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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

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IPCC graph shows accelerating global warming trend

What the science says...

All of the statements made in the IPCC report regarding the figure in question are correct and supported.

Climate Myth...

IPCC graph showing accelerating trends is misleading

"The IPCC’s Fourth Assessment Report, 2007, carries in three places a graph in which the Hadley Center’s global mean surface temperature anomaly dataset from 1850-2005 is displayed with four arbitrarily-chosen trend-lines overlaid upon it. At each place where the altered graph is displayed, the incorrect conclusion is drawn that because trend-lines starting closer to the present have a steeper slope than those starting farther back, the rate of warming is accelerating and that we are to blame." (Christopher Monckton)

Some 'skeptics', most vocally Christopher Monckton, have taken issue with this figure from the 2007 IPCC report:

IPCC-graphic

 

Figure 1: Depiction of various long-term global temperature trends in the 2007 IPCC report

The figure is used in FAQ 3.1 and the Technical Summary of Working Group 1Monckton asserts that this graph uses a "fraudulent statistical technique" and

"At each place where the altered graph is displayed, the incorrect conclusion is drawn that because trend-lines starting closer to the present have a steeper slope than those starting farther back, the rate of warming is accelerating and that we are to blame."

This is simply a misrepresentation of the IPCC report.  The IPCC makes the following claims using this figure:

1)  The pace of warming accelerated over the course of the 20th Century. Notice the past tense.  Here is the specific claim (from the caption for Figure 1 of FAQ 3.1, emphasis added):

"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."

2)  That the pace of warming over the last 25 years is greater than that in preceding years on the record.

3)  That the "... global average temperature has increased, especially since 1950."

All of these statements are true.  The IPCC does not state that the rate of warming continues to accelerate, and does not use this figure to claim that humans are to blame for the accelerated warming, although in the FAQ 3.1 figure caption, the IPCC does explain how we know humans are the cause of the acceleration:

"From about 1940 to 1970 the increasing industrialisation following World War II increased pollution in the Northern Hemisphere, contributing to cooling, and increases in carbon dioxide and other greenhouse gases dominate the observed warming after the mid-1970s."

Monckton's claims of a "fraudulent statistical technique" are without merit, and a misrepresentation of the IPCC report's actual content.

Last updated on 9 February 2012 by dana1981. View Archives

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Comments 1 to 25 out of 123:

