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Chookmustard at 22:49 PM on 14 May 20122012 SkS Weekly Digest #19
Hi guys, love the site, long time reader first time poster! I don't have enough confidence to ask a question as I feel my knowledge level is not high. Is there a 101 section? Keep up the good work!Moderator Response: Welcome! At the top of the Home page, click the big button "Newcomers Start Here." After you've read that page, click the big button "The Big Picture." Comments must be on the appropriate thread, but if you are uncertain which thread that is, you can either pick the most apparently relevant one from the Arguments list (click the "Arguments" link at the left end of the blue horizontal bar across the top of the page), or use the Search function that is just under that link. -
Alexandre at 22:45 PM on 14 May 20122012 SkS Weekly Digest #19
About the issue of the week: No, no fear of getting lectured. Mostly I just feel I have nothing to add. Bert from Eltham at 13:47 PM on 14 May, 2012 wuwt has many of those. And they all nod along as long as it sounds vaguely anti-Hansen, anti-Gore, anti-Michael Mann... -
Carbon500 at 22:09 PM on 14 May 2012101 responses to Ian Plimer's climate questions
Although I haven’t as yet obtained a copy of Plimer's publication, as judged by the Australian government’s response on your website his questions raise interesting points. It’s essential that children learn to think, question, compare and contrast sources, and form opinions of their own in science. The governmental response lacks detail and references - for example, in the answer to question 8, it states ‘the oceans are warming’. Yet on page 48 of the IPCC’s Climate Change 2007 is the statement ‘ Whilst the global trend is one of warming, significant decadal variations have been observed in the global time series, and there are large regions where the oceans are cooling.’ A rather more complicated picture than the government presents, isn’t it? Then there’s the matter of oceanic pH. The government answer to question 95 states that ‘the pH of seawater has historically remained at about 8.2 ’ This is followed by the claim that human activities have ‘caused the pH of ocean surface waters to drop by 0.11 pH units.’ There’s no reference for this, but on page 405 of Climate Change 2007 the IPCC state ‘The mean pH of surface waters ranges between 7.9 and 8.3 in the open ocean, so the ocean remains alkaline (pH>7) even after these decreases.’ The government’s use of the words ‘equivalent to 30 percent increase in acidity’ is misleading. So how has this increase of surface ocean waters been measured? Climate Change 2007 states on p48 that ‘the overall pH change is computed from estimates of anthropogenic carbon uptake and simple ocean models.’ Computations from estimates! Mercifully, they follow this with ‘Direct observations of pH at available stations for the last 20 years also show trends of decreasing pH, at a rate of 0.02 units per decade.’ Empirical data, thank goodness. The answer to question 68 paints a rosy picture of computer modelling, yet on p21 Climate Change 2007 gives a more realistic ‘there is still an incomplete understanding of many components of the climate system and their role in climate change. Key uncertainties include aspects of the roles played by clouds, the cryosphere, the oceans, land use and couplings between climate and biogeochemical cycles.’ I’ll be interested to see Ian Plimers’s answers to his own questions. I hope that the science teachers in Australia do their homework well! -
mspelto at 21:42 PM on 14 May 2012Analysis of Speed of Greenland Glaciers Gives New Insight for Rising Sea Level
Moon et al (2012) further the examination of flow velocities of Greenland glaciers. The results in terms of flow speed changes fit previous observations. Zebras in Greenland examined the reasons why the glaciers behave differently. The sea level change noted by Moon et al (2012) is for dynamic changes only not for increased basal or surface melting. Epiq Sermia is one of the glaciers that has not accelerated dramatically but has still thinned and retreated. Upernavik Glacier did accelerate quite a bit and has lost even more area -
cynicus at 20:30 PM on 14 May 2012Analysis of Speed of Greenland Glaciers Gives New Insight for Rising Sea Level
Agnostic, in Hansen and Sato's discussion their scenario is very explicit: "If either ice sheet [[Greenland and Antarctica]] were to lose mass at a rate with doubling time of 10 years or less, multi-meter sea level rise would occur this century." Hansen and Sato's prognosis explicitly depends on continued acceleration and the new work of Howat et.al. seems to put upper limits on this acceleration. Let's hope they are correct. Both studies however seem to agree on eventual (on centuries timescales) multi-meter sealevel rise. So the discussion here is the rate of change, not the scale of the change. -
skywatcher at 18:09 PM on 14 May 2012IPCC graph showing accelerating trends is misleading
