Guest post by Jens Raunsø Jensen
Preamble
Inspired by a statement by Dr. Kevin Trenberth in the e-mails referred to as Climategate 2.0 (#3946 discussed here), it is hoped that climate scientists will have “an open enough mind to even consider” that the global warming of the 20th century could have occurred mainly as abrupt changes in mean temperature linked with natural events. Observational data supports that claim, at variance with the AGW “consensus view”.
Summary
Abrupt or step changes in temperature regime has been the subject of many discussions on this and other blogs and in the peer reviewed literature. The issue is not only statistical. More importantly, any presence of major step changes in mean temperature regime may contradict the claims of the AGW theory and models, i.e. the claims of increasing and accelerating temperature and of human emissions of GHGs being the major cause for the relatively high temperatures in the second half of the 20th century.
In this post, 232 complete and unadjusted GHCN station records are analysed for step changes in the period 1960-2010, and it is argued that:
- Abrupt changes in temperature linked with natural climate events may be widely responsible for the “global warming” during the second half of the 20th century.
- 50% of sample stations have not experienced increased mean temperature (”warming”) for more than 18 years.
- 70% of Europe stations have not experienced warming for more than 20 years.
- The relative role of natural processes in global warming is very likely underestimated by IPCC.
- The global average temperature curve is ”apples and oranges” and is widely misinterpreted using linear trend and smoothing techniques as indicating a pattern of widespread uniformly increasing temperature.
Objective and methodology.
The post is in continuation to my earlier post on the subject (http://wattsupwiththat.com/2011/08/11/global-warming-%e2%80%93-step-changes-driven-by-enso/ ), now including a near-global station level analysis. The post is based on a ppt presentation including additional details given at a researcher’s workshop at University of Copenhagen, 15th November 2011 (http://www.danishwaterforum.dk/activities/Researchers_Day_Climate_Change_Impact_2011.html ).
The objective with this analysis has been (i) to examine the land-based temperature records at station and higher levels for the presence of step changes during the period 1960-2010, and (ii) to assess the implications for our assessment of global warming during that period. Please note that the objective has not been to dismiss a (likely) presence of an anthropogenic warming signal, or to establish a climate model, or to make projections for the future. The issue is step changes in observational data during 1960-2010.
I have used the documented Regime Shift Detection tool of Rodionov (2004, 2006; www.beringclimate.noaa.gov/ ). The results are considered to be statistically robust (ref. the ppt presentation for details on parameter settings and a verification of the assumptions of constant variance and a likely negligible influence of autocorrelation).
The station level data is from GHCN (“after combine”, http://data.giss.nasa.gov/gistemp/station_data/ ) and include ALL stations with a complete record in the period 1960-2010 in broadly defined sampling regions (ref. Fig. 1).
A total of 232 stations were identified, with 54% located in Europe and Russia. The sampling criteria result in wide differences between the “regions” in terms of station number, density and distribution. Also, the “regions” are more or less homogeneous climatologically. However, this is not of material importance for the following discussion and conclusions.
Fig. 1. Distribution of sample stations according to sampling criteria.
Results
Significant step changes are widely found in the T-records and representative examples for 3 “regions” are shown in Fig. 2a-c. The temperature increase in the steps is typically of a size which is comparable to the often quoted global warming during the 20th century.
Fig. 2a. Alaska T-anomaly (n=9). Step, 1977; T-change = 1.5 oC; significance 0.000001
Fig. 2b. Fichtelberg, Europe. Step, 1988; T-change = 1.0 oC; significance 0.00009
Fig. 2c. Malacca, South-East Asia. Steps: 1978, 1990 and 1998; T-change = 0.4+0.3+0.4 = 1.1 oC; significance, 0.0004, 0.0007 and 0.003.
Warming during 1960-2010 was clearly a non-linear process at station level, with the step pattern differing among the “regions”. The global average T-anomaly curve, constructed by averaging across station-level T-anomaly curves, is therefore highly deceptive in propagating a message of near-linearly increasing temperatures, contrary to the actual processes at station level. Thus, the global T-anomaly curve is inherently “apples and oranges” and can not be used to identify a meaningful global AGW trend if the step changes are neglected. Then, the apparent AGW trend will in reality mainly capture the aggregated effect of the sudden step changes (as e.g. in Foster and Rahmstorf, 2011).
