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  • PCA details « RealClimate
    perhaps 6 eigenvalues are distinct from the noise eigenvalue continuum Comments Off on PCA details Comments are closed Site Google Custom Search Recent Comments Unforced Variations Feb 2016 Digby Scorgie Unforced Variations Feb 2016 T What is the best description of the greenhouse effect Jim Eager What is the best description of the greenhouse effect Patrick Eriksson What is the best description of the greenhouse effect Kevin McKinney Anti scientists Carbomontanus What is the best description of the greenhouse effect Spencer Marvel et al 2015 Part III Response to Nic Lewis SteveS What is the best description of the greenhouse effect Chris Colose Blizzard Jonas and the slowdown of the Gulf Stream System doiknow With Inline Responses Marvel et al 2015 Part III Response to Nic Lewis SteveS Marvel et al 2015 Part III Response to Nic Lewis steve s Marvel et al 2015 Part III Response to Nic Lewis Andrew Kerber Blizzard Jonas and the slowdown of the Gulf Stream System Hank Roberts Blizzard Jonas and the slowdown of the Gulf Stream System doiknow Marvel et al 2015 Part III Response to Nic Lewis MartinM Anti scientists Don McKenzie Marvel et al 2015 Part III Response to Nic Lewis Matt Skaggs Anti scientists mikeworst New On line Classes and Models Marcus Pages Acronym index Data Sources Categories Climate Science Aerosols Arctic and Antarctic Carbon cycle Climate impacts Climate modelling El Nino Geoengineering Greenhouse gases Hurricanes Instrumental Record IPCC Oceans Paleoclimate Sun earth connections Communicating Climate Reporting on climate skeptics Extras Attic Comment Policy Contributor Bio s FAQ Glossary In the News Reviews Supplemental data Tutorials hydrological cycle Open thread RC Forum Scientific practice statistics The Bore Hole Books Contributors Highlights Dummies Guide to the latest Hockey Stick controversy El Nino Global Warming and Anomalous U S Winter Warmth Hurricanes

    Original URL path: http://www.realclimate.org/index.php?p=9 (2016-02-13)
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  • Ne faisait-il pas plus chaud au Moyen-Age, pendant “l’Optimum climatique”, que maintenant? « RealClimate
    addresses this here and for an example of a contrarian tactic that can make it appear otherwise or that the current 4 Understanding Global Warming says 6 Jan 2008 at 9 08 PM and had relatively little impact on the global averages Dr Michael Mann addresses this here and for an example of a contrarian tactic that can make it appear otherwise or that the current 5 Hypography Science Forums Co2 Acquittal says 1 Feb 2008 at 1 35 AM by mitigating our impact And I know you like this place so yes I did look here RealClimate Here is an interesting article 6 Earth The Climate Wars Wildlife and Environment Forums says 20 Sep 2008 at 12 52 AM of the little ice age and medieval warm period and many other discussions of climate change RealClimate To summarise the ideas very simplistically I think this is what they say the little ice age and 7 Understanding the Basics of Global Holocene Climate Change Understanding Global Warming says 16 Mar 2009 at 8 57 PM magnitude of medieval warmth was weaker than that of today Dr Michael Mann also addresses this here and for an example of a contrarian tactic that makes it appear otherwise or that the current 8 Understanding Global Warming says 17 Mar 2009 at 1 46 PM magnitude of medieval warmth was weaker than that of today Dr Michael Mann also addresses this here and for an example of a contrarian tactic that makes it appear otherwise or that the current 9 Ben s Blog Blog Archive Head to head with a Cardinal says 24 May 2009 at 10 58 PM qualified in a way that I and the good Cardinal are not The medieval warm period wasn t warmer Warming didn t stop in 1998 But most appalling to me was this childish attempt to use his Site Google Custom Search Recent Comments Unforced Variations Feb 2016 Digby Scorgie Unforced Variations Feb 2016 T What is the best description of the greenhouse effect Jim Eager What is the best description of the greenhouse effect Patrick Eriksson What is the best description of the greenhouse effect Kevin McKinney Anti scientists Carbomontanus What is the best description of the greenhouse effect Spencer Marvel et al 2015 Part III Response to Nic Lewis SteveS What is the best description of the greenhouse effect Chris Colose Blizzard Jonas and the slowdown of the Gulf Stream System doiknow With Inline Responses Marvel et al 2015 Part III Response to Nic Lewis SteveS Marvel et al 2015 Part III Response to Nic Lewis steve s Marvel et al 2015 Part III Response to Nic Lewis Andrew Kerber Blizzard Jonas and the slowdown of the Gulf Stream System Hank Roberts Blizzard Jonas and the slowdown of the Gulf Stream System doiknow Marvel et al 2015 Part III Response to Nic Lewis MartinM Anti scientists Don McKenzie Marvel et al 2015 Part III Response to Nic Lewis Matt Skaggs Anti scientists mikeworst New

    Original URL path: http://www.realclimate.org/index.php/archives/2004/12/werent-temperatures-warmer-during-the-medieval-warm-period-than-they-are-today/langswitch_lang/fr/ (2016-02-13)
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  • Mid-Holocene Climatic Optimum « RealClimate
    Digby Scorgie Unforced Variations Feb 2016 T What is the best description of the greenhouse effect Jim Eager What is the best description of the greenhouse effect Patrick Eriksson What is the best description of the greenhouse effect Kevin McKinney Anti scientists Carbomontanus What is the best description of the greenhouse effect Spencer Marvel et al 2015 Part III Response to Nic Lewis SteveS What is the best description of the greenhouse effect Chris Colose Blizzard Jonas and the slowdown of the Gulf Stream System doiknow With Inline Responses Marvel et al 2015 Part III Response to Nic Lewis SteveS Marvel et al 2015 Part III Response to Nic Lewis steve s Marvel et al 2015 Part III Response to Nic Lewis Andrew Kerber Blizzard Jonas and the slowdown of the Gulf Stream System Hank Roberts Blizzard Jonas and the slowdown of the Gulf Stream System doiknow Marvel et al 2015 Part III Response to Nic Lewis MartinM Anti scientists Don McKenzie Marvel et al 2015 Part III Response to Nic Lewis Matt Skaggs Anti scientists mikeworst New On line Classes and Models Marcus Pages Acronym index Data Sources Categories Climate Science Aerosols Arctic and Antarctic Carbon cycle Climate impacts Climate modelling El Nino Geoengineering Greenhouse gases Hurricanes Instrumental Record IPCC Oceans Paleoclimate Sun earth connections Communicating Climate Reporting on climate skeptics Extras Attic Comment Policy Contributor Bio s FAQ Glossary In the News Reviews Supplemental data Tutorials hydrological cycle Open thread RC Forum Scientific practice statistics The Bore Hole Books Contributors Highlights Dummies Guide to the latest Hockey Stick controversy El Nino Global Warming and Anomalous U S Winter Warmth Hurricanes and Global Warming Myth vs Fact Regarding the Hockey Stick On attribution On mismatches between models and observations On Sensitivity Part I Tropical Glacier Retreat Water Vapour feedback

    Original URL path: http://www.realclimate.org/index.php?p=67 (2016-02-13)