Helena, you're really not making much sense. Progressively increasing or decreasing gradients of the lines prove concavity of the curve, as opposed to it being flat or curved the other way. The same applies for 'decelerating' curves, whether you like it or not. They don't say anything about the specific function that best fits the curve - there may be a single breakpoint where the temperature accelerated, or it may smoothly 'accelerate', but it demonstrates that the rate of temperature increase is faster now than it was earlier in the last century. Noise may temporarily disrupt the pattern, but as you'll see from my graphs above, the pattern for HadCRUT3 is one of progressive acceleration. It says nothing about the future evolution of the temperature profile either - that depends on the balance of forcings of course. But the IPCC was quite justified in using this example, and you have provided no coherent reason why it is an illusion, rather than a simple illustration of the obvious. -
Nick Stokes at 16:48 PM on 14 May 2012Turbines in Texas mix up nighttime heat
Riccardo, I have to agree - when I look at the derivation of Betz, it is odd. It assumes total downstream KE is derived from the axial flow component, which ignores swirl. But the flow exerts a torque on the turbine; the turbine must exert a torque on the air. I guess that's one more layer of mystery. Anyway, I'm convinced by SM's second argument about the smallness of temperature change. -
Helena at 16:31 PM on 14 May 2012IPCC graph showing accelerating trends is misleading
"Therefore this test does not detect accelerating curves per se, but acceleration within a curve." Ahah, we're getting there. -
Helena at 16:29 PM on 14 May 2012IPCC graph showing accelerating trends is misleading
Tom : Moreover, the example you give of decreasing accelerated curve is a very specific one, part of the "punctual counterexemples" i said would exist because you take it all smooth with no noise or bumps. However, the larger subset of all decreasing decelerated curves contains much more curves that *do* have increasing trends with shorter time periods. Any noise, any bump (i.e. anything but the ideal case you present) will tend to ensure that what i say is correct. Do you agree with that ? -
Helena at 16:11 PM on 14 May 2012IPCC graph showing accelerating trends is misleading
Erratum : "IPCC does neither constraint the slope of the trends (they just have to be increasing) nor the form of the underlying function (as it is what they want to infer)." Please read : "IPCC does neither constraint the slope of the trends (they just have to be *greater than the longer one*) nor the form of the underlying function (as it is what they want to infer)." They do not have to be increasing, just greater than the previous one. -
Kevin C at 15:30 PM on 14 May 2012Analysis of Speed of Greenland Glaciers Gives New Insight for Rising Sea Level
While the changes in the Arctic are indisputably very dramatic, I am hesitant to draw too simplistic an extrapolation of what is going on. I presume the long term impact of this work, if correct, would be that the current quadratic trend in the GRACE Greenland ice loss will at some point hit a maximum rate and then stop accelerating. That doesn't seem fundamentally implausible to me. When it comes to experts, while I go to Hansen first on climate modelling, when it comes to glaciology I'll certainly pay careful attention to what the specialists in that field have to say. Having said that, all new results are provisional, and many turn out to be wrong. -
GillianB at 14:41 PM on 14 May 2012Turbines in Texas mix up nighttime heat
As Scott Mandia said -- Moving money from one bank account to another won't make you richer, so windmills just move air around, they don't make it warmer. Blogged here... http://thisnessofathat.blogspot.com.au/2012/05/windmills-move-air-like-banks-move.html -
Bert from Eltham at 13:47 PM on 14 May 20122012 SkS Weekly Digest #19
I have been intimidated by the knowledge shown on this site. It was then I realised that I just did not know. On looking at wuwt I found this gem. Heat from the sun cannot get into the ocean due to surface tension! You blokes are doing it all wrong as you should let the scientific illiterati just say nonsense. That way they are all happy calling all outsiders nasty names from an enclave of idiocy! Bert -
DaneelOlivaw at 12:21 PM on 14 May 20122012 SkS Weekly Digest #19
"Are you reluctant to ask a "dumb question" on a comment thread for fear of being lectured to by one or more of members of the SkS author team?" No, but sometimes I don't post on a comment thread when there are too many comments and there's already a conversation going. -
Tom Curtis at 12:01 PM on 14 May 2012IPCC graph showing accelerating trends is misleading