The steps are concentrated in few short periods. Disregarding 39 steps after 2005 (considered highly uncertain and “in progress”; 2/3 ups and 1/3 downs), it is found that:
- The steps occur predominantly (58%) in three 3-year periods: 1977/79, 1987/89 and 1997/99 (Fig. 3).
- 72% of all stations, and more than 50% of stations in each “region” (except Arctic), have one or more steps during these periods (e.g. 89%, 56% and 93% of Europe, Russia and South-East Asia stations, respectively; Fig. 4).
- 78% of Europe stations have a step change in 1987/89, during which the major part of the entire warming of the 2nd half of the 20th century apparently took place.
- 2 or 3 steps are common in South-East Asia (especially 1987/89 and 1997/99), but one step only is common in records from Alaska (1977/79), Europe (1987/89) and Russia (1987/89).
Fig. 3. Distribution of step changes by year of change.
Fig. 4. Percent of stations with one or more steps in indicated 3 periods.
Similar step changes are identified in national average records (ref. link to presentation above): US contiguous 48 states (GISS): 1986 and 1998; Australia (BOM): 1979 and 2002; and Denmark (DMI): 1988. The steps in the Global T-records are: Crutem3gl: 1977, 1987 and 1998; GISS L/O: 1977, 1987 and 1998; and Hadcrut3: 1977, 1990 and 1997.
The steps are statistically highly significant. But are they supported by a probable physical cause? The answer must be yes for the majority of steps. The steps occur in a temporal and spatial pattern coinciding with well-documented events and regime changes in the ocean-atmosphere system:
- 1976/77: the great pacific shift from a “cold” to a “warm” mode (e.g. Trenberth, 1990; Hartmann and Wendler, 2005).
- 1987/89 and 1997/99: the two clearly most intense El Niños of the period, 1986/88 and 1997/98, with the intensity here defined as event-accumulated nino3.4 anomalies (NOAA’s ONI index); there were two less intense events in 1982 and 1991, the impact of which was probably occluded by the major volcanoes El Chichon and Mt. Pinatubo.
- A regime shift in NH SST in 1988/89 (Yasunaka and Hanawa, 2005).
- A new regime of constant temperature after the 1997/98 El Niño, i.e. the now widely accepted “hiatus” in global warming.
- Documented step changes and regime shifts in marine ecosystems, e.g. the late 1980s in Europe and in the Japan/East Sea.
- The short-term regionally diverse global impact of ENSO events is generally well-known.
The empirical evidence, from this station level analysis and other sources, is unequivocal: the step changes in mean temperature are likely real and associated with natural events. The physical mechanisms remain to be understood, and this is certainly not to claim, that ENSO events are the only elements of the natural cause-effect chain.
It is therefore concluded, that the major part of the temperature change (global warming) in the 2nd half of the 20th century occurred as abrupt changes in mean temperature associated with natural events in the ocean-atmosphere system. Still, a warming/cooling trend – albeit relatively small compared with the step changes – could of course be hidden by the regime change model. But it seems inconceivable, that steadily increasing CO2 levels could be responsible for the major sudden changes observed as e.g. in Alaska in 1977, Europe in 1988 and South-East Asia in 1998. In principle, the natural events and step changes could have been amplified by human caused warming, but this is currently pure speculation.
Implications when accepting the presence of steps
“Increasing temperature and accelerated warming” : this study does not support general statements like that. The bulk of the “global warming” has likely taken place in abrupt steps, and 50% of the stations analysed has not experienced any significant warming for more than 18 years (Fig. 5). In Europe, 70% of the stations have not experienced significant change in mean temperature for more than 20 years.
In South-East Asia, the median value is 13 years as many stations here also experienced a step change in 1997/98 (Fig. 4).
Fig. 5. Years of constant T-mean prior to 2010. Box-Whisker plot, 1st and 3rd quartiles. (note: uncertain up and down step changes during 2006-2010 are disregarded).
