Do European tree ring analyses indicate unusual recent hydroclimate?

by Frank Bosse and Nic Lewis

Not really.

A recent paper (M. B. Freund et al 2023, MBF23 thereafter) in “Nature communication earth and environment” investigates the variability of the summer drought events since 1600. It uses the method of “stable isotope analyses C13/O18” to extend the “Standardised Precipitation-Evapotranspiration Index (SPEI) from 1950 to now back to 1600.

The paper describes and uses a multi proxy network over large parts of Europe (see Fig. 1 of MBF23) to reconstruct the history of summer droughts for a longer historic period. It finds interesting results about the dependency of those events on volcanos and solar forcing. It’s a worthwhile read and we were interested in whether the headline title is justified and likewise this claim in the Abstract:

“We show that the recent European summer drought (2015–2018) is highly unusual in a multi-century context…”

Thanks to the authors the used SPEI reconstruction annual data are available, so we were able to perform calculations to check these assertions.

An apparent first “confirmation” of the headline title of the paper appears in Figure 3a in MBH23:

Screen Shot 2023-02-21 at 6.59.27 PM

Fig.1: A reproduction of Fig. 3a of MBH23. Annual European mean SPEI-data in blue/red, the low pass filter output is shown in black.

The black line in this figure shows the effect of applying a 13-year low-pass smooth, so it relates to the recent past. Indeed, after 2010 the used 13-year Chebyshev filter shows a “dramatic” downward dip to a far lower precipitation index than at any other time during the 1600-2018 reconstruction period. However, when eyeballing one finds also dry periods, before 1950, the onset of the classical SPEI dataset marked with “SPEI”, or before 1880 marked with dark grey in Fig.1, and the low pass filter didn’t react in the way it did after 2010.

The reason for this behaviour is quite simple: All smoothing filters struggle with the beginning and the end of a filtered dataset. They estimate the output because there are no precursors/ successors in the raw data. To test the impact of this properties we used the same data with a similar filter (Loess) and made a comparison with Fig. 1 but stopped the filtering in 1949:

Screen Shot 2023-02-21 at 7.00.54 PM

Fig. 2: Fig.1, but with the smoothed SPEI-Index ending in 1949.

If the paper was written in 1950 it would find “unusual recent hydroclimate”, in 2023 it finds the same for the recent conditions due to a filter issue. The beginning after 1600 is also very unusually wet in the filter output for the same reason.

The dip in the end in Fig.3a of MBH23 is not real, it’s an artefact of the used filter.

A simple running mean filter which while it has no output in the early years, is unartefacted, gives a fairer smoothing of fluctuations over 1600-2018:

Screen Shot 2023-02-21 at 7.01.48 PM

Fig. 3: Summer SPEI-Data (black) filtered with a trailing running mean (red). The historical minimum of this filter is shown as a broken red line. Clear to see minima in the 1870s and 1680s in addition to at the end of the 1600-2018 period.

Fig. 3 gives the contrary result of the headline title of MBF23: to 2018 (the last datapoint in the set in MBF23) it indicates that the recent European summer hydroclimate was NOT unusual, the SPEI index was in the ballpark of natural variability.

To show that also the claim in the Abstract (“2015-2018 highly unusual”) is not true we had a deeper look in the data and calculated those 4 years averages over the whole timespan.

It turned out that during many periods the average of 4 years in the SPEI data was more negative than during 2015-2018, for which this average is -0.273:

Since 1900 there have been four such periods, all in the years leading up to 1950: 1947-1950; 1946-1949; 1945-1948; 1944-1947. The period before 1950 (not strongly influenced from anthropogenic forcing) was indeed marked by very dry summers, not mentioned in one word in MBF23.

Before 1900 there are also some periods:

1892-1895; 1760-1763; 1759-1762; 1738-1741; 1688-1691.

The “European summer drought 2015-2018” was NOT highly unusual in a multi-century context”, as falsely claimed in the abstract.

To further bolster this point we looked also if longer period averages were “highly unusual”.

It turned out that a trailing average of 5 years produces 10 periods during 1600-1950, a time span predominantly affected by natural variability, with more negative SPEI-values than the most recent period to 2018; a 10-years average gives 9 such pre-1951 periods.  And a 3-year trailing average produces no less than 57 pre-1951 periods with more negative SPEI values than the most recent period.