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  • RealClimate
    has been added and will come online on Monday called Global Warming II Create Your Own Models in Python or Fortran This takes advantage of new code grading machinery at Coursera to automatically run your code through its paces There is also a peer code review step where you will get feedback on your commenting and variable naming skills and provide feedback to others The class gives detailed instructions to create simple models of time evolution of global temperature the ice albedo feedback drop into snowball Earth an ice sheet and a shallow water circulation model The class is intended for people who are new to programming or new to Python or wish to enhance their understanding and appreciation of some cool science of Earth s climate system The classes are supported by the same interactive on line interactive climate system models as before at http climatemodels uchicago edu with some new additions both of which generate animations of their time dependent solutions One is a Hurricane simulator using a model from Kerry Emanuel which can demonstrate the sensitivity of ocean temperature ocean mixing and atmospheric structure on hurricane evolution The other the Permafrost model is a simulation of a soil or sediment column in which ice and methane hydrate can form The model shows how the brine salinity thermodynamically excludes methane hydrate from forming until you get to the base of the permafrost zone and also how long it takes to warm a soil column by warming the surface This model shows why I do not believe in an imminent methane climate catastrophe from Arctic Ocean methane hydrates Comments pop up 21 Unforced Variations Feb 2016 Filed under Climate Science Open thread group 1 February 2016 This month s open thread Just so you know a lot of people have complained that these threads have devolved particularly when the discussion has turned to differing visions of solutions and have therefore become much less interesting Some suggestions last month were for a side thread for that kind of stuff that wouldn t clog interesting issues of climate science Other suggestions were for tighter moderation The third suggestion is that people really just stay within the parameters of what this site has to offer knowledgeable people on climate science issues and context for the science that s being discussed elsewhere For the time being let s try the last one combined with some moderation The goal is not to censor but rather to maintain somewhere where the science issues don t get drowned out by the noise Comments pop up 105 Older Entries Site Google Custom Search Recent Comments Unforced Variations Feb 2016 Digby Scorgie Unforced Variations Feb 2016 T What is the best description of the greenhouse effect Jim Eager What is the best description of the greenhouse effect Patrick Eriksson What is the best description of the greenhouse effect Kevin McKinney Anti scientists Carbomontanus What is the best description of the greenhouse effect Spencer Marvel et al 2015 Part

    Original URL path: http://www.RealClimate.org/ (2016-02-13)
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  • Are Temperature Trends affected by Economic Activity? « RealClimate
    found coefficients of similar magnitude for the factors McKitrick and Michaels proposed as important I am guessing there is some qualifier missing above As it stands I find it hard to place this in the semantic context of the article This tends to indicate that the article was assembled with insufficient care To make matters worse we have this In their reply to my comment McKitrick and Michaels 2004b note that I do not dispute their choice of data or their methodology While that is true they should not confuse this with my vouching for their approach I have not commented on their choice of methodology or data simply because that is beside the point This is perfectly coherent in a logical way but not everyone reads with precision Many people reading casually as web users are wont to do will see I do not dispute to mean I agree The following sentences will then be lost in the shuffle in ways that they would not be in apurely academic environment It would be better to say something like McKitrick and Michaels 2004b misleadingly cliam that I do not dispute their choice of methodology A methodology is only valid when correctly applied and this M M 2004 have egregiously failed to do Or something like that presuming that I take the meaning correctly Response Again thanks for your constructive criticism We have revised the posting significantly to address among other things the various issues you ve raised Please see our revised version as of 12 14 04 Worst of all even though I work in the climate field at a major and well endowed university I have no access to the journal in question and am therefore unable to make much of the argument without going to considerable effort Consider how much more difficult this will be for the general readership Response Well this we can t do much about However we have linked to a pdf version of the Benestad 2004 article we don t have access to the other articles cited Something like this article may belong in the journal in question but the purpose of this site is outreach to the general public both directly and through journalists This article does not succeed in this effort I appreciate that the effort is finally being made and for what it s worth I m willing to help but one should have no illusions that the task is easy I hope that in future even the primary contributors will not simply allow but demand some editorial input to ensure that their contributions are appropriate for a general audience More articles like the current one will reduce realclimate org to just another professional mailing list with negligible impact on public discourse Response Again we hope you find the revised version of our posting an improvement over the original We would certainly like to encourage you to consider contributing guest postings if you feel so inclined And again we appreciate very much your helpful feedback on the current content of the site 5 Jim Dukelow says 14 Dec 2004 at 9 34 PM It is interesting that McKitrick and Michaels would not account for the effect of correlations between nearby stations on the size of confidence intervals and on statistical significance since Ross McKitrick lectured me quite correctly several years ago on the similar effect of autoregressivity in temperature time series Jim Dukelow 6 James Acres says 26 Dec 2004 at 5 49 PM I hate to be blunt and mean You guys are wasting your time No one who doesn t agree with you is going to fight through your essays as currently writen You are fighting the good fight but you ve no chance of winning I used the readability tool in MS Word to check your entry Are Temperature Trends Affected by Economic Activity Your piece is less readable than journal articles in Harvard Law Review Your piece is slightly easier to read than the average insurance policy Clarity and efficiency in writing is important on the web and in email More important than on the printed page Computer screens cause substantially more eye fatigue than do printed pages So people scan to compensate For clarity