I expect this to be my last post on this issue. That is because Helena's misrepresentation of what I said, and her refusal to acknowledge that misrepresentation makes conversation with her, IMO, pointless. At best, she is simply not open to new ideas that do not suite her preconceived opinions. Reviewing Helena's claims, we find that first she claimed that Monckton was correct, even though she has argued her case on entirely different grounds to that used be Monckton. That means that even if she could establish her case, she would not establish that Monckton was "right", and her claim that he was remains false. Second, Helena argued that the claim in the original post that "(2) ... the pace of warming over the last 25 years is greater than that in preceding years on the record". When challenged, however, it was found that in all her supposed counter-examples, the trend in the 25 years to 2005 was in fact greater than that in her supposed counter-examples. Therefore her claim was false, and based simply on inadequate inspection of the data. The more significant claim that the data does not support the categorical assertion of (2), but only the very qualified assertion that "on balance of probabilities" or, in the IPCC's jargon, "it is more likely than not" that the 25 year trend to 2005 is larger than any prior 25 year trend in the instrumental record. Of more concern to me is that it is not even clear that the IPCC ever asserted (2). The closest I can find to their asserting that is the assertion that,"An increasing rate of warming has taken place over the last 25 years, and 11 of the 12 warmest years on record have occurred in the past 12 years."
(IPCC FAR, WG1, FAQ 3.1, My emphasis, note the tense.) This, however, is an assertion of increasing warming, not of a greater rate of warming than any comparable period. In other words, it merely reasserts the claim of accelerating warming in different words. I would be interested to see if anyone can find an actual assertion of (2) by the IPCC. Failing that, the OP should be updated to correct this potential error. I recall (vaguely) having some input into this post, and therefore bear some responsibility for this error, if error it is. For that I apologize. Finally, Helena continues to insist that a pattern of increasing trends with decreasing trend length can never be evidence of an accelerating trend. Her claim is, frankly, is nonsense. To see this, consider a smooth, and accelerating curve, ie, a curve whose slope is steeper at later times than it is at any earlier time. We can express this mathematically by saying the curve satisfies the condition that slope(t) < slope(t+x) for all x greater than 0. The second curve in the figure below gives an example of such a curve. A decelerating curve shows the opposite pattern, ie, the slope at any time t is greater than the slope at time t + x where x is greater than 0, bearing in mind that large negative numbers (and hence negative slopes) are smaller than small negative numbers and positive numbers. (Common language and intuitions are sometimes confused on this point.) The first curve in the figure below is an example of a decelerating curve. However, as the reasoning is parallel in both cases, I will not discuss it further.
A linear trend is a type of average of the slopes of a curve. It is not the same as the mean of the slopes of a curve, or the mode, but it is an average never-the-less, and consequently has some of the properties of averages. One of those properties is that if you include more low value terms, ie, if the curve has more low slopes, the linear trend will be lower. In contrast, if you include more high value slopes, the linear trend will be higher.
If you have an accelerating curve, with no noise, and take trends of successive periods, each being a whole number multiple of some value (say, 25 years), and each terminating at the same point, an interesting thing occurs. Whatever the value of the first trend you take, the second trend will include all the data points of the first, plus some some additional points. Because the trend is accelerating, these additional points will have a lower value than the original points (by definition of accelerated). Therefore the calculated trend of the larger interval will be lower than than the calculated trend of the smaller interval.
This point follows by logical necessity. It is true of any accelerating curve segments with no noise. Therefore for any such curve segments, finding this pattern is sufficient proof that the segment is accelerating.
Please note that Helena has repeatedly contradicted the bolded claim above. She has done so with no supporting argument, and he contradiction of that claim represents the bedrock of her case. It also logically indistinguishable from a simple assumption that no curve is accelerating.
Of course, the temperature curve is not a curve with no noise. When you introduce noise, an interesting thing happens. Suppose the noise in the signal is so small relative the signal that it cannot be distinguished from the arc of the curve as drawn on a graph. Then clearly the reasoning above will still apply. In contrast, if the noise is very large relative to the curve segment, the reasoning will not apply. That is because most of the data in each successive period will be noise rather than the underlying curve. Therefore this method of detecting acceleration will only work when the signal to noise ration is large, or stated alternatively, when the difference in the trends of successive intervals is a sizable fraction of the 2 sigma confidence interval (and ideally, larger than it).