  1. I dont like Monckton, but he's right on that one .... Here are two assertions : Linear trend fits to the first 20 (1860-1880), 40 (1860-1900), 100 (1850-1950) and for the full 150 years (1860-2010)are shown. Note that for periods ending closer to us, the slope is smaller, indicating decelerated warming. The pace of warming over the full 150years (1860-2011) has been slower than during the first 20, 40, and 100 years of the instrumental record. Are those two assertions wrong ? If they are not, will we get a chance to read them in the next IPCC report ? And in the SPM which also had a sentence comparing the linear warming trend over the last 50 years with the linear trend for the last 100 years and did not put it in perspective with the first 20 years (for example). Of course you cannot compare trends on different time periods.... ! On any given day, the trend from midnight to midday is about 1°C/hour (+/-0.5), which far exceed any global warming trend over any time period you want [1]. I can give show you global cooling too if you want. [1] 1°C/hour = 87 600°C/decade "That the pace of warming over the last 25 years is greater than that in preceding years on the record." How does the trend of the last 25yrs compare with the trend between 1915 and 1940 ? (same 25yrs basis)
  2. Helena @1, we would be more impressed if you did not so obviously have to cherry pick your data points to reach your conclusion. If we in fact take the first 20 years of the HadCRUT3v temperature index, ie, from 1850 to 1870, the linear trend is 0.00238824 C per year. The trend for the first 40 years (1850-1890) is 0.00309971 C per year, showing an increase, not a decrease in the trend. The trend for the first 100 years is 0.00231824 C per year, barely lower than the trend for the first twenty years, and I doubt the difference is statistically significant. Finally, the trend for the first 150 years is 0.00369995 C per year, significantly greater than any of the other three trends examined. As the longest of the start year trends is also the largest trend of those examined, the series certainly does not show deceleration. Even if I plot from the cherry picked start point of 1860, except for 1860-1880, the later the end point of the trends examined, the larger the trend. Again this clearly does not show deceleration. What is more, even the 1860-1880 trend is inconsequential. The data for that period comes almost exclusively from Europe, the North Atlantic and the Eastern US. As such it represents a regional rather than a global temperature, and regional temperatures have larger trends than global temperatures. (Note I used the period 1860-1960 for the 100 year trend to keep the cherry picking to a minimum.) So, contrary to your apparent claim, 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. More importantly, your argument entirely misses the more important point that Monckton completely misrepresents the nature of the IPCC's argument premised on the graph in question. Note: trends simply cut and paste from Wood for Trees, and the number of "significant figures" in no way represents a claim of statistical significance. Graph of the trends can be found here.
  3. I hadn't done the precise graph. Before I answer on point 1, the tool you used allowed me show that point number 2 ""That the pace of warming over the last 25 years is greater than that in preceding years on the record."" is wrong : link
    Response: TC: Edited link to preserve page format.
  4. This video at 6mins in shows Monckton explain that the climate system is like a sign wave and that the IPCC are drawing the trend lines on the up ward slop of this sign wave of climate change. He seems to be changing his angle of attack and trying to trick his audience into thinking that the reason he is right and the IPCC are wrong, is that we are going to see a cooling period.
  5. "More importantly, your argument entirely misses the more important point that Monckton completely misrepresents the nature of the IPCC's argument premised on the graph in question." And you miss the most important point that you cannot compare trends over different time periods. It's all i aimed to show (with wrong numbers possibly, but i gave you a simple counterexample with the midnight thing). Take for endpoint today at midnight, and you'll see that you have a cooling trend over the past 12h but a warming trend of the past 30years.
  6. Ok here it works with a common starting point in 1910 link 1 By the way, isn't it weird that IPCC represents 25, 50, .., 100, and 150 ? They're missing 75 (and 125). Well, that's because with 75 (1930-2005), it doesn't work :). link 2
    Response: TC: Edited links to preserve page format.
  7. To sum it up (sorry for the length of the links, i hope it's not considered as spamming) : - I did find a counterexemple, that is say if you start in 1910 you can find that the first 25yrs trend is higher than the first 50yrs trends which is also higher than the full 100yrs 1910-2010 trend. - The IPCC picture does not work if you take the 75yr trend (1930-2005) that they don't depict (they skip from the 50yrs to the 100yrs) : the 75yrs trend is smaller than the 100years trend. How is taking the 75yrs chery picking, as you are stating yourself that it is based on 25years intervals ? - But maybe you think 75yrs is cherry picked and the 25yrs of your 2nd point applies to any 25yr-period ? Then I also showed you that the past 25yrs (1980-2005) have been warming at the same rate as the 1915-1940 25yrs period.