of writing on the web I ve found the work of Dr Rudolf Flesch helpful He developed a formula back in the 40 s for readability I ve begun using it for my own web writing and email and noticed real improvement in audience comprehension A quick review of his work is here http pages stern nyu edu wstarbuc Writing Flesch htm Newer versions of MS Word include a readability checker with the other grammar tools Suggestions 1 Revise your pieces using some sort of readabilty tool in your word processor While imperfect it will give an objective idea of how readable your pieces are 2 Get a grad student from the Lit or Writing department to write for you Personally I wish all researchers would do this with all their publications Apologies for being so brutal What you guys are doing is great Research is of much greater utility when it s more accessible I just worry you ll get discouraged from the lack of success James Acres 7 rasmus says 31 Dec 2004 at 7 37 AM Response to James Acres I understand your comment and yes this piece is very technical indeed It also discusses several points which makes it even more complex I felt it was important to include the technicalities in order to convince By popularising the piece the article loses its edge I guess that there is a similar reason why articles in Harward Law Review are not popularised either Maybe I can write a more understandable translation for the lay person Or re cap in one sentence the analysis by MM04 can be thought analogous to conducting a survey where 10 individuals are asked the same question 100 times and then presenting the results as

    Original URL path: http://www.realclimate.org/index.php?p=41 (2016-02-13)
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  • On Yet Another False Claim by McIntyre and McKitrick « RealClimate
    the beginning will allow decision makers to scan your work and get the rational message contained within Keep up the good work sir D 2 Ken says 9 Jan 2005 at 2 19 PM All of this technical statistical jargon is over my head but I get the impression that the data on which the climate reconstruction is based is so sparse and uncertain that you can t draw any firm conclusions supporting either MM s or Mann s side of the debate Response Even without technical training or a statistical background you should have an adequate basis for discerning which of the two parties is likely wrong here Only one of the parties involved has 1 had their claims fail scientific peer review 2 produced a reconstruction that is completely at odds with all other existing estimates note that there is no sign of the anomalous 15th century warmth claimed by MM in any of the roughly dozen other model and proxy based estimates shown here and 3 been established to have made egregious elementary errors in other published work that render the work thoroughly invalid These observations would seem quite telling mike The question that I wish someone would address is What difference does it make CO2 is reaching levels that haven t existed for hundreds of millennia and it seems to me that on that time scale the climate a few hundred years ago provides no better basis for extrapolating future climate than does yesterday s weather Can any conclusion regarding future climate change be drawn from the hockey stick reconstruction and can any level of statistical confidence be placed on the conclusion Response Refer to this post and references therein for a detailed discussion of how comparisons of proxy based climate reconstructions with theoretical climate model simulations can inform our assessment of the role of both natural and anthropogenic factors in recent climate change It is often more instructive in this regard however to compare not just hemispheric mean series but the actual spatial patterns of estimated and observed climate changes in past centuries See e g the review paper Schmidt G A D T Shindell R L Miller M E Mann and D Rind 2004 General circulation modelling of Holocene climate variability Quaternary Sci Rev 23 2167 2181 doi 10 1016 mike 3 Bill Hemmer not on CNN says 9 Jan 2005 at 5 00 PM In considering the issue of earth warming I believe that the question of Is it or is it not occurring is irrelevant The more important question is it seems to me How should we behave In this I take my thinking from Pascal There are two realities and two behaviors paired to give us four scenarios 1 We behave as though earth warming is not occuring and it isn t 2 We behave as though earth warming is not occuring and it is 3 We behave as though earth warming is occuring and it isn t 4 We behave as though earth warming is occuring and it is If one thinks through the implications of each of these four scenarios our course of action seems clear What s the problem 4 Stephen Nodvin says 9 Jan 2005 at 11 07 PM Mike According to lay people that I talk to who have been influenced by the op ed pieces that you mention global warming has been disproved The MM story is indicative of a pattern in which industry and now our own government PR machines latch on to minority scientific articles to claim that an environmental issue has no basis The journal Science in the late 70s or early 80 s once published an article in which the author claimed that the major components of acid rain were weak acids The article should have failed peer review and never been published the scientist conducting the work titrated the samples in open air effectively measuring not only the weak acids in the samples but also the carbon dioxide from the room The work was plain wrong Nevertheless representatives of the power companies parroted the findings for several years to claim that acid rain was NOT related to industrial air pollution Stephen 5 Scott Robertson says 10 Jan 2005 at 12 40 PM Great Piece Mike If you are familiar with Tim Lambert he has spent much time discussing discrediting MM As an aside are you familiar with Positive Matrix Factorization PMF We are using it in lieu of PCA for samples we analyzed from a dust storm experiment in Asia It has several major advantages over PCA including that it doesn t produce negative non real results and you can incorporate uncertainty into the analysis so you can limit significance of low level or missing data Keep it up guys I have a brother in law who is a Fox News Talk Radio junky and he insists global warming is a myth yet has never read or seen a scientific article Truly unbelievable Response Thanks very much for your comment Scott Indeed there are other statistical approaches as you note to the problem of climate field reconstruction many of which are somewhat more sophisticated than and arguably preferable to PCA based approaches In this previous post here we discuss the results from a recent paper in press in Journal of Climate by Rutherford et al that uses the Regularized Expectation Maximization RegEM algorithm to reconstruct past temperature patterns from proxy data the results are remarkably consistent with past proxy based reconstructions using other e g PCA based methods Applications to reconstructions of patterns of past continental drought from tree ring data can be found here RegEM is an iterative approach for estimating the data covariance of an incomplete data set and imputing missing values in the process using what is sometimes referred to as ridge regression In this approach the main diagonal of the estimated data covariance matrix is inflated using a smoothing parameter determined by generalized cross validation GCV