There are a couple of important nuances to this argument. The first is that if your "curve" consists of two straight line segments meeting at a particular point, and if your successive trends all overlap that point, this method will still show the curve as accelerating. This is not a flaw. The "curve" has in fact accelerated. It has just done so at a precise point rather than continuously and smoothly. Therefore this test does not detect accelerating curves per se, but acceleration within a curve.
Second, like all statistical tests, this test does not test for what the data will do outside the segment tested. A curve may repeatedly, and at regular intervals, accelerate than decelerate as with a sine curve. If you test the appropriate segment, you will find the acceleration that is actually occurring by this test, but it will not tell you whether the acceleration will continue, stop, or reverse.
Of course, the IPCC does not claim, based on this test, that the acceleration will continue. The claim that it does is a key misrepresentation by Monckton, discussed in the OP.
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Riduna at 11:46 AM on 14 May 2012Analysis of Speed of Greenland Glaciers Gives New Insight for Rising Sea Level
These findings, that loss of ice from the GIS are likely to contribute no more than 4 inches to sea level by 2100 stand in stark contrast to the Hansen and Sato (2011) prognosis that total ice sheet loss can be expected to double per decade resulting in SLR of 5 metres by 2100. Given the speed with which atmospheric and sea temperature is rising in the Arctic, on-going loss of albedo, and the rate of loss of land-based ice over the period 2000-2009, the conclusions reached in this article should, perhaps, be regarded with …. skepticism. -
skywatcher at 11:26 AM on 14 May 2012IPCC graph showing accelerating trends is misleading
Lest there be any great confusion about the selection of start and end years, as Helena implies, here's a couple of simple graphs that demonstrate the fallacy of her claims:
The first image shows the gradient of all trends longer than 25 years that have an end date in 2005. Years the IPCC used for their example are marked with a red star. The pattern of generally increasing trend rate is obvious, and the red stars are obviously not cherry picks.
The second image shows a similar thing, but for >25 year trends beginning in 1850, with the 25, 50, 100 and 150 year trends marked with an asterisk. First data point is 1850-1874 trend, last data point is 1850-2005 trend. This is what Helena suggested would be awkward. Y-axes are to the same scale. What is interesting here, is that the trends are once again generally increasing from about 1918 onwards. There are large variations in the 19th Century when coverage was poorer and there was no clear trend in global temperatures. Once you reach the 20th Century, when the rising trend in the actual data kicks in (and the data coverage is more-or-less global), you get the same pattern of increasing warming rate, thus accelerating actual warming. It is only a less pronounced increase because the time periods are longer in this 'wrong-way-round' graph.
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muoncounter at 09:15 AM on 14 May 2012IPCC graph showing accelerating trends is misleading
Further to this supposed counter example: We were discussing increasing functions with increasing slope. Your cosine does not apply. -
Riccardo at 06:43 AM on 14 May 2012IPCC graph showing accelerating trends is misleading
Helena while you keep ignoring the meaning of your original claim you also ignoreed my full answer, despite I underlined the relevant part. Somehow I expected your selective reading. Quite telling. -
Daniel Bailey at 05:52 AM on 14 May 2012IPCC graph showing accelerating trends is misleading
Henri has led us on a merry chase, no? -
muoncounter at 05:47 AM on 14 May 2012IPCC graph showing accelerating trends is misleading
Helena#67: "i don't see how you can infer a deceleration." That's just silly. I live in a world where 3/4"/hour is a higher rainfall rate than 1/4" per hour. A world where calculus works and thus I can infer deceleration when the trend is decreasing. #69: "Examples: x^2, x^3, etc (for x>0)." Wrong " Show how x^2 does not have increasing slopes over progressively shorter intervals (as used here) when x>0. #70: "imagine a temperature graph that looks like a cos function with a 25year period. The secular trend is almsot flat." Your 'counter-example' requires at least one full cycle to have a flat secular trend. Do any of the graphs of real-world temperature variation shown here, especially fig 1, look anything vaguely like a full cycle cosine function with a 25 year period? Let's say the secular trend is the one established over the longest time interval (150 years) in Figure 1. Do you agree that the most recent 25 year period in Figure 1 shows a trend (0.18) that is greater than this secular trend (.05)? What do you propose this change in trend signifies? -
