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Bob Lacatena at 07:42 AM on 15 May 2012Global warming stopped in
1998,1995,2002,2007,2010, ????
matzdj, That's a very pretty up-down escalator you've created. Read this post and then this one. Some places to start (I won't argue with you, if you're as open minded and concerned as you say, then you should be able to figure this out very easily for yourself). 1) Don't use Spencer's graphs. He uses lots of "tricks" like stretching the Y axis, and adding the rather silly "polynomial fit for entertainment purposes." Try woodfortrees.org, like this. 2) Don't use short trends. They're useless. Your entire 2002-2012 choice is a waste of everyone's time. 3) Forget "step changes." There's no such thing. That's for the wave-your-arms-magic-and-fantasy crowd. 4) Read about Foster and Rahmstorf 2011. 5) Look at this post giving another perspective on how to look at temperatures. 6) Look harder for the ocean heat content information. This site is a good place to do that. There's actually a post coming up on that within a few days. A few of them, actually. Bottom line: a) Don't use short trends. b) Don't assume that because the simple observations are noisy that you can't extract a clearer signal from the data. c) When you do look at the signal, and you also consider the complexity and other factors in the system, everything makes sense. d) Read and learn more before you adopt a position. -
KR at 07:12 AM on 15 May 2012IPCC graph showing accelerating trends is misleading
SRJ - If your concern is autocorrelation, I would suggest looking at the SkS Trend Calculator, which calculates uncertainties including autocorrelation effects, using the techniques of Foster and Rahmstorf 2011. Period ____ 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/decade Even 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. -
matzdj at 07:05 AM on 15 May 2012Global warming stopped in
1998,1995,2002,2007,2010, ????
This is my first post here. I hope the note and images come through properly. ***************************************** I’m afraid that your negation of the skeptics arguments was in itself too simplistic and inappropriate. I agree with your preliminaries and with what you showed through Figure 2. However, only the TV talking heads would try to use Figure 2 as you show it. Let me suggest another possible view of the same data from UAH (extended to April 2012). I would appreciate your comments on the analysis.
First, let’s look at the 17 years from 1979 through 1996.
The green line is my “eyeball-least-squares-fit” to the data. A more precise analysis might not exactly match, but it certainly wouldn’t show a significant increase or decrease in global temperature during this period.
Now let’s look at the more recent years. Obviously, we want to try to avoid confusing the analysis with an El Niño, so let’s just look at the period from 2002 to 2012.
Can anyone show me the temperature global temperature increase that has happened during this last decade. If this data is real, I can’t see any response to an accelerating atmospheric CO2 concentration. (Does anyone challenge the raw data or its reduction to this curve?)
Now if we put these two together, it seems to indicate that there were a step change that occurred between about 1996 and 2002.
Yes., it’s warmer now than it was in 1979. Yes, the last decade has been the warmest in a while, but how can you, in good conscience, draw a straight line from 1979 to 2012 and relate that to any parameter that as been rising steadily at an accelerating rate? It may be mathematically, and statistically, correct, but it is a scientifically poor analysis of this data.
I have also seen some analysis on this site that say that just because temperature change isn’t happening, doesn’t mean climate change is over. What was cited was that what was really important was Global Heat Content, because that was how to understand the net increase in heat being captured by the oceans. A curve was shown through about 2003 and looked to show a steadily increasing global thermal heat content. You almost had me convinced.
Global heat content does look to be a pretty sound way to look at whether the earth is absorbing more heat or not. However, the data stopped at 2003. I searched around and found a figure on the NOAA site
.
Now please help me understand what is steadily increasing in response to the accelerating atmospheric concentration of CO2 .
For reference, I am a liberal research engineer, who also happens to be an anthropogenic global warming (nay , climate change) skeptic. Not a non-believer, a skeptic. I agree there are changes happening. I’m sure that man is causing at least some of it. But the doomsaying conclusions I hear being expounded just don’t seem to be justified by the data that I have been able to find. I would be happy for you to help me see the error in my ways.
Your site has the potential to be a place where data can be discussed and countered and recountered. The other sites all seem to be only one sided. Are you willing to open this site to not only beating down the stupid comments made by the right wing talking heads on TV, but to honestly looking at the experiments, the data, the interpretation of that data, and the alternative conclusions that can be drawn?
