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Comments 113701 to 113750:

  1. Why I care about climate change
    Thank you for sharing. As a fellow Christian, I wholeheartedly agree with you. And I find it sad that so many of our faith don't feel the same call to care for the poor and downtrodden. I can assure you that each of us who reads and participates on this blog appreciates what you do. Each of us has our own, and often very different, reasons or logic, but that's part of the beauty of it, isn't it?
  2. Why I care about climate change
    Thank you for all that you do here at SkSc.
  3. Why I care about climate change
    I very much enjoy this blog and all its contents, delighted by the scientific line of thinking which cares not about politics, status or ancient scriptures, but about the truth (or pursuit thereof) through proven and peer reviewed research. I wish more people and communities would share that same philosophy, which is also why I am a complete a-theist. I mean, if you really think in a scientific way, how could anyone believe in a supernatural being? So it surprised me that the man behind the pushing of a scientific philosophy is doing it, besides common, social sense, because of religion. But I'm happy you're doing it anyway :-) and applaud you for this one-time personal openness. I'll also scrap my request to you to set up something similar to show the scientific evidence (or lack thereof) for any supernatural being and the true, scientific history of all religous books. I'm guessing you're a skeptic / denialist at that subject ;-). Meanwhile the government in my country (Holland) is shaping a right wing, conservative, xenophobic and islamophobic government that thinks immigration is one of the biggest problems (even though the science indicates that from the discussed islam-countries there are more people leaving than coming) and that funding to windmills and solar panels should be stopped but nuclear power stations should prevail (even though the science there also indicates investing in wind and solar is a much more effective, safere and more durable solution). Why is science so ignored? Thanks for caring, here's to hoping the site gets more and more momentum. The iPhone app has helped me a lot already to switch people's thoughts about the subject. Thanks again!
  4. Why I care about climate change
    For me, it's a combination of scientific curiosity, and John's reason of wanting to leave the world a better place (and not be blamed for the mess!). But the XKCD reason has an element of truth, too - I hate seeing things that are just plain *wrong*, it irks me no end... :-P Oh, and miekol: yes, it's a (relatively) tiny amount, but don't think of it as a small force pushing a whole planet. Think of it as a small weight added to a finely balanced set of scales, with the two sides being energy in (mostly from the sun) and energy out (mostly via radiation to space). That will change your perspective as to how much forcing is required to effect significant change.
  5. Why I care about climate change
    @6 miekol, Skeptic argument #29. Refuted here.
  6. Why I care about climate change
    Me, I don't like vandalism. Not of personal reputations or the planet. Tagging people and the world with graffiti gibberish and ineradicable messes really gets my goat.
  7. Why I care about climate change
    A great site John. I'm still having great difficulty coming to terms that its supposedly man's production of CO2 that is causing the increase in global temperature. The CO2 we produce is only 0.28 of one percent of greenhouse gases. Such a tiny amount. There has to be some other cause, but I'm at a loss to see it.
    Response: The CO2 we're emitting has actually raised atmospheric CO2 to its highest levels in over 15 million years. How do we know whether this has any effect? We directly measure the increased greenhouse effect, using both satellites that measure heat escaping to space and surface measurements that measure the heat returning back to Earth. These both obtain consistent results - more heat is being trapped at CO2 wavelengths.

    It's not based on models or political ideology or environmentalism. It's based on direct empirical evidence - multiple lines of evidence. All this heat is being trapped by CO2. To try to blame it on some other cause, you also need to account for what's happening to the CO2 heat.
  8. Rob Honeycutt at 09:47 AM on 3 August 2010
    Visually depicting the disconnect between climate scientists, media and the public
    A few objective measures of quality in modern art? A unique approach. Something not done before. A sense of place within historical context. How does the work fit within the context of other artists past and present? An understanding and creative use of color, color balance. An understanding and creative use of composition. A genuine exploration of the media. Pushing boundaries. Personality. The work has life to it. That's a few. For someone in the field of art these are very distinct and clear measures.
