# 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:

*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 1. Monckton 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

acceleratedwarming."

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

skywatcherat 11:26 AM on 14 May, 2012alltrends 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 trendsbeginning 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.Tom Curtisat 12:01 PM on 14 May, 2012firstshe 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, (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 curvesper 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.Helenaat 16:11 PM on 14 May, 2012Helenaat 16:29 PM on 14 May, 2012Helenaat 16:31 PM on 14 May, 2012skywatcherat 18:09 PM on 14 May, 2012proveconcavityof 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.Bernard J.at 23:03 PM on 14 May, 2012muoncounterat 23:06 PM on 14 May, 2012Bob Lacatenaat 23:37 PM on 14 May, 2012andan unwillingness to reason -- only to lecture and malign -- suggests a trollish behavior that does not warrant feeding. You be the judge whether or not you think this is an accurate portrayal, but to me pursuing this conversation simply lets the troll grow larger and larger, until it breaks the very bridge it lives beneath.KRat 00:29 AM on 15 May, 2012veryinformative graphs; well worth including in the main post on this thread. As multiple posters have noted, a linear trend increasing over time is a clear indicator of acceleration(with, albeit, increasing variations for shorter time periods, as seen in skywatchers graphs). Helena's objections are mathematically unsupportable, and the constant repetition is simply (IMO) trolling. And, returning to the original subject, Monckton's objections to the IPCC graph are in one sense incorrect(acceleration is definitely shown), and in another a strawman argument(the IPCC did not base the conclusion of anthropogenic influence on this graph).SRJat 04:14 AM on 15 May, 2012Helenaat 04:34 AM on 15 May, 2012Response:[DB] "

It's sad the IPCC didn't use it and instead used one that can be rightfully criticized..."As many have already pointed out, you have not "

rightfully" proved this assertion.Tone-trolling snipped.

Dikran Marsupialat 04:51 AM on 15 May, 2012Dikran Marsupialat 05:00 AM on 15 May, 2012Howeverthe diagram is in a FAQ and is not intended to be part of the IPCC's scientific explanation or evidence of anything. It is obviously intended as an illustration designed to convey a basic point, which is that the rate of warming has been accellerating. There is a difference between the FAQs and the body of the report and Monckton surely knows that.Dikran Marsupialat 05:05 AM on 15 May, 2012"and continued but not significant warming from 2003 to 2011"This is such a short period that one would not expect the observed trend to be statistically significant,even if it continued at the previous rate or even slightly higher. Looking at it the other way, there is no statistically significant evidence that the warming from 2003 to 2011 was less than from (say) 1980 to 2003.lesat 05:23 AM on 15 May, 2012Helenaat 05:49 AM on 15 May, 2012Helenaat 06:02 AM on 15 May, 2012Dikran Marsupialat 06:11 AM on 15 May, 2012SRJat 06:12 AM on 15 May, 2012"The derivatives suggest two periods of significant increase in temperature (at the 99% level); during the inter-war years and post ~1975. The second period of significant increase in global annual mean temperature appears to persist until ~2005. After that time, we have insufficient data to distinguish the fitted increasing trend from a zero-trend post 2005. It would be wrong to interpret the lack of significant change during periods where the fitted trend is either increasing or decreasing as gospel truth that the globe did or did not warm/cool. All we can say is that given this sample of data, we are unable to detect any further periods of significant change in temperature other than the two periods indicated in blue. This is because our estimate of the trend is subject to uncertainty."# 91 les I think that Skywatchers contribution suffers from the same problem as the IPCC graph, namely comparing trends over periods of different length.Dikran Marsupialat 06:18 AM on 15 May, 2012SRJat 06:38 AM on 15 May, 2012SRJat 06:57 AM on 15 May, 2012KRat 07:12 AM on 15 May, 2012Period ____ Trend GISTEMP 1980-2005 _ 0.156 +/-0.051 C/decade 1955-2005 _ 0.123 +/-0.023 C/decade 1905-2005 _ 0.071 +/-0.011 C/decade 1855-2005 _ 0.059 +/-0.007 C/decadeEven with autocorrelation uncertainties the increase in trends is quite notable. All of this kerfluffle, however, is really over such a tiny point. Monckton was incorrect over the observed acceleration in warming, and in his strawman argument(as the IPCC conclusion of anthropogenic influences was not from this graph). This graph is merely an illustrative demonstration of "simple fits" to the temperature record(as per the IPCC illustration). Personally, I would consider this illustration (a) quite supportable as the simple demonstration it is, and (b) most definitely not the basis of conclusions about anthropogenic warming.SRJat 08:36 AM on 15 May, 2012