Helena at 05:34 AM on 14 May 2012IPCC graph showing accelerating trends is misleading
67 : it was sunny for 2 hours and a half and not 1hour and a half (so it adds up to 4hours). -
Helena at 05:29 AM on 14 May 2012IPCC graph showing accelerating trends is misleading
Ricardo / Munoucounter, here is a simple example : Let's imagine a temperature graph that looks like a cos function with a 25year period. The secular trend is almsot flat. The short term trend (50 and 25) get higher and higher. You would have accelerating trends, you would infer accelerated warming, and you would be wrong because there would be no warming or cooling trend. -
Helena at 05:26 AM on 14 May 2012IPCC graph showing accelerating trends is misleading
Muoncounter "Functions that produce statistically meaningful trends that increase over time are far more likely to be increasing and concave up (which we agree is one form of 'accelerating'). Examples: x^2, x^3, etc (for x>0)." Wrong -
Helena at 05:22 AM on 14 May 2012IPCC graph showing accelerating trends is misleading
(The first part is for Ricardo) -
Helena at 05:21 AM on 14 May 2012IPCC graph showing accelerating trends is misleading
"It's not a proof of your original claim. " It proves that, chosen at random (i.e no cherry picking), it is more likely that the slope of long trends will be smaller that the slope of short trends. Do you agree with that ? "The asnwer is yes" Wrong. You cannot infer accelerated warming from greater slopes for shorter recent periods Muoncounter 66 : Your example for rain is not exactly correct. First, I don't understand how those two sentences "It rained really hard the other night, 2" an hour for a bit. Then the rainfall rate decreased. " fit with the rest. The exercise is correct if you "only know" the various trends, and nothing else. So let me start here : I do not know if it rains after or not. I do not know if it was raining before or not. Here is how i write your exercise "Over the course of 4 hours, there is 3" of rain. The rate over the entire period is thus 3/4" per hour. The rate in the last half hour is 1/4" per hour." You take these changing trends as an indicator that the rainfall rate is decreasing. I'm sorry but i don't see how you can infer a deceleration. Maybe you do that because you already assume that it stopped raining after that, or that it must rain at a constant rate, or because you've lived it, but here you're adding crucial extra information that are not contained in the trend itself ! What if i tell you that it rained (3-1/8)" during the first hour, then it was sunny during 1h and half and then it rained again 1/8 (rate of 1/4" for half an hour). Maybe it's a new cloud coming and it's gonna rain for the next 5 hours. Who knows ? You've been adding the information that it's zero after that, but when you do that you do more than comparing the trends to infer the deceleration. -
muoncounter at 04:56 AM on 14 May 2012IPCC graph showing accelerating trends is misleading
Helena#53: "we are on planet SKEPTSCIENCE. ... an indicator that we have an accelerated warming on this planet?" I prefer to work on this planet (for the time being). It rained really hard the other night, 2" an hour for a bit. Then the rainfall rate decreased. Over the course of 4 hours, there was 3" of rain. The rate over the entire period was thus 3/4" per hour. The rate in the last half hour was 1/4" per hour. I took these changing trends as an indicator that the rainfall rate was decreasing. In your hypothetical, I assume you refer to trends calculated from time intervals starting progressively closer to the present, as illustrated in the OP's figure 1 and in DB's response here. Let's also stipulate that each of these calculated trends is statistically significant - neither an artifact of any carefully selected time periods nor some artfully constructed noise. Functions that produce statistically meaningful trends that increase over time are far more likely to be increasing and concave up (which we agree is one form of 'accelerating'). Examples: x^2, x^3, etc (for x>0). On the other hand, functions that are increasing and concave down (decelerating) show the opposite behavior: 'older' trends are greater than more recent trends. Examples can be found among trig functions (5-5 Cos[x]), x between 0 and Pi. Add random noise if you like. Let's not devolve this discussion into wrangling over what the word 'indicate' means. -
Riccardo at 04:48 AM on 14 May 2012IPCC graph showing accelerating trends is misleading
