the climate system But you seem to have missed the point entirely The calculation is being done to show that it does not provide a good constraint Looking at just the last 30 years would be even worse gavin 12 DrMaggie says 31 Jan 2005 at 9 02 AM Re 4 Judging from information at the WWF International website www panda org I believe the WWF report referred to by e g BBC is to be found via this link The text linked to in 4 above is rather an abstract for a paper to be presented at the upcoming climate conference in the UK 13 Scott Robertson says 31 Jan 2005 at 12 15 PM If you can believe it this link is from Fox News re Shrinking Glaciers Although it is an AP story they still ran it without contrarian opinion http www foxnews com story 0 2933 145824 00 html 14 Dave Frame says 31 Jan 2005 at 1 10 PM Hi Gavin I enjoyed your discussion of the Stainforth et al paper and agree with a lot of what you have to say These are preliminary results and we have yet to apply tougher constraints Claudio Piani is currently working on a paper which attempts to provide a measure of model skill compared to recent climate this work is in parallel to the sorts of things David Sexton has been doing at the Hadley Centre for the QUMP experiment and similar to some of the work that has been undertaken as part of CMIP 2 That may well rule out quite a few models not just or maybe even the high sensitivity ones We also have plans to use the results from this first phase of the experiment in a fully coupled ensemble which will simulate 1950 2000 which will be a significant step along the road Later this year we hope This will allow us to compare models to data under realistic 20th century forcings where realistic is an ensemble in itself That should provide quite a good constraint on the models As you say paleoclimate simulations provide a constraint on this sort of experiment and we are proposing a paleo prediction net ensemble with Paul Valdes in a follow up experiment currently under peer review for funding If I had to bet a fiver on it I d agree with you that the high sensitvities are unlikely but until we ve run the ensemble accounting for uncertainties in the paleo record and cogniscent of the possibilities of a non constant sensitivity between now and the reasonably distant past amongst other things I don t think we re in a position to actually rule them out Interestingly our results are actually pretty consistent with a lot of the recent literature on sensitivity All studies comparing simple models with recent climate change from Andronova and Schlesinger 2001 onwards find high sensitivities more than 8K say are consistent at the few percent level with the observed record unless they are ruled out a priori Now we find general circulation models displaying such sensitivities that are not significantly less consistent with current climate observations than the standard models used by the IPCC As coordinator of climateprediction net and as an author on Stainforth et al I groaned at some of the media coverage London s Metro was particularly bad and I was a bit embarrassed by the way Sky News edited an interview I did with them I made a whole bunch of qualifications none of which were aired Where they got a chance to tell the full story I think Dave Stainforth and Myles managed to get the message across reasonably well but where the journos were clearly focused on the 11 degree angle of the story which is a part of it things got a lot more untidy Worst of all were the second hand articles Anyway thanks for the article which adds a lot of context that mainstream media reports usually lack Good luck with the site which is an excellent idea and thanks for thinking of us in your links If we can contribute anything to realclimate org please just let us know it s a very worthwhile endeavour Cheers Dave Frame climateprediction net coordinator Response Thanks for your response The Andronova study like the Forest and Knutti papers uses the instrumental period to try and constrain sensitivity and so suffers from the same problems discussed above I agree that a priori we can t assume that the high end simulations will fall by the wayside once more validation is done but that is my hunch based on model valdiation that we perform at GISS and my own experience with paleo climate modelling The media can be a difficult beast to control and I ve found through much trial and error that as well as telling them what you want them to say you have to be extremely clear about what you don t want them to say I wish you luck in the next phases of the project and look forward to seeing the results gavin 15 John Finn says 31 Jan 2005 at 1 19 PM The forcings have been increasing since 1850 see here I ve seen there and the net cumulative total forcings are zero negative up until atound the mid 1920s But any increase then won t have any effect for several years surely because of the lag you ve discussed earlier 16 Tom Huntington says 31 Jan 2005 at 1 40 PM It is my understanding that the uncertainties regarding climate sensitivity to a nominal 2XCO2 forcing is primarily a function of the uncertainties in 1 future atmospheric aerosol concentrations both sulfate type cooling and black carbon type warming 2 feedbacks associated with aerosol effects on the properties of clouds e g will cloud droplets become more reflective 3 changes in surface albedo of snow ice due to changes in temperature and deposition of mineral and black carbon particulates and last but arguably most significantly 4 the intensity of the positive feedback that comes from the inevitable increase in the concentration of water vapor in the atmosphere as the atmosphere warms as indicated by the Clausius Clapeyron equation Your analysis of the issue of sensitivity seems to be largely restricted to the effects of aerosols On a separate point my understanding of the global dimming issue is that aerosols responsible for dimming were possibly masking a higher climate sensitivity to GHG increases than would have been inferred in the absence of this dimming suggesting that further increases in GHGs without compensating aerosol increases would result in more warming than would have been predicted prior to the acknowledgement of the global dimming phenomenon Response You may be confusing two issues here The 2xCO2 experiment is not in any sense a prediction It is just an experiment done to estimate the climate sensitivity and it is not affected by uncertainies in other historical forcings like solar or aerosols Note that the water vapour feedback in the 2xCO2 experiments is an important part of the response Projections for the future and indeed hindcasts for 20th Century do depend on the other forcings It is the uncertainty in those forcings particularly aerosols and their various direct and indirect effects that prevent the historical period from constraining global climate sensitivity The reason therefore why global dimming really doesn t have an implication for the climate sensitivity is precisely because of those uncertainties look at the error bars on my back of the envelope calculation in paragraph 3 gavin 17 John Finn says 31 Jan 2005 at 1 53 PM A couple of questions on the following A reasonable estimate of the forcings is 6 6 1 5 W m2 roughly half from albedo changes slightly less than half from greenhouse gases CO2 CH4 N2O This implies a forcing of 3 W m2 for albedo changes presumably due to additional ice snow sheets Is there a reference somewhere which explains how this is calculated I understand that the current albedo of the earth is responsible for about 107 W m2 Also what forcing is assumed for the reduction of water vapour It would help if any response to this included current forcing for WV I accept this may be variable but some approximate range of values will do Also on a previous post regarding the application of the Stefan Boltzmann you say The Earth is not a blackbody Therefore theories that apply to blackbodies don t work I know the earth is not a true black body but I thought the equation still held if an emissivity factor was included As the earth s emissivity is around 90 this will admittedly increase the sensitivity but not substantially Response All forcings are calculated by changing the boundary conditions in this case the distribution of glacial ice and looking to see what the change in net radiation is while keeping everything else constant Water vapour is a feedback not a forcing though since people keep failing to understand the distinction I will do a post on this topic at some point S B works only in the absence of feedbacks The quantification of the feedbacks is the whole point of the exercise gavin 18 Mike Atkinson says 31 Jan 2005 at 2 21 PM It seems that the ice age climate constraining a 2xCO2 doubling Climate Sensitivity is dependent on the assumption that the sensitivity is linear in the entire range of CO2 values from ice age levels much below present to 2x preindustrial values You also seem to be apportioning ice age climate sensitivity among albedo CO2 and atmospheric dust ignoring other forcings in a way that the errors in CO2 forcing and temperature change are correlated and then assuming that they are uncorrelated I may be wrong about this I m still learning and you may be justified in treating them as uncorrelated even if they are correlated Can other ice age forcings be ignored In particular variations of the Solar constant how I love variable constants and ozone Response All of these are good points Actually the basic assumption is that climate sensitivity is the roughly constant not linear for warming and cooling effects This is not the case exactly in climate models but it s a reasonable approximation We could argue about the exact size of the effect but I doubt that it would exceed the error bars quoted The LGM forcings include other well mixed GHGs CH4 and N2O since they are constrained by ice core records Other forcings O3 solar other aerosols may play a role but are currently extremely poorly constrained i e not at all If subsequent investigation found that they were indeed important which a priori they aren t expected to be then the calculation would need to be revised It seems more likely that we have considered the biggest players I don t understand your point about errors in CO2 and T being correlated The CO2 level comes from half a dozen different ice core analyses while the temperature data come from marine sediments pollen analyses isotopes corals etc Why would the errors in the different proxies be correlated gavin Response also re solar forcing and ice ages the ice ages are fairly regular and match the timescales of orbital forcing There is no known solar variation on this timescale It would be odd if there just happened to be a solar cycle on exactly the 100 kyr timescale William 19 Joel Shore says 31 Jan 2005 at 2 37 PM Just to follow up on John Finn s question 10 if one puts in a rough value for the emissivity of the earth whatever that might be so one is no longer assuming it is a perfect blackbody then does the resulting estimate for climate sensitivity correspond to what one would expect in the absence of any feedback effects I e does that provide a reasonable estimate of the direct effect of the forcing before feedbacks or are there other reasons why it still too simplistic even for that Response In the absence of any feedbacks that is what you d get But feedbacks are the whole point if you have any kind of climate system you get feedbacks The interesting question is how big they are and you can t get that assuming Stefan Boltzmann gavin 20 Mike Atkinson says 31 Jan 2005 at 2 54 PM About CO2 sensitivity temperature correlation I meant that the attribution of the forcing between Ice albedo CO2 etc might be dependent on the temperature For instance would the CO2 sensitivity in C W m2 be dependent on the temperature whether a 5 or 6 C drop Response Yes Sensitivity is the ratio of the temperature to the forcings so if the temperature estimate changed so would the implied sensitivity I built in an uncertainty of 0 5 C in that but you can easily do the math if you think I underestimate the error or got the mean wrong gavin 21 Lynn Vincentnathan says 31 Jan 2005 at 3 05 PM It is sort of reassuring that 11 degrees C is far fetched I say sort of since 5 8 degrees which you suggest as the more scientifically founded upper possibility may be dangerous enough Please correct my faulty understanding but I have read secondary sources that 251 million years ago it is thought there was 6 degrees global warming from natural causes and that this triggered massive CO2 and CH4 releases leading to runaway global warming and massive extinction Is this wrong I understand 5 8 is a possibility not a high probability but if such warming were to happen could this lead to runaway global warming Or would that require something higher or is that whole scenario so unlikely as to be dismissed outright Response The 5 8 degrees is not for climate sensitivity that is a projection for 2100 using the biggest likely sensitivity and the fastest growth in greenhouse gases Many of the media reports also confused the two temperature ranges The biggest sensitivity currently for any of the state of the art climate models is 4 1 deg C for 2xCO2 but it may be as high as 5 deg C As far as information concering the Permian Triassic extinction event goes it is all pretty speculative The amount of available data is very sparse and so while these kind of deep time paleoclimate questions are a lot of fun the lack of detail means that they have limited implications for today s climate Runaway greenhouse warming can occur for really extreme conditions Venus at present Earth in maybe 5 billion years time when the sun becomes a red giant but is not a possibility for the next hundred years I find it rather an overused term in climate discussions gavin 22 Peter J Wetzel says 31 Jan 2005 at 8 44 PM Just to quickly interject a little help for Gavin The Stephan Boltzman argument applies to the top of atmosphere exchange of and balance of radiation But all the really meaty good stuff regarding feedbacks and climate change happens between the top of the atmosphere and the surface where we are attemting to define sensitivies How does CO2 increase affect the water vapor exchange the cloud amount and its incredibly complex feedbacks involving aerosols precipitation efficiency and the resultant radiation balance at the 1 2 meter height thermometer shelters where humanity defines his her climate How do the complex feedbacks change atmospheric circulation patterns and the interaction of these patterns to changes in ice cap topography e g at the LGM How do these feedbacks and the atmospheric circulation changes interact to affect the ocean circulation including shifts in location of deep water formation and cold water upwelling depth of the thermocline etc etc The problem is mighty complex Science is doing its best to grapple with all this complexity to understand it and to model it under the constraints of finite computational power Earth system modeling is a valuable tool for testing the sensitivities