Furthermore we had a look at the variability of the annual data after 1950 (the time span of the “native SPEI”) and before this year, the time span of the reconstruction of the “European hydroclimate based on a network of tree-ring stable isotopes of oxygen and carbon ratios” in MBF23. We calculated running 21 years standard deviations (sigma) of the annual data (Fig.4):

Screen Shot 2023-02-21 at 7.03.23 PM

Fig. 4: The variability of the annual SPEI data. The averages before 1950 and after this year are marked with a dotted line. Note the jump.

The lower time variability of the reconstruction cast some doubts, as to whether the reconstruction of the SPEI 1600…1950 is useful to compare 1:1 the newer native SPEI data with the historical reconstruction data pre- 1950. It looks as if the reconstruction, even if otherwise valid, significantly understates natural variability. This is a common problem with proxy-based reconstructions. It results in the extent of fluctuations during the post-1950 instrumental SPEI era being an exaggerated relative to natural variability, so that normal fluctuations can appear to be unusual.


MBF23 is a very valuable paper when it comes to the description of the variability of European summer droughts since 1600. However, neither its title “European tree-ring isotopes indicate unusual recent hydroclimate” nor the claim in its Abstract that “recent European summer drought (2015–2018) is highly unusual in a multi-century context” are justified by the data used in the paper.

The lower resolution in time and spatially of the reconstruction before 1950 in relation to the determined SPEI after 1950 casts some doubts if the comparison of some years after 1950 to the historical reconstructed values is appropriate.

MBF23 should be corrected and retitled because some key conclusions, including the headline claim in its title, are not supported by proper statistical analysis of the SPEI values that their reconstruction method produces. The recent European drought to 2018 remained within the range of natural variability.

68 responses to “Do European tree ring analyses indicate unusual recent hydroclimate?

  1. How does something like the get through peer review?

  2. Thank you for this analysis. I was going to quote and provide links to papers that found no unusual patterns of recent droughts in other regions of the globe compared to other periods, but I realized they were too numerous to list. There is too much research for too many periods for too many regions to get excited about the recent droughts and conclude that anything is highly unusual or unprecedented.

    This issue is like SLR. There is no there there.

  3. Those are mathematical rookie, totally obvious, and massive statistical mistakes from Ms. Mandy B Freund, which is understandable on her part being a properly indoctrinated recent PhD from the University of Melbourne (even though she claims to be an expert specifically in statistics (Haha!)), and which is also why you were able to point it out in a few sentences of junior high school level mathematics. What is a real shame, however, is that the editors and the much vaunted peer reviewers of the various allegedly highly respected journals that she publishes in not only allow, but promote, the publication of such total scientific garbage. I wonder if it will take another generation or more to clear the intellectual garbage that permeates our climate science institutions and publications at every level. Thank you Nic and Frank for bringing this unadulterated nonsense to our attention. I wish more so-called climate scientists would learn a little bit of basic mathematics and stop the propaganda.

    • “I wonder if it will take another generation or more to clear the intellectual garbage that permeates our climate science institutions and publications at every level.”

      One wonders how such a clearing of intellectual garbage could occur when the minds that produce it are not taught the skills of critical thinking and rational analysis, unencumbered by culturally-enforced biases that preclude independent thought.

      I recall my daughter reporting what she was taught in one of her college courses about scientific method: “You start with something you want to prove and then look for evidence that supports it.” She was abhorred. I was outraged.

      The intellectual rot is very, very deeply entrenched. It’s not just a matter of the political agenda baggage that is heaped onto every aspect of the “education” experience, which is hard enough to overcome. The more fundamental problem is the unquestioning acceptance of “authority”, the dominance of moral relativism, and the absence of the rational mindset required to sort through the intellectual entropy.

    • The limitations of filters like this are hardly “junior high school math”. That is absurd. I suspect one could find textbooks in statistics that do not include this case.

      • You’re right David, I was actually doing far more complex math than this in 5th grade. I should have said elementary school math.

      • Sadly high school or even undergraduate or graduate training does not seem to teach science students the very basics of how to use ( and how NOT to use) filters.
        “A simple running mean filter which while it has no output in the early years, is unartefacted, gives a fairer smoothing of fluctuations over 1600-2018:”

        unartefacted? FFS, that is not even a word. And , yes , running means have terrible artefacts. Nic Lewis should konw better than this but stock market guys love trailing means.