  9. Rob Honeycutt at 09:44 AM on 3 August 2010
    Visually depicting the disconnect between climate scientists, media and the public
    Chris... Quality is really not so hard to determine in modern art. Quality is not a subjective measure of art. If you put a painting in front of a dozen professional artists and art critics you will get very consistent answers about whether it is a quality work or not. In fact, in many cases it can be shocking how consistently this works. But the thing is, you have to be trained. You have to know the field very very well. In science it would work the same way. The people best suited to evaluate the quality of a paper are going to be peers in the same or similar fields.
  10. Has Global Warming Stopped?
    fydijkstra #19: "Every natural scientist knows, that linear trends never continue ad infinitum!" Since we're not even close to a theoretical maximum (like, how hot would the Earth get with a 100% GHG atmosphere?), more-or-less linear trends can continue for quite a while. So why consider polynomial trends that show any kind of saturation or decline?
  11. Visually depicting the disconnect between climate scientists, media and the public
    If 137 is the numerator and the total number of universities and libraries is the denominator, in what fraction of universities and libraries may E&E be found? And how many angels can dance on the head of a pin?
  12. Visually depicting the disconnect between climate scientists, media and the public
    robhon at 09:24 AM on 3 August, 2010 ...ooops, didn't catch your post robhon (you brought up modern art!). Never mind. However difficult it might be to assess the quality of modern art, we can certainly assess objectively the quality of science and scientific publications ...
  13. Visually depicting the disconnect between climate scientists, media and the public
    It might be worth adding that whenever any of us goes for a job interview, our interviewers are very likely to have drawn up an explicit list of the attributes they seek in an individual, in terms of relevant experience and evidence of past success and productivity, appropriate personal skills and attributes and so on. Interviewees are asessed on quality in relation to the specific criteria relating to the objectively-defined requirements of the interviewers (that's not to suggest that some seemingly subjective elements won't come into play since personal relationships are involved!). We can pretend that quality can't be objectively defrined (according to specified criteria). But in the real world we know better... ...of course if we are talking about "quality" in modern art, things are a little more difficult, and the criteria for assessing quality will be necessarily less objective ('specially if you're a bit of a philistine like me and not too impressed with Tracy's unmade beds and elephant poo). But why bring up modern art when we're talking about science? It's silly to suggest that the quality of science and scientific publications can't be objectively defined...
  14. Rob Honeycutt at 09:24 AM on 3 August 2010
    Visually depicting the disconnect between climate scientists, media and the public
    Chris... I actually brought up the issue of modern (i.e., 20th century) art. My point was that quality, even in a highly aesthetic field, is not subjective. Maybe Poptech's gramma likes different art than I do, but if you take a sampling of artist and art critics you can create a clear definition of quality. I took a lot of art history classes in college (they were some of my favorite courses) and I can tell you, almost the same way Toyota can and does lay out parameters for what constituted quality in a vehicle, the art world does the same for art. Just because gramma likes your 7 year old niece's paintings (subjectivity) does not mean it is a masterpiece (quality). And because that same niece has painted 6000 of these works (quantity) also does not mean they are great works. Subjectivity is a way of personally quantifying how much you like something. Quality if a broader measure of how well work is executed and stands up to time.
  15. Visually depicting the disconnect between climate scientists, media and the public
    Sorry, dud link: Solipsism.
  16. Visually depicting the disconnect between climate scientists, media and the public
    Poptech #62 In some sense everything is subjective. A call for solipsism will not get you very far. The rest of your latest comment is more of the LALALA I CAN"T HEAR YOU stuff we're used to. canbanjo's #61 post is very informative about the quality of your list. Consider my discussion with you finished as you clearly only have one point to make, you do not make it well, and you make it repetitiously.
  17. Why I care about climate change
    Pretty much the same here, except I'm not a Christian, and I am a scientist working in the area. Have to admit though, I really love driving the brand new top-of-the-line BMW 5 year old Yaris that I bought on all that grant money hire-purchase.
