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A matter of divergence: Tracking recent warming at hemispheric scales using tree ring data.

Fig. 1. Tree ring based reconstructions of ENH temperatures.

Figure 1. Tree ring based reconstructions of ENH temperatures. The series have been scaled to mean annual land (20-90°N) extratropical temperatures over the 1850-1988 period. DWJ2006: D'Arrigo et al. 2006; ECS2002: Esper et al. 2002; BRF2000: Briffa 2000.
A matter of divergence: Tracking recent warming at hemispheric scales using tree ring data.

Journal of Geophysical Research - Atmospheres
Vol. 112, D17103, doi:10.1029/2006JD008318
11 September 2007.

Rob Wilson1,2, Rosanne D'Arrigo2, B. Buckley2, U. Büntgen3, J. Esper3, D. Frank3, B. Luckman4, S. Payette5, R. Vose6, and D. Youngblut7
1 Grant Institute, University of Edinburgh, Edinburgh, UK
2 Tree-Ring Laboratory, Lamont-Doherty Earth Observatory, Palisades, New York, USA
3 Swiss Federal Research Institute WSL, Birmensdorf, Switzerland
4 Department of Geography, University of Western Ontario, London, Ontario, Canada
5 Centre d'Études Nordiques, Université Laval, Québec, Quebec, Canada
6 National Climatic Data Center, Asheville, North Carolina, USA
7 Department of Geography and Environmental Studies, Carleton University, Ottawa, Ontario, Canada
No current tree ring (TR) based reconstruction of extratropical Northern Hemisphere (ENH) temperatures that extends into the 1990s captures the full range of late 20th century warming observed in the instrumental record. Over recent decades, a divergence between cooler reconstructed and warmer instrumental large-scale temperatures is observed. We hypothesize that this problem is partly related to the fact that some of the constituent chronologies used for previous reconstructions show divergence against local temperatures in the recent period. In this study, we compiled TR data and published local/regional reconstructions that show no divergence against local temperatures. These data have not been included in other large-scale temperature reconstructions. Utilizing this data set, we developed a new, completely independent reconstruction of ENH annual temperatures (1750-2000). This record is not meant to replace existing reconstructions but allows some degree of independent validation of these earlier studies as well as demonstrating that TR data can better model recent warming at large scales when careful selection of constituent chronologies is made at the local scale. Although the new series tracks the increase in ENH annual temperatures over the last few decades better than any existing reconstruction, it still slightly under predicts values in the post-1988 period. We finally discuss possible reasons why it is so difficult to model post-mid-1980s warming, provide some possible alternative approaches with regards to the instrumental target and detail several recommendations that should be followed in future large-scale reconstruction attempts that may result in more robust temperature estimates.
Download data from the WDC Paleo archive:
Northern Hemisphere Tree-Ring-Based Temperature Reconstruction, Text or Excel format.

To read or view the full study, please visit the AGU website.
It was published in Journal of Geophysical Research - Atmospheres, Vol. 112, D17103, doi:10.1029/2006JD008318, 11 September 2007.
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