        The filters used in the paper look very dodgy. The first thing to do is find out what this “Chebeychev” actually is. How it is implemented. AFAIK this is only possible as interative filter and if run forwards in time should have converged by the end and would NOT produce such an artefact at the end. IMO they probably did some home spun , ad hoc, games like running fowards then backwards ( a totally invalid trick Mickey Mann invented with some other filter ). This means it had NOT converged when run backwards and both ends of the filter output are garbage.

        That the output of their filter is well below ANY of the input data for that period should be an obvious red flag to any author or reviewer.

      • I wrote to the study author Ms. Mandy B Freund, asking her for the specifics of precisely which Chebyshev filter she used and for the code used to implement (as she offers on the page where her paper is published), but, OF COURSE, have received no response. This is how the communist / facist / totalitarian / moron / non-scientist “climate scientists” operate. (1) Fail math class, (2) become a “climate scientist”, (3) publish fictional garbage, (4) hide the decline, (5) fail to respond to all queries, and (6) call anyone who points out their obvious errors “climate deniers”.

      • Filters as applied in the discrete digital world are nothing more than convolutions. Convolution is a simple mathematical concept certainly taught in junior high school. I actually learned it in the 4th or 5th grade.

  4. Wolfgang Richter

    This is a paper on droughts in Europe with a different result than the M. B. Freund et al 2023 paper:
    “Past megadroughts in central Europe were longer, more severe and less warm than modern droughts”

  5. Frank & Nick … Just curious, did you submit this to the journal and/or the authors? Great job!

  6. Kenneth Fritsch

    A quick Google search showed this posted rejoinder first followed by lots of unquestioning summaries of the drought paper. It will be interesting to see how Nic and Frank’s analysis is handled by the media.

  7. Michael Mann is shaking his head — amateurs…

  8. Joe - the non climate scientist

    Curious if any of the proxies used in the study and the conclusions were reconciled with the various contemporaneous written record of Europe by farmers wine makers, etc. . As I recall the book “times of feast, times of famine” Le roy Ladurie had quite a few discrepancies between the written record and the proxy reconstructions.

  9. Typo? “MBH23” appears in 3 places.

  10. UK-Weather Lass

    The only serious droughts we are experiencing currently are in competent climate science, the peer reviewers of same, and media capacity to be openly intelligent in criticism.

    Meanwhile as a consquence of these droughts we are all being charged more for less for absolutely no good reason at all.

  11. Damn.

    How is that not fraud?

  12. This paper ‘The forgotten drought of 1765-1768. Reconstructing and re-evaluating historical droughts in the British and Irish Isles’ By Conor Murphy, Robert Wilbey et al notes in its literature review that

    Major drought events in England and Wales occurred in 1798 -1808, 1854 – 60, 1887- 88, 1890 – 1909, 1921 – 22, 1933 – 34,1959, 1976, 1990 – 92, 1995 -97.

    The UK likely suffered clusters of dry seasons or years 1740 – 44,
    1780 – 81, 1785 – 86, and shorter droughts in 1705, 1736, 1765 and 1788.

    Less well documented droughts occurred in 1722 – 26, 1730 – 34, 1783 – 91, 1801 – 08,, 1833 – 36, 1870 – 82.

    Drought periods are obviously fairly common.

    • Michael Cunningham aka Faustino aka Genghis Cunn

      I recall the 1976 drought, when from memory there was no rain for over four months. (I wasn’t in the UK for the later droughts.)

  13. Great Blue Heron

    The conclusion of the paper that “…the recent European summer drought (2015–2018) is highly unusual in a multi-century context” is not based on the smoothed SPIE data discussed here by Frank and Nic. The conclusion is not “an artefact of the used filter.” Please read the paper.

    • We did, did you?

    • Are you saying that their conclusion is not based on data? (that would b an even stronger critique in that paper)

      What are their conclusions based on in your opinion?
      And is the critique presented here justified in your opinion?

      • We say that PARTS of the conclusions, abstract and the headline titel are not bolstered by proper statistical analyses of the used data..

