A pointer to the Paleoclimate Reconstruction Challenge

In early 2008, Caspar Ammann published a short note in the PAGES news. It called for and provided an outline for efforts to (re)assessing the methods for paleoclimate reconstructions: the Paleoclimate reconstruction challenge (PR challenge) organized by Ammann, Nick Graham, Rosanne D’Arrigo and Thorsten Kiefer.

The re-assessment appeared necessary, since it was/is unclear whether differences in the various reconstructions

“result from the selection of specific proxy networks, the potential inability of the included proxies to resolve information at all timescales, or the algorithms themselves (National Research Council, 2006).”

Ammann (2008) named as main goal of the PR challenge

“to document how much of the true climate can be described with the combined set of reconstruction results, to determine which aspects of the overall or regional climate are captured well, and whether important elements are being missed.”

The idea was to coordinate the exchange of (pseudo-)proxy data from state of the art climate simulations and the reconstructed results via the NOAA World Data Center to allow for the comparison of the various methods within a common framework. However, it took more than three years, before Nick Graham and Eugene Wahl in 2011 announced the start of the pseudo-proxy data (again in the PAGES news). The underlying model simulation data was from the COSMOS simulations for the last millennium by Johann Jungclaus et al. (2010) and Caspar Ammann’s Millennium simulation (Ammann et al., 2007). The pseudo-proxies were calculated as pseudo-tree-ring-widths with the “VS-Lite” tree growth model of Suz Tolwinski-Ward et al. (2010).

Four themes were presented, three of which were intended to assess how the number and the spatial coverage of the proxies affected the skill and the quality of the reconstructions for northern hemisphere mean temperature and the spatial fields for northern hemisphere and global temperatures. The fourth theme is meant to explore similar topics but for drought. At this point the PR challenge team consisted of Nick Graham, Rosanne D’Arrigo, Kevin Anchukaitis, Eugene Wahl, and David Anderson, of which Graham and Anchukaitis signed responsible for the pseudo-proxy data in the database.

As far as I can see, no group has so far participated in the challenge, i.e. the challenge so far remains unanswered. This is a pity from my point of view but may be explained by the PAGES-2K effort and the IPCC AR5 procedures. This implies that the challenge may now spur some method intercomparisons; a hope that is supported by the (subjectively perceived) increased interest in the forward modelling of tree-ring proxies for reconstruction-method intercomparison articulated at the Madrid 2K-reconstruction-simulation-intercomparison workshop.

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