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SRJ at 06:57 AM on 15 May 2012IPCC graph showing accelerating trends is misleading
# 96 Dikran I think we are talking past each other. The fitted model is statistical significant over the 2 periods mentioned in the quote from Gavin Simpson. The model is estimated from all data so I do think it makes sense to say it is insignificant from 2003 on. Because the model for the period 2003-2011 is estimated from more data than just these few years. But I am coming a bit out of my depth so I will refer you the blog post I mentioned and the documention for the mgcm package: http://stat.ethz.ch/R-manual/R-devel/library/mgcv/html/gamm.html http://stat.ethz.ch/R-manual/R-devel/library/mgcv/html/s.html My reason for my original statement "and continued but not significant warming from 2003 to 2011" was exactly that I didn't want people to interpret the lack of significance as indication of no warming. And I do think that we can agree on that? I -
SRJ at 06:38 AM on 15 May 2012IPCC graph showing accelerating trends is misleading
# 94 Dikran I don't think it will be useful or meaningful to fit a a linear model since these trends are extremely autocorrelated as they have so much data in common. I. e. the data point for 2010 is estimated from the period 1986-2010 while the data point for 2011 are estimated over the period 1987-2011, to they have 24 common years. And yes, my graph shows that the 25 year trend has increased since 1850-1874. It also shows that around 1940 the 25 year trend were as high as today. That does not contradict IPCC, my graph are just showing more details about 25 years trend. In fact, doing my analysis with the other timespans IPCC also use shows: 50 yrs trends: Increased since 1850-1899, around 1940 as high as today 75 yrs trends: Increased since 1850-1924, recent trends are highest observed 100 yrs trend: monotone increase since 1850-1950, but in recent years they have stabilised In agreement with IPCC - but I still don't like that graph -
Dikran Marsupial at 06:18 AM on 15 May 2012IPCC graph showing accelerating trends is misleading
SRJ, one must be very careful of mentioning statistical significance in the climate debate as it is very widely misunderstood. Over short timescales it is meaningless to say that the trend is statistically insignificant as this will be the case purely because there is insufficient data in the period to reliably asses what the trend actually is. If you do specifically point out that something is not statistically insignificant then it is important to also mention whethe the power of the test is sufficiently high for the lack of statistical significance to be meaningful or even surprising. Unless you do this, then there will be those who misinterpret the significance of insignificance! ;o) -
SRJ at 06:12 AM on 15 May 2012IPCC graph showing accelerating trends is misleading
# 90 Dikran I agree completely with your last statement. But please note that my statement you quote was not about linear trends but about the significance of the locally fitted generalized additive model. It is not an attempt to use only the 2003-2011 data, I just simply state the fact that the fitted model is not showing an significant increase after 2003. But it is still increasing. If you read Gavins Simpsons blog post he notes that the model is significant until 2005, but with the addition of the slighly cooler year 2011, the significance only extends to 2003. What I tried to emphasize was that the lack of statistical significant warming does not mean that there is no warming, basically I was summarizing Gavin Simpsons comment about the graph: "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 Marsupial at 06:11 AM on 15 May 2012IPCC graph showing accelerating trends is misleading
Helena/SRJ If you fit a linear model to the trends computed by SRJ, it will slope upwards, which implies that the rate of warming has increased over the period 1850-present, i.e. warming has on average been accellerating. As far as I can see SRJ's method is in agreement with the the IPCC diagram. -
tomfid at 06:10 AM on 15 May 2012There's no correlation between CO2 and temperature
Looking at temp-CO2 correlations is a bad idea for the very fundamental reason that temperature indicates the accumulation of forcing, so there is an integration between flow (CO2 forcing) and stock (heat or temperature). In general, you can't expect to see a correlation between a flow and stock time series, even when causality is perfect. It happens that some relationship is evident for CO2-temp because the time constant of surface heat is fairly short, but this is not terribly informative. This topic gives the impression that it's OK to look for temp-CO2 or forcing-CO2 correlations, if you just look for them the right way. It would be better if the message were that looking at stock-flow correlations (CO2-temp, or worse, emissions-temp) is basically misleading, unless you explicitly consider the dynamics. -
Helena at 06:02 AM on 15 May 2012IPCC graph showing accelerating trends is misleading