But fundamental research into understaning the processes that drive the Earth system is also still rapidly advancing The best answer science can provide today is sure to be superceded by a much better answer quickly Hang loose and keep an eye on this site P S A lot of reseach energy is being devoted to the study of Methane Clathrates a huge source of greenhouse gases which could be released from the ocean if the thermocline the buoyant stable layer of warm water which overlies the near freezing deep ocean dropped in depth considerably due to GHG warming or especially if the deep ocean waters were warmed by very very extreme changes from the current climate such that deep water temperatures no longer hovered within 4C of freezing but warmed to something like 18C It would seem to be required that very drastic warming of the deep ocean is the only way that this source of Methane would be released and trigger a runaway greenhouse warming 23 dave says 31 Jan 2005 at 10 33 PM Re 21 The End Permian Extinction I think it is a mistake to casually dismiss recent findings on this extinction as all pretty speculative More and more data is coming to light on this event There are complete sediment records especially in China that have allowed much more thorough inspection events at the Permo Triassic boundary Take a look at How to kill almost all life from which I quote Since then and especially since 1995 the whole story has become clearer Four main parallel themes have arisen noted here not necessarily in chronological order First the Permo Triassic PTr boundary has been dated precisely to 251 My ago Mya Second the Siberian traps vast volumes of volcanic lavas have also been dated more precisely than had been possible before and the peak of their eruption history matches the PTr boundary Third extensive study of rock sections that straddle the PTr boundary and the discovery of new sections began to show a common pattern of environmental changes through the latest Permian and earliest Triassic 253 249 Mya Fourth studies of stable isotopes oxygen and carbon in those rock sections revealed a common story of environmental turmoil The oxygen isotope record does indeed indicate a rise of about 6 degrees C just before the worst happened Global warming brought on by increased atmospheric CO2 from volcanism is thought to be the cause of this extinction A theory about an impact at the time has little support Furthermore the large negative shift in the C13 isotope at the time can only be explained by the release of light carbon from methane clathrates 22 A new paper by Ward et al Science Jan 20 2005 provides more light on what happened Oxygen levels dropped the oceans became stratified a critical warming threshold was exceeded I m not saying we re on the verge of another extinction like the end Permian However with these big numbers being thrown around for example 8K in Dave Frame s post 14 it seems prudent to remember what may have happened 251 mya when over 90 of Earth s species went extinct 24 John Finn says 1 Feb 2005 at 5 49 AM Response All forcings are calculated by changing the boundary conditions in this case the distribution of glacial ice and looking to see what the change in net radiation is while keeping everything else constant Water vapour is a feedback not a forcing though since people keep failing to understand the distinction I will do a post on this topic at some point S B works only in the absence of feedbacks The quantification of the feedbacks is the whole point of the exercise gavin Right So can we take it from this that the climate forcing from feedbacks are far and away the most dominant factor despite the fact that they haven t been accurately quantified We can wait for the post on Water Vapour and feedback effect for a response to this Also could you include a comment on the NASA report around March 2004 by Minschwaner which from observations suggested that we may be over estimating feedbacks But a question for now The 0 5 deg C which is still in the pipeline when is this going to become evident Put it this way if atmospheric levels of CO2 were fixed at to day s level 380ppm indefinitely when would we see global temperatures 0 5 deg C higher than to day 25 John Finn says 1 Feb 2005 at 6 12 AM Just to quickly interject a little help for Gavin The Stephan Boltzman argument applies to the top of atmosphere exchange of and balance of radiation But all the really meaty good stuff regarding feedbacks and climate change happens between the top of the atmosphere and the surface where we are attemting to define sensitivies Peter This is fair enough But surely S B can be applied at the surface asw well Around 240 W m2 are emitted from the top of the atmosphere at around 255k as S B confirms but around 390 W m2 at 288k are emitted from the surface The difference is due as you say to the meaty bit in the middle A rough calculation here would suggest a sensitivity of about 0 22 deg C BUT after a long drawn out process we ve established not just that feedbacks are not included as Gavin seems to think I ve misunderstood but the actual magnitude of the feedbacks These seem to be around 2 3 times the direct forcing from CO2 alone It would help if someone could confirm this 26 Jeffrey Davis says 1 Feb 2005 at 10 09 AM In reference to dave s comment 23 Ward s time frame for the Permian extinction is 10 million years Human beings won t be human beings in 10 million years regardless of CO2 levels 27 Lynn Vincentnathan says 1 Feb 2005 at 10 41 AM Re 21 thanks for the clarification I guess what I meant by runaway global warming was could a high end warming scenario using the biggest likely sensitivity and fastest growth in GHGs eventually trigger natural positive feedback loops of GHG emissions not referring to people using their ACs more due to the warming thus emitting more GHGs causing more warming even if people reduced their GHG emissions say by 90 in which the emissions from nature the warming would continue to increase for at least some time period I understand we are too far from the sun to have a permanent and extreme Venus effect unless the sun becomes a lot hotter brighter And I m not necessarily looking at only 2100 but simply in the future by 2200 or 2300 or whatever As mentioned in an earlier post as a layperson I am more interested in avoiding false negatives so I don t need 95 90 or even 20 certainty to be thinking about this For example I might take an umbrella if only a 20 chance of rain has been predicted And regarding an article I read in 2004 about 2 years of acceleration in atmospheric CO2 concentrations What if this were to become a trend and continue would this indicate the positive feedback loops are becoming more prominent and the negative feedback loops less prominent I know most of you on this site both the questioners experts are way above my knowledge on the subject but I do appreciate your efforts to explain this to layperson like myself I do talk about the subject and I would not want to be way off track 28 dave says 1 Feb 2005 at 3 35 PM Re dangerous interference As of today the Avoiding Dangerous Climate Change is in session at the Hadley Centre Here is the program for the conference Many of the papers being presented there are available online 29 Peter J Wetzel says 1 Feb 2005 at 3 43 PM For John Finn The S B relationship is fundamental to define the climate of the Earth at every level of the atmosphere from the top to the surface At the crux of cliate models you will find the integration of that equation through all atmospheric layers accounting for the emission contributions of all the radiationally active matter in those layers You ve used the S B formula to calculate dQ dT at typical terrestrial temperatures Your calculation describes how much difference in infrared radiational heating dQ results from a given increment of temperature change assuming emissivity and everything else remain fixed CO2 sensitivity is defined by doing the integration of the S B equation through an ensemble of typical present day atmospheric conditions twice first with CO2 at 280ppm then with it at 560ppm Because CO2 makes the atmosphere more opaque to infrared radiation and because the atmosphere gets colder as you get higher the effective radiation temperature of the infrared radiation leaving the earth is made colder by increasing CO2 fewer Watts per square meter of infrared radiation leave the top of the atmosphere It is the reduced amount of radiation leaving the top of the atmosphere that changes the earth s balance of heat and therefore defines the direct radiative forcing caused by doubling CO2 Now it should be obvious that this pair of calculations using a fixed present day atmosphere with 1xCO2 and 2xCO2 does not account for the feedbacks If 4W m2 less heat escapes the top of the atmosphere but the same amount of heat is still coming in from the sun some physical change must occur in order to restore the energy balance The most intuitively reasonable thing that could happen is that the atmosphere would warm up until 4 more W m2 are emitted by the S B law But how will this warming be distributed through the atmosphere This is where the complexity of the feedbacks begins The temperature sensitivity discussion is all about how the atmosphere the oceans the biosphere and the cryosphere adjust to this forcing change The degrees of freedom and the range of time scales involved in the adjustment process are immense and are not all well understood And many things besides just temperature end up adjusting I apologize if this was all too basic Maybe I missed the point But I d like to inject one more facet of the discussion The uncontrolled experiment which we are performing and attempting to observe and model involves many more anthropogenic forcings than just CO2 The infamous IPCC Figure 6 6 actually just skims the surface of the impacts humanity is imposing on Earth The figure is infamous from my perspective because it conveys an impression of much more certainty than I believe a responsible flagship figure featured prominently in the executive summary should do The big big HUGE uncertainty bar that you do not see there belonging to the cloud feedbacks is the most egregious issue Beyond that there are other major missing components left out because they are the most uncertain and certainly not because they can be expected to have little affect Of these others the most important ones are the 2nd aerosol indirect effect and Land use change effects beyond albedo especially the infrared emission effect Both of these just happen to be very likely to be net cooling effects 30 Pat N Self only says 1 Feb 2005 at 10 39 PM I would like to see discussion about the most recent period of rapid global warming leading to the Paleocene Eocene Thermal Maximum PETM about 55 million years ago including differences and similarities to the climate projections for this century and beyond There is evidence that a large area of dense forests rapidly became swamp where the northern Great Plains now lie Evidence includes fossils of subtropical tropical conditions existing 50 million years ago in the lakes of the area now known as southwest Wyoming northeast Utah and northwest Colorado Diplomystus fossil fish from southwest Wyoming can be viewed here at realclimate by clicking my name a hotlink that follows 31 dave says 1 Feb 2005 at 10 48 PM Re 26 and the end Permian 23 I know this is a comment thread but the comment 26 distorts the science so let s get that right The period of study by Ward et al is 10 million years That is not the time scale of the extinction I haven t gotten a look at that paper yet although the title is Abrupt and Gradual extinction The actual extinction took place at the boundary sediment beds 25 26 in the paper I cited synchronous with the Siberian trap volcanism 251 1 3 mya on a scale which is 3 orders of magnitude less counted in 10 s of thousands of years than the 10 million years you cite Measurements from 251 mya can not be more precise Look at the paper I cited in 23 and Rapid and synchronous collapse of marine and terrestrial ecosystems during the end Permian biotic crisis by Richard J Twitchett abstract here Sorry not online The time frame given there is 10 to 60 kya At this level of resolution nothing further can be said about time scales So your comment does not affect mine at all Obviously what was happening at the end Permian is very different than what is going on now I merely said it is prudent to keep these kind of results in mind and would further add that the Earth s systems may have surprises in store for us If you require further references I will be pleased to provide them 32 Jan Hollan says 2 Feb 2005 at 9 05 AM Regarding the correspondence of temperature and radiative S B fluxes I made a scheme back in 1999 trying to visualize the problem With newer numbers it s now available as warmin ppf within http amper ped muni cz gw articles there are the source PostScript I wrote easy to edit and pdf png made from it I left the current forcing at 3 W m2 even if may be too much I did not want to change the greenhouse scheme warmin en The equivalent bb temperatures of downward atmospheric radiation are 1 8 3 05 and 6 2 Â C jenik 33 DrMaggie says 2 Feb 2005 at 9 15 AM Re 30 While it of course is very interesting to find out more about the climate in different parts of the world during ancient periods of Earth s development I feel that it might be quite important to remember that e g 55 million years BP the distribution of land masses across the globe was quite different from what it is now Some interesting illustrations of continental drift can be found here Could one of the experts comment on how this would affect the balance of the various climate forcings I guess that e g the overall albedo could be affected as well as the solar heating of the oceans and the land surfaces continents were placed at different latitudes Also the potential pathways of oceanic circulation patterns would be affcted and the presence or absence of large mountain ranges would impact on wind and precipitation patterns 34 John Finn says 2 Feb 2005 at 9 59 AM Re 29 Peter Many thanks for your response No need to apologise for being too basic it helps to confirm my understanding My posts on S B were intended to provoke discussion on issues similar to the ones you raised in your post Hopefully realclimate will do an article some time Thanks again 35 Tom Huntington says 2 Feb 2005 at 10 10 AM For Peter Wetzl If the second indirect effect of aerosols can be simplified as the development of precipitation and thus the cloud liquid water path lifetime of individual clouds and the consequent geographic extent of cloudiness quoted from the IPCC TAR http www grida no climate ipcc tar wg1 185 htm and the evidence now points towards increasing evaporation at least over the oceans and precipitation globally can you explain how this is very likely a net cooling effect as described in Comment 29 when it could also be argued that this is consistent with an increase in lower atmospheric water vapor content this particular feedback resulting in warming What is the best guess of the experts regarding the balance of the cooling versus warming effects of increasing clouds water vapor Will increasing cloudiness necessarily result in net cooling What is the balance of the cooling effects of reflectivity versus warming effects of insulation at night Can you suggest an updated revision to IPCC Figure 6 6 that reflect advances in understanding since its publication in 2001 I would also love to see a comparable figure that showed the feedbacks like water vapor in the same watts per square meter format Response The most up to date estimates that we have made to the forcings diagram are available http www giss nasa gov data simodel efficacy and in particular fig 28 gavin 36 Jeffrey Davis says 2 Feb 2005 at 12 12 PM Responding to 31 My reference to the 10 million year