    Original URL path: http://www.realclimate.org/index.php/archives/2005/01/on-yet-another-false-claim-by-mcintyre-and-mckitrick/%5C (2016-02-13)
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  • Et si …. la “Crosse de Hockey” était fausse ? « RealClimate
    described as a putter golf Here s my complaint Michael Mann and colleagues have been exemplary in carefully detailing the 2 standard error uncertainty envelopes to their findings Taking the ruler straight handle of a hockey stick and keeping it within this envelope one can produce a wide range of linear trends that remain entirely within that envelope at all times all the way from 200AD until 1980 when the envelopes end due to lack of further sufficient data to produce the 40 year smoothing of the proxy data The lines that can be drawn range from a temperature decrease from 0 05 in AD 200 to 0 10 in 1980 along the upper edge of the envelope to a temperature increase from 0 50 in 200AD to 0 35 in 1980 The pitfalls of producing statistical judgements are endless however I just want to note that it is only right at the very very end within just a few years of 1980 that the instrumental record or any of the proxies first emerge above any of the possible projected lines that can be drawn through the uncertainty envelope I do seriously question the motives of the authors in including in bright red a smoothed instrumental record which is not smoothed using the same 40 year smoothing which was applied to the proxies In fairness for comparison purposes and because a reasonable estimate of climate cannot be made without applying such a broad smoothing to yearly data I do not feel it is appropriate for the figure to include a shorter term more noisy representation for the observations than are used to display the proxies So I dismiss the tail of the red curve I do this knowing full well that the numbers are real But I dismiss them because they cannot tell us anything about the true long term climate trends And having dismissed most of the blade of the hockey stick I am left with as I said more of a putter To summarize my perspective I see the GHG climate signal emerging but only just so I understand the spirit of the detection and attribution work which in theory allows us to project the current trends based on their demonstrated cause using model results But this is all theory and I fear that some of the detection and attribution work as well as the modeling work have suffered from not being double blind if you know what you re looking for you re much more likely to find it So from my perspective the on the ground trend is the kind of solid evidence that the average person will react to Inertia makes the public perception slow to turn But if the trend continues as IPCC projects and as nearly all reasonable scientists including myself expect then the changes will get their attention But I don t subscribe to the use of scare tactics even by those who are honestly scared I reject the hype in a recent article in the Independent about a point of no return for CO2 emissions When CO2 emissions are reduced climate will respond Meanwhile the intriguing affairs of human politics will surely produce more catastrophic outcomes from other causes unrelated to climate 5 John Bolduc says 27 Jan 2005 at 5 15 PM Regarding comment 4 I ve asked the following question under other topics but have not gotten a direct response Peter asserts his faith in humanity s instinct not to soil it s own nest I would generally subscribe to that faith myself The troubling aspect of climate change to me as a layperson is that as others have analogized it is like the frog placed in a pot of water that is brought slowly to boil The frog doesn t know that it should jump out My rudimentary understanding of the accumulation of greenhouse gases is that they persist for a relatively long time The problem with greenhouse gas emissions is that the problem is different in character compared to CFCs etc there is a relatively short time between action and result Therefore switching over to fusion or other non fossil fuel sources decades from now will put us in the position of significantly higher atmospheric concentrations of GHGs that will take a long time to dissipate through natural processes unless someone comes up with an effective sequestration method I suppose And given that people have a very poor understanding of the stocks and flows nature of GHG s see John Sterman s paper Cloudy Skies Assessing Public Understanding of Global Warming http web mit edu jsterman www I m not as comfortable as Peter that there will be timely breakthroughs in technological fixes public understanding and policy So my question again is how long can we afford to wait to reduce GHG emissions I m not asking this rhetorically Can those of you who model climate shed any light for us laypeople on what happens if we wait 10 20 50 or 100 years to reduce emissions Putting the effects of higher atmospheric concentrations aside if we double triple quadruple CO2 concentrations how long does it take to reduce those emissions I m assuming that if technological fixes come along that society will still have to deal with decades or centuries of climate change impacts before we return to normal levels of GHGs in the atmosphere Thanks 6 Mark Bahner says 27 Jan 2005 at 11 21 PM John Finn writes If anyone s running a book on Crichton v IPCC I ll have a couple of hundred on Crichton Gavin Schmidt replies I would recommend you not be so free with your lira There s a pretty easy way to resolve this matter In fact there is a non profit organization designed especially for such matters Long Bets Wigley and Raper Interpretation of High Projections for Global Mean Warming Science Vol 293 20 July 2001 assume a log normal distribution for the IPCC TAR projections and come up with the following temperature rise probability distribution for the year 2100 relative to 1990 see log all 1 1 29 degrees Celsius 5 1 68 degrees Celsius 25 2 42 degrees Celsius 50 3 06 degrees Celsius 75 3 78 degrees Celsius 95 4 87 degrees Celsius 99 5 61 degrees Celsius Michael Crichton s 0 8 degrees Celsius prediction as I understand it is for the 21st century So if we ratio that for the 110 years from 1990 to 2100 the value would be 0 8 110 100 0 88 degrees Celsius Let s take that as Crichton s 50 probability value and use the exact same ranges described by Wigley and Raper for the IPCC For example Crichton s 75 value would be 0 88 degrees Celsius 0 72 degrees Celsius which is 3 78 minus 3 06 or 1 6 degrees Celsius Completing the calculations for Crichton s predictions 1 0 89 degrees Celsius cooling 5 0 50 degrees Celsius cooling 25 0 24 degrees Celsius warming 50 0 88 degrees Celsius warming 75 1 60 degrees Celsius warming 95 2 69 degrees Celsius warming 99 3 43 degrees Celsius warming I will bet Gavin Schmidt or any other author on this website 200 on LongBets org that Michael Crichton s projections for temperature increases are more accurate than the IPCC assuming that the temperature being projected is average lower