The Truth Sometimes Will In

It’s not always true that “the truth will out”.

Scott Johnson has a nice article in Ars Technica describing the outlines of a real scientific controversy.

Many of the trees used for temperature reconstructions grow at high altitudes, where their growth is limited by temperature. For some, a large, sudden cooling could push the tree below the minimum temperature threshold for growth. …

By using a simple model of tree ring growth that simulates artificial records, Mann and his colleagues found that taking this into account could produce hypothetical reconstructions that better matched the climate model predictions.

Many of the dendrochronologists who compile these tree rings records took offense to the idea that they hadn’t noticed such an important error. After all, researchers always cross-check tree ring records with other trees in the area to look for issues like skipped rings and growth variation between individual trees. …

In the published reply by Mann, Fuentes, and Rutherford … the researchers explain why they think it’s possible that missing rings could have slipped past dendrochronologists, despite their cross-checking. They believe that the cold temperatures associated with the eruption would prevent any of the trees in a region from growing. To detect the missing ring, the trees would have to be cross-checked with trees sufficiently far away to have experienced warmer temperatures.

And Ars actually provides DOIs! Nature Geoscience, 2012. DOI: 10.1038/ngeo1394, 10.1038/ngeo1645, and 10.1038/ngeo1646 . Hello, the rest of the world! This is how you do it!

Based on the report itself, I am leaning to Mike’s side. Of course, we don;t really know whether “To the dendrochronologists who submitted their comment, that’s irrelevant until there’s solid evidence for it (which they don’t believe will turn up).” is fair reporting (there’s a possibility of a fair amount of projection here). That position as stated makes no sense. If a plausible improvement in the data model moves the data into closer agreement with a process model, that actually is evidence. The failure to understand this is at the root of the systematic undervaluing of “models”, generally expressed with a sneer by people who don’t like a particular result. But it’s all models.

Even an old-fashioned mercury thermometer is a model. It’s a proxy, not a temperature, whose parameters are expressed by lines marked on a glass tube.

But I’m also struck by the overconfidence in the “truth will out” conclusion.

Eventually, if Mann’s hypothesis is found to be correct, we’ll be able to improve the temperature reconstructions. If, instead, the dendrochronologists are vindicated, that could lead to a different understanding of what the discrepancies mean. Since this is a scientific debate, the data will get the last word—and, right now, the data aren’t in yet.

Well, probably. I suppose we can think of some feasible tests in this case.

But the world needs to understand that science is not all-powerful. In an email exchange, John Mashey quotes the famed applied mathematician John Tukey:

‘The combination of some data and an aching desire for an answer does not ensure that a reasonable answer can be extracted from a given body of data.’

In any case, this pretty much should put the kibosh to any lingering suspicion you may have (I lost mine some time ago) that Mike Mann is a hack. This is a pretty creative and courageous hypothesis to be challenging.

I hope the truth in this matter eventually stops inning. But by its nature this is a question that could stay open for a long time.


  1. The controversy is fascinating in and of itself, but it also crystallized just how damnably hard it must be to correlate these tree ring records across large distances.

    It's also worth noting that Mike worked with tree ring records and models for quite a few years before this issue occurred to him.

    A perhaps amusing story: A couple of weeks ago (at Stoat IIRC) there was a persistent denialist commenter making numerous claims supposedly based on inside knowledge from scientists who dislike Mike. S/he had gone on at length about the deficiencies of the volcano paper, and wound up with pointing out that the paper was doubtless just another manifestation of the Mannian conspiracy to suppress late Holocene climate variability. Oops. After I pointed out the contradiction, s/he neglected to make a further comment.

  2. The estimation of long term climatic trends from tree rings is *extremely* problematic as currently conducted, which is a euphemism for "almost completely unreliable". They are NOT trustworthy do to mathematical issues; I am 100% convinced of this. I have an eight part (and growing) series on these issues on my blog and papers in the review process. The first installment of the series is here:

    I encourage people to read the series if possible.

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