Helena you consistently avoid to address the weaknesses other commenters and I point out. In your last reply to me you end with the trivial fact that long term trends are more constrained than shorter ones. I agree, but it does not mean that they are larger (or smaller for that matter) in any way. It's not a proof of your original claim. On the other hand you still do not see the difference between starting at an old date and going forward from strating today and going backward. I don't want to pile up with other commenters and anyway untill you properly address this point, which is the source of disagreement with us all, the discussion can not move forward. P.S. Let me answer to your question to Tom: can one infer accelerated warming from greater slopes for shorter recent periods (150-10-50-25yr periods like in the IPCC)? The asnwer is yes, the trend has lately accelerated with respect to the secular trend. This is what that graph tells us. Now a hint, applying the same logic to your analysis, what does it tell us? -
Helena at 04:19 AM on 14 May 2012IPCC graph showing accelerating trends is misleading
Well then let's have Tom answer on the important question (for the n'th time) : can one infer accelerated warming from greater slopes for shorter recent periods (150-10-50-25yr periods like in the IPCC). Tom, yes or no ? -
Bob Lacatena at 04:15 AM on 14 May 2012IPCC graph showing accelerating trends is misleading
62, Helena, Yes, you did. I don't see how it can be read any other way. -
Helena at 04:10 AM on 14 May 2012IPCC graph showing accelerating trends is misleading
Tom61, i don't misrepresent any of your claim, but i guess it's easy on a forum to make people think that. Anyway, can you tell me what you think of KR claim that "If those trend changes are statistically significant, and increasing (and they are both), you can infer acceleration." Thanks (that is the same as my yes/no question #53 -
Tom Curtis at 04:07 AM on 14 May 2012IPCC graph showing accelerating trends is misleading
Helena @57 misrepresents my claim, and I believe deliberately so. My stating what her argument is is not the same as my agreeing with her argument, and no reasonable person could expect it to be so. -
Helena at 04:07 AM on 14 May 2012IPCC graph showing accelerating trends is misleading
KR : "If those trend changes are statistically significant, and increasing (and they are both), you can infer acceleration." Sorry but this is wrong. -
KR at 04:02 AM on 14 May 2012IPCC graph showing accelerating trends is misleading
Helena - "...one cannot infer accelerated warming from greater slopes for shorter recent periods." As I stated earlier, "Shorter terms will certainly have higher variances, but absent an underlying change in rate, randomly selected time periods and lengths would statistically average out to the same trend." If those trend changes are statistically significant, and increasing (and they are both), you can infer acceleration. That's the entire point of looking at statistical significance, to judge whether or not apparent indicators are indeed evidence. -
Helena at 03:54 AM on 14 May 2012IPCC graph showing accelerating trends is misleading
... from greater slopes for shorter recent periods -
Helena at 03:53 AM on 14 May 2012IPCC graph showing accelerating trends is misleading
Tom56, i've already agreed on the 25yr trend quite some time ago and i had noted that ironically it would be wrong if stated in AR5 as 1987-2011 is quite smaller. "Your argument against the inference that the warming is accelerating is a claim that the inference is not justified statistically. " Great to see that, based on common sense statistics, you agree that point 1 is incorrect i.e. the word "indicate" is wrong as one cannot infer accelerated warming. -
Tom Curtis at 03:41 AM on 14 May 2012IPCC graph showing accelerating trends is misleading
Helena @51, if you want to claim that claim (2) from the OP is false, you need to show a 25 year trend earlier than the record that has a statistically significant greater trend. As it happens, you cannot even find one with a greater trend, let alone a statistically significant trend. If instead you want to simply claim that it was unjustified, ie, if you change your claim, then statistical significance becomes important. As it stands, given the available data the IPCC is justified in asserting that "it is more likely than not" that the 25 year trend terminating in 2005 was larger than any other 25 year trend on the instrumental record, both because. They are justified in doing so because the measured trend is in fact larger than any prior trend in the HadCRUT3v data, and because on the GISTEMP and NCDC data, which are more extensive, it is also larger than any prior 25 year trend, and by a larger margin. Your argument against the inference that the warming is accelerating is a claim that the inference is not justified statistically. Therefore you cannot ignore statistical significance. The problem here is not that I am asserting a double standard, but that you will not accept any standard which falsifies your claims, however, well justified those standards are. -
Helena at 03:38 AM on 14 May 2012IPCC graph showing accelerating trends is misleading
"my linear trends and the IPCC linear trends" = "my evolution of linear trends and the IPCC evolution linear trends" -
Helena at 03:36 AM on 14 May 2012IPCC graph showing accelerating trends is misleading