tropospheric temperature as measured by satellites With regard to the present debate about satellite measurements I m sure it will be resolved to the satisfaction of everyone by 2100 Just to make sure we all understand the terms of the bet suppose the lower troposphere warms by 1 60 degrees Celsius from 1990 to 2100 According to Crichton there s a 25 chance that the lower troposphere will warm by that much But according to the IPCC there is only about a 4 chance that the lower troposphere will warm by that little So if the lower troposphere warms by 1 60 degrees Celsius Crichton and I would win the bet Conversely if the warming was 2 69 degrees Celsius for example the IPCC and Dr Schmidt or whomever else is willing to bet against Crichton would win We ll call this bet the Julian Simon Memorial Bet I m waiting gentlemen And I m not kidding Mark Bahner environmental engineer Response There are at least three things wrong with this idea First and foremost neither you nor I will be around to collect so this appears a little pointless Secondly Crichton did not assume the same uncertainty as IPCC and in fact made his estimate to 7 or so decimal places That you would win if temperature changes were 1 6 twice his estimate but within the IPCC range seems a little perverse Thirdly we are not in the fortune telling business The reason why different projections are used is precisely because we have no clue how technology or economic growth are going to change things 100 years down the line However given a particular increase in greenhouse gases we can say reasonably precisely how much it will warm The current energy imbalance at the surface as demonstrated by the increasing heat content of the oceans implies there is at least a further 0 5 deg C surface warming in the pipeline As I said keep your money in your pocket gavin Response I m a bit more keen on this idea though it remains to be worked out Its been discussed on sci env recently But its a bit far out of RC s remit Go to sci env or my blog William Response There s another more serious problem with this bet All these scenarios are non mitigation scenarios i e they tell us what would happen if we did nothing to slow down or stop climate change We re unlikely to ever see the outcome of this hypothetical experiment I think it s very unlikely that humanity will sit and do nothing about the problem until 2100 I think it is quite possible perhaps even likely that warming by 2100 will be 1 6 degrees Celsius but not because Crichton was right but because people recognised he was wrong and implemented measures to halt the warming Stefan 7 Bruce Stram says 28 Jan 2005 at 9 56 AM You may well have addressed this at another place and another time but at least in this sequence I m left grasping You seem to argue explicitly that no evidence about what has happened in the past millenium is significant with regard to the conclusion that human caused global warming is upon us because we can come to that conclusion based upon analysis of what has happened over the past century This arguement would seen to hold as well for the whole history of the earth That seems to raise an obvious queston how is it that a relative eyeblink of time can be so definitive with regard to a warming trend that as far as I know has been significantly exceeded in the past Response The answer is very simple if you want to study the causes of 20th Century warming you need to look at 20th Century data And not just the climate response but more importantly the forcings Otherwise you cannot determine the cause E g to check whether solar variability may have caused 20th Century warming you need to look at 20th Century solar data Information on temperatures in the 15th Century doesn t help much to answer that specific question except for giving you some rather general information on possible climate system behaviour If you want to study the causes of a warming or cooling in period X of Earth history you study the data from period X Stefan Let me clarify this a bit Stefan is not saying we don t learn anything from paleoclimate records To the contrary we have learned a lot about how the system works A particularly good example is that of abrupt climate change as recorded in Greenland ice cores which few scientists thought was likely or even possible prior to those discoveries eric 8 Rick Watkins says 28 Jan 2005 at 3 39 PM Regarding 4 If anyone can suggest to me why I should not use these two examples as a model for how humanity will and should respond to our release of chemicals into the atmosphere I ll be happy to listen Cause and effect in the two examples given were readily apparent and the link between the two short and easy to grasp in the public mind in my daily experience this is far from true in the case of global warming Further the two examples required no personal sacrifice or change of lifestyle on the part of the general population concerned or otherwise which seems to be unavoidable to curb emissions of GHG s unless a way can be found to deliver the goods to the world population while at the same time reducing emissions drastically can t see that somehow My little bit of pollution is insignificant even countries reason that way I m not going to going to whatever and miss out until so and so next door does I ve seen no letup in rampant consumerism and selfishness in the last 50 years Finally the lag as I understand it between cause and effect with respect to global warming will probably mean that by the time mankind in general and leaders in particular are concerned enough to do anything meaningful it will probably be too late Though I admire your faith in human nature I fear that it is sadly futile An excellent site just what was needed I think information regarding emerging climate trends and their correlation to climate models would be useful though understandably at this time tentative 9 dave says 28 Jan 2005 at 4 49 PM Re The main reason for concern about anthropogenic climate change is not that we can already see it although we can The main reason is twofold Of the emitted CO2 from burning of fossil fuels about 50 is absorbed by the ocean and terrestrial carbon sinks at present See Sarmiento and Gruber Although the residence time of a CO2 molecule in the atmosphere is about 5 years due to the photosynthesis respiration flux and the atmosphere ocean flux the actual time that the excess CO2 remains in the atmosphere is long it is thought to be about 100 years This is due primarily to the fact that CO2 is non reactive in the atmosphere and it takes quite a while for natural processes mostly in the ocean to scrub it out Also it thought that the easy carbon sinks are becoming saturated and will be less and less effective over time This means that a greater percentage of future emissions will stay in the atmosphere Now add to this some bad news about increased use of Coal as reported in New coal plants bury Kyoto Contains a quote from Gavin Coal is dirtier than oil or natural gas with respect to CO2 emissions in a ratio of about 3 coal 2 oil 1 gas The main culprits usual suspects are the U S China and India Now suppose the likely climate sensitivity for doubled CO2 is at the IPCC low end 1 5 C which it isn t it is probably at least 2 0 C Stefan says The IPCC