Challenging the IPCC consensus view, i.e.: “Most of the observed increase in global average temperature since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse-gas concentrations”. However, the finding above, that abrupt changes linked with natural processes likely account for most of the increase in temperature during 1960-2010, contradicts the IPCC claim regarding the relative importance of natural and human causes. Thus, when IPCC (AR4) can only reproduce the T-curve by including GHG effects, then logically
- either the IPCC GCM models do not adequately model the natural processes of high significance for the temperature variations (there is still low confidence in the projection of changes in the ENSO variability and frequency of El Niños, ref. the recent SREX-SPM IPCC report),
- or/and the IPCC has overestimated the climate sensitivity to CO2 changes by eg. attributing natural temperature increases to CO2-induced feed-back processes.
In either case, the relative importance of natural processes for the T-changes has likely been underestimated by IPCC.
Conclusion
This study has established that step changes in land-based temperature records during 1960-2010 are common and very likely real and linked with natural climate events. The step changes are statistically highly significant and with a systematic yet regionally diverse pattern of occurrence coinciding with major climate events and regime shifts. This finding has far reaching consequences for our analysis of climate records and for our assessment of global warming.
Thus, although many different statistical models can be applied to explore the pattern of T-change, the presence of step changes invalidates the widely used statistical techniques of linear trend and smoothing as means of identifying the pattern of temperature variation during 1960-2010.
Furthermore, the step changes account for the main part of the temperature changes during the 2nd half of the 20th century. The logical consequence is that natural processes have been the major cause for the temperature change during this period, leaving a secondary role to other causes such as the anthropogenic greenhouse effect.
Just looking at figure 3 again
I wonder how much of that step change towards the end of the 80’s could be caused by the introduction of new equipment & recorders (e.g. with certain type (K?) thermo couples) that monitors temperature on a continuous basis.
In turn, this could mean that a lot of the observed warming
ca. 0.14 C /decade since 1974
as established by me and others
e.g.
http://www.letterdash.com/HenryP/henrys-pool-table-on-global-warming
is actually just due to much improved readings and accuracy.
If I were to simply not accept that jump as being correct, at all,
and eyeballing it a bit,
I can predict that our figures of 0.14 C warming per decade could be out by as much as 30% simply because of improved readings and recordings.
I am not saying that current readings are not good. I am saying older readings were probably too low, too infrequent, and too inaccurate, more biasedly wrong towards the lower temps.,
leading us us to actually over-estimate modern warming.
Jens,
with all due respect: You cannot have your cake and eat it, too. I have, in fact, read your post (several times). You are trying to claim that:
Are you or are you not trying to make a case that a) the rise in temperatures in the years 1960-2010 (the interval you have selected yourself, ferrgodnessake) is dominated by natural forcings, causing stepwise changes, with CO2 having a secondary role? And b) do you or do you not link these stepwise changes you claim to have identified as coinciding to mainly ENSO? (Allow me to remind you of the title of your earlier post: “Global warming – step changes driven by ENSO?”)
If the answer to these two questions is yes, then you are certainly claiming that natural forcings – as exemplified by ENSO (i.e. the only example you really elaborate on) – are the main cause of the temperature rise in your peiod of choice, causing most of the stepwise changes you claim to identify. I have noticed that you appear to have trouble realising this, but it really should not be that hard to see for any open mind.
If your answer is no, then there is no point in your entire post………
As Utahn has pointed out, you have a similar problem with internal contradiction when it comes to the alleged stepwise changes themselves:
If the fact that Rodionov´s step detection software will detect “steps” in almost any dataset is so utterly trivial even to you, then how on earth can you claim that the mere interpretation of the model of alleged “steps” somehow invalidates the presence of a true linear trend? And if you acknowledge that there might indeed be an underlying linear trend which is masked, then what on (this) earth in this analysis enables you to see whether this trend has a stronger or weaker overall signal than your alleged “steps”? Once again, your sources for your “regime changes” plainly do not support this thesis of yours at all>/i>, whether you like it or not.
If you still wish to try to claim that your “steps-show-natural-forcings-dominate-CO2-1960-2010” thesis is valid, then you need to demonstrate at least three things:
I) That your identified steps are present not only locally, but globally (locally, atmospheric circulation patterns can indeed overwhelm signal for several decades, but globally, various sources of noise will have opposite signs on different places of the planet and thus cancel each other out much more quickly)
II) That the stepwise change model is indeed a better description of the data than a linear model, and
III) that your physical explanations of these steps is coherent. Again, I know you are not trying to build a complete GCM model, but when you (as you do) try to link these steps to a physical mechanism like ENSO, you really need to explain why you think ENSO is able to cause an abrupt warming in its warm El Niño phase in 1997/98, when it apparently is unable to cause any similar cooling in the many equally cold La Niña phases in the interval 1960-2010 (e.g. 1988-89 or 1999-2000).