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  • Assombrissement Global II « RealClimate
    So the burden would seem to be completely on the aerosol indirect effects since they must first counteract the moisture starvation thinner cloud effect then go on to actually reduce the total observed solar radiation If this argument is sound it seems to suggest that aerosol indirect effects may actually be stronger than first thought Comments 3 Beate Liepert says 20 Jan 2005 at 2 52 PM Thank you for your encouragements Let me explain my arguments a bit better 1 In Feichter et al 2004 we describe a modelling study were we run the climate model twice One run is with estimates of present day anthropogenic and natural aerosols and green house gases called present day scenario 1985 In the second simulation we reduce the aerosols to the natural concentrations called pre industrial 1885 and keep the greenhouse gases constant at present day level 1985 This is what you would assume as a scenario when we clean up aerosols See table 4 AP experiment in the paper we turn the argument around and discuss the effect of aerosol increase The result is a temperature increase of 0 8 degree Celcius in this particular model MPI Hamburg Note that this model does not include ocean dynamics Subjectively I find 0 8 degree a lot hotter 2 I agree my 2004 paper provides counterintuitive arguments Let me please explain it in more detail and I hope you ll see my point The key is the difference between moisture storage and moisture fluxes GHGs modify storage and fluxes and aerosols modify fluxes When temperature increases in the atmosphere due to GHGs the moisture holding capacity should go up following the Clausius Clapeyron formulation The simulated model atmosphere is indeed moister absolute humidity goes up It is relative humidity not absolute humidity that governs cloud formation Relative humidity is fairly constant because it depends on other meteorological factors such as circulation e g ITCZ Once cloud formation takes place in a moister atmosphere these clouds hold more water and should be optical thicker Optically thicker clouds reduce sun light Reduced sunlight reduces evaporation Now you say this should lead to moisture starvation in the atmosphere Correct but BUT there is another way to increase atmospheric moisure Leave moisture in the atmospheric storage for a longer time with the same or less fluxes in and out Lifetime of water vapor goes up from 10 to 10 1 2 days The indirect effect as it is simulated in this model reduces precipitation efficency and helps keep rel humidity and cloud cover constant This is indeed as you mention important to actually tip the balance towards reduced evaporation in a moister and warmer world Note the the indirect effect is highly uncertain Hence you are right that indirect aerosol effect is important But moisture can increase because the atmosphere can hold more due to warming Hence it IS the combination of both Incidentally even in greenhouse gas only simulations when you have an increase in rainfall and evaporation this increase is not as great as you d expect from Clausius Clapeyron because of the fairly constant rel humidity and cloud coverage Even in greenhouse gas only simulations the lifetime of water vapor increases The lifetime effect counteracts the increases in rain and evaporation due to the Clausius Claperyron In these GHG experiments however the lifetime effect is small compared to the Clausius Clapeyron effect Thus it is plausible to get a warmer moister darker world where it rains less 4 Peter J Wetzel says 20 Jan 2005 at 6 10 PM Thank you I understand and accept that The GHG warmed atmosphere maintains a greater moisture reservoir through which moisture cycles more slowly than its pre industrial counterpart That is what your model reveals and it is also fairly intuitive Still there remains a question in my mind about the relative importance of the GHG warming and the aerosol indirect effects on global dimming If I understand you correctly the model you use demonstrates that a net reduction in solar radiation a portion of the dimming is caused by the GHG warming effect alone However there is a lack of consensus among the 10 models quoted in IPCC TAR on this issue See Fig 7 2 with the accompanying statement that In response to any climate perturbation the response of cloudiness thereby introduces feedbacks whose sign and amplitude are largely unknown first paragraph I would appreciate your perspective on this Specifically what fraction of the dimming would you estimate from your work to be caused by the GHG warming And finally if it is fair to make this request how much would you estimate this fraction to vary among the 10 models quoted in IPCC TAR 5 Beate Liepert says 20 Jan 2005 at 8 00 PM The relative importance of GHG warming and indirect effect and a revised version of the IPCC TAR of the cloud feedback is exactly what I am working on Results should be out soon Sorry I can t tell more Patience Beate 6 Peter J Wetzel says 20 Jan 2005 at 9 43 PM Reluctantly I shall wait As Gavin and Mike recently posted regarding peer review science normally advances in baby steps The quantum leaps that the general public perceives are almost always the result of a long and unheralded period of foundation building behind the scenes I hope you will post here when a paper is accepted Best wishes Pete 7 Ferdinand Engelbeen says 21 Jan 2005 at 4 54 AM Some more questions 1 The emission of sulphate aerosols in Europe is drastically reduced since the mid seventies 70 The largest effect of this reduction should be found downwind of the main sources According to the Hadcm3 model a difference of 5 K in north Scandinavia Russia over a 10 years time span But there is no difference in trends attributable to aerosols between less contaminated area s and the area with the highest contamination See aerosols

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  • Global Dimming II « RealClimate
    day anthropogenic and natural aerosols and green house gases called present day scenario 1985 In the second simulation we reduce the aerosols to the natural concentrations called pre industrial 1885 and keep the greenhouse gases constant at present day level 1985 This is what you would assume as a scenario when we clean up aerosols See table 4 AP experiment in the paper we turn the argument around and discuss the effect of aerosol increase The result is a temperature increase of 0 8 degree Celcius in this particular model MPI Hamburg Note that this model does not include ocean dynamics Subjectively I find 0 8 degree a lot hotter 2 I agree my 2004 paper provides counterintuitive arguments Let me please explain it in more detail and I hope you ll see my point The key is the difference between moisture storage and moisture fluxes GHGs modify storage and fluxes and aerosols modify fluxes When temperature increases in the atmosphere due to GHGs the moisture holding capacity should go up following the Clausius Clapeyron formulation The simulated model atmosphere is indeed moister absolute humidity goes up It is relative humidity not absolute humidity that governs cloud formation Relative humidity is fairly constant because it depends on other meteorological factors such as circulation e g ITCZ Once cloud formation takes place in a moister atmosphere these clouds hold more water and should be optical thicker Optically thicker clouds reduce sun light Reduced sunlight reduces evaporation Now you say this should lead to moisture starvation in the atmosphere Correct but BUT there is another way to increase atmospheric moisure Leave moisture in the atmospheric storage for a longer time with the same or less fluxes in and out Lifetime of water vapor goes up from 10 to 10 1 2 days The indirect effect as it is simulated in this model reduces precipitation efficency and helps keep rel humidity and cloud cover constant This is indeed as you mention important to actually tip the balance towards reduced evaporation in a moister and warmer world Note the the indirect effect is highly uncertain Hence you are right that indirect aerosol effect is important But moisture can increase because the atmosphere can hold more due to warming Hence it IS the combination of both Incidentally even in greenhouse gas only simulations when you have an increase in rainfall and evaporation this increase is not as great as you d expect from Clausius Clapeyron because of the fairly constant rel humidity and cloud coverage Even in greenhouse gas only simulations the lifetime of water vapor increases The lifetime effect counteracts the increases in rain and evaporation due to the Clausius Claperyron In these GHG experiments however the lifetime effect is small compared to the Clausius Clapeyron effect Thus it is plausible to get a warmer moister darker world where it rains less 4 Peter J Wetzel says 20 Jan 2005 at 6 10 PM Thank you I understand and accept that The GHG warmed atmosphere maintains a greater moisture reservoir through which moisture cycles more slowly than its pre industrial counterpart That is what your model reveals and it is also fairly intuitive Still there remains a question in my mind about the relative importance of the GHG warming and the aerosol indirect effects on global dimming If I understand you correctly the model you use demonstrates that a net reduction in solar radiation a portion of the dimming is caused by the GHG warming effect alone However there is a lack of consensus among the 10 models quoted in IPCC TAR on this issue See Fig 7 2 with the accompanying statement that In response to any climate perturbation the response of cloudiness thereby introduces feedbacks whose sign and amplitude are largely unknown first paragraph I would appreciate your perspective on this Specifically what fraction of the dimming would you estimate from your work to be caused by the GHG warming And finally if it is fair to make this request how much would you estimate this fraction to vary among the 10 models quoted in IPCC TAR 5 Beate Liepert says 20 Jan 2005 at 8 00 PM The relative importance of GHG warming and indirect effect and a revised version of the IPCC TAR of the cloud feedback is exactly what I am working on Results should be out soon Sorry I can t tell more Patience Beate 6 Peter J Wetzel says 20 Jan 2005 at 9 43 PM Reluctantly I shall wait As Gavin and Mike recently posted regarding peer review science normally advances in baby steps The quantum leaps that the general public perceives are almost always the result of a long and unheralded period of foundation building behind the scenes I hope you will post here when a paper is accepted Best wishes Pete 7 Ferdinand Engelbeen says 21 Jan 2005 at 4 54 AM Some more questions 1 The emission of sulphate aerosols in Europe is drastically reduced since the mid seventies 70 The largest effect of this reduction should be found downwind of the main sources According to the Hadcm3 model a difference of 5 K in north Scandinavia Russia over a 10 years time span But there is no difference in trends attributable to aerosols between less contaminated area s and the area with the highest contamination See aerosols 2 An investigation in Switzerland presented at the latest dimming conference on your pages see dimming conference shows that the reduction in surface solar insolation was compensated by increased downward LW radiation This was attributed to the measured increase of water vapour But should one not expect less water evaporation with decreased insolation And what part of the SW of incoming sunlight is absorbed by water vapour and how much W m2 Response due to the complexities of the system there is no need for decreased evap if its occurred to result in lower WV In fact a bit speculative it can be the other

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  • Liens entre Pollution et Climat « RealClimate
    ailleurs dans le monde Plus précisément l augmentation des émissions de méthane ailleurs dans le monde pourrait accroître les niveaux de base d ozone sur les USA conduisant à une pollution en 2030 analogue à celle que nous avons vue dans les années 1990 Il y a donc encore beaucoup à apprendre sur les liens entre le climat et la pollution Comme l ozone de surface et les MP ont des effets négatifs sur la santé humaine il est important de connaître ces liens References Aw J and M J Kleeman Evaluating the first order effect of intraannual air pollution on urban air pollution J Geophys Res 108 4365 10 1029 2002JD002688 2003 Fiore A M D J Jacob B D Field D G Streets S D Fernandes and C Jang Linking ozone pollution and climate change The case for controlling methane Geophys Res Lett 29 1919 doi 10 1029 2002GL015601 2002 Hogrefe C B Lynn K Civerolo J Y Ku J Rosenthal C Rosenzweig S Gaffin K Knowlton and P L Kinney Simulating changes in regional air pollution over the eastern United States due to changes in global and regional climate and emissions J Geophys Res 109 D22301 doi 10 1029 2004JD004690 2004 Mickley L J D J Jacob B D Field and D Rind Effects of future climate change on regional air pollution episodes in the United States Geophys Res Let 30 L24103 doi 10 1029 2004GL021216 2004 Comments pop up 8 8 Responses to Liens entre Pollution et Climat 1 Dano says 26 Apr 2005 at 10 35 AM Good piece Loretta and the GRL paper looks good A question many of the precursors to O3 formation are VOCs and my study area trees contribute a significant fraction of VOCs to the atm Tree canopies also can change the boundary layer mixing in cities making it harder for wind to sweep out the goop in the air Were you able in your work for this paper to contact anyone and explore whether elevated CO2 levels decrease tree metabolic rates and thus decrease VOC emissions Best D 2 Tim says 27 Apr 2005 at 6 07 AM Unfortunately there isn t yet much understanding of the large amount of interannual variability in blocking high pressure systems seen in the last few decades So it is very hard to make a prediction of what might happen to blocking in a climate change experiment Whilst it is important to consider the possible effects of climate change on problems such as this I think it is best to emphasise that the dominant cause is the availability of the precursor pollution and that reducing