It seems that Columbia’s Rosanne D’Arrigo thinks Mann’s tree ring study isn’t representative proxies for volcanic eruptions, nor good for dendrochronology, though Mike Mann seems to think so. This Twitter interchange via Alexandra Witze from the AGU Chapman Conference on Volcanism and the Atmosphere in Selfoss, Iceland 10–15 June 2012 tells the story:
And Witze goes on to say that there’s a rebuttal paper in the works, but Mann is not amused. Mann responds (TRW means Tree Ring Width):
I still don’t think Dr. Mann has a basic handle on Liebigs Law.
Its seems a rebuttal is in the works
(h/t to Tom Nelson)
Here is what the Twitter fight is all about, this paper published in February:
Abstract from Nature Geoscience here
Underestimation of volcanic cooling in tree-ring-based reconstructions of hemispheric temperatures
- Received 14 June 2011 Accepted 11 January 2012 Published online05 February 2012
The largest eruption of a tropical volcano during the past millennium occurred in AD 1258–1259. Its estimated radiative forcing was several times larger than the 1991 Pinatubo eruption1. Radiative forcing of that magnitude is expected to result in a climate cooling of about 2 °C (refs 2, 3, 4, 5). This effect, however, is largely absent from tree-ring reconstructions of temperature6, 7, 8, and is muted in reconstructions that employ a mix of tree-rings and other proxy data9, 10. This discrepancy has called into question the climate impact of the eruption2, 5, 11.Here we use a tree-growth model driven by simulated temperature variations to show that the discrepancy between expected and reconstructed temperatures is probably an artefact caused by a reduced sensitivity to cooling in trees that grow near the treeline. This effect is compounded by the secondary effects of chronological errors due to missing growth rings and volcanically induced alterations of diffuse light. We support this conclusion with an assessment of synthetic proxy records created using the simulated temperature variations. Our findings suggest that the evidence from tree rings is consistent with a substantial climate impact2, 3, 4, 5 of volcanic eruptions in past centuries that is greater than that estimated by tree-ring-based temperature reconstructions.