Tom52 : Qualitatively, my linear trends and the IPCC linear trends contain the same qualitative information about the underlying temperature function : NONE. That's the only point i'm making. You can answer my yes/no question on message 53 if you wish. -
Helena at 03:34 AM on 14 May 2012IPCC graph showing accelerating trends is misleading
Muoncounter, i have a yes/no question (with explanations if you want of course) for you : Forget about Earth, we are on planet SKEPTSCIENCE. A scientist comes to you and tells you that, when he calculates the past 150, 100, 50, and 25yr temperature trends for the planet, he finds that for the shorter recent periods, the slope is greater. Do you understand what he just told you as an indicator that we have an accelerated warming on this planet ? Thanks for your answer -
Tom Curtis at 03:26 AM on 14 May 2012IPCC graph showing accelerating trends is misleading
To reinforce my points @45 and 49, I note that the difference between the 25 year and 100 year trend in the IPCC example is 0.0103 C per annum. That is nearly double the 95% confidence interval of the 25 year trend, ie, 0.0052 C per annum, and greater than the confidence interval for the trend calculated using the trend calculator of 0.0078 C per annum. In contrast, in Helena's cherry picked example, the difference is 0.0063 C per annum, just barely larger than 95% confidence interval for the 25 years from 1981 to 2005, and less than the interval calculated using the trend calculator. In other words, Helena cannot show a statistically well based inference that the 25 year trend is different from the 100 year trend in her example. Given that, insisting that it should be treated as qualitatively the same as the IPCC example is just bizarre. -
Helena at 03:25 AM on 14 May 2012IPCC graph showing accelerating trends is misleading
Tom49: This is getting tiring, in message 12 you were saying that error bars didn't matter, now they do. A "consistent picture" is one where there is no "exception, especially when the "consistent picture" is based on N=5 trends. And you can get a very large "relative magnitude in the changes in the slopes", with increasing slopes, with an underlying cooling temperature. Back to the quantitative/qualitative discussion, it's tiring. Muoncounter50 : Let me start by the end : "Do you agree that the rate of warming is accelerating? " On the graph ? Yes. "If so, do you agree that an appropriate description of a graph representing that behavior is 'increasing and concave up'? " Yes, already answered that. Now to the relevant point : "You've agreed that the qunderlying function is increasing and accelerating: that's what is relevant." I've agreed to it because you asked me the question directly. And that's the good way to do it, no need to do that linear trend torturing just find the coefficient in front of the x^2 (if it positive, then you have an acceleration). But the IPCC does not start with that. They start with the linear trends. And those increasing linear trends supposedly indicate an accelerated warming. I say that's wrong, and i've proven it. -
muoncounter at 03:09 AM on 14 May 2012IPCC graph showing accelerating trends is misleading
Helena#42: "you can have "trend-lines starting closer to the present have a steeper slope than those starting farther back" and an underlying function that is not "an increasing and accelerating function"" Good: we are now talking about the underlying function (temperature anomaly vs. time), which gets us away from the artifice of choosing time intervals for 'trend' calculation. You've agreed that the underlying function is increasing and accelerating: that's what is relevant. Describing that function by selecting 10 year, 20 year or 100 year intervals does not change the function. #47: "We are not discussing whether temperature is accelerating or not." This isn't a forum for semantics and tautology. The statement in the OP is "the incorrect conclusion is drawn that ... the rate of warming is accelerating". Questions: Do you agree that the rate of warming is accelerating? If so, do you agree that an appropriate description of a graph representing that behavior is 'increasing and concave up'? -
Tom Curtis at 03:06 AM on 14 May 2012IPCC graph showing accelerating trends is misleading