this pollution by making changes to transport systems and industry is the best way of tackling this problem 3 Dan says 27 Apr 2005 at 7 16 AM Biogenic VOCs are highly reactive and the emissions are substantial especially in humid warm seasons I wonder in the case of blocking patterns leading to drought and well above normal temperatures if biogenic VOC emissions might actually decrease Short of the vegetation actually dying from the drought of course 4 Dusty Bradshaw says 29 Apr 2005 at 11 12 PM I know this study focuses on ambient air pollution but has anyone looked into trends to see if we humankind in developed nations stay indoors more during heat waves thereby subjecting ourselves to increased levels of indoor air pollution Common sense tells me to stay in where its cool when its hot Should we be asking if indoor air pollution will become a bigger issue as summers get hotter due to the effects of Global Warming DB 5 Ferdinand Engelbeen says 2 May 2005 at 5 36 AM I have the impression that the prediction of future climate pollution links is rather speculative In the not so long past the worst pollution was during cold calm high humidity weather at the time coal was used in open fire places leading to the infamous pea soup smog in London killing elderly people Since that time SO2 and lead were reduced with over 80 PM10 with over 60 and NOx with over 40 in all Western countries As NOx is the main driver for low level ozone formation it s further reduction should have a large impact About biogenical VOC s these are mainly formed in summer where high temperatures and secondly high light photosynthesis are the primary drivers Natural VOC s exceed anthropogenic emissions with a factor 3 8 Some interesting literature about biogenical VOC s http boreal fmi fi biphorep report chapter7 pdf and http ethesis helsinki fi julkaisut mat kemia vk hakola biogenic pdf 6 Loretta says 2 May 2005 at 6 02 AM Responses 1 and 3 Yes the emissions of volatile organic carbon VOCs from vegetation play a role in ozone formation In cities like Atlanta with lush vegetation biogenic VOCs together with anthropogenic nitrogen oxides can have a significant impact on regional pollution The emissions of biogenic VOCs increase rapidly as temperatures increase But plants also respond to changing CO2 While some plants may flourish in an enriched CO2 atmosphere VOC emissions may decrease And as Dan points out below vegetation may also suffer from heat or water stress in a changing climate It s a complicated picture I did not include any of these biogenic effects in my simple sensitivity study I kept emissions of pollution precursors constant All I wanted to see was this if I increase the long lived greenhouse gases like CO2 in the model and let the climate respond what happens to the patterns of air circulation What I found was that stagnation events lasted longer in the future model atmosphere On the other hand Hogrefe et al 2004 did include the biogenic VOCs that Dano and Dan are talking about Of the effects listed above Hogrefe et al 2004 considered only the temperature effect on biogenic VOC emissions They found a 10 50 increase in these emissions with climate change

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  • Pollution-Climate Connections « RealClimate
    D Fernandes and C Jang Linking ozone pollution and climate change The case for controlling methane Geophys Res Lett 29 1919 doi 10 1029 2002GL015601 2002 Hogrefe C B Lynn K Civerolo J Y Ku J Rosenthal C Rosenzweig S Gaffin K Knowlton and P L Kinney Simulating changes in regional air pollution over the eastern United States due to changes in global and regional climate and emissions J Geophys Res 109 D22301 doi 10 1029 2004JD004690 2004 Mickley L J D J Jacob B D Field and D Rind Effects of future climate change on regional air pollution episodes in the United States Geophys Res Let 30 L24103 doi 10 1029 2004GL021216 2004 Comments pop up 8 8 Responses to Pollution Climate Connections 1 Dano says 26 Apr 2005 at 10 35 AM Good piece Loretta and the GRL paper looks good A question many of the precursors to O3 formation are VOCs and my study area trees contribute a significant fraction of VOCs to the atm Tree canopies also can change the boundary layer mixing in cities making it harder for wind to sweep out the goop in the air Were you able in your work for this paper to contact anyone and explore whether elevated CO2 levels decrease tree metabolic rates and thus decrease VOC emissions Best D 2 Tim says 27 Apr 2005 at 6 07 AM Unfortunately there isn t yet much understanding of the large amount of interannual variability in blocking high pressure systems seen in the last few decades So it is very hard to make a prediction of what might happen to blocking in a climate change experiment Whilst it is important to consider the possible effects of climate change on problems such as this I think it is best to emphasise that the dominant cause is the availability of the precursor pollution and that reducing this pollution by making changes to transport systems and industry is the best way of tackling this problem 3 Dan says 27 Apr 2005 at 7 16 AM Biogenic VOCs are highly reactive and the emissions are substantial especially in humid warm seasons I wonder in the case of blocking patterns leading to drought and well above normal temperatures if biogenic VOC emissions might actually decrease Short of the vegetation actually dying from the drought of course 4 Dusty Bradshaw says 29 Apr 2005 at 11 12 PM I know this study focuses on ambient air pollution but has anyone looked into trends to see if we humankind in developed nations stay indoors more during heat waves thereby subjecting ourselves to increased levels of indoor air pollution Common sense tells me to stay in where its cool when its hot Should we be asking if indoor air pollution will become a bigger issue as summers get hotter due to the effects of Global Warming DB 5 Ferdinand Engelbeen says 2 May 2005 at 5 36 AM I have the impression that the prediction of future climate pollution links is rather speculative In the not so long past the worst pollution was during cold calm high humidity weather at the time coal was used in open fire places leading to the infamous pea soup smog in London killing elderly people Since that time SO2 and lead were reduced with over 80 PM10 with over 60 and NOx with over 40 in all Western countries As NOx is the main driver for low level ozone formation it s further reduction should have a large impact About biogenical VOC s these are mainly formed in summer where high temperatures and secondly high light photosynthesis are the primary drivers Natural VOC s exceed anthropogenic emissions with a factor 3 8 Some interesting literature about biogenical VOC s http boreal fmi fi biphorep report chapter7 pdf and http ethesis helsinki fi julkaisut mat kemia vk hakola biogenic pdf 6 Loretta says 2 May 2005 at 6 02 AM Responses 1 and 3 Yes the emissions of volatile organic carbon VOCs from vegetation play a role in ozone formation In cities like Atlanta with lush vegetation biogenic VOCs together with anthropogenic nitrogen oxides can have a significant impact on regional pollution The emissions of biogenic VOCs increase rapidly as temperatures increase But plants also respond to changing CO2 While some plants may flourish in an enriched CO2 atmosphere VOC emissions may decrease And as Dan points out below vegetation may also suffer from heat or water stress in a changing climate It s a complicated picture I did not include any of these biogenic effects in my simple sensitivity study I kept emissions of pollution precursors constant All I wanted to see was this if I increase the long lived greenhouse gases like CO2 in the model and let the climate respond what happens to the patterns of air circulation What I found was that stagnation events lasted longer in the future model atmosphere On the other hand Hogrefe et al 2004 did include the biogenic VOCs that Dano and Dan are talking about Of the effects listed above Hogrefe et al 2004 considered only the temperature effect on biogenic VOC emissions They found a 10 50 increase in these emissions with climate change over the eastern U S Unfortunately there isn t yet much understanding of the large amount of interannual variability in blocking high pressure systems seen in the last few decades So it is very hard to make a prediction of what might happen to blocking in a climate change experiment 2 I agree with Tim that more work is needed to understand what controls cyclone and anticyclone variability in the observation record A number of model studies such as our own have found a decline in cyclone number in a future atmosphere The model trends can be explained with mechanisms such as the flattening of the temperature gradient from equator to pole Improving our understanding of present day variability will give us greater confidence in what these models

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  • Un avenir brillant pour l’assombrissement global ? « RealClimate
    the same thing BUT these results have only just been published they need to be digested and considered by the experts Happily they are about in time to feed into the next IPCC report AR4 William 9 Michael Jankowski says 16 May 2005 at 3 05 PM It seems to me that AGD imming would precede AGW Is that not a reasonable assumption and why The earliest AGD information I can find is from the late 1950s What about before then Is AGD a possible contributor the LIA Doesn t the idea AGD conflict with the measure temperature rise during the first part of the 20th century After all if there were AGD at that time and the temperature rise of the first part of the 20th century is attributed as it normally is to natural attenuation then that would indicate a higher level of natural variation than previously thought Response Radiometer values are probably too imprecise and too few to make useful estimates pre 1950 it is apparently rather harder than one might suspect to measure downwards solar to the degree of precision required with no long term drift Anthro influence on climate is generally considered to start about 1850 ish so connecting it to the LIA is unlikely William 10 paul cole says 16 May 2005 at 5 36 PM Couldn t variations in dimming simply be due to volcanic activity and the amount of matter in the atmosphere caused by eruptions 11 John Finn says 17 May 2005 at 4 49 AM So the incoming solar is not just being reflected out to space at least not totally or even largely it may be partly it must be being redistributed either scattered and being absorbed somewhere above the surface or some other effect William Fair point some may be absorbed elsewhere But it s reasonable to assume that some is also reflected back into space The some no longer being reflected could easily account for the 1990s warming In fact what about this for a hypothesis Early 20th century reduced volcanic activity plus increased solar activity leads to increased global temperatures this is pretty much accepted anyway Mid 20th century increased aerosol effect reverses warming trend to produce slight cooling again more or less in line with current thinking Late 20th century cleaner technology results in reduced aerosol effect in atmosphere and a return to a warming trend I think I ve cracked it Response I think you re over interpreting it William 12 Michael Jankowski says 17 May 2005 at 8 46 AM Anthro influence on climate is generally considered to start about 1850 ish so connecting it to the LIA is unlikely I m well aware of this but aren t people usually thinking in the context of GHGs not particulates As for the pre 1950 dimming values air pollution was extremely bad at times Waves of deadly smog and black fog have been recorded Couldn t these have been significant enough to affect global temps and if so then wouldn t they have masked some of the natural warming that we witnessed in the first part of the 20th century Response The true answer to both your questions is I don t know for sure But to some extent particulates aerosol scales with GHG emissions Which is why pre 1850 the values are likely to have been small globally however large they may have been locally But also yes its possible that they may well have had effects pre 1950s its just that the obs to verify this are hard to come by William 13 Ken says 18 May 2005 at 3 05 AM I ve had climateprediction running on my computer for a few months but I m not sure I m getting my money s worth Why hasn t global dimming brightening shown up in the models Is this sort of thing beyond the predictive capability of climate science Response It depends on the kind of experiment you are running If it is either a control or a CO2 doubling run you probably won t see it though that will depend on the cloud feedbacks in your configuration If you are doing a greenhouse gas sulphates run though I m not sure that is on offer then it s likely to be clearer You should probably ask on their message boards how you could diagnose this you need to find a diagnostic that sounds like incident solar radiation at ground gavin Response HadAM3 certainly includes sfc downwards SW as a diag 1 235 I think but whether its available from within the CP net framework is doubtful William 14 Jan Hollan says 18 May 2005 at 5 44 AM There is a simple reason why dimming or brightening have not so much to do with forcing Changes in daytime solar radiation reaching ground due to changes in atmospheric albedo by anthropogenic short lived tropospheric aerosols are large but they are compensated quite a lot by more thermal insulation working day and night for longwave infrared radiation clear sky insulates much worse Amount of compensation is difficult to compute This is the main idea which remained in my mind after reading all the papers and discussions about the problem the last time and forgetting them again I hope I don t oversimplify it Of course soot is warmed directly by sun so there is some redistribution too dimming is not the same as increased albedo 15 Michael Jankowski says 18 May 2005 at 8 35 AM Some pollution enhances the greenhouse effect some particulate pollution has slowed global warming and as stated in the link below some particulate pollution enhances both global warming and polar ice cap melting http www livescience com environment 050328 arctic soot html As if climate modeling weren t complicated enough 16 John Finn says 18 May 2005 at 9 21 AM I ve had climateprediction running on my computer for a few months but I m not sure I m getting my money s worth Why hasn t global dimming brightening shown up in the models Is this sort of thing beyond the predictive capability of climate science Sulphate aerosol features are not available as standard in current versions of climateprediction These will however be available in climateprediction version 3 7 1 22 which is due for release on April 1st 2006 It is possible though to get additional climate factors by downloading the Fudge Factor suite of plug ins absolutely free of charge Response JF is correct Maybe many people don t realise exactly what they