      • Great Blue Heron

        Hi morfuo3 –

        Thanks for asking.

        The abstract states: “We show that the recent European summer drought (2015–2018) is highly unusual in a multi-century context and unprecedented for large parts of central and western Europe.”

        Frank and Nic imply that this conclusion is based on the end-point behavior of the smoothed 13-year
        Chebyshev low-pass filter shown in Fig. 3a. Thus they devote several paragraphs to the demonstration that the end-points introduce spurious local trends – artefacts. But the conclusion stated above is not based on the smoothed data; it is based on the individual, spatially specific data summarized in Fig. 4e.

        The authors emphasize the spatial heterogeneity of the trends, and the fact that wet trends in one area are often offset by dry trends elsewhere. Thus the continent-wide data (Fig. 3) has the usual effect of obscuring local tends. Thirty and 100 year trends in continent-wide average SPIE are illustrated in Fig. 4. Their conclusions do not appear to be in conflict with those of Nic and Frank. For example:

        “At the continental scale, there is no significant 30-year drying trend.”

        Now you are welcome to dismiss the significance of spatially specific trends, or quibble with the wording of the article’s title, but accusations of statistical naivete hardly seem justified.

      • Great Blue Heron

        morfuo3 – To answer your questions explicitly:

        1. No, I am not saying that their conclusion is not based on data.
        2. Their conclusions are based on data treatments described in their sections “SPEI reconstructions” and “Change point trend analysis”.
        3. The main critique, that an artefact has led to incorrect conclusions, is not justified.

      • GBH: “Frank and Nic imply that this conclusion is based on the end-point behavior of the smoothed 13-year.”
        No, we also also re- calculated the raw data! Please read the post completely.

    • Juerg Brechbuehl, Biologist

      I did read the paper. The relevant passage is in the first paragraph on page 6:

      Large parts of central and western Europe, southern
      Spain and parts of Italy encountered this recent 4-year drought
      episode, unprecedented relative to both the instrumental record
      and the past four centuries. In contrast, during this period, parts
      of northern Europe including Scotland and parts of Fennoscandia,
      as well as southeastern regions, including Greece and Turkey
      experienced unusually wet conditions.
      These opposing conditions
      highlight the importance of spatial climate reconstructions.

      The meaning is that the spatial pattern of drought events shifts in the course of the centuries, and this particular pattern has not been found previously.

      The title is misleading only in the context of the present climate alarmism, because it can be interpreted that the authors detected a change in overall trend.

  14. I am curious if you have looked at similar analyses presented in papers about the Colorado River and the claim of “driest in 1200 years”

    • The 1930s would be the first place to compare.

      “The drought came in three waves: 1934, 1936, and 1939–1940, but some regions of the High Plains experienced drought conditions for as many as eight years.”

    • I suspect that the low reservoirs are more caused by various states and localities using their full quotas whereas in the past they did not. Las Vegas has been booming. In the 1930’s it was just a gas station and a store. Lots of new golf courses in Arizona and Nevada too.

      • Dave … You’re right that Arizona has grown, however water usage measured per capita might surprise you.

        Page down to Arizona’s Water Management Success. The state is using slightly less water with approximately +4 times the population from 1957 to 2019. Phoenix has become the fifth most populous city in the USA, at 1.6M. From our perspective as Arizonans, California is the culprit. They own the senior (priority) rights to the Colorado and they have slow walked any in state reservoir construction to the point that none have been built in a decade. Much of the bomb cyclone water that recently hit the state could have been saved in reservoirs. No one is running the store there. (Should have said the inmates are running the asylum.)

      • Thanks for the information Bill.

  15. It’s really very simple. As Nic and Frank have succinctly shown, Freund’s math is wrong. It’s that simple, end of story.

  16. Can’t be a coincidence that popular music since the 1950s features amplified electric guitar… Global Warming???

  17. 1688-1698, the coldest part of Maunder in CET:

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  19. Apologies for slightly OT.

    This comment is not about the linked study specifically, even though it says this in part,

    “… The wood density of tree rings is a widely used parameter to study past temperature changes. Despite wood density being widely used and considered excellent for this type of research, deriving comparable measurements at different laboratories and using a variety of techniques are proving challenging. …..The review is also complemented with a careful comparison of a set of new measurements derived at 17 laboratories, using several different techniques. We find that there are substantial differences in measurements performed among laboratories…..”