  18. Why I care about climate change
    Eloquent, thoughtful post. Kudos. I share the same sentiment as your first reason. I depart from you on your second. As a humanist, I simply look at the world as a place where we all have to live, and therefore all are its stewards. This requires a certain level of responsibility on the part of all of us, regardless of the status of any higher authority. As you also said, we will all draw our own reasons. I have found, much to my dismay, that I can far too easily get drawn into an XKCD-approved SIWOTI defense, for example. I would therefore only add one more critical reason as I interpret: the defense of truth for the sake of its value as truth. Striving to not be wrong is its own reward, if done with integrity and humility.
  19. Why I care about climate change
    Here, here, agreed. If you have faith does not that faith require stewardship? So much of the climate change argument is about averages, put weather back into those averages and it gets scary. What will the extremes be like?
  20. Has Global Warming Stopped?
    The statistical significance argument is also of limited value when you're dealing with a variety of indicators. The Jones example just refers to one - the HadCrut analysis. There is also the GISS and NOAA analysis, which (correct me if I'm wrong) reaches the 95% confidence level over the same time period. Now these aren't entirely independent. Then there is satellite data, which is mostly independent. I believe these reach similar levels of confidence as HadCrut over this time period. Not to mention that HadCrut neglects the Arctic. http://www.woodfortrees.org/plot/hadcrut3vgl/from:1995/to/trend/plot/gistemp/from:1995/to/offset:-0.09/trend/plot/rss/from:1995/to/offset:0.15/trend/plot/uah/from:1995/to/offset:0.15/trend Then we have the rapid melting of global glaciers and ice sheets observed over this period, along with a notable increase in ocean heat content. The existence of independent indicators is important. If I wanted to analyze the assertion that a slot machine has a net negative expected value for the player, I could observe a single player, accumulating a significant number of rounds, observing a downward trend in his bankroll, and reaching a 90% confidence level. Pretty good, but what if we include 3 other players, let them play the same number of rounds, and they reach 90-95% confidence also with a similar downward trend. Wouldn't true confidence be higher when such independent observations are combined? Not a precise analogy, I know.
  21. Why I care about climate change
    And in doing so you are also standing up for science. You go about this in the best way - using the scientific literature to support your arguments. People can look up the information themselves.
  22. Visually depicting the disconnect between climate scientists, media and the public
    Poptech at 03:51 AM on 3 August, 2010 Poptech at 08:48 AM on 3 August, 2010 As robhon has pointed out "quality" certainly isn't subjective. The assessment of “quality” is made in relation to specific criteria, but these criteria can be objectively defined (they may have fuzzy edges!), especially so for science (and why bring "modern art" into it!?). Here’s a relevant real world example: At the moment the entire UK academic research community is gearing up to the latest of its periodic “research assessment exercises (“RAE”; though this is now called “REF”!). This is an assessment of a department's research quality and is not a notional exercise; the results of REF determine how major elements of government funding are allocated to Universities; REF matters and it matters a lot. How is research quality assessed? A major element is the quality of publications. Each and every research-active researcher in every scientific department in every University in the UK will be submitting their “best” four publications for the period (start 2008 to end 2011). How is the “quality” of a paper assessed? This can be done reasonably objectively in two ways. Scientific journals are ranked within subjects according to their impact factor (average # of times papers in that journal are cited within 2 or 3 years of publication; other defined criteria can be used); papers that have been in print sufficiently long can be assessed in terms of the number of times the specific paper has been cited by others. Each of these is recognised to be an objective measure of research quality (clearly in order to publish a highly cited paper in a good journal I will likely have obtained funding, have done a significant body of research on an important problem and produced a piece of work of high quality). Note that commentaries and reviews don’t count (one can say whatever one likes in a commentary, these are usually not peer reviewed and reviews themselves are not a necessary indicator of research quality). It’s obvious that major elements of UK government funding (and academic and industrial scientific appointments throughout the world) are based on research and publication quality, and that these have definable and objective assessment criteria (even if we may consider that the metrification of quality has gone rather too far). I can understand why you feel the need to downplay what are very obvious real world criteria of research and publication quality. Your odd list of disparate bits and pieces including numerous commentaries in various magazines, duplicated entries and articles that simply don’t correspond to your criterion (“supporting scepticism of man made global warming alarm”) is astonishingly low on quality. That's an objective interpretation based on real world and definable criteria.