are running from CP net If you look at http climateprediction net science strategy php you ll see that the existing runs are 15 years each of calibration pre industrial CO2 then 2 CO2 Phase 2 not yet available is simulations of the last 50 years but this requires a full ocean which is rather harder to set up and slower to run factor of 2 at least and possibly 4 William 17 Michael Tobis says 18 May 2005 at 12 55 PM Re 8 Scientists have gut instincts as much as anyone else but we know or at least ought to know better than to rely on them Sometimes nature takes us by surprise All scientists must always be vigilant about not letting our expectations color our results I think climate scientists should be especially scrupulous to avoid reporting our intuitions and having them enter into public discourse 18 Dave Dardinger says 18 May 2005 at 6 23 PM Since nobody else appears to have mentioned it let me throw out a possibilty which would combine the global brightening results with the recent finding that the earth s energy balance is off IR is absorbed in the top few mm of ocean but visible light is only absorbed at greater depths which depend on the exact wavelength Now if we ve had a recent post space age clearing in the atmosphere then there will be on average more visible light absorbed by the ocean Since this energy is absorbed at depth it will much more easily mixed with deeper water resulting in not being sent back to space OTOH additional IR from GHGs in the atmosphere will be largely used to evaporate more water vapor from the water s surface The net result is that the ocean surface will be absorbing more energy than it emits until such time as either more cloud cover occurs or when sufficient heat is absorbed to equilibrate the oceans to a higher temperature Response Solar does penetrate into the ocean but I suspect that the bulk of it is absorbed in the top say 10 meters Over a fairly large fraction of the ocean the mixed layer wherein the ocean is close to isothermal is deeper than this So that probably means that the solar stays close to the surface and is thermally in contact with the surface values Its also the case that we don t need anything else to explain the heat balance of the ocean being off that is already explainable Indeed any additional explanation would probably leave the balance off again William 19 Dave Dardinger says 19 May 2005 at 1 19 PM Oh my William I have to laugh at your supposed point Reread what you wrote and tell me it doesn t amount to We ve gotten the results we want let s quit while we re ahead This is rather an inside joke among skeptics concerning warmers but to actually hear one say it even if just as a slip of the tongue is risible However to pass on to the factual point could someone point to where we can find how mixing in the top layer of the ocean occurs and how fast It may well be that the top few meters of ocean mix quickly but even so that doesn t mean we re dealing with something which can be ignored After all the total amount out of balance is less than 1 watt M2 For instance might we assume that a given amount of solar radiation which penetrates to 5 meters is equally likely to mix downward to 10 meters as to rise to the surface Response Williams point is accurate The maximum penetration of solar radiation is down to about 80m but anyone who has ever done any diving will have noticed that most of the red and yellow parts of the spectrum have been absorbed even in crystal clear water by about 15m depth Mixed layer depths range from a few tens of meters in the tropics to hundreds of meters in the North Atlantic and so the penetration of solar radiation directly below the mixed layer is very small Heat gets into the mixed layer which mixes quite fast as a function of the wind and buoyancy forcing through long wave and solar radiation as well as through sensible heat Those heat anomalies effectively diffuses into the deeper ocean and that is what s being seen in the ocean heat content diagnostics gavin Response Rather than laughing you might be better off thinking We have a physically and observationally consistent theory and model for the radiation inbalance Why would we want to substitute for that a physically unrealistic mechanism If there was a puzzle needing explanation as for example the mid tropospheric temperatures then speculation looks more sensible William 20 Allen says 19 May 2005 at 2 42 PM A worldclimatereport com article approaches this topic with a mix of caution and dramatic statements on the potential implications See http www worldclimatereport com index php 2005 05 10 global warming something new under the sun Perhaps RealClimate could address some of the most visible interpretations that are popping up in response to these papers Thanks Response WCR perceptively notes that Obviously something is very wrong here but its probably their own analysis which makes the std mistake of assuming that these changes in direct solar translate directly into changes in the radiative forcing of the earth William belatedly signed 21 Dave Dardinger says 19 May 2005 at 4 01 PM Re Gavin s response to 18 Not having ever studied Oceanography I went looking to find out a bit about Bouyancy Forcing Found an interesting paper http opd apl washington edu dasaro FLOATTECH DAsaro01 pdf What I liked is a set of data at the bottom of page 8 which describes the contributions to buoyancy flux for various factors It shows Buoyancy flux is the sum of that due to short and longwave radiation and that due to sensible and latent heat fluxes Average values of these quantities are 41 22 4 and 27 W m 2 respectively This shows I think that more short wavelength radiation will produce more mixing while more long wavelength IR radiation for instance from more GHGs will result in less mixing It would seem to me that this difference in mixing should result in global brightening sending more heat to depth quite irrespective of how much short wavelength radiation is absorbed below the mixed layer Response Err no Any increase in heating from whatever source causes less mixing because it makes the surface more buoyant than before There is a slight difference in this effect because the solar radiation penetrates a little further in but since wind mixing is such a strong factor in practice this is not a significant effect However the changes in ocean heat content are not being driven by big changes in mixing depths they are mainly driven by the diffusion of heat anomalies at the base of the mixed layer and that is the same whatever the mechanism is for warming the mixed layer itself gavin 22 Steve Bloom says 22 May 2005 at 4 28 AM Re 20 Note that the principal writer for World Climate Report site is none other than Pat Michaels which means that the site is another member of the happy ExxonMobil family See http www exxonsecrets org html orgfactsheet php id 85 23 Ferdinand Engelbeen says 22 May 2005 at 9 30 AM With some delay Science needs two weeks to arrive in the library here I have read the different articles about global dimming and I must say I am confused First the magnitude of the changes These are enormous compared to what can be expected for the change in greenhouse gases and aerosols in the period of interest according to models About the suggestion that aerosols may be involved Although the emissions in Western Europe have sharply declined over 50 since 1975 the timing doesn t correspond to the decrease in insolation until 1990 and the recovery thereafter Neither does that correspond to the increase in solar radiation in Australia and Antarctica since 1990 where human made aerosols have no measurable impact Moreover the global emission of sulphate aerosols is near steady since 1975 but with a large shift from Europe and North America toward SE Asia This may be seen in the data of India but China with an explosively increasing industry shows increasing insolation Further more insolation also means less reflection of incoming light as good as by clouds as by the surface itself But that is contradicted by the earthshine measurements which measure how much visible light is reflected by the earth s atmosphere on the dark side of the moon These trends show exactly the opposite of what is measured at the surface and by earth orbiting satellites Further direct and reflected solar light is only one part of the balance downward IR radiation from water vapour and other GHG s and IR radiation from the surface water evaporation precipitation â all play a role in distributing energy from warmer to cooler places and what is received from the sun and emitted back to space Interesting is that in the 20N 20S even 30N 30S area the amount of extra solar energy on the surface 2 W m2 in the last decades is more than compensated by more IR radiance back to space 5 W m2 measured at the top of the atmosphere How the balance for the whole earth is is not known to me and I haven t found the data yet Thus what causes global dimming and back I suppose that most is by changes in water vapour as can be seen in data from the Alps The change in water vapour there is three times larger than expected from CO2 induced water vapour feedback by models and the downward IR radiation more than compensates for insolation losses It is impossible to distinguish between natural water vapour variability and feedback induced by CO2 But by searching for surrogate water vapour levels as indicated by discharge river flows there is no trend in the river Rhine figure 13 North Alps discharge but a solar cycle related trend in the river Po South Alps discharge â Thus probably induced by the prevailing SW winds from over the warmer Atlantic As the Swiss have surface based upward and downward IR measurements on different places between 370 m and 3580 m elevation in the Alps some of them equipped with several filters on different wavelengths of interest it should be possible to make a difference in trends between CO2 induced downward IR radiation and that induced by water vapour This may give a better indication of what happens in the atmosphere today Response Be careful that you don t compare apples and oranges Flux changes at the surface are NOT the same as flux changes at the tropopause the definition used for the forcings bar chart The surface numbers can be quite large and yet have little or no impact at the tropopause In the case of global dimming aerosols and clouds have an effect both at the ground and at the tropopause but the ground numbers are much bigger Secondly 1990 is not a magic turnaround date Instead

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  • Global Dimming may have a brighter future « RealClimate
    Is AGD a possible contributor the LIA Doesn t the idea AGD conflict with the measure temperature rise during the first part of the 20th century After all if there were AGD at that time and the temperature rise of the first part of the 20th century is attributed as it normally is to natural attenuation then that would indicate a higher level of natural variation than previously thought Response Radiometer values are probably too imprecise and too few to make useful estimates pre 1950 it is apparently rather harder than one might suspect to measure downwards solar to the degree of precision required with no long term drift Anthro influence on climate is generally considered to start about 1850 ish so connecting it to the LIA is unlikely William 10 paul cole says 16 May 2005 at 5 36 PM Couldn t variations in dimming simply be due to volcanic activity and the amount of matter in the atmosphere caused by eruptions 11 John Finn says 17 May 2005 at 4 49 AM So the incoming solar is not just being reflected out to space at least not totally or even largely it may be partly it must be being redistributed either scattered and being absorbed somewhere above the surface or some other effect William Fair point some may be absorbed elsewhere But it s reasonable to assume that some is also reflected back into space The some no longer being reflected could easily account for the 1990s warming In fact what about this for a hypothesis Early 20th century reduced volcanic activity plus increased solar activity leads to increased global temperatures this is pretty much accepted anyway Mid 20th century increased aerosol effect reverses warming trend to produce slight cooling again more or less in line with current thinking Late 20th century cleaner technology results in reduced aerosol effect in atmosphere and a return to a warming trend I think I ve cracked it Response I think you re over interpreting it William 12 Michael Jankowski says 17 May 2005 at 8 46 AM Anthro influence on climate is generally considered to start about 1850 ish so connecting it to the LIA is unlikely I m well aware of this but aren t people usually thinking in the context of GHGs not particulates As for the pre 1950 dimming values air pollution was extremely bad at times Waves of deadly smog and black fog have been recorded Couldn t these have been significant enough to affect global temps and if so then wouldn t they have masked some of the natural warming that we witnessed in the first part of the 20th century Response The true answer to both your questions is I don t know for sure But to some extent particulates aerosol scales with GHG emissions Which is why pre 1850 the values are likely to have been small globally however large they may have been locally But also yes its possible that they may well have had effects pre 1950s its just that the obs to verify this are hard to come by William 13 Ken says 18 May 2005 at 3 05 AM I ve had climateprediction running on my computer for a few months but I m not sure I m getting my money s worth Why hasn t global dimming brightening shown up in the models Is this sort of thing beyond the predictive capability of climate science Response It depends on the kind of experiment you are running If it is either a control or a CO2 doubling run you probably won t see it though that will depend on the cloud feedbacks in your configuration If you are doing a greenhouse gas sulphates run though I m not sure that is on offer then it s likely to be clearer You should probably ask on their message boards how you could diagnose this you need to find a diagnostic that sounds like incident solar radiation at ground gavin Response HadAM3 certainly includes sfc downwards SW as a diag 1 235 I think but whether its available from within the CP net framework is doubtful William 14 Jan Hollan says 18 May 2005 at 5 44 AM There is a simple reason why dimming or brightening have not so much to do with forcing Changes in daytime solar radiation reaching ground due to changes in atmospheric albedo by anthropogenic short lived tropospheric aerosols are large but they are compensated quite a lot by more thermal insulation working day and night for longwave infrared radiation clear sky insulates much worse Amount of compensation is difficult to compute This is the main idea which remained in my mind after reading all the papers and discussions about the problem the last time and forgetting them again I hope I don t oversimplify it Of course