... that's why when you start in 1850 (his graph2) the full 150yrs trend is so low even though you've just "added in" the massive 1970-2000 increase : the increase gets diluted by T. In the same way, when you start in the present (his graph1 and the IPCC), you're not being "fair" to the past as its trend gets mechanically diluted. You "force-flaten" long trends. That's why you can't compare trends that have different T. -
Helena at 05:49 AM on 15 May 2012IPCC graph showing accelerating trends is misleading
les : "Just how someone thinks SRJ analysis is a good approach to the acceleration question and yet fail to acknowledge skywatchers contribution is, let's say, baffling. " skywatcher76 graph and method are already much better than the IPCC method, but they still have two flaws : - for science reasons : his method implies comparing different trends, thus having the problem of flattening long trends as you can see in the two graphs. You're then really not comparing the same thing (the slope of different trends) on the same graph as the slope is itself a function of the time period. His graphs seem to be 1D functions slope(t), but in fact they really are 2D functions slope(t,T). You would need to correct his graph for T. - for communication reasons : a decreasing decelerated temperature would look the same as his first graph (you would just be starting in the negatives), which is not very good if you want a clear picture. SRJ method addresses those two problems. (sorry for this last last message, but les was new to the discussion and had kind words on saying it was an interesting one) -
les at 05:23 AM on 15 May 2012IPCC graph showing accelerating trends is misleading
Well, having followed this dialogue; I think it's worth letting the various contributors know that, frustrating as it may be, the general flow has been educational... Just how someone thinks SRJ analysis is a good approach to the acceleration question and yet fail to acknowledge skywatchers contribution is, let's say, baffling. -
otter17 at 05:07 AM on 15 May 2012Lindzen's Clouded Vision, Part 2: Risk
This one is getting bookmarked. It is nice to have a collection of some of the economic analyses in one place. It seems many that disagree with the scientific stance have an issue with the solutions, so I make it a point to get straight to the point. -
Dikran Marsupial at 05:05 AM on 15 May 2012IPCC graph showing accelerating trends is misleading
SRJ wrote "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. -
Dikran Marsupial at 05:00 AM on 15 May 2012IPCC graph showing accelerating trends is misleading
The reservation I have about the IPCC graph is that a linear model is obviously not appropriate for timespans greater than 30 years or so, because of changes in forcings means that the residuals have structure, and so violate the modelling assumption. Not that big a deal as the fact is clearly evident in the plot and nobody is drawing any firm statistical conclusions from it. However the 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 Marsupial at 04:51 AM on 15 May 2012IPCC graph showing accelerating trends is misleading
Helena, Just a thought, but trends ending at the current time tell you about the change in gradient (i.e. curvature) around the current time. Trends starting at (say) 1860 give you an indication of the change in gradient (i.e. curvature) around 1860, not the present date (note that the two differet sets of trends have a different common point, one is "today", the other is 1860). Hence it is no big surprise that the analysis gives a different result. -
Helena at 04:34 AM on 15 May 2012IPCC graph showing accelerating trends is misleading
My last message here : you know my stand, it's useless to discuss it further, and (-snip-) Skywatcher : "Progressively increasing or decreasing gradients of the lines prove concavity of the curve" Gradients prove concavity yes, but 4 trends calculated on different time scales no. That's my whole point. Muon : I agreed to those three points (he yes/no questions) with .... you ! Not the IPCC ! There is no yes/no question in the legend of the IPCC graph, right ? You cannot start from saying it's an accelerated warming, then plot the 4 trends and say "well, the 4 trends increase, that surely indicates accelerated warming", that would be circular reasoning. What you must do is start with 4 increasing trends, not knowing anything else. What can you conclude from that ? My stand is : not much. KR: "As multiple posters have noted, a linear trend increasing over time is a clear indicator of acceleration " First, please note that Tom Curtis said : "Therefore this test [linear trend increasing over time] does not detect accelerating curves per se, but acceleration within a curve" You got 4 linear trends calculated. Can you really conclude or infer that the underlying curve depicts an accelerated warming ? SRJ : I support your method and i think your comment should replace or be added to the article on this website. It's sad the IPCC didn't use it and instead used one that can be rightfully criticized...Moderator Response:[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.
