The Paleoclimate Reconstruction Challenge

The PR Challenge 2008

Detailed understanding of the full range of annual and seasonal climate variability over the past millennium forms an important basis for the interpretation of the observed record, and for gauging the response of the climate system to various forcings. Using different methods and proxy networks, the climate reconstructions available show general similarity in their depiction of large-scale mean-temperature evolution, particularly at the decadal to centennial timescale.

There are, however, important differences in reconstructions at the interannual and multi-centennial to millennial scale. It is unclear whether these differences 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).

The paleoclimate community needed to establish a protocol for reassessing its methods to rebuild confidence in the reconstruction efforts.

The last millennium Paleoclimate Reconstruction Challenge (PR Challenge) 2008 —run under the auspices of the CLIVAR/PAGES Intersection and co-sponsored by the Electric Power Research Institute (EPRI) — was designed to directly address these concerns and to establish objective reconstruction benchmarks.

The PR Challenge 2008 implementation team consisted of Caspar Ammann, Nicholas Graham, Rosanne D’Arrigo and Thorsten Kiefer.

Read more about the goals, key components and methodology behind the PR Challenge 2008 (PAGES news (2008)16(1):4).

Caspar Amman introduces the PR Challenge at the PAGES 2009 Open Science Meeting > view video

The PR Challenge 2011

Launched in July 2011, the last millennia Paleoclimate Reconstruction Challenge (or PR Challenge) was a model-based venue for experimenting with climate reconstruction methods. It was based on the initial 2008 PR Challenge with some modifications and was designed to engage the scientific paleoclimate community in examining its methods in a common framework for the purpose of evaluating their relative strengths and weaknesses.

A key design element of the challenge was to allow true "apples to apples" comparison of reconstruction methods across identical experimental platforms. The ultimate goal was to improve last two millennia PR methods so that paleoclimate science could offer the best possible information to help understand both natural and anthropogenic climate change.

The challenge was organized around 4 themes. In each theme, a set of long (1,000+ yrs) forced global climate model (GCM) integrations was used to formulate simulated paleoclimate proxy data (pseudo- proxies) and to provide pseudo-instrumental climate data for calibration and examination of reconstruction fidelity. Several different GCM runs provided a range of simulated climate evolutions that presented different reconstruction scenarios. In each theme, the reconstruction method used was at the prerogative of the participants.

Theme 1: Reconstruction of Northern Hemisphere temperature with strongly limited proxy data set.
Theme 2: Reconstruction of Northern Hemisphere temperature and spatial patterns with a richer, but still somewhat limited proxy data set.
Theme 3: Reconstruction of Northern Hemisphere temperature and global spatial patterns using a relatively rich proxy data set.
Theme 4: Reconstruction of spatial drought patterns.

The Paleoclimatology Branch of NOAA's National Climatic Data Center/World Data Center for Paleoclimatology provided the simulated proxy and instrumental data sets for the PR-Challenge and also archived the contributed reconstructions so that they could be cross-compared at:

The PR Challenge 2011 implementation team consisted of Nicholas Graham, Rosanne D'Arrigo, Kevin Anchukaitis, Eugene Wahl, and David Anderson.

The PR Challenge 2011 was sponsored by NOAA's Office of Oceanic and Atmospheric Research/Climate Program Office (Climate Change Data and Detection Program, grant NA08OAR4310732) and the CLIVAR/PAGES Intersection.

Read the announcement (PAGES news (2011) 19(2):71).


NOAA houses the pseudo-proxy and pseudo-instrumental data sets produced for the PR Challenge at:, so that scientists, students,and citizens interested in exploring paleoclimate reconstructions can continue to have access to this set of simulations, which were state-of-the-art and included forward modeling of proxy properties driven by climate variables.