gives the uncertainty range as 1 5 4 5 ºC Only if this is wrong and the true value is lower can we escape the fact that unabated emissions of greenhouse gases will lead to the warming projected by the IPCC Well given humankind s renewed eagerness to burn fossil fuels and their long lifetime in the atmosphere even a climate sensitivity below the low end estimate which no one believes or at the low end which is highly unlikely can still be overwhelmed by CO2 emissions going forward How about a tripling about 850 ppmv Anybody want to go for a quadrupling I see that some people here like to gamble 2 6 Too bad and how convenient they won t be around to see the results But future generations will As regards a fundamental faith in human nature We will not soil our own nest 4 I ll believe that when I see it 10 Jeffrey Davis says 28 Jan 2005 at 5 19 PM We will not soil our own nest I remember the PBS show which took Michael Palin to China He visited the filthiest grimiest city I ve ever seen Heartbreaking The Red Chinese make our rapacious extractives look sunshine fresh So suddenly Red China is going to turn green I don t think so And in all of the dismissals of GW I hear some high priest from Rapa Nui insisting that what the world needs is another stone head Woodsman don t spare that tree 11 Bill Hicks says 28 Jan 2005 at 5 44 PM Thank you for another interesting and usefull post It is important to remember now to get too bogged down in arguments over details when they don t affect the big picture John Finn and Mark Bahner thank you for an amusing end to a hard week of work Wow 2100 Remember Julian Simon was an economist who knew something about what he was talking about and Ehrlich didn t represent a consensus among the scientific community or even demographers You might want to be careful about relying on a work of admitted fiction when making predictions Response It is worth adding that Ehrlich has detailed a host of predictions that Simon would not bet on when Ehrlich offered Ehrlich did this not because he thought betting was a useful way to produce good science or good policy but to show that the emporor Simon has no clothes eric 12 Jo Calder says 28 Jan 2005 at 8 07 PM Stefan writes Carbon dioxide and other greenhouse gases are increasing rapidly in the atmosphere due to human activity This is a measured fact not even disputed by staunch climate skeptics But he should have written more carefully Indeed it appears that C02 levels are rising but to interpolate due to human activity implies that skeptics believe in an anthropogenic cause That s plain wrong So now let s consider the question of whether on geological timescales C02 trends anticipate or lag behind temperature trends Response It is unclear what you are saying is wrong here That CO2 levels are caused by something other than human activity or that the skeptics believe that CO2 levels are caused by something other than human activity In any case we ve adddressed both the issues of CO2 causes and lags and leads in previous posts on RealClimate See here and here eric 13 George Roman says 28 Jan 2005 at 8 52 PM Re 11 I have yet to hear any skeptic claiming that rising atmospheric CO2 is some sort of natural coincidence If they are I don t think they are a credible source See this post here from Dec 22 http www realclimate org index php p 87 14 dave says 28 Jan 2005 at 8 55 PM Re 11 anticipate or lag sorry this is too much fun I ll bet you guys at realclimate never anticipated this kind of response The comment assumes that there is no evidence that fossil fuel emissions add CO2 to the atmosphere and that CO2 increases in the atmosphere may lag some natural variability that nobody can identify Perhaps that variability is caused by Q waves from the Galaxy Ignorancia 331A An uncertainty in some ice core results is somehow translated into a statement about current CO2 emissions data in the 20th and 21st centuries which can be measured precisely However Q waves are not taken into account Now if you respond that seems ridiculous the true premise underlying the climate warming problem needs no defense On the other hand if you don t respond you leave the statement out there hanging in the wind for perhaps inhabitants of the galaxy alluded to above to pick up on Oh Earth to Jo Earth to Jo 15 dave says 28 Jan 2005 at 9 19 PM There was a timing problem When I said 11 in my comment 14 it turned out to be 12 from Jo Calder Well I m off to Galaxy Ignorancia 331A for a bit of rest And please look into those Q waves 16 Tom says 29 Jan 2005 at 10 46 AM Reponse to 4 If anyone can suggest to me why I should not use these two examples as a model for how humanity will and should respond to our release of chemicals into the atmosphere I ll be happy to listen I have to respond to this one too The reason I m concerned that we won t respond to this global threat in a rational way is that huge amounts of intellectual and writing talent are being exerted to make sure we don t This site is an important addition to the cause of pushing out accurate information I don t think the previous campaigns you mentioned to stop nuclear testing or limit CFC use had huge armies of paid writers and skeptics backed by organizations with political and economic interests in confusing and skewing the debate 17 tom says 29 Jan 2005 at 11 55 AM At some point it had to be pretty obvious to a significant number of the stone head people that the trees were going to be decimated But at a certain point tipping point it also probably became clear that the pooch was already screwed And so why not build a few more heads After all like our SUVs and trophy homes they were a big status symbol Given a lot of the commentary on this site I feel we may have already screwed our own particular pooch Even if you are a believer you reach the point where it all seems hopeless So why not get on the band wagon to hell and enjoy the ride Especially scary to me was the comment that excess CO2 remains in the atmosphere for 100 years What does this mean even assuming that we cut our emissions by say 50 Rearding the above comment in 9 I am still a bit confused with respect to the difference between residence time 5years and remain time of 100 years I would appreciate some clarification of that issue Response Residence time in the atmosphere refers to the average time before a molecule is reabsorbed into the ocean mixed layer However the ocean mixed layer equilibrates quickly to the atmospheric concentration but has a very slow equilibration time with the deep ocean So any anomaly in the atmosphere ocean mixed layer takes a long time to disappear This long time 100 yrs is essentially is the residence time for the atmopshere ocean mixed layer combination of reservoirs gavin 18 Peter J Wetzel says 29 Jan 2005 at 1 23 PM There is of course a wide spectrum of greeness among the governments of the world And there is an equally wide spectrum of suppression and or neglect of the populations they serve Governments do shift policy sometimes rapidly At other times change is agonizingly slow What is the most reliable way to convince each of the disparate governments to mandate reductions in CO2 emissions Governments act in their own best interests first and foremost they have as much instinct for self