Advancing North American climate field reconstructions: Data sources, methods development and comparisons

1st PAGES North America-2k Workshop, Flagstaff, USA, 8–10 May 2011

The principal goal of the North America 2k (NAm2k) Working Group (WG) is to synthesize high-resolution, proxy-based climate reconstructions for North America for the past 2000 years. The motivation is to enhance our understanding of the patterns of natural variability of climate in North America and possible forcing mechanisms, and for comparison with high-resolution Earth System Models.

We assembled a group of climate and paleoclimate experts (see for details of members) to provide an initial assessment of our capacity to carry out the task of producing a high-resolution reconstruction of key North American climate variables with at least a decadal resolution. The WG considered the following:

- Identification of the key paleoclimate time series available for analysis.

- Evaluation of available spatiotemporal reconstructions of the key regional climatic parameters (surface air temperature and precipitation) and reconstructions of large-scale circulation modes (e.g., AMO, PDO, ENSO).

- Validation of reconstructions through statistical methods and comparison with existing hemispheric- to global-scale multiproxy based reconstructions and climate model simulations.

The following are the major findings and action items from this workshop:


Figure 1: Central Mexico June Palmer Drought Severity Index (PDSI) correlated across North America, 1950-2003 A) Reconstructed from tree rings, B) Observed. Figure from Stahle et al. (Climate Dynamics, in review), courtesy of Dave Stahle.

1) By far the most numerous climate proxy records for North America are tree-ring data (see e.g., Fig. 1), which are available at annual or better resolution over much of the continent. These records are sensitive to both temperature and precipitation variability. There is an extensive amount of peer-reviewed literature from more than 50 years of climatic reconstruction work that can be used for the NAm2k effort. The North America Drought Atlas (Cook et al. 2004) is currently the most extensive, high-temporal resolution paleoclimate record available for North America. It consists of gridded summer (JJA) Palmer Drought Severity Index values for the past 500–2000 years, with a trend towards longer records in western North America compared to eastern areas.

2) Other proxy records from lakes (e.g., isotopes, varves, chironomids, pollen, charcoal) are available for a number of sub-continental areas, and speleothem proxy records of precipitation are available for selected areas, such as the US Southwest. These records will generally reflect climate drivers for at least the last 2000 years, but with lower temporal resolution (generally) and with more limited spatial coverage than tree ring records. It was agreed that the temporal resolution of the proxy records needed for this activity would be on the order of at least 50 years, with minimum record lengths of 500 years.

3) A first step will be to develop an integrated inventory and archive of paleoclimate records for possible use in the NAm2k climate reconstruction. The goal is also to integrate the available data sets and reconstruction fields with those of the Arctic2k WG. A recommendation was made for the NOAA World Data Center for Paleoclimatology in Boulder, Colorado to become the central repository of data sets used in the NAm2k effort. The metadata could be mirrored with the PAGES 2k metadata archive on the PAGES website section for NAm2k.

4) A sub-working group composed of Scott Anderson, Henry Diaz, Darrell Kaufman, Brian Luckman, Dave Meko, Greg Pedersen, Dave Stahle, Valerie Trouet, Andre Viau and Gene Wahl will work toward the goal of assimilating (blending) the different input data sources and exploring mapping tools.

An analysis and synthesis workshop for the tree-ring chapter of the NAm2k Working Group is being organized, tentatively titled “North American Dendroclimatic Data: Compilation, Characterization, and Spatiotemporal Analysis” led by Valerie Trouet.

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