  23. Why I care about climate change
    I didn't know there was anyone WRONG on the internet John? Who? Where? What?
  24. Has Global Warming Stopped?
    As to fydijkstra's graph. In addition to what the others have said, it's worth thinking about what the poster is implying. That we have all been getting hot and bothered over nothing - that we thought we were climbing inexorably up a graph that led to 1 degree, 2 degrees, 6 degrees of warming, when, silly old us, it was just that we were cursed by living in interesting times. That we just happened to be lying on the temporarily upward slope of a polynomial wave graph (and of course that this temporary upward slope just happened to coincide with the rapid increase in CO2 levels being spewed out by the rapid industrialisation of the planet. Pure chance it was, and lucky that the deniers stopped us greenies taking western civilisation back to mud huts. Only the deniers managed to keep their nerve while all around were losing theirs). Trouble is, as with all of this kind of amateur graph reading from the deniers, there is no mechanism presented for explaining how the change in global temperatures could be polynomial rather than linear. Where is the negative feedback that takes CO2 back out of the air once it reaches a a certain concentration? Or, conversely, what is the mechanism that allows CO2 and the greenhouse effect to keep on up and up and up while temperatures go back down down down? Proper science doesn't work post hoc. That is, you need to work out an hypothesis for the climate systems of the planet, then test that against the actual data. You can't simply try to see patterns that apparently emerge from the data after the event. I'm sure we've discussed this before.
  25. On Consensus
    "How about this one" Wallace Broecker concluded: "Our efforts to understand and EVENTUALLY to predict these changes need to be redoubled" Science is about prediction based on mathematical models. Broecker was not claiming he had high confidence in a quantitative model. His paper was much more qualitative in nature. A good model would define a function that twenty years into the future that would contain all the variables needed to make the prediction. Solar variability, CO2 and other GHG, volcanic activity, etc. Then, the twenty years of data is plugged in to see if the model from 20 years in the past can produce a prediction that is 90% accurate. If that can be done for many years without a need to constantly add more factors to the model in order to improve its accuracy, then Climate science will have arrived at the magical 4.5 level of confidence. I predict that will not actually happen for at least another 50 years. In the mean time, over the next twenty years, the IPCC predicts developing nations emissions of CO2 will dwarf current levels and thus allow climate scientists to have increasing amounts of CO2 to better test their climate models.
  26. Has Global Warming Stopped?
    Careful with Poptech! He's been suspended from both Deltoid and WUWT for posting personal details about another commenter.
  27. What's in a trend?
    Then #21 should say "every indication that the cool period is now should be upon us. As was pointed out here two years ago, the PDO lacks any long term information about global temperature rise. #22: "I do hope the last few summers here are not representative of a "cooling period"." Same here. If this is cool, hot will be really ugly.
  28. September 2010 Arctic Ice Extent Handicapping Via ARCUS
    Tamino teases the tea leaves, looking at variances between years w/regard to extent versus area versus phasing of changes. Lovely arcana. Also a prediction is ventured, with methods.
  29. Visually depicting the disconnect between climate scientists, media and the public
    Had a sim through the poptech list, noted the publications include: The Electricity Journal New Zealand Geographer Irrigation and Drainage Iron & Steel Technology Nordic Hydrology Bulletin of Canadian Petroleum Geology New Concepts In Global Tectonics Weather ICE - Civil Engineering Hungarian Meteorological Service Monthly Weather Review Energy Policy Economic Affairs Economic Analysis and Policy Energy Fuels Area Social Studies of Science Regulation Journal of Forestry Public Administration Review Journal of Chemical Education Journal of Cosmology The Review of Economics and Statistics Malaria Journal Weather and Forecasting Journal of the American Water Resources Association Leadership and Management in Engineering Environmental Politics Society The Independent Review World Economics New Literary History Quarterly Journal of Austrian Economics Waste Management The Cato Journal Economics Bulletin World Economics Economic Affairs Canadian Journal of Agricultural Economics Arizona Journal of International and Comparative Law and of course E&E
  30. Dikran Marsupial at 08:30 AM on 3 August 2010
    Has Global Warming Stopped?
