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Comments 26 to 50 out of 82:

26. muoncounter at 13:22 PM on 13 May, 2012
    Helena#21: "Increasing trends don't (-snip-) an accelerated warming, and decreasing trends ... a decelerated warming. They don't (-snip-) anything." That has to be a new highpoint in doublespeak. Changing trends don't indicate anything? That requires that 'there's been no warming since xxxx' doesn't indicate anything; nor is there anything indicated by 'there is no scientific basis for saying that warming hasn't stopped'. I suppose 'concave up' doesn't mean anything either. Do we really need trends to see what's been happening?
27. Bob Lacatena at 14:48 PM on 13 May, 2012
    Helena, I did look at your links and graphs, and what I'm saying is that they don't show what you claim they show. Let's try it this way... list the ranges of years, and the slope. Just do that. Let's see you cherry pick the years to make this work.
28. Helena at 19:08 PM on 13 May, 2012
    Sphaerica27 : It's really a pain to understand what you're looking for. Everything is done on woodfortrees with HadCRUT3 variance adjusted global mean. First my homework : what i showed, responding to Tom's challenge : "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. You have no counter example to the IPCC's procedure. " is that there exist a common start point for which it works : 1910-1934 > 1910-1959 > 1910-2009 gives a decreasing trend as you get closer to present : 25yr trend #Selected data from 1910 #Selected data up to 1934 #Least squares trend line; slope = 0.013717 per year 50yr trend #Selected data from 1910 #Selected data up to 1959 #Least squares trend line; slope = 0.00773312 per year 100yr trend #Selected data from 1910 #Selected data up to 2009 #Least squares trend line; slope = 0.00742333 per year The closer you get to present, the smaller the trend. Uhhhhhhhhhh Back to IPCC graph. The second thing i showed it that the not depicted 75yr period 1931-2005 is > the 100yr period 1906-2005, which goes against the increasing trend assertion by the IPCC. 100yr #Selected data from 1906 #Selected data up to 2005 #Least squares trend line; slope = 0.00724928 per year 75yr #Selected data from 1931 #Selected data up to 2005 #Least squares trend line; slope = 0.00659195 per year 50yr #Selected data from 1956 #Selected data up to 2005 #Least squares trend line; slope = 0.0124017 per year muoncounter26 : concave up would be correct. Nobody is saying it didn't warm here. Had it been the statement written in the IPCC, i wouldn't be here discussing it with you. The problem is the IPCC saying that linear trend fits to the last 25, 50, 100 and 150 years indicate warming. You can easily imagine records where linear trend fits to the last 25, 50, 100 and 150 years (and even 75 :) ) increase but where the is no warming. I really don't understand how you guys can defend the idea that the IPCC trend graph & statement support or indicate anything. "Do we really need trends to see what's been happening?" I agree with that. But you should tell that to IPCC. I'm the one criticizing their (mis)use of trends to support a statement.
29. Eric (skeptic) at 22:46 PM on 13 May, 2012
    "concave up would be correct. Nobody is saying it didn't warm here." Helena, your phrasing is regrettably imprecise. Muoncounter pointed out that the warming is accelerating by a concave graph. "You can easily imagine records where linear trend fits to the last 25, 50, 100 and 150 years (and even 75 :) ) increase but where the is no warming." Again the issue is acceleration of warming, not simply "warming". The IPCC caption is

    "...Linear trend fits to the last 25 (yellow), 50 (orange), 100 (purple) and 150 years (red) are shown, and correspond to 1981 to 2005, 1956 to 2005, 1906 to 2005, and 1856 to 2005, respectively. Note that for shorter recent periods, the slope is greater, indicating accelerated warming".

    The IPCC graphic is overly simplistic (IMO) since it does not discuss the extent of natural acceleration and deceleration that could lead to a superimposed natural and manmade acceleration. That would require a paper. But the IPCC claim is that there is acceleration of warming (unattributed) and that the acceleration is current (as of 2005).
30. Helena at 23:32 PM on 13 May, 2012
    Eric most of what you say is out of topic we're not discussing natural or man-made acceleration here. We're just discussing the IPCC graph and their use of trends as an indicator of accelerated warming or to support their specific statement.
    Response:

    [DB] Actually, most of what Eric has stated is on-topic and germane to this discussion. You are tortuously arguing against a very simple point:

    "Note that for shorter recent periods, the slope is greater, indicating accelerated warming."

    Using Woodfortrees, this is easily seen, thusly:

    

    [Source]

    Or just the trends themselves:

    

    [Source]

    Where is the disagreement from the statement to the graphics? It really is that simple.