soot is warmed directly by sun so there is some redistribution too dimming is not the same as increased albedo 15 Michael Jankowski says 18 May 2005 at 8 35 AM Some pollution enhances the greenhouse effect some particulate pollution has slowed global warming and as stated in the link below some particulate pollution enhances both global warming and polar ice cap melting http www livescience com environment 050328 arctic soot html As if climate modeling weren t complicated enough 16 John Finn says 18 May 2005 at 9 21 AM I ve had climateprediction running on my computer for a few months but I m not sure I m getting my money s worth Why hasn t global dimming brightening shown up in the models Is this sort of thing beyond the predictive capability of climate science Sulphate aerosol features are not available as standard in current versions of climateprediction These will however be available in climateprediction version 3 7 1 22 which is due for release on April 1st 2006 It is possible though to get additional climate factors by downloading the Fudge Factor suite of plug ins absolutely free of charge Response JF is correct Maybe many people don t realise exactly what they are running from CP net If you look at http climateprediction net science strategy php you ll see that the existing runs are 15 years each of calibration pre industrial CO2 then 2 CO2 Phase 2 not yet available is simulations of the last 50 years but this requires a full ocean which is rather harder to set up and slower to run factor of 2 at least and possibly 4 William 17 Michael Tobis says 18 May 2005 at 12 55 PM Re 8 Scientists have gut instincts as much as anyone else but we know or at least ought to know better than to rely on them Sometimes nature takes us by surprise All scientists must always be vigilant about not letting our expectations color our results I think climate scientists should be especially scrupulous to avoid reporting our intuitions and having them enter into public discourse 18 Dave Dardinger says 18 May 2005 at 6 23 PM Since nobody else appears to have mentioned it let me throw out a possibilty which would combine the global brightening results with the recent finding that the earth s energy balance is off IR is absorbed in the top few mm of ocean but visible light is only absorbed at greater depths which depend on the exact wavelength Now if we ve had a recent post space age clearing in the atmosphere then there will be on average more visible light absorbed by the ocean Since this energy is absorbed at depth it will much more easily mixed with deeper water resulting in not being sent back to space OTOH additional IR from GHGs in the atmosphere will be largely used to evaporate more water vapor from the water s surface The net result is that the ocean surface will be absorbing more energy than it emits until such time as either more cloud cover occurs or when sufficient heat is absorbed to equilibrate the oceans to a higher temperature Response Solar does penetrate into the ocean but I suspect that the bulk of it is absorbed in the top say 10 meters Over a fairly large fraction of the ocean the mixed layer wherein the ocean is close to isothermal is deeper than this So that probably means that the solar stays close to the surface and is thermally in contact with the surface values Its also the case that we don t need anything else to explain the heat balance of the ocean being off that is already explainable Indeed any additional explanation would probably leave the balance off again William 19 Dave Dardinger says 19 May 2005 at 1 19 PM Oh my William I have to laugh at your supposed point Reread what you wrote and tell me it doesn t amount to We ve gotten the results we want let s quit while we re ahead This is rather an inside joke among skeptics concerning warmers but to actually hear one say it even if just as a slip of the tongue is risible However to pass on to the factual point could someone point to where we can find how mixing in the top layer of the ocean occurs and how fast It may well be that the top few meters of ocean mix quickly but even so that doesn t mean we re dealing with something which can be ignored After all the total amount out of balance is less than 1 watt M2 For instance might we assume that a given amount of solar radiation which penetrates to 5 meters is equally likely to mix downward to 10 meters as to rise to the surface Response Williams point is accurate The maximum penetration of solar radiation is down to about 80m but anyone who has ever done any diving will have noticed that most of the red and yellow parts of the spectrum have been absorbed even in crystal clear water by about 15m depth Mixed layer depths range from a few tens of meters in the tropics to hundreds of meters in the North Atlantic and so the penetration of solar radiation directly below the mixed layer is very small Heat gets into the mixed layer which mixes quite fast as a function of the wind and buoyancy forcing through long wave and solar radiation as well as through sensible heat Those heat anomalies effectively diffuses into the deeper ocean and that is what s being seen in the ocean heat content diagnostics gavin Response Rather than laughing you might be better off thinking We have a physically and observationally consistent theory and model for the radiation inbalance Why would we want to substitute for that a physically unrealistic mechanism If there was a puzzle needing explanation as for example the mid tropospheric temperatures then speculation looks more sensible William 20 Allen says 19 May 2005 at 2 42 PM A worldclimatereport com article approaches this topic with a mix of caution and dramatic statements on the potential implications See http www worldclimatereport com index php 2005 05 10 global warming something new under the sun Perhaps RealClimate could address some of the most visible interpretations that are popping up in response to these papers Thanks Response WCR perceptively notes that Obviously something is very wrong here but its probably their own analysis which makes the std mistake of assuming that these changes in direct solar translate directly into changes in the radiative forcing of the earth William belatedly signed 21 Dave Dardinger says 19 May 2005 at 4 01 PM Re Gavin s response to 18 Not having ever studied Oceanography I went looking to find out a bit about Bouyancy Forcing Found an interesting paper http opd apl washington edu dasaro FLOATTECH DAsaro01 pdf What I liked is a set of data at the bottom of page 8 which describes the contributions to buoyancy flux for various factors It shows Buoyancy flux is the sum of that due to short and longwave radiation and that due to sensible and latent heat fluxes Average values of these quantities are 41 22 4 and 27 W m 2 respectively This shows I think that more short wavelength radiation will produce more mixing while more long wavelength IR radiation for instance from more GHGs will result in less mixing It would seem to me that this difference in mixing should result in global brightening sending more heat to depth quite irrespective of how much short wavelength radiation is absorbed below the mixed layer Response Err no Any increase in heating from whatever source causes less mixing because it makes the surface more buoyant than before There is a slight difference in this effect because the solar radiation penetrates a little further in but since wind mixing is such a strong factor in practice this is not a significant effect However the changes in ocean heat content are not being driven by big changes in mixing depths they are mainly driven by the diffusion of heat anomalies at the base of the mixed layer and that is the same whatever the mechanism is for warming the mixed layer itself gavin 22 Steve Bloom says 22 May 2005 at 4 28 AM Re 20 Note that the principal writer for World Climate Report site is none other than Pat Michaels which means that the site is another member of the happy ExxonMobil family See http www exxonsecrets org html orgfactsheet php id 85 23 Ferdinand Engelbeen says 22 May 2005 at 9 30 AM With some delay Science needs two weeks to arrive in the library here I have read the different articles about global dimming and I must say I am confused First the magnitude of the changes These are enormous compared to what can be expected for the change in greenhouse gases and aerosols in the period of interest according to models About the suggestion that aerosols may be involved Although the emissions in Western Europe have sharply declined over 50 since 1975 the timing doesn t correspond to the decrease in insolation until 1990 and the recovery thereafter Neither does that correspond to the increase in solar radiation in Australia and Antarctica since 1990 where human made aerosols have no measurable impact Moreover the global emission of sulphate aerosols is near steady since 1975 but with a large shift from Europe and North America toward SE Asia This may be seen in the data of India but China with an explosively increasing industry shows increasing insolation Further more insolation also means less reflection of incoming light as good as by clouds as by the surface itself But that is contradicted by the earthshine measurements which measure how much visible light is reflected by the earth s atmosphere on the dark side of the moon These trends show exactly the opposite of what is measured at the surface and by earth orbiting satellites Further direct and reflected solar light is only one part of the balance downward IR radiation from water vapour and other GHG s and IR radiation from the surface water evaporation precipitation â all play a role in distributing energy from warmer to cooler places and what is received from the sun and emitted back to space Interesting is that in the 20N 20S even 30N 30S area the amount of extra solar energy on the surface 2 W m2 in the last decades is more than compensated by more IR radiance back to space 5 W m2 measured at the top of the atmosphere How the balance for the whole earth is is not known to me and I haven t found the data yet Thus what causes global dimming and back I suppose that most is by changes in water vapour as can be seen in data from the Alps The change in water vapour there is three times larger than expected from CO2 induced water vapour feedback by models and the downward IR radiation more than compensates for insolation losses It is impossible to distinguish between natural water vapour variability and feedback induced by CO2 But by searching for surrogate water vapour levels as indicated by discharge river flows there is no trend in the river Rhine figure 13 North Alps discharge but a solar cycle related trend in the river Po South Alps discharge â Thus probably induced by the prevailing SW winds from over the warmer Atlantic As the Swiss have surface based upward and downward IR measurements on different places between 370 m and 3580 m elevation in the Alps some of them equipped with several filters on different wavelengths of interest it should be possible to make a difference in trends between CO2 induced downward IR radiation and that induced by water vapour This may give a better indication of what happens in the atmosphere today Response Be careful that you don t compare apples and oranges Flux changes at the surface are NOT the same as flux changes at the tropopause the definition used for the forcings bar chart The surface numbers can be quite large and yet have little or no impact at the tropopause In the case of global dimming aerosols and clouds have an effect both at the ground and at the tropopause but the ground numbers are much bigger Secondly 1990 is not a magic turnaround date Instead it is the date that BSRN network was established to provide better quality data for these questions while the older data only went up to 1990 The Earthshine measurements are indeed contradicted by the CERES measurements presented by Wielicki et al Thus there is some more work to do on this I think that the Wielicki results have a better sampling and a simpler calculation however we will have to wait until the dust settles before coming to a conclusion However

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  • Planetary energy imbalance? « RealClimate
    in any particular flux which can be large and the second is the error in the overall balance which is very small To see why these things are different think of a lake which is fed by a number of streams of uncertain flow and drains into a river If the lake level is steady I know that the inputs are balancing the outputs even if I don t know their exact magnitude If I now observe the lake level change I can calculate very exactly the net imbalance regardless of the error in my estimate of the individual streamflows gavin 9 Robert Simmon says 3 May 2005 at 6 06 PM regarding comment 6 but measured by the same satellites They re not the same satellites Hansen et al used sea surface altimetry data TOPEX Poseidon and Jason Wielicki et al and Chen et al used flux measurements CERES Thus any imbalance no matter what the origin is which leads to higher SSTs is counteracted by more loss of energy to space Is inaccurate From A Delicate Balance a NASA article I illustrated â We are likely seeing a decadal fluctuation here Right now we are looking at what might lead to such a fluctuation â says Chen He believes that this is a natural climate anomaly much like El Nià o La Nià a or the North Atlantic Oscillation It is a natural part of the rhythms of the Earthâ s climate system But unlike these other anomalies the Hadley Walker cell fluctuates over the course of decades instead of years Chen feels that this phenomenon has no direct relation to global warming or any other hypothesis related to climate change including the Iris Hypothesis The Iris Hypothesis states that as sea surface temperature increases due to climate change the increase will alter the extent of certain types of overlying clouds so that the excess heat is allowed to vent through the top of the atmosphere Though the Iris Hypothesis may seem to jibe with what has occurred over the past 15 years in the tropics Chen says that the thermal radiation leaving the top of the atmosphere has increased much too rapidly Evidence has also shown that the clouds above the tropics are not changing in the ways predicted by the Iris Hypothesis 10 Doug says 3 May 2005 at 7 59 PM The report says Continuation of the ocean temperature and altimetry measurements is needed to confirm that the energy imbalance is not a fluctuation If it were a fluctuation could that mean the imbalance is just a short term thing that could reverse in a few years If so does that invalidate the following claim just posted Firstly as surface temperatures and the ocean heat content are rising together it almost certainly rules out intrinsic variability of the climate system as a major cause for the recent warming Response The longer the record the more sure we will be that what is seen is more than a fluctuation However given the match of the data and models using the most up to date