preservation as individual organisms do And like living organisms the strongest motivators for change are usually greed fear and pain Convince a government that CO2 reduction will cause them and in the case of democracies their populations less pain and suffering will provide them with greater security and safety and will improve their economic condition Frankly I don t think the pure science of the global warming issue has clearly identified enough of a global threat of pain and suffering nor of security and safety And the economic cost benefit ratio argument has always been a difficult one in the absence of cheap clean widely available alternative energy sources Pain and suffering Creeping sea level rise gets juxtaposed with tsunamis and with engineering marvels such as the Dutch Polders Encroaching drought in the sub tropics is juxtaposed with improved growing season length CO2 fertilization and potentially more precipitation for more polar nations Etc etc Security and safety The current consensus among scientists is that sudden catastrophic climate change is very unlikely The threat of a generally more volatile and uncertain insecure climate is perhaps the strongest argument science has been able to make And many governments have been convinced on the strength of these findings Yet the science in this area still has much work to do Extreme events are notoriously the most difficult phenomena to correctly represent in climate models Progress is continuing apace and when I choose to use that word rather than if the science becomes more robust and when or if the corresponding climate trends toward volatility of weather emerge clearly from the background noise of natural daily weather then more and more governments will find motivation to act Hopefully breaks in alternative energy technology will accompany the progress in climate science That coupled with the increased urgency which will or might arise if climate becomes more obviously destructive should in my view eventually open the eyes of enough of the power brokers of the world so that meaningful policy actions will begin to be implemented 19 Eli Rabett says 29 Jan 2005 at 9 36 PM With respect to residence time in the atmosphere and mixed layer of the ocean most carbon cycle models I ve seen also include the biosphere and the residence time among these three is often given as much longer than 100 years but shorter than a millenium My question is what is the average time for the excess atmospheric CO2 produced by burning fossil fuels to mix into the deep ocean reservoir Response The mixing into the deep ocean is not a simple process it is enhanced by the rain of organic matter through the ocean column but decreased by the rain of carbonate shells It is enhanced too by the formation of deep water in the polar regions but slowed by the warming of the surface ocean The complexity of these processes mean that the decay of the CO2 impulse into the atmosphere ocean mixed layer cannot be characterised by a single exponential time scale The best estimates are for the average are therefore a little uncertain and range between 50 and 200 years gavin 20 Eli Rabett says 30 Jan 2005 at 4 34 PM If I understood your answer it is not the answer to the question I asked Perhaps I was not clear I accept that the mixing into the mixed layer is 50 200 years However the mixed layer being accessible to turbulent wave mixing with the atmosphere is essentially in contact with the atmosphere and over fairly short times equilibrates with it and other parts of the biosphere Moreover the amount of carbon in the three reservoirs the atmosphere mixed layer and the surface biosphere are approximately equal Given this situation a pulse of CO2 injected into the atmosphere will fairly quickly relax to 1 2 1 3 of the injected value This is what we have seen My question was how long it would take for the excess injected into the upper three reservoirs to relax into the much larger deep ocean reservoir Only when this happens will todays observed increase in CO2 mixing ratio decrease It was my impression that this was the 500 1000 year process admittedly it is not a single process but a complicated melange Just to be clear I am not talking about incorporation into rocks which will take much longer and be the final dilution Response Maybe I wasn t clear the mixing time for the atmosphere ocean mixed layer to come into equilibrium is short around 5 years the longer time scales of 50 200 years are for the mixing into the deep ocean and are thus the appropriate time scale for your question There is a long tail of the response 1000 years due to the slow mixing of deep ocean waters which makes it dificult to give just one number As you say the timescale for full sequestration is more like 50 000 years gavin 21 George Roman says 30 Jan 2005 at 8 51 PM This is a well written piece that covers the issue very well However the wording of the sentence the point of conducting science is to give an early warning rather than just wait until the facts are obvious to everyone is the weakest part of the entire argument Not surprisingly today I read an editorial by Mark Milke in the Calgary Herald exploiting this weakness for maximum rhetorical effect The editorialist removes the sentence from the context of the preceding text and then argues Readers should examine the above point by Rahmstorf because it contains shaky reasoning If it is indeed the case as McKitrick and McIntyre claim that the science behind Kyoto is not solid then to argue that the only thing that proves is that our data are not yet good enough assumes the very conclusion one is trying to reach He then goes on to say that McKitrick and McIntyre s article undermines claims about what caused late 20th century warming essentially ignoring most of the points made above by Rahmstorf I wrote a letter to the editor to try to expose some of these tactics and to more clearly convey the original message of this post It will be interesting to see if they publish it To give the editors some credit they did state at the bottom of the op ed piece that an associate of Michael Mann has promised to send a response to the McKitrick and McIntyre allegations in the coming days Ther position is outlined at http www realclimate org and http www climate2003 com 22 Bruce Stram says 31 Jan 2005 at 3 51 PM RE No 7 I m sorry but your response still doesn t have me quite with the program Indeed yes one must look to 20th century events approximately to understand 20th century outcomes But given what I understand to be true that greater warming has occured than in the distant past than is currently occurring how can we be so sure we are examining all the right 20th century events since these earlier warmings were clearly caused by events other than human driven carbon dioxide emissions 23 Jo Calder says 31 Jan 2005 at 7 09 PM Further to 12 and eric s response I m sorry if I wasn t clear enough in the second sentence by Stefan that I quoted this can only sensibly refer back to the whole of the first sentence giving the reading That carbon dioxide and other greenhouse gases are increasing rapidly in the atmosphere due to human activity is a measured fact not even disputed by staunch climate skeptics Further to 14 from dave I m happy for him