Helena @47, No! The differences in trend in your example are very small relative to the error margin of the trends, and are significantly inconsistent in showing deceleration. Therefore your conclusion does not follow. In contrast, in the IPCC example, the differences in trend are large relative to the error margin of the trends, and with one exception, they all show the consistent pattern. The size of the effect relative to the error margin is a critical factor in determining whether or not a statistical inference is warranted. You choose to ignore that factor simply because it suites your argument. However, I will not. The difference in visual impact between your cherry picked example and the IPCC example comes primarily from the relative magnitude in the changes in the slopes, which is the critical factor on whether the inference is valid or not. Your argument, in the end comes down to just three points: 1) Ignore the magnitude of effects, thereby assuming that the magnitude of the effect has no consequences for statistical inferences; 2) Assume that any noise in the data automatically invalidates any statistical inferences (as when you argue the 75 year trend to 2005 invalidates the overall pattern, while scrupulously ignoring the fact that the 125 year trend reinforces the pattern); and 3) Assume that the possibility that a statistical inference can reach a false conclusion proves that the statistical inference is invalid ,ie, that the fact that inductive arguments are not deductive arguments proves that they are not valid inductive arguments (as when you argue that the 1910 example invalidates the IPCC inference, and even then you must assume that the size of effects is irrelevant to begin with). -
Helena at 02:57 AM on 14 May 2012IPCC graph showing accelerating trends is misleading
Tom45 : i hadn't seen you had depicted the 75yrs trend. Please read my yes/no question as if it wasn't there (like the IPCC, otherwise there is no discussion as their statement "for shorter recent periods, the slope is greater" is an untrue statement and therefore this website article is wrong too). -
Helena at 02:49 AM on 14 May 2012IPCC graph showing accelerating trends is misleading
Tom45 : The first graph shows that, over the 1910-2010 the trend was steep at the beginning of the century, and as we were advancing in the century, it has been decreasing. Do we agree that all of these statements in this sentence are true ? (Please answer yes/no + comments if you wish) But maybe you do realize that it's not such a good idea to compare a short trend to a long trend ? :) KR46 : No, it is not on the point, and no it's not incorrect. You can have a global cooling and still have increasing slopes as depicted by IPCC. But i think you don't understand what we are discussing. We are not discussing whether temperature is accelerating or not. We are discussing whether the IPCC trend torturing supports the accelerating temperature statement. -
KR at 02:36 AM on 14 May 2012IPCC graph showing accelerating trends is misleading
Helena - Regarding my first point, that the forcings are accelerating, and hence an accelerating temperature trend is only to be expected, is entirely to the point. "...the fact that the IPCC method finds smaller slopes for longer trends has nothing specific to an accelerated warming..." Shorter terms will certainly have higher variances, but absent an underlying change in rate, randomly selected time periods and lengths would statistically average out to the same trend. Your assertion is quite incorrect. -
Tom Curtis at 02:35 AM on 14 May 2012IPCC graph showing accelerating trends is misleading
Let us be quite clear, Helena's supposed counter example is not qualitatively equivalent to what the IPCC did: Helena's cherry picked example:
IPCC example:
Her insistence that the two are equivalent merely shows, IMO, that her reasoning is driven by the conclusions she wishes to draw rather than by the facts on the ground.
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Helena at 02:26 AM on 14 May 2012IPCC graph showing accelerating trends is misleading
Sphaerica43 : Sorry maybe it was obvious for you, but not for Tom, as he is the one who said that contrary to my apparent claim (and now also yours), it is not possible to pick arbitrary end points mimicking the IPCC graph, and to show a deceleration over the temperature record as a result. Glad to see you agree that it's possible. "while the IPCC method simply and logically says "from X years ago to now"." Again, the fact that the IPCC method finds smaller slopes for longer trends has nothing specific to an accelerated warming, therefore it cannot "indicate" an accelerated warming.Moderator Response: TC: Edited to comply with comments policy. The comments policy is not optional. It contains instructions for html coding of emphasis, so failure to use that resource is not a sufficient excuse for failure to comply with the comments policy. As this is the second time you have been warned on this issue, future all caps will result in the deletion of the offending post. -
Bob Lacatena at 02:19 AM on 14 May 2012IPCC graph showing accelerating trends is misleading
Helena, Your entire argument hinges on cherry-picking a well-known, very short period (25 years) with a very rapid temperature increase, the 1910 to 1934 period, and then supplementing that with a similar period ending in 1959. No one is arguing that you can't cherry pick ranges to give the appearance of a decelerating trend. What we can point out is that your method requires cherry picking, while the IPCC method simply and logically says "from X years ago to now".
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