forcings we are reasonably confident that it is not a fluctuation There is always a chance that nature is conspiring against us and so continued monitoring is essential to stregthen the conclusions gavin 11 Dave Dardinger says 3 May 2005 at 8 57 PM Just how accurate are the temperature measurements made in the ocean Working through the numbers we re only talking a few hundredths of a degree a year of temperature change It looks like your reference 19 J K Willis D Roemmich B Cornuelle J Geophys Res 109 C12036 doi 10 1029 2003JC002260 2004 would be the one with the data Is it available on line Response Try here In general ocean temperature measurements are very high quality and routinely reported to the third decimal place The bigger problem is spatial coverage but the addition of integrated constraints from the altimeter data goes some way to correcting for that gavin 12 Isaac Held says 3 May 2005 at 9 03 PM Gavin I agree completely with the standard picture that you describe but I don t agree with the claim that as surface temperatures and the ocean heat content are rising together it almost certainly rules out intrinsic variability of the climate system as a major cause for the recent warming Suppose that there has been a multi century increase in the poleward heat transport in the oceans due to internal variability which warms the poles reduces ice extent and albedos and thereby warms the planet The land surface and atmosphere go along for the ride having little heat capacity There is no evidence for anything of the sort but I don t see any logical inconsistency we need to be careful not to claim too much thereby creating an opportunity for a critique that is besides the point The consensus picture that you paint is convincing because the estimated forcings the models and the observations are all consistent not because of an argument that internal variability has to cool one part of the system in order to warm another Response Isaac I agree with your general point that a redistribution of heat in the system can alter feedbacks in a way that could affect the energy balance The obvious example is collapse in the North Atlantic MOC which leads to more sea ice etc However the impact on global as opposed to local temperatures of even large variations in the overturning is very small Thus it doesn t appear to be much of a practical effect For the case at hand though the distribution of heat anomalies in the ocean makes a redistribution feedback effect very unlikely gavin 13 dave says 3 May 2005 at 10 42 PM Good post What are the model assumptions about radiative forcing from clouds Is Earth s cloud cover increasing decreasing Are there any new observations about this and the types of clouds involved Response The models cloud radiative forcing is a diagnostic of the model rather than an assumption that is built in Clouds are however very important and we and other groups are trying hard to analyse what they are doing Comparison with data such as ISCCP is problematic because they records are noisy short and may still have systematic problems that affect the trends As and when those analyses are done we will report on them here gavin 14 g says 4 May 2005 at 2 25 AM I ll have to go to the primary references but this raises a few questions for me Is the record detailed enough to understand 3 dimensional changes in sea temperature or is it mostly based on sea surface altimetry In particular is there an observed or predicted change in the temperature or volume of mode waters or rates of deep water formation Can you use whole planet radiation budgets to calculate the planet s net entropy gain Is there a way to budget how much of that entropy gain is due to life 15 John Finn says 4 May 2005 at 4 59 AM Gavin You say since the current unrealised warming in the pipeline is related to the net imbalance 0 85 0 15 W m2 implies an further warming of around 0 5 0 7 C I am interested as to when this 0 6 C increase will become evident I have had a quick look at the Hansen paper and in it he says something to the effect that the time lag is roughly proportional to the square of the sensitivity So does this mean that if t is the time delay in years and s is the sensitivity t can be expressed as t k s 2 Dr Hansen also states that time delay could be as short as a decade if climate sensitivity is as small as 1 4 deg C per W m2 Substituting this i e t 10 s 0 25 into the above equation yields k 160 very rough I know Also in the paper the sensitivity resulting from the models appears to be about 2 3 deg C per W m2 so if we maintain the current level of forcing indefinitely this suggests the time delay before equilibrium is established is as follows t 160 x 4 9 which is over 70 years or have I got something wrong Also could you tell me if the increase in temperature towards equilibrium is expected to be linear This would mean a steady increase of 0 1 deg decade 0 6 in 70 years if my interpretation is correct Response This is all discussed more thoroughly in Hansen et al 1985 no online version unfortunately The basic idea is that since feedbacks are a large part of the response lags due to ocean thermal inertia slow down the full feedback response For the current imbalance and idea of how long it will take for the warming to come down the pipe can be seen in the figures in the Wigley and Meehl et al paper referenced above In the GISS committed climate change simulations most of the additional warming has occured by 2050 but there remains a slow increase for decades afterwards gavin 16 Isaac Held says 4 May 2005 at 9 00 AM Gavin Following up on my comment above my concern is with the smoking gun language and whether it might be counterproductive The idea is that there is a small set of observations and a theoretical argument that goes along with it that is essentially irrefutable even if one is unfamiliar with or rejects the rest of the edifice of global warming science I am not sure that this is a good tack to take since the argument in fact is not irrefutable and probably is not very convincing to someone who has no intuition for internal climate variability and how it manifests itself I wasn t supporting the idea of the dominance of internal variability but just addressing the logical consistency of the argument I think we need to emphasize the consistency of the whole picture and not place too much emphasis on one line of argument which is what the smoking gun language tends to encourage 17 Henry Molvar says 4 May 2005 at 11 37 AM Time September 27 2105 Place Orlando Island off the SE coast of NCSA Scene SW Seawall Mickey Crichton Chief Climatologist for the New Confederate States Department of Coastal Defense gazes towards the noon ferry arriving from the port city of Lakeland fifty miles to the southwest Although this is not an official visit Disney has given Mickey permission to examine the feverish efforts to strengthen the eastern and southern portions of the seawall Hurricane Johnnie now a devastating Category 5 is projected to arrive in the next four to five days Although few people seriously expect it to breach the 120 foot high seawall surrounding this privately owned island city it could seriously tax the pumping system that keeps the tourist mecca dry Since purchasing it from the NCS government right after the revolution Disney has spent trillions on its defense system against the rising ocean but now This prescient short story Disney the Fall of an Empire by John M Crichton III written in 2035 by the young great nephew of the famous novelist finally galvanized the public and with it the Federal Government into action Sadly it was too late Although scientists and foreign governments had been urging the US to cut back CO2 emissions for decades the legacy of the second Bush administration and the influence of Crichton IIIâ s great uncle had been too strong The public had been in denial and the massive disinformation campaign by the fossil fuel industries had stymied any legislative effort to enforce cutbacks Now although the draconian laws passed in 2037 have cut CO2 emissions in half the US is in a state of near collapse Federal money diverted to the emissions effort has wiped out Social Security Most other unneeded programs such as environmental transportation health education housing etc have been eliminated or cut to the bone The Defense budget has tripled due to threats of invasion by the EU and the Asian Alliance Sea levels continue to rise at a rate never envisioned by climatologists and other scientists in the late 1990â s and early 2000â s due to the unforeseen effects ofâ 18 Ferdinand Engelbeen says 4 May 2005 at 12 50 PM Re comment 9 of Robert Simon Thanks for the correction It seems to me that deducing heat content from altimetry is less accurate than from direct measurements as altimetry is influenced by wind speed and barometric pressure too The comment from NASA about the Wielicki findings and what models predict is very interesting especially at http earthobservatory nasa gov Study DelicateBalance balance4 html IMHO the increase in speed of the Hadley Walker cells may be the result of higher ocean temperatures or temperature differences over long distances not the origin or to a lesser extent as less clouds lead to some extra insolation thus warming Some indication for that can be found in several studies one of them at http hydro jpl nasa gov sst sst html This is not the same as the Iris hypotheses as that is on a much smaller scale but over the whole tropics subtropics The loss of energy to space measured by Wielicki e a in the past 15 years is of near the same magnitude as what the theoretical increase in greenhouse effect is from the extra greenhouse gases since the beginning of the industrial revolution That is a large impact Remains to be seen if the current 0 85 0 15 W m2 imbalance found by Hansen e a is not simply a part of the natural variability found by Wielicki if it is natural at all 19 Dave Dardinger says 4 May 2005 at 11 02 PM Re response to 11 Thank you Gavin for the link I ve sort of skimmed it so far There s a lot more to be looked at But I m afraid I m unconvinced that the 85 15 w m2 figure is very believable The problem is figure 6 which shows the spatial extent of the various storage values for each year They show both high resolution and high variability over short distances This wouldn t seem to me to be a sign of a highly accurate system Further compare say 1997 and 1998 where we switched to the super El Nino situation Very striking but also quite a problem The same areas of the ocean went from something like 80 w m2 to 80 w m2 or vice versa in less than a year And we re not talking single pixels but large sections of the ocean With such gigantic variability common expecting a decadal global average to be accurate within about 1 of the annual variability is asking a lot Response Well the 0 85 number is the mean from the models and so is not directly related to the uncertainty in the data However it s easy to assess the error in the global mean ocean heat content based on the measurement error and spatial variability and that is done in the Willis et al paper Despite the variability the global means are relatively well defined The key is that the tropical Pacific is actually very well sampled through the TOGA COARE array and the patterns you see in the annual means change slowly enough for the heat content anomalies to be well characterised As Willis et al states the errors due to spatial coverage rather than variability are more important Given that it s clear that the longer the record the more confident we will be gavin 20 Alain Henry says 5 May 2005 at 4 37 AM Thanks for another enlightening article When looking at the total forcing in the second part of the first graph whoch summarises forcings over the 1850 2000 period there is at first sight a long term rising trend including in the 1940 70 period well there is a significant fall in the sixties though due to solar irradiance I am thus looking for an explanation of the 1940 1970 cooling strong quotes The global temperature fall in the sixties can be linked to solar irradiance I assume But is there a good and intuitive explanation for the 1940 1960 period where it looks more like a global temperature stabilisation than a cooling or is it just the result of the complex interaction of the climate system Thanks Alain 21 Alain Henry says 5 May 2005 at 1 56 PM In comment 20 I mentionned solar irradiance as falling in the sixties and possibly explaining the low global temperature in the sixties I actually meant stratospheric aerosols I got confused by looking at a black and white printout of the figure Apologies for the confusion Alain 22 Dave Dardinger says 5 May 2005 at 2 07 PM re response to 19 OK I see what the 85 is then though I m not sure it s meaningful in that case It s very close to what the article you linked me to has 85 12 BTW Looking further at that article I examined figure 6 It shows a graph of the global heat storage over time I did a quick analysis of that estimating the value by eyeball for each year I ended up with 7 0 rather than 8 5 as I suppose it should be giving you an idea of how my aging eyes are doing I then put those figures in a spreadsheet calculated the trend y 1213x subtracted again by eye to get the difference total off by 3 and then calculate the RMS of the differences which amounts to ironically 85 Again it doesn t look real robust in terms of the trend being real as opposed to a fluxuation I d have been real careful about letting words like Smoking Gun be associated with your findings BTW since the data ends in 2002 have you gotten any preliminary data for 2003 and 2004 This would certainly help since the ending trend seemed to be down 23 Ferdinand Engelbeen says 5 May 2005 at 2 30 PM While rereading the ocean heat content changes by Levitus 2005 at http www nodc noaa gov OC5 PDF PAPERS grlheat05 pdf a remarkable sentence was noticed However the large decrease in ocean heat content starting around 1980 suggests that internal variability of the Earth system significantly affects Earth s heat balance on decadal time scales Thus it may be that the 1993 2003 period of ocean warming used by Hansen e a is an entirely natural warming My question The GISS climate model follows the 1993 2003 trend quite good But does it follow the 1980 1990 cooling trend as good 24 Stephen Berg says 6 May 2005 at 11 47 PM I thought you would be interested in this story http www cbc ca story science national 2005 05 06 global dimming050506 html Response Indeed This relates to a trio of papers in Science this week A commentary will be forthcoming gavin 25 Rick Watkins says 8 May 2005 at 3 33 AM I read in a school textbook that it takes as much energy to convert 1gm of ice at 0oC to 1gm of water at 0oC as it does to heat said gram of water from 0oC to 80oC With recent talk of the extra heat the earths system is absorbing hiding here and there is there a connection The energy taken from the system to cause the observed glacial melting worldwide thinning and shrinkage of Arctic sea ice melting collapsed Antarctic iceshelves etc