  8. Helena @3, the trend for 1982-2006 (the last 25 years of the temperature record used by the IPCC) is 0.0202857 C per year. That from 1915-1940 is 0.014621 C per year, which is substantially less. That from 1980-2005 is 0.0180092 C per year. Of these three trends, that from 1915-1940 is lowest. That fact could easily have been checked by examining the raw data of your own plot. So, what you have shown is not that point number 2 is wrong, but merely that you are prepared to assert that it is without properly checking the data.
  9. Tom @ 8 Uhh i didn't know you could get the raw data, nice tool. Well, then i switched to to the 1917-1942 25yr-period. slope = 0.0178289 per year For the 1980 to 2005 period : slope = 0.0180092 per year And don't tell me error bars are smaller than 0.0002 °C/decade ! PS : How can the last point on the IPCC graph be 2006 as 2005 is not even depicted ?
  10. I meant 0.02°C/decade (and 0.0002°C per year)
  11. Ouch still a zero missing, sorry
  12. Helena @9, you are obviously grasping at straws. It is not necessary that the error bars be miniscule for the purported IPCC claim to be correct. It is only necessary that the measured trend be greater. And the last datum on the IPCC graph is 2006. However, having just checked FAQ 3.1, I notice the IPCC calculated trends terminate in 2005. So, comparing the 1981-2005 trend (0.0188397 C per year), to that for 1917-1941 (0.0171067 C per year) and 1918-1942 (0.0171202 C per year). The difference is approximately 0.002 C per year. (Please note that 1980-2005 is a 26 year period.) Finally, with regard to your post 5, 12 hours is not a period long enough to represent a climatology. Therefore your analogy is specious.
  13. True, that was a 26year period. So there is a 0.0017°C/year difference in the trend. Well i guess you're right if we stick to semantics, not to science rigor as the statement seems very much sensitive to error bars and to endpoints (ironically the statement would be wrong in AR5 as 1987-2011 is 0.0155809 per year). What about the 75yr trend i was talking about ? And the 1910 thing ? "Finally, with regard to your post 5, 12 hours is not a period long enough to represent a climatology." You know as much as i do that 30yrs it nothing more than a convention. Of course daily temperatures don't define a climatology, but 25year periods don't define one either (except by convention) and you cannot prove that the impossibility to go from hours to 25 years is qualitatively different than the one going from 25years to 150years. That's the whole point i'm making : having similar time periods is the minimum required (but not sufficient) when you compare trends !
  14. Helena, you seem to miss the point of this post. All the IPCC is doing is saying that in recent years/decades, global warming has accelerated. That is true. It doesn't mean that there can't be prior years with similar warming trends to that in recent years. We have discussed the 1910-1940 warming here and here. There's certainly nothing "misleading" about the IPCC figure.
  15. Helena#13: "you cannot prove that the impossibility to go from hours to 25 years is qualitatively different than the one going from 25years to 150years. " Really? 150/25 = 6:1 25 years = 219150 hours. Your examples of comparing temperatures 12 hours apart to temperatures 25 years apart yields 219150/12 = 18262.5:1 Comparing temperatures (and temperature trends) over short time frames to long time frames is qualitatively different - and extremely misleading.
  16. dana @14 : don't you agree that my assertion stating that, over the 1910-2010 period, the decreasing slope for the linear trends of the first 25, 50 and the full 100years *indicates* cooling is untrue ? Well, in the same way, the assertion by the IPCC that the increasing slope for the linear trends over the last 25, 50, 100 and 150 years *indicates* accelerated warming is also untrue. Moreover, as shown above, the linear trend for the last 75 years goes in the wrong direction, so at the very least it should be considered as cherry picking the trend baseline to pick only the trends that agree with what you want to assert. This has nothing to do with climate science or denying that the world is warming (it is), it's just scientific rigor. Muoncounter @15 : Sorry but i am asking for qualitative reasons, not quantitative ones. "Short" and "long" are quantitative assessments : of course there are order of magnitudes of difference between the two timescales, but that's the whole point of my example. You cannot just say that because there are orders of magnitude of difference, the system has qualitatively a different behavior. Here is an analogy : From 101°C and orders of magnitude up, water is qualitatively the same : vapor. But from 99°C to 101°C, it is qualitatively different (phase transition) even though the temperature changes very little. The underlying question is : in a complex system, how do you know the timescale (if any) over which you can say that "internal variability" (to be defined) is filtered out. But that's out of topic here.
  17. At the end of my first paragraph, replace "cooling" by "decelerating warming"
  18. Helena, Nothing you are saying makes any sense... or bears out, when I look at the actual data. Up is up, no matter how you try to stand it. Please produce a graph (use woodfortrees.org if you like) that clearly proves your point. And try to do it without cherry picking end points and ranges.