31. Helena at 00:54 AM on 14 May, 2012
    Well, first the trends you calculated are NOT the ones shown on the IPCC. Second, you can easily imagine a temperature record with, as shown by IPCC, a greater slope for shorter periods indicating accelerated warming but where the temperature is in fact cooling.
32. Helena at 00:56 AM on 14 May, 2012
    (therefore your trends don't indicate anything for the behavior of temperature, as i said)
33. Riccardo at 01:01 AM on 14 May, 2012
    Helena I didn't follow the discussion but at a cursory reading of your claim I find it like a world upside down. You start at an early time and go forward while the IPCC goes the other way around. Are you surprised that you get different or even opposite results? The problem is the meaning and that's what (it seems to me) your're missing.
34. Helena at 01:14 AM on 14 May, 2012
    Ricardo, what i am showing is that, on a very general basis, longer trends tend to have smaller slopes. And therefore what the IPCC shows as an indicator of accelerated warming is merely a statistical artifact. They start with a long trends small slope and end up with a small trend large slope (accelerated warming). I start with a small trend large slope and end with a large trend small slope (decelerated warming).
35. Helena at 01:17 AM on 14 May, 2012
    Moreover, the evolution of the slope does not indicate anything about what the record is actually doing : the record can be going down while the slope of the various trends can be increasing simply because the trends get calculated on smaller time periods.
36. Helena at 01:19 AM on 14 May, 2012
    small trend = trend over a small time period long trend = trend over a long time period
37. Riccardo at 01:23 AM on 14 May, 2012
    No Helena, you di not show that "on a very general basis, longer trends tend to have smaller slopes." You can easily find short term trends with smaller slopes if you change your start point. Again, you are misinterpreting the meaning of what you calculated.
38. Helena at 01:52 AM on 14 May, 2012
    Ricardo "you did not show that "on a very general basis, longer trends tend to have smaller slopes." " I did not *show* that because the fact that trends over long time periods generally imply smaller slopes is a simple statistics, especially for a physical phenomenon like temperature. Of course you can find punctual counterexamples, but they are punctual. Just think about it : let's say, i'm sure you'll agree, over the past millenium, global temperature was constrained between 0 and 30°C (so we make it very very general). That means that the largest linear trend you can find if you look for the trend over the last 1000 years is 0.3°C/decade. Now let's look on year to year basis, and let's assume that the maximum year to year variation for global temperature is 0.3°C/yr. That's 3°C/decade, already ten times more than the millenium one (which was calculated supposing a 30°C variation !!!). Anyway, i guess you get it : long time trends are much more constrained that short time trends, and therefore you get on average more big trends on shorter times than on longer times. Are you convinced ?
39. KR at 01:53 AM on 14 May, 2012
    Helena - "... read KR response ... What he says is not entirely correct, the exponential of the CO2 is taken care of by the log of forcings, it doesnt really play there (the exponential, not the CO2 !)." Actually, Helena, Tamino has demonstrated that CO2 forcing is increasing at a rate greater than exponential, meaning that CO2 forcing is increasing at a rate greater than linear. Meaning that the CO2 forcing component is accelerating. However, the core of your posts here have been nit-picking, and incorrect, complaints that the IPCC graphic shown in the opening post is somehow proven wrong by cherry-picked short term trends, or by wordplay with longer terms. Your arguments have the appearance of someone torturing the data to support a favored point, rather than considering the data for it's worth - I sincerely hope that's not the case.
40. Helena at 02:04 AM on 14 May, 2012
    KR : on your first point, it's out of topic here and i don't wanna have troubles with moderators. On the second point, don't you agree with me with the fact that, on average, slopes for longer trends are smaller that slopes for shorter trends, no matter whether you are in a warming or a cooling world, but because it's a simple statistical result ? The only data i have been torturing is when i answered Tom's challenge (proving you can have decreasing 25-50-100 year trends). My torturing of the data was the same that the one the IPCC used for their graph. Therefore i guess we'll agree that what i did for Tom is at the same level as what the IPCC did : poor scientific rigor !
41. muoncounter at 02:05 AM on 14 May, 2012
    Helena #28: "concave up would be correct." This is in reference to a graph presented without any selective trend calculation. I note that you did not challenge the accuracy or applicability of the BEST temperature anomaly vs time graph, so we must take that to mean you accept it's use in this context. So let's go to yes/no questions. You have already agreed that the graph in question is concave up: -Do you agree that concave up is defined by a positive second derivative? -If yes, do you agree that when both first derivative (slope) and 2nd derivative (rate of change of slope) are both positive, the graph describes a function that is accelerating? -If yes, do you agree that an increasing and accelerating function is correctly described by "trend-lines starting closer to the present have a steeper slope than those starting farther back"?
42. Helena at 02:16 AM on 14 May, 2012
    Yes Yes Yes (in general, you can find punctual counterexamples but that's not what we're talking about) but what's important is that the converse is not true i.e 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" And it is the converse that the IPCC is saying. They say : "Note that for shorter recent periods, the slope is greater" ==indicating=>> "accelerated warming" That is NOT true. And that's because steeper slopes for short period trends and smaller slopes for long period trends is a general statistical fact. "Note that for shorter recent periods, the slope is greater" can also indicate a cooling trend if you want. You cannot deduce anything from the fact that "for shorter recent periods, the slope is greater", it's just a general statistical fact.
43. Bob Lacatena at 02:19 AM on 14 May, 2012
    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".
44. Helena at 02:26 AM on 14 May, 2012
    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.
    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.
45. Tom Curtis at 02:35 AM on 14 May, 2012
    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.
46. KR at 02:36 AM on 14 May, 2012
    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.
47. Helena at 02:49 AM on 14 May, 2012
    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.
48. Helena at 02:57 AM on 14 May, 2012
    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).
49. Tom Curtis at 03:06 AM on 14 May, 2012
    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).
50. muoncounter at 03:09 AM on 14 May, 2012
    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'?

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