    Poptech said: 'Sorry boys 95% is what statistically significant means. Anything less would not be "statistically significant".' My previous post was based on a misunderstanding of what Poptech wrote. In actual fact, the 95% level is merely a convention, a rule of thumb, with no deeper significance. You can claim statistical significance at any level you like (as long as you are clear about it), however nobody will be greatly impressed by a result that is significant at the 50% level of certainty. The 95% level is a sensible default, but it isn't set in stone. Bayesian significance tests also have a similar set of conventional threshold values for the Bayes factor, but likewise they are merely a useful rule of thumb.
  31. 10 key climate indicators all point to the same finding: global warming is unmistakable
    Stmwatkins, indeed there is the rough equivalent of an Arctic Ice Fantasy League (AIFL, sounds legit!) in play. Not exactly to the level of hulking guys with five-o'clock shadows clutching fistfuls of sweaty money and chomping on stogies while hunched over a pair of dice, but near enough. September 2010 Arctic Ice Extent Handicapping Via ARCUS is one parlor where you can make your bets. Daft it is, at least on an inter-annual basis. Morbidly fascinating, too.
  32. 10 key climate indicators all point to the same finding: global warming is unmistakable
    CBDunkerson #125 I would like to change my use of the term skepticism to the term question and state that I have a very conservative science background. It appears that using the term "skeptic" is a bit like waving a red cape around here :) Also, I need to change my current job if I thought computer models were nonsense. My question was about differentiating the anthropogenic forcing from natural forcing, and that appears to be mainly through the GCM's. Like I stated in my initial post, I believe there is a anthropogenic component. My question is how much? Which I am slowly looking into. More to this thread topic. Is there some type of Arctic Sea Ice fantasy league going on? I am very conservative (no s-word used) on AGW issues but this is a bit daft. Increasing Arctic Sea Ice would be a good thing but it does not signify some type of scientific victory one way or the other.
  33. The Past and Future of the Greenland Ice Sheet
    Re: Tenney Naumer:"Newer studies indicate that the runoff is moving closer to half of the mass balance decline." were you thinking of Broeke et al., Science, Vol. 326. no. 5955, pp. 984 - 986, 2009 "Partitioning Recent Greenland Mass Loss" from the abstract: "The total 2000–2008 mass loss of ~1500 gigatons, equivalent to 0.46 millimeters per year of global sea level rise, is equally split between surface processes (runoff and precipitation) and ice dynamics." Certainly makes me look at Figure 4 from Pffefer above in a whole new light. http://www.sciencemag.org/cgi/content/abstract/326/5955/984 sidd
  34. Visually depicting the disconnect between climate scientists, media and the public
    Poptech #43 This LA LA LA I CAN'T HEAR YOU mode of argument is pretty tiresome. 1. As I said, you're welcome to try coming up with a better systematic criterion for expertise. This concept is more important and achievable than objectivity. 2. Again you are confusing your self-appointed expertise with the idea that a systematic procedure if fairly applied across the sample of interest is adequate. Your self-professed expertise on the workings of Google Scholar is irrelevant here. 3. By other measures, E&E is not a good quality journal (e.g. library holdings) - it's actually quite difficult to get hold of, only being held in about 50 libraries. It's also clearly contaminated by the editorial desire to confound research results and political ideology - a kiss of death for a journal focusing on social science. You do seem to enjoy talking around in circles, I suspect it's due to the weakness of your argument, and lack of range of what you will argue about.
  35. Has Global Warming Stopped?
    (cont) Also your analysis indulges in a bit of cherry picking. Why not evaluate the linear trend since 1960? The R2 and p value will be pretty high for that too.
  36. Has Global Warming Stopped?
    fydijkstra #19 What you're doing there with your polynomial fit is almost certainly something called overfitting. This is where your model is describing the noise component of the relationship rather than the signal. Of course as Dikran points out, the noise could relate to ENSO in this instance.