  19. Helena @13: 1) Nobody who is arguing a case that depends critically on choosing just one of two available temperature indices should be talking about "arguing mere semantics". The Gistemp Land Ocean Temperature Index (LOTI) shows a trend of 0.0169576 C per year from 1981-2005, a trend of 0.0139565 C per year from 1917-1941, and a trend of 0.0134231 C per year from 1918-1942. For what it is worth, HadCRUT4 also shows a reduced trend over the 1910-1940 period, and an increased trend over the 1970-2010 interval, although obviously I do not have precise trends. 2) The 75 year trend is 0.00650795 C per year, compared to 0.00722857 C per year for the 100 year trend. The difference, less than 0.001 C per year is less than the difference in trend you dismiss as merely semantic when it suites you. It is certainly not enough to alter the visual impact of the graph, or to alter the conclusions of the IPCC. 3) The 50 year trend from 1910 is 0.00761979 C per year; the 100 year trend is 0.00749844 C per year. The difference is just over 0.0001 C per year. What was that you said about merely semantic differences again? More importantly, the pattern is not preserved in Gistemp, in which the 50 year trend is greater than the 100 year trend. Clearly, therefore, you do not have an example showing deceleration in which successive trends from the start point are less than each other by a large (although not quite statistically significant in one case) margin. The reason is that you are, fairly obviously, cherry picking artifacts of noise in an accelerating temperature trend.
  20. In a previous thread about the graphic above, I basically agreed with KR"s conclusion here. I think the graphic shows a particular type of acceleration over the long term (century timescales). As I noted in that thread they left out the 75 and the 125 year trends which narrows their definition of acceleration and would add noise to the visual. The idea of noise from natural variation is an important part of the analysis of acceleration which this graphic does not attempt to provide.
  21. Sphaerica @18 What are you talking about ? I did provide graphs (cf previous posts) Tom @19 1/ As i said, that merely shows that uncertainties on the trends are quite large. 2/ So you do agree with me that the 75yr trend goes against the picture presented of increasing trends, right ? You said yourself : "It is not necessary that the error bars be miniscule for the purported IPCC claim to be correct. It is only necessary that the measured trend be greater." Therefore, according to your own standards, i did show that the measured trend for the 75yr trend was not greater, and that had the IPCC been consistent and depicted all 25yr periods without leaving out the 75yr trend (cherrypicking ?), the IPCC assertion would not have been possible. According to my standards, all i am doing here is pointless because, as i said, comparing trends of different lengths is meaningless. You can find any result you are looking for. 3/ You challenged me by saying "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. " I found the counterexample with an arbitrary starting point (1910) and decreasing trends mimicking the IPCC graph (25, 50, 100yr trends). Again, according to your own standard and following IPCC procedure where, as you say yourself "it is only necessary that the measured trend be greater", i've succeeded. Now that you have it you seem unhappy that it exists. "The reason is that you are, fairly obviously, cherry picking artifacts of noise in an accelerating temperature trend. " Of course I am cherry picking the starting point ! You challenged me by saying that i wouldn't be able to find an arbitrary point and mimick the IPCC procedure with decelerated trends. So i looked for it and found it. Now let's get back to what it all means : what the ipcc says is that their increasing trends (-snip-) accelerated warming. Clearly that statement is wrong. Increasing trends don't (-snip-) an accelerated warming, and decreasing trends (my example) don't (-snip-) a decelerated warming. They don't (-snip-) anything. I don't understand that you guys can defend such a graph. Isn't it easier to just admit that it was not the best chosen graph to depict that warming is accelerating ?
    Response:

    [DB] Please acquaint yourself with this site's Comments Policy (link next to every comment input box). It is noted that, more than anything, you are simply being argumentative for its own sake.

    Multiple usages of all-caps snipped.

  22. Perhaps it was your use of all-caps (tat is forbidden)
  23. Eric : We'll see, if it disappears again i'll get rid of the all caps for the word "indicate". My all caps is Tom's bold (dunnow how to get my text in bold here). Anyway, on your message 20, here we are merely discussing communication skills and scientific rigor, not the reality of warming. Anyone who looks at the temperature trend see that it is warming. I've read KR response on the other thread about linear increase or acceleration in temperature trend and exponential CO2. 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 !). What matters (in a simplified version) is the relaxation time. That tells you whether the response will be linear or quadratic. But it's out of topic here. Anyway, i'll just wait a few mins see if my post stays, then gotta go. Thanks for the discussion. Cheers
  24. In my message 21 "(-snip-)" = "indicate" Sorry for the all caps.
  25. Obviously your post is staying since it got fixed. I disagree with your assessment of the log of the exponential and it is addressed here

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