    This study is emblematic of a lot of efforts by climate scientists to understand the past. In paragraph after paragraph here they chronicle the limitations and difficulties in understanding that past. For most of the studies in every aspect of climate science the professionals are forthright about the challenges that confront their field.

    This is not a criticism of the working scientists of this paper or the thousands of others who are trying to understand the climate. It’s a criticism of the clowns, wannabes, activists and climate hustlers who are taking advantage of the gullibility of the public for their own purposes to make it appear that all is cut and dried and the exam has been aced. It hasn’t been. I think this paper is a perfect metaphor for the inherent uncertainties in climate science.

    • I’m not an expert in tree ring analyses, however: your linked study is about wood denstiy measurements. In MBF23 they use isototope analyses. Don’t know if the found issues in your linked paper also hold for the used method there.

      • Frank

        Yes, I was aware of that. I started out researching the uncertainties of tree rings but found this paper. What is interesting to me, and the reason I made a comment about it, is how many issues there are surrounding the use of this method of research. I’m not criticizing the paper or authors. To the contrary, they are upfront about the challenges. Most papers about a lot of aspects of climate science readily identify the levels of unconstrained factors.

        My main interest was that the favored narrative glosses over the many problems in sorting out what the facts are. As I was reading this paper it reminded me of some similar generic issues with satellite data on SLR. Reason for caution on any conclusions.

        I’m still going to make another comment, also slightly OT, but along the lines that we just don’t know as much as we think we know.

        I enjoyed reading this paper since it covered some technical issues I wasn’t remotely aware of.

      • CKid: D’accord about uncentainty in data and overconfidence in conclusions. Judy would apploud. :-) This was the main message of our comment: Take care!

  20. I believe the problem of not understanding the limitations of statistical analysis began in the late 60s early 70s when Spectral Dynamics came out with spectral analyzers and engineers began relying on computers to process data. Prior to that it required selecting filters, sweep generators, multipliers, etc. and understanding the limitations. Now all you need is a computer, no training, and a finger to push a button.

  21. The basic problem of using tree ring width and MXD for temperature proxies arises from the practice of selecting proxies, from the many available, post facto and not having criteria for selection ex ante and using all proxies thus selected. I would suspect that the same problem arises from using trees to proxy available moisture for growth.

    Using all tree ring and MXD data available for temperature proxies would I suspect give an very uninformative flat line response and even when confined to locals where precipitation is not expected to interfere with the temperature response.

    In one of Mann’s temperature reconstructions an MXD proxy was truncated in the historical period because their densities did not show the expected temperature increases.

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  27. I wanted to know more about the uncertainties of Dendrochronology so I read a few papers, including a nice discussion of the fundamentals involved

    and a few others that covered the subjectivity (Buntgen, 2021), Dendrochronology and radiocarbon dating (Pearson, 2022) and limitations of tree ring chronologies (Couhlthard).

    I also read the paper by Cook, 2011 which spoke about the complexities and uncertainties about the research in this field.

    More than the uncertainties, the discussion of emergent properties concepts was of special interest to me.

    “:It’s now so clear that every time you have a more complex system, new qualities appearthat you could not have predicted from the components.” Ernst Mayr 1997

    That paper led to this paper “The Theory of Everything”

    “ The emergent physical phenomena regulated by higher organizing principles have a property, namely their insensitivity to microscopics, that is directly relevant to the broad question of what is knowable in the deepest sense of the term.”

    “ The fact that the essential role played by higher organizing principles in determining emergent behavior continues to be disavowed by so many physical scientists is a poignant comment on the nature of modern science. To solid-state physicists and chemists, who are schooled in quantum mechanics and deal with it every day…….the existence of these principles is so obvious that it is a cliché not discussed in polite company. However, to other kinds of scientist the idea is considered dangerous and ludicrous, for it is fundamentally at odds with the reductionist beliefs central to much of physics. But the safety that comes from acknowledging only the facts one likes is fundamentally incompatible with science. Sooner or later it must be swept away by the forces of history.”

    “ We have succeeded in reducing all of ordinary physical behavior to a simple, correct Theory of Everything only to discover that it has revealed exactly nothing about many things of great importance.”