  37. Visually depicting the disconnect between climate scientists, media and the public
    Oh, brother, I just noticed that the Financial Times piece redlined by The Way Things Break included a quote from none other than Steve Goddard who claims therein that temperature data is "fabricated." So FT's credibility is now on a par with The Register. Nice.
  38. Dikran Marsupial at 06:39 AM on 3 August 2010
    Has Global Warming Stopped?
    fydijkstra, there is however a problem with any purely statistical argument, which is that they ignore existing knowledge. For example, the cause of the apparent flattening is very probably ENSO. So just because a non-linear model gives a better fit (including the additional degrees of freedom) doesn't say anything about the underlying situation. It is entirely possible that a linear model works rather well after the effects of ENSO have been filtered out. In that case, there is still no evidence that (anthropogenic) global warming has stopped, just that it has been temporarily obscured by the effect of the (quasi-cyclic) ENSO.
  39. Has Global Warming Stopped?
    Useful perspective, more informative in some ways than a linear trend IMHO fydijkstra, but why do you then spin it with "This trend clearly shows a flattening of the warming trend, if not the beginning of a decline" when "flat" only pertains to the last two years of the 1960-2009 graph by imaginative squinting and no decline is visible? Why introduce the term "decline" when no such decline is visible? More generally, it's acknowledged that a monotonic rise is not a feature we're going to see, which is why a linear treatment is in some ways better for looking at this problem. Even if we could successfully imagine the extension of fydijkstra's graph and could see a decline we'd not be surprised. Jones was speaking of specific claims in any case.
  40. Dikran Marsupial at 06:28 AM on 3 August 2010
    Has Global Warming Stopped?
    I would say "There has been no statistically significant warming since 2008 [if I had performed the test of course], however the statistical power of a test over such a short period would be so low that the results of such a test would be essentially meaningless." I would of course also be happy to explain what "statistical power" meant and other caveats about statistical hypothesis testing as required. However, the first thing I would do is give a direct answer to a direct question. Note it is entirely plausible that most climatologists have better things to do than read climate blogs, and hence may not have been that familiar with the sort of misunderstandings propagated via blogs rather than the journals.
  41. Rob Honeycutt at 06:04 AM on 3 August 2010
    Has Global Warming Stopped?
    Dikran Marsupial... I disagree. I could ask the question as: Do you agree that from 2008 to the present there has been no statistically significant warming? How would you answer that question? "Well, stupid, that's only two years. Of course there was no statistically significant warming." The formation of the question is the heart of the issue. Due to the noise level of climate you would not EXPECT to see statistical significance achieved in that time frame. It has almost nothing to do with the amount of warming. It has everything to do with the noise to signal ratio. So, rather than falling for the trap the questioner had obviously set it would have been more beneficial to point out the trap rather than stepping in it.
  42. Has Global Warming Stopped?
    This analysis is correct, as far as linear trends are considered. The linear trend for 1995-2009 has an r2-value of 0.2269, which corresponds (for 15-2=13 degrees of freedom) to a significance of about 92%. However, if global warming has stopped or weakened, we do not talk about linear trends. Breaking down a 50-year trend into arbitrarily chosen 15-year intervals is not a technique that any serious statistician would apply. If the warming trend has flattened or reversed, we should look for non-linear trends. A convenient tool available in Excel is the polynomial function. Application of a fourth degree polynomial function to the trend for 1995-2009 gives the following picture.
    This trend shows a clear decline, with r2=0.4115. The significance of this trend is 99%, much higher than Phil Jones’ linear trend. Application of a polynomial function to the trend for 1960-2009 gives the following picture. .
    The significance of this trend is very high: r2=0.8448. With 48 degrees of freedom, this has a significance of 99.9% or more. This trend clearly shows a flattening of the warming trend, if not the beginning of a decline. Saturation functions are much more probable in natural processes than linear functions. Every natural scientist knows, that linear trends never continue ad infinitum!
  43. Dikran Marsupial at 06:00 AM on 3 August 2010
    Has Global Warming Stopped?