And regarding you being “academically offended”:
To my mind, my above questions (and those of other people like Utahn or Svalgard) are perfectly legitimate, based in scientific facts and politely posed, too. So far, you have either given evasive answers that makes one wonder whether you actually understand some of the important basics, or simply ignored them, instead complaining loudly about “ad hominem attacks”. Sorry, Jens, but I´m sure you know very well that the natural sciences can be a tough environment, that extraordinary claims require extraordinary proof, and that one needs to be sceptical about one´s own results, too. It is perfectly fine that you are not a climatologist, and that you still dare to try to disprove one of the core findings of mainstream climate science, and that you chose to do so on a blog run by another climate amateur who is, a priori, sympathetic to your views – but then you really should not be surprised when your claims are being challenged by other people when your facts do not hold up, and that you also run a high risk of being wrong and even end up being laughed upon, especially when you fail to acknowledge obvious errors. The other half of your cliché about the importance of being open minded says that one shouldn´t let the brain fall out either, remember?
If you actually wish to convince people who aren´t already convinced that the whole AGW hypothesis is wrong, a scam or a conspiracy that you have a legitimate challenge to mainstream climate science, then you need to adress the above obvious holes in your arguments. If you are happy just to preach some non-academic, seemingly plausible but unsupported bedtime stories to the choir that you would prefer not to be met with counterarguments, then it´s your choice – but then do me a favour and spare me the BS about being “academically” offended.
P.S: I guess I should be flattered by you thinking that I, a mediocre PhD student in a field at best on the fringe of climate science, be able to “corner” an internationally recognised and distinguished atmospheric scientist like Kevin Trenberth, just by sending him a mail. But no, all I did was to ask him about ENSO and your claims. I provided a link to this post and some quotes from it, along with a couple of questions summing up the substance. You quote Trenberth among others as evidence that your regime changes are real, and you are undeniably trying to make a case that naturally forced regime changes have overwhelmed manmade GHGs. This is squarely at odds with almost all published research on the field, including the well known conclusion of the IPCC AR4 report that “Most of the climatic warming over the last 50 years is likely to have been caused by increased concentrations of greenhouse gases in the atmosphere”, of which Trenberth was a lead author. That he finds that you use his 1990 paper completely out of context and/or reach an erroneous conclusion not supported by the papers you quote should thus come as no surprise to you, and I honestly don´t understand why you think that I should apologise for anything in this regard.
But to settle the dispute, I suggest that you write this up as a paper and submit it to a serious journal (e.g. not Energy & Environment, blogs or some non-refereed Danish language newspapers) so that competent experts in all fields might have a chance to analyse your claims. My prediction is that you will be asked many of these same questions, and possibly many more thorough ones people here have not thought of – and that after having accounted for errors and weaknesses, you will end up having no base at all for your claims about natural forcings contradicting AGW/leaving a secondary role for GHGs (surely not on a global scale).
And regarding you being “academically offended”:
To my mind, my above questions (and those of other people like Utahn or Svalgard) are perfectly legitimate, based in scientific facts and politely posed, too. So far, you have either given evasive answers that makes one wonder whether you actually understand some of the important basics, or simply ignored them, instead complaining loudly about “ad hominem attacks”. Sorry, Jens, but I´m sure you know very well that the natural sciences can be a tough environment, that extraordinary claims require extraordinary proof, and that one needs to be sceptical about one´s own results, too. It is perfectly fine that you are not a climatologist, and that you still dare to try to disprove one of the core findings of mainstream climate science, and that you chose to do so on a blog run by another climate amateur who is, a priori, sympathetic to your views – but then you really should not be surprised when your claims are being challenged by other people when your facts do not hold up, and that you also run a high risk of being wrong and even end up being laughed upon, especially when you fail to acknowledge obvious errors. The other half of your cliché about the importance of being open minded says that one shouldn´t let the brain fall out either, remember?