    The point of all this? Sometimes our hubris should be checked at the door. It’s always nice to be reminded that we don’t know as much as we think we know.

    • Try McShane und Wyner their original paper, the comments to it and the rejoinder:–A-statistical-analysis-of-multiple-temperature-proxies/10.1214/10-AOAS398REJ.full

      In my opinion a fun read and this discussion shows a clear and very devastating critique of the methods of M. E. Mann and other big names at that time.. It also showcasing the very entertaining helplessness when these scientists try to argue against a mathematician..
      I actually contacted the main author a few years later asking if in his opinion more recent publication are better.
      His wording was very careful, but I understood him, that his critique is still fully valid for most recent publications in this field.

      • Thanks for the link. It’s difficult to be anything but critical, cynical and skeptical about a catastrophic future when each time a deep dive into the science reveals major issues with certainty. One of the authors in a link I provided admitted to having to guess. Can’t blame them. But how many in the public know some of this is just that, guessing.

  28. Juerg Brechbuehl, Biologist

    I find it extremely disturbing, that such statistical blunder ist not detected and corrected in peer review. I don’t know how often this happens in climate sciences.

    However, as a vegetation ecologist I find it very common, that publications in journals do not hold what they promise in their title and abstract. Five out of six papers do not properly answer the questions asked in the introduction. It is extremely common for the statistical methods not to be adequate.

    The result in my line of work is an enormous waste of working hours spent on sorting out the enormous amounts of junk from all the published research.

    • Hey, but it’s a living.

    • Juerg Brechbuehl wrote:
      I find it extremely disturbing, that such statistical blunder ist not detected and corrected in peer review. I don’t know how often this happens in climate sciences.

      As Mattias Desmet points out in Chapter 1 his book The Psychology of Totalitarianism, “in economics research, replication failed about 50 percent of the time, in cancer research about 60 percent of the time, and in biomedical research no less than 85 percent of the time. The quality of research was so atrocious that the world-renowned statistician John Ioannidis [in 2005] published an article bluntly entitled Why Most Published Research Findings Are False.”

      Ioannidis summarized the situation nicely in one of his subheads, “Most Research Findings Are False for Most Research Designs and for Most Fields”!

      And I would add that today, “climate science” is probably in the worst shape of all fields by far. It is basically a total joke at this point, which is why virtually the only serious scientists in this field today are retired, emeritus, or otherwise not beholden in any way to the evil communist / academic / government-funded-and-run cabal which funds, supports, publishes, and promotes almost exclusively garbage and purposeful lies.

      • Juerg Brechbuehl, Biologist

        The issue is, that academic research that can not be reproduced inflicts enormous cost on the industrial research and development department, because they spend terrifying amounts of money sorting out what can be used and what not.

        I remember a guest lecturer from Novartis in Basel (Switzerland). In their search for new drugs, they sift throug academic papers. Whenever they find a promising mechanism to attac a human disease, they hand it into their own lab in order to reproduce the findings from academic research. They found that five out of six studies in life sciences can not be reproduced. This one company literally spends billiongs each year just on sorting out the trash from academic research.

        Now I imagine what cost is inflicted on us taxpayers when goverment decisions are based on defective scientific findings!

        Personally, as an ecologist with a focus on nature protection, I fear the worst for the reputation of my field when the public and the mainstream press detect how much fake there is in climate science.

      • “ They found that five out of six studies in life sciences can not be reproduced.”


        After reading the comments by Jonathan and Juerg, my dwindling confidence in the research world is dropping even more quickly.

        I don’t really want to be a sourpuss about academia but it’s hard not to be. It seems every time I turn around I find another reason to be skeptical about the end of the world because of CAGW.

        Thanks for your input.

    • Re “I find it very common, that publications in journals do not hold what they promise in their title and abstract”

      It’s a ramification, symptom, and manifestation of a much much bigger overall reality — living in a society and world where mendacity systemically rules …

      “Separate what you know from what you THINK you know.” — Unknown

  29. Mandy B Freund, et al, also argues that El Niño events have become more ferocious and powerful in recent decades, c. 2019.

    SEE The Hockey Stick graph as the first illustration, from a previous publication in Nature Geosciences.

    This woman is really in the band of the Ruling Class wagon.

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