    As an aside, Paul the octopus provides a good example of the problems with tests of statistical significance. Paul apparently predicted the results of 10 games in the recent football world cup, with 100% accuracy, but does that mean than Paul actually had some skill? If we simpify by ignoring draws, then just guessing would give a probability of a correct prediction of 1/2, i.e. just like flipping a coin. So we could hypothesise that Paul's true accuracy p > 0.5 (the "alternative hypothesis" H_1), with the null hypothesis (H_0) being that Paul was just guessing, i.e. p = 0.5. The p-value is the probability of the observed results assuming that the null hypothesis is correct, so p(D|H_0) = 0.5^8 = 0.0036. This is less than the usual alpha = 0.5, so we would conclude that Paul has statistically significant skill (at the 99.61% level, no less)! So, does this prove that Paul has skill - of couse not, he's a bloody octopus!!! So why does he pass the test of statistical significance - simple, because of cherry picking. We only know about Paul because he was successful; if you have a large enough pool (sic) of predictors, a few of them are bound to be 100% correct, simply by chance. The reason the test is fooled is because frequentist tests are based on the idea of the frequencies of events in a large number of random replications of an experiment. The test of statistical significance assumes that the predictions were a random sample of predictions made by a large number of "alternate Pauls" (or equivalently the predictions of one Paul for a large number of independent world cups). However, this is not the case, we were only interested in Paul after he had already got four predictions correct, so he isn't a random selection of anything, but a biased choice. The statistical significance of trends likewise assumes some fictitious large population of alternate Earths, of which this one is a random sample (or alternatively the particular period of observation being a random sample from a large set of such periods). However the period in question is nothing of the sort. The "skeptics" only became interested when the significance of the trend suited their argument, and they tend to cherry pick the start date to maximise its value (for instance start dates of 1998 and 2002 are used, but not 2000 for some reason ;o). Again, it isn't a random sample of anything, so the underlying assumptions of the test are invalidated (and hence so it the test). As a Bayesian, I find frequentist significance tests a rather odd (for example, why is the criterion independent of the alternate hypothesis?) and a bit of a minefield, but then Bayesian equivalents are not without their problems either. Admission: I was going to work all that out myself, but I found Wikipedia has done it already!
  44. Has Global Warming Stopped?
    Well, not quite 100%. >95%, anyway, and poptech will tell you that the 5% confidence level is a long way away from statistical significance.
  45. Has Global Warming Stopped?
    I'd really like to turn this question around. Dr. Jones's response is the correct answer to a statistical test that is set up with a null hypothesis being no warming, or a slope of zero. According to the variability in the too-short dataset, this null hypothesis cannot be rejected with 95% confidence (only 92%). However, if you want to claim that global warming has stopped, you should really formulate the null hypothesis as continued warming at the prior rate - that is, you should start with a null hypothesis that the slope is equal to 0.101 degrees per decade. In that case, given that the slope from 1995-2009 was 0.116 (larger), there is no evidence that the warming has stopped. If I do a two-tailed test (checking to see whether the slope is simply different than 0.101, in either direction), I get a p-value of 0.40. In other words, I can statistically interpret the data from 1995-2009 in multiple ways: - If I say that there is evidence in this series (all on its own) of a warming trend, I have an 8% chance of being wrong (according to Dr. Jones). - If I say that the evidence shows that the rate of warming has changed (from 0.1 degrees/decade), I have a 60% chance of being wrong. - If I say that there is evidence in this series that the prior warming trend has stopped, I have a 100% chance of being wrong.