If you actually wish to convince people who were not already convinced that the whole AGW hypothesis is wrong, a scam or a conspiracy that you have a legitimate challenge to mainstream climate science, then you need to adress the above obvious holes in your arguments. If you are happy just to preach some non-academic, seemingly plausible but unsupported bedtime stories to the choir that you would prefer not to be met with serious counterarguments, then it´s your choice – but then do me a favour and spare me the BS about being “academically” offended.
P.S: I guess I should be flattered by you thinking that I, a mediocre PhD student in a field at best on the fringe of climate science, be able to “corner” an internationally recognised and distinguished atmospheric scientist like Kevin Trenberth, just by sending him a mail. But no, all I did was to ask him about ENSO and your claims. I provided a link to this post and some quotes from it, along with a couple of questions summing up the substance. You quote Trenberth among others as evidence that your regime changes are real, and you are undeniably trying to make a case that naturally forced regime changes have overwhelmed manmade GHGs. This is squarely at odds with almost all published research on the field, including the well known conclusion of the IPCC AR4 report that “Most of the climatic warming over the last 50 years is likely to have been caused by increased concentrations of greenhouse gases in the atmosphere”, of which Trenberth was a lead author. That he finds that you use his 1990 paper completely out of context and/or reach an erroneous conclusion not supported by the papers you quote should thus come as no surprise to you, and I honestly don´t understand why you think that I should apologise for anything in this regard.
But to settle the dispute, I suggest that you write this up as a paper and submit it to a serious journal (e.g. not Energy & Environment, blogs or some non-refereed Danish language newspapers) so that competent experts in all fields might have a chance to analyse your claims. My prediction is that you will be asked many of these same questions, and possibly many more thorough ones people here have not thought of – and that after having accounted for errors and weaknesses, you will end up having no base at all for your claims about natural forcings contradicting AGW/leaving a secondary role for GHGs – surely not on a global scale, which is the scale for which the AGW claims you want to refute have been made.
Jens,
Thank you for your interesting and informative post; your temperate and patient replies to questions and challenges in the subsequent commentary are similarly thoughtful and reserved. The same courtesy and professionalism has been demonstrated by some others, but not all. It is a great pity that so often personal convictions stir the emotions and cloud judgment, a behaviour we can all observe so often in the debates over climate change.
I’m neither mathematician nor scientist. I’ve come to this thread late, as I have to the climate change debate. Quite some years ago I accepted what we were being told by the “climate scientists” about anthropogenic-released carbon dioxide as the cause of global warming, but in the earlier part of the last decade, I started to have some doubts. At last I’ve had the time to do some reading at the detailed level, which I’m doing because I no longer have confidence in what is presented through official channels, or the media. Both avenues are full of assertion and persuasion, and precious little well-based argument. But now to your post.
1. It seems to me that this instance of using a well-recognised mathematical tool to determine step changes, is just the kind of arms-length analysis that is too often missing in this debate. I agree with your suggestion that “major step changes in mean temperature regime may contradict the claims of the AGW theory and models” – and I applaud your use of the word “may”, demonstrating a conservative perception that some respondents to your posts seem to have missed entirely. I may have missed something, but could you indicate in more detail where or how these step changes may challenge the validity of the more recent IPCC models of temperature change? (The flatter and cooler changes measured over the last decade have clearly shown that temperature predictions of prior models have proven deficient.)
2. Accuracy of the raw data, and instrumentation changes? I think we’re stuck with what we have historically, and that’s what we have to work with; but I’m very pleased to see that the raw data is being analysed, not some massaged set or imputed metrics for blank cells, nor those bland averages which as said by someone earlier in the commentary are like putting Paris Hilton in a burlap sack , which contain the data but lose the interesting contours and prominent features.
3. Most of the discussion above has raged over the issue of step changes. But I thought your charts and summary points about temperature stability also very interesting. I quote:
a. “50% of sample stations have not experienced increased mean temperature (”warming”) for more than 18 years.
b. 70% of Europe stations have not experienced warming for more than 20 years.” This finding prompts me to ask what other zero increases in temperature over appreciable time periods, may be found in raw data elsewhere?
4. The average person in the street would have to ask, if we started to come out of a Little Ice Age in 1680, when so much of northern Europe was so cold that the Thames itself froze, what caused things to warm up prior to the Industrial Revolution? And are not the same factors at work today? Yes, AGW may exacerbate the warming, but should we not consider that the deep forces at play between 1680 and 1850 may still be operating?
Please keep up your good work.
.