that he has the power to measure ignorance from such a distance Further to 13 although I m not so sure that George s message is a response to mine a mode of explanation seen at What does the lag of CO2 behind temperature in ice cores tell us about global warming allows an appeal to some currently unknown process If we don t know what that process was how do we know that it isn t happening now or didn t start happening 50 years ago Regards Jo 24 Joel Shore says 1 Feb 2005 at 11 11 AM Directed to Jo 23 What the skeptics tend to dispute is that the warming seen in the 20th century is mostly due to anthropogenic causes and the rise in CO2 in particular They do not tend to dispute that the rise in CO2 is due to anthropogenic causes The evidence that the CO2 rise is due to humans is incontrovertable For one thing the timing with the industrial revolution is hard to dismiss as a coincidence especially since it is known that CO2 levels haven t been as high as they are now for at least 1 million years over which we have very good data from ice cores and likely for the last 20 million years Secondly the amount of the concentration rise is in line with the amount we know we are putting into the atmosphere through the burning of fossil fuels Actually the rise in CO2 concentrations is generally running at a rate of about 1 2 of what we know we are adding to the atmosphere showing that the biosphere and hydrosphere is able to take up some but not all of our additions Thirdly I believe that by looking at the different isotopes of carbon and or oxygen in the CO2 the additional CO2 can be attributed directly to the burning of fossil fuels Of course what is true is that as we warm the atmosphere the not well understood processes by which CO2 and methane seem to get released as the earth warms may come into play again and create a positive feedback If this occurs we will start to see an acceleration in the increase in concentration of CO2 and it could even start to rise at a rate greater than the amount we ourselves are directly adding to the atmosphere 25 George Roman says 1 Feb 2005 at 8 40 PM Another thought along these lines Suppose that scientists are completely wrong and that no future climate change will result from increased CO2 in the atmosphere of course we must ignore basic laws of atmospheric physics for this but let s for the sake of argument assume that this were true Then surely there would be no reason for concern over greenhouse gas emissions This might be true when only considering climate change impacts But CO2 is accumulating in the OCEAN also causing changes to ocean pH and biogeochemical cycles and thereby posing risks to marine ecosystems coral reefs and fisheries resources In recent years many papers in Nature have been published on this topic e g Kleypas 1999 Riebesell et al 2000 Caldeira and Wickett 2004 also see this paper http www stabilisation2005 com 55 Jerry Blackford pdf Decreased calcification of corals due to higher aqueous CO2 is already occurring and coral reefs are important for fisheries tourism and recreation coastal protection and pharmaceuticals It seems to me that this alone is enough reason for concern that greenhouse gas emissions pose risks to society and nature These risks are completely independent of any of the risks related to climate change One could even imagine a hypothetical situation where the scientific consensus stated that human induced climate change is of no concern but that the long term risks of CO2 accumulation in the ocean are reason enough for multi lateral international agreements to reduce CO2 emissions 26 dave says 1 Feb 2005 at 9 14 PM Re 17 19 20 and what I said in 9 Also it thought that the easy carbon sinks are becoming saturated and will be less and less effective over time This means that a greater percentage of future emissions will stay in the atmosphere There is an interesting discussion of this by Chris Jones et al of the Hadley Centre Impact of Climate Carbon Cycle Feedbacks on Emission Scenarios The paper is part of the current Avoiding Dangerous Climate Change conference happening now in England The discussion talks explicitly about how

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  • Peer Review: A Necessary But Not Sufficient Condition II « RealClimate
    changes in past centuries and insights into the roles of external forcing and internal modes of variability such as the North Atlantic Oscillation or NAO and the El Nino Southern Oscillation or ENSO in explaining this past variability For example it is relatively well established now that the Little Ice Age represented only a moderate cooling for the Northern Hemisphere on the average because larger offsetting regional patterns of temperature change both warm and cold tended to cancel in a hemispheric or global mean Modelers now are comparing not just hemispheric mean series but the actual spatial patterns of estimated and observed climate changes in past centuries See e g our review paper Schmidt et al 2004 where the response of a climate model to estimated past changes in natural forcing due to solar irradiance variations and explosive volcanic eruptions is shown to match the spatial pattern of reconstructed temperature changes during the Little Ice Age which includes enhanced cooling in certain regions such as Europe as well as the smaller hemispheric mean changes References Benestad R E Are temperature trends affected by economic activity Comment on McKitrick Michaels Climate Research 27 171 173 2004 Mann M E R S Bradley and M K Hughes Global scale temperature patterns and climate forcing over the past six centuries Nature 392 779 787 1998 Mann M E R S Bradley and M K Hughes Northern Hemisphere Temperatures During the Past Millennium Inferences Uncertainties and Limitations Geophysical Research Letters 26 759 762 1999 McIntyre S and R McKitrick Hockey Sticks Principal Components and Spurious Significance Geophys Res Lett 32 2005 Rutherford S Mann M E Osborn T J Bradley R S Briffa K R Hughes M K Jones P D Proxy based Northern Hemisphere Surface Temperature Reconstructions Sensitivity to Methodology Predictor Network Target Season and Target Domain Journal of Climate in press 2005 Schmidt G A D T Shindell R L Miller M E Mann and D Rind General circulation modelling of Holocene climate variability Quaternary Sci Rev 23 2167 2181 doi 10 1016 2004 Wilks D S Statistical Methods in the Atmospheric Sciences Academic Press 1995 Comments pop up 5 5 Responses to Peer Review A Necessary But Not Sufficient Condition II 1 scitech library question says 1 Feb 2005 at 7 37 PM RealClimate Climate Scientists Use The Blog RealClimate is new blog launched in December 2004 by a group of concerned climate scientists which describes it as a commentary site RealClimate is a commentary site on climate science by working climate scientists for the interested public and jo 2 Russell Seitz says 3 Feb 2005 at 2 02 AM it would be constructive if younbwereto present a 1000 word precis of this to the editor of TCS I for one would endorse threir running it but then I would endorse a full fledged public debate between the warring parties in this matter at AEI 3 CharlieT says 3 Feb 2005 at 3 59 PM Mike What is your position on

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