must be hidden in the meltwater unrecordable by themometer Does this amount of energy rate a mention in the earths energy equation or is it too insignificant to bother with Response The latent heat of melting for ice is indeed large but given the amount of heat we are talking about and the relatively small amount of ice melt seen so far it is negligible Levitus et al 2001 did the calculation and the ocean heat content is by far the biggest term gavin 26 dave says 8 May 2005 at 6 50 PM Re Response Times It seems to me that Earth s Energy Imbalance paper is not strictly a science paper there are also policy warnings e g this example 0 6 C warming in the pipeline implies the need for near term anticipatory actions This deserves some more comment since the situation could be even worse than the paper states and this comment is not peer reviewed It is my understanding of the paleoclimate that only about half of the rise during interglacials to 280ppmv and fall during glacial maximums to 190ppmv of CO2 levels can be accounted for by climate models The rest presumably comes from unknown feedbacks in the biosphere The paper and presumably the climate model used does not deal with this issue but notes the sawtooth pattern Also it could be argued that the initial stages of ice sheet disintegration have already been detected WAIS Greenland but admittedly no one knows what this looks like Recent accelerated rates of ice sheet melting and our current ignorance is cause for alarm given that the destabilizing issue of comparable ocean and ice sheet response times is apparent The inferred positive eustatic GLSR from the ice sheets is a recent result But the real problem as I see it is that the slow response times of the oceans and ice sheets creates slow human response times with respect to policy to stabilize GHG levels So an equilibrium response is a convenient fiction which enables the science but is not a goal of policy makers and so can not exist in the real world Also the GISS model with it s 2 7c sensitivity is on the low end The Kerr 2004 Science Three Degrees of Consensus summary cited in the paper but not online gives the current range across models for climate sensitivity as 2 5c to 4 0c So there is ample reason to worry This paper dovestails nicely with Elizabeth Kolbert s 3 part series in the New Yorker on climate change Try here I ll let you know how it ends This is the last sentence of part 3 It may seem impossible to imagine that a technologically advanced society could choose in essense to destroy itself but that is what we are now in the process of doing Apocalypse Later 27 Stuart Hobbs says 8 May 2005 at 9 14 PM As a lay person to the climate sciences the debate over anthropogenic global warming is very confusing since there appears to be so many contradicting opinions For instance a candian television program about anthropogenic global warming seems to say almost the exact opposite of what is being stated here and in some of the recently published articles in Science Any opinion on this particular program and the bona fides of its experts 28 dave says 9 May 2005 at 10 40 AM Re 27 Confusing The friends of science website you reference is a propoganda site designed to sow the kind of confusion you feel Most such sites are sponsered by fossil fuels industry Here s an introduction to such sites at Mother Jones called As The World Burns Welcome to RC 29 Dave Dardinger says 9 May 2005 at 11 08 AM Re 28 Errr Mother Jones is not a propaganda site It s certainly far left 30 Stephen Berg says 9 May 2005 at 11 55 AM Friends of Science are an industry funded group affiliated with the Fraser Institute in Canada which receives funding from ExxonMobil to disinform and confuse to obfuscate the public They are certainly not what their name says Because of this I like to call Foes of Science As for the Errr Mother Jones is not a propaganda site It s certainly far left Mother Jones is a centre left newsmagazine which features excellent journalism and analysis Two of the three I don t know who Chris Mooney is who wrote in the As The World Burns issue are very good I have met Ross Gelbspan and he is a brilliant journalist hence his Pulitzer award Bill McKibben is also brilliant I would definitely recommend anyone read their work 31 dave says 9 May 2005 at 5 39 PM Re 24 Dimming I could have added in my remarks in 26 that these new global dimming results point to the conclusion that negative forcing from sulfate aerosols masked the actual ongoing warming up to about 1990 I look forward to your post on this subject Re 29 Yes sorry I couldn t find anything pertaining to climate skeptics in the Wall Street Journal 1 in Google for the query climate science skeptics Try Ross Gelbspan s Disinformtion page His site is The Heat Is Online linked in here at Real Climate 32 Manny says 9 May 2005 at 7 07 PM Re 28 I find it interesting that a particular organization might be indicted for supposedly being funded by the fossil fuel industry when so many organizations and studies fueling the global warming alarmism are funded by governments and not suprisingly endorse MORE government in the form of regulations regulatory agencies taxes fees etc as a supposed solution to the problem Talk about conflict of interest 33 Joseph O Sullivan says 9 May 2005 at 8 17 PM For Stuart Hobbs much of the information disputing climate change science is politically driven There is scientific consensus about climate change the earth is warming this warming is mostly caused by humanities release of greenhouse gases and this could be harmful There is scientific consensus because the evidence is overwhelming Look at the just what is this consensus Dec 22 post here on realclimate If the consensus is accepted the next step is to take action Action would mean enacting laws and regulations limiting the emissions of greenhouse gases These regulations would probably be extensive and be expensive A group of conservatives who favor small government and industries who could lose financially are adamantly opposed to these regulations and are the most vocal opponents They are hostile to environmental regulation generally and climate change regulation especially Current environmental regulations were passed after environmental groups ran political campaigns that reflected the public s call for action addressing environmental problems Conservatives and industry were stung by these political defeats Noting the success of environmentalists conservatives and industry founded their own political advocacy groups to oppose environmental regulation The groups spearheading this opposition are not independent academic institutions They are political advocacy groups as are many of these think tanks They advance conservative and corporate political agendas That is why conservative foundations and industry fund them For examples see http www environmentaldefense org article cfm contentid 3804 CFID 21084385 CFTOKEN 29888831 Being politically active for industry environmentalists or any other group is not a bad thing Any political advocacy group has an agenda and when evaluating their messages about climate change science it is important to examine how they advance this agenda Every political group uses spin to try to persuade the public but some of the groups that represent conservatives and industry use what can be called extreme tactics in the climate change science debate These groups including Fraser Institute and Friends of Science are waging a public relations campaign against environmental regulation Because climate change science when objectively examined supports environmental regulation science scientific institutions and scientists have also been subject to criticism The goal is to publicly cast doubt on the science so the public will not support climate change legislation See http www luntzspeak com graphics NewYorkTimes NewsStory pdf Without public support it is unlikely any climate change regulation will be enacted Even conservative politicians who support climate change legislation have been targeted The claims about climate change science made by these conservative industry groups have questionable scientific value Most of these claims are political attacks that promote a partisan agenda and are not objective information about climate change science Concern about policies based on science is understandable and can be used to create better policies but in many cases the concern about policies is prompting some to misrepresent the facts about climate change science 34 Manny says 9 May 2005 at 9 31 PM There is scientific consensus about climate change Perhaps you have not seen the video at the link Stuart provided Regardless of what you think of how they are funded the video clearly shows climatologists disputing the consensus viewpoint 35 Joel Shore says 10 May 2005 at 9 24 AM Re comment 34 Consensus does not mean unanimity You can find a few PhD biologists who dispute the theory of evolution too but that doesn t mean there is a lack of consensus on the issue in the peer reviewed scientific literature If you look around the Friends of Science site you will see just how pathetic it is Their motto probably should be No argument is too ridiculous for us They even try to sow doubt over whether the current rise in CO2 levels is primarily the result of humans 36 Thomas Nephew says 10 May 2005 at 3 12 PM I can t tell from Table 1 what share of GHGs are contributed by volcanic greenhouse gases is this an unknown part of the 2 75W m2 figure Or are volcanic GHGs known to be negligible I m obviously a newcomer to these questions Also are undersea eruptions likely to contribute significant heat to ocean temperatures If so perhaps the argument is still that your model matches observed temperatures well enough so adding this input is unnecessary But assuming a number could be put to this heat source would it draw down the other forcings proportionately or would it all come out of GHGs 37 Stephen Berg says 10 May 2005 at 3 55 PM Re 36 Read my comment 20 on the thread for my answer to Also are undersea eruptions likely to contribute significant heat to ocean temperatures http www realclimate org index php p 124 38 Thomas Nephew says 10 May 2005 at 5 22 PM I have no idea how frequent undersea eruptions are or how constant their rate is from one century to the next I m guessing you probably don t either But you raise a good point that if the heat release per century is constant that can t account for rising temperatures Maybe one can reasonably infer fairly constant undersea vulcanism from on land vulcanism I m hoping I ll find out here But the thing is even if it s constant if there s a lot of it I would think that might affect the man made GHG argument It seems like it would have to come at the expense of some other heat source for the model to work as well as it does On the other hand then it might take less GHG to cause the observed temperature increase That might actually be good news in that reducing GHG would have a correspondingly big effect too 39 Dano says 11 May 2005 at 11 50 AM Re 34 there is only one climatologist in the video and that person didn t bother to correct the copy that allowed the non climatologist to state the UHI is contributing to the surface temperature rise That very simple fact should raise alarm bells and cause one to scrutinize other statements in the video D 40 John Dodds says 11 May 2005 at 4 21 PM Do I understand this Ocean data correctly It was said above that the ocean is warming just like the land air and ice sheets glaciers that the heat in the ocean dwarfs that in the land and air that the warming is due to the net solar imbalance solar in less LW out no mention of CO2 Response The NYT quote from Wielicki is incomplete he meant that the net imbalance measured by CERES SW and LW is consistent with the ocean heat storage data I quote from an email posted on the climatesceptics group From Bruce A Wielicki To Willis Eschenbach Subject Re The Studies of Drs Wielicki and Hansen Willis The times reporter got the sense of it but not all the specifics your confusion is about longwave flux forcing of CO2 vs shortwave solar albedo changes my comment to the times was that if you put the shortwave reflected and thermal infrared emitted energy terms together and look at them over the last decade for 1992 to 2004 you get variations in net radiation into the Earth that vary up and down with peak variations of about 1 W m 2 but that have fluctuations very consistent with total ocean heat storage as they should The net planaetary imbalance has very little to do with the sun gavin THE SUN IS CAUSING THE GLOBAL WARMING and we can t do a damn thing about it makes sense to me since it is also the sun that supplies the heat to drive the greenhouse effect SO no matter what we do to CO2 by Kyoto we are at the mercy of the sun and the imaginary Pipeline and when the sun decides to cool off and reverse its 300 year warming trend see IPCC solar irradiance history http www grida no climate ipcc tar wg1 245 htm we will go into global cooling like we did from 1300 to 1700 and 1940 1970 It will cool off someday it always has in the past just look at the sawtooth ice core temperature data Which by the way will immediately eliminate the energy in the imaginary Pipeline seems as if this happens just after noon every single day The next conclusion is that any prediction of air temperatures for the next 50 years is totally dependant on the assumption made for what the solar irradiance levels are Which according to this study is a factor of TWO total incredulity Excuse the dumb question but why are we wasting our research time on CO2 emissions rather than the cause of changes in solar irradiance BUT that if we continue to add CO2 to the air the air has the added heat capacity to get warmer IF and ONLY IF driven by the sun but rapidly come to equilibrium with the ocean by means of rain and the daily heating condensation of the water vapor feedback mechanism BUT already the air never gets to maximum heat capacity anyway Other than the fact that CO2 is necessary to human survival we breathe it out after processing hydrocarbon food and for 98 of the energy that has allowed us to live longer and improve the standard of living over the last 300 years just why exactly do we even care how much CO2 is in the air especially if the temp of the ocean which is dictated by the sun will dictate the air temp I observe this daily in chilly San Francisco 41 Dave Dardinger says 11 May 2005 at 5 05 PM re 39 The question isn t whether UHI contributes to surface temperature rise but whether it affect temperature measurements sufficiently to bias the measured averages All I can say is that in the northern US at least the temperatures in the outlying suburbs were always lower than those at the airport and higher than those in the countryside And Columbus OH was not that large a city in the 50s and 60s that it probably has had much of an adjustment made to its temperatures 42

    Original URL path: http://www.realclimate.org/index.php?p=148 (2016-02-13)
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