Yamal and Polar Urals: a research update

1: Why we didn’t use the Polar Urals “update”

We have been criticised for not archiving the Polar Urals “update” data. The “update” data were in fact archived at the ITRDB thirteen years ago. We have been criticised for not publishing an updated Polar Urals chronology using the updated data (and accused of worse here). The supposed reason for our decision not to do this was that the ‘update’ does not support our supposedly desired message of unprecedented modern warmth (because they appear to suggest that tree growth rate was greater during earlier times including the medieval period; Figure 2b, compare purple and black lines).

However, as reported in BEA13, it turns out that during the medieval period these Polar Urals “updates” are dominated by samples taken from the root collars of trees. Ring widths measured in such root-collar samples tend to be systematically larger than equivalent rings measured higher in the boles (stems) of the same trees. The reason for larger tree-ring widths during medieval times in the Polar Urals “updates” is now clear: it is because more samples were from the root collar with their inherently wider rings. Interpreting this as evidence for warmer temperatures is wrong.

Conclusion: the so-called “Polar Urals update” chronology is severely biased and should not be used as evidence of past changes in temperature; nor should our critics present it as evidence that we had committed scientific fraud by failing to publish a chronology using these data.

2: The Yamal record was not biased by omitting data

CRU has been accused of deception by presenting a Yamal tree-ring chronology biased by the omission of otherwise suitable data. A particular theme, originating again from ClimateAudit, is that tree-ring data from Khadyta River had not been used and would have dramatically altered the character of the chronology – and the NH temperature reconstructions that used the Yamal chronology – if these data had been used (Figure 2b, compare blue and black lines).

As reported in BEA13, through collaboration with our Russian colleagues who have extensive knowledge of tree-rings in this region, we have learnt that the Khadyta River site has problems related to the particular site conditions that differ from other sites in this region, and maybe influenced by changing permafrost. Certainly the trees have reduced growth and appear to be unhealthy, and some even dying. Thus the Khadyta River data that some claimed as being more representative than the data we used turn out to have a common signal that is inconsistent with the majority of site chronologies in this region. They could potentially bias the Yamal chronology had they been included and so for this reason we excluded these data from the main analysis in the new paper.

Conclusion: claims of a deceptive and biased Yamal chronology turn out to rely on outlier data that should be omitted; our new research, based on a greatly expanded dataset, supports the finding that tree-growth (and inferred summer temperature) in this region are likely greater in the last 100 years than for any previous century in the last 2000 years.

3: We did not withhold a combined Yamal and Polar Urals chronology

Separately, some of our incomplete and unpublished work on the Yamal and Polar Urals tree-ring data has been the subject of multiple requests under UK FOI/EIR legislation. (See this previous post for background). To be clear, this was not a request for the raw data that we were using in this area of northern Russia – the raw data were and are freely available. Instead, the request was for a tree-ring chronology that formed part of work that was, at the time, still ongoing.

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