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Composer99 at 04:17 AM on 15 May 2012101 responses to Ian Plimer's climate questions
Carbon500: What I get from "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." is the oceans are warming The extra nuance in the more fleshed-out description does not alter the accuracy of the simpler one. Finally, I find your accusation of misleading terminology in the DCCEE response to Plimer is without merit. Any decrease in pH is necessarily an "increase in acidity" (which is why the change in ocean pH is "ocean acidification"), without regard to the final state of the system or entity in which the decrease has occured. -
SRJ at 04:14 AM on 15 May 2012IPCC graph showing accelerating trends is misleading
I also do not like that figure from IPCC. I think it is comparing apples to oranges when trend lines over 150 years are compared with 25 year trend lines. Skywatchers graphs do the same, i.e. comparing trends over longer times with trends over shorter times. Consider replacing the trend with the mean. Would it make sense to compare the mean of the temperature over the last 150 years to the mean over the temperature over the last 25 years? What I would do is to calculate ALL 25 years trend over the entire lenght of the series, then plot these vs. end year. In that way, trends of equal lenght are compared I had already the code ready for this, using annual data for HadCru I get this plot, click to enlarge:
The 25 year trends are increasing up to 2005 (marked by a vertical line), from there on they are decreasing. However, the trends after 2005 are still positive and significant, so warming is indeed continuing.
Error bars shown are not corrected for autocorrelation.
In general, I do not like the concept of calculating trends on more or less arbitrary subsets of the data. Another approach using all the data to fit a generalized additive model is outlined by Gavin Simpson in a blog post here.
Using the code provided I have updated his graph, and it shows a significant warming until 2003, and continued but not significant warming from 2003 to 2011:
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Pete Wirfs at 02:59 AM on 15 May 20122012 SkS Weekly Digest #19
Nope, not intimidated. Pete -
otter17 at 01:46 AM on 15 May 20122012 SkS Weekly Digest #19
Issue of the Week: I think the authors and the people that comment here are great examples of civility and are excellent teachers. One just has to look at the succinct clarity in the 170 or so articles covering climate science myths to see what a great teaching service is provided. Some might feel intimidated if they see comments from someone that has no interest in learning about the peer review literature, but that isn't Skep Sci's fault. I have seen many examples of Skep Sci trying to put the science in understandable terms when posed a question from a non-expert. As an engineer, I have learned quite a bit, though I only pop in once in a great while to post my thoughts.. -
KR at 00:29 AM on 15 May 2012IPCC graph showing accelerating trends is misleading
skywatcher - Those are very informative 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). -
Bob Lacatena at 23:37 PM on 14 May 2012IPCC graph showing accelerating trends is misleading
Helena's pretentious "I'll teach you guys what I mean by my genius" attitude, combined with a very thorough lack of clarity and an 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. -
muoncounter at 23:06 PM on 14 May 2012IPCC graph showing accelerating trends is misleading
Helena#78: "where did we say that we were considering increasing functions ?" Here, where you agreed the curve under discussion is concave up. Here, where you agreed with 'increasing and accelerating', which I re-stated here. And here. This is now straightforward: a. If the temperature function over the period in question was increasing and linear, there would be no change in slope regardless of the interval used. b. If the temperature function was increasing and accelerating (which you agree means concave up), slopes starting in later periods would be greater (more positive) than slopes from periods starting earlier. Here is an illustration of this from first-year calculus:
The slope of the line crossing the curve at x=1 is the smallest. Subsequent lines have increasing slope. Subsequent lines cross the curve at x>1. The slope of the last line shown (purple) is calculated from a very small interval around x=2 and is the largest. Work it backwards: the pattern of lines is sufficient to infer the shape of the curve.
To insist otherwise at this point suggests you have an interest in prolonging this agonizing (and frankly uninteresting) back-and-forth.
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Bernard J. at 23:03 PM on 14 May 2012IPCC graph showing accelerating trends is misleading
"Helena" sounds like Girma Orssengo. -
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)
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