  46. 1934 - hottest year on record
    Further to Broadland's remarks, here's something that just popped up: The year 2010 is now tied with 2007 as the year with the most national extreme heat records--fifteen. There has been one country that has recorded its coldest temperature on record in 2010; see my post last week for a list of the 2010 records. My source for extreme weather records is the excellent book Extreme Weather by Chris Burt. His new updates (not yet published) remove a number of old disputed records. Keep in mind that the matter of determining extreme records is very difficult, and it is often a judgment call as to whether an old record is reliable or not. For example, one of 2007's fifteen extreme hottest temperature records is for the U.S.--the 129°F recorded at Death Valley that year. Most weather record books list 1913 as the year the hottest temperature in the U.S. occurred, when Greenland Ranch in Death Valley hit 134°F. However, as explained in a recent Weatherwise article, that record is questionable, since it occurred during a sandstorm when hot sand may have wedged against the thermometer, artificially inflating the temperature. Mr. Burt's list of 225 countries with extreme heat records includes islands that are not independent countries, such as Puerto Rico and Greenland. Seventy four extreme hottest temperature records have been set in the past ten years (33% of all countries.) For comparison, 14 countries set extreme coldest temperature records over the past ten years (6% of all countries). I thank Mr. Burt and weather record researchers Maximiliano Herrera and Howard Rainford for their assistance identifying this year's new extreme temperature records. Jeff Masters Weather Blog
  47. Waste heat vs greenhouse warming
    CBDunkerson at 20:32 PM, with regards to the 2 hot skewers, what difference would there be in the cooling rate of one hot skewer of mass X compared to two hot skewers each of mass x/2? It appears to me that such comparisons seem to overlook that the mass increases when another object is introduced into the vicinity/equation.
  48. Dikran Marsupial at 05:01 AM on 3 August 2010
    Has Global Warming Stopped?
    Poptech@10 - yes, which is why Prof. Jones was quite happy to explicitly state that the trend was not staitsically significant. But then again, statistical significance becomes meaningless if you cherry pick the start date to get the longest trend that fails to be statistically significant, just as it is meaningless if you cherry pick the start date at 1998 to bias the trend to show cooling. Basically this is because the cherry picking involves performing multiple hypothesis tests and not making the appropriate statistical adjustment to cater for it. BTW, failing to be statistically significant does not mean that a warming trend does not exist, or that it doesn't reflect a real physical process. It doesn't even mean (if it is a frequentist test) that we are 95% confident that the trend is positive. Tests have Type I errors (false positives) and type-II errors (false negatives). The "alpha" mentioned by dcruzuri in 11 refers to type-I errors, there is also a "beta" for type-II errors (retaining the null hypothesis when it is false), known as the "power" of the test (hardly ever mentioned). It should be no surprise if a trend fails to pass a test of statistical significance if the power of the test is very low, perhaps because there is too little data (as Prof. Jones pointed out). Essentially a failed statistical test means "insufficent evidence", nothing more. Easterling and Wehner (2009) is an excellent source of information for this one. They show that the trend is smaller in magnitude than the natural variability due to things like ENSO, and so we should expect to find the occasional decadal (10-20 year) tends that don't show significant warming, or even cooling. These have happened before (as shown above) and also appear in the output of the climate models. Thus is it completely unsurprising that "skeptics" can cherry pick an "inconvenient trend". However it is a specious argument.
  49. On Consensus
    Actually Thoughtfull I think of it as something like "unnatural variability." Social scientists are trying to better tease out the effect of the email hacking event and heavy snowfall in some regions last winter. There are not enough numbers to say for sure but it seems to me there are at least some hints of effects from those in the statistics. I also wonder if the publicity around the 2007 Arctic ice anomaly influenced the 2008 numbers. I'm left to imagine the situation may be largely static in terms of trends, something that fits with what scientists have learned of ideology being the gatekeeper controlling integration of information into our worldview.
  50. Has Global Warming Stopped?
    ABG, Thanks for a interesting and well thought out post. I sadly suspect that your prediction for 2013 will come true-- that is the beauty of cherry-picking short windows in noisy datasets such as the SAT record, once can play that game of deception to the end of time. If I recall correctly, for the data and cherry-picked window in question (i.e., up until 2009 in the HadCRUT data), the warming is statistically significant at the 93% level. Poptech might want to inquire why and how Lindzen chose/cherry-picked this particular start date. I'll help, go here. Those in denial about AGW/ACC might also want to do some research on the meaning of statistical significance before pontificating. It seems that they are only too happy to hear what they wish to hear.

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