Low-frequency Temperature Variations from a Northern Tree Ring Density Network

Fig.1 Locations of Proxy Data and Region Definitions Low-frequency Temperature Variations from a Northern Tree Ring Density Network
Journal of Geophysical Research,
106 D3 (16-Feb-2001) pp. 2929-2941

K. R. Briffa*, T. J. Osborn, F.H. Schweingruber, I.C. Harris, P. D. Jones, S.G. Shiyatov, and E.A. Vaganov.

*Climatic Research Unit, University of East Anglia, Norwich NR4 7TJ, UK.

*To whom correspondence should be addressed.
E-mail: k.briffa@uea.ac.uk


ABSTRACT:
We describe new reconstructions of northern extratropical summer temperatures for nine subcontinental-scale regions and a composite series representing quasi "Northern Hemisphere" temperature change over the last 600 years. These series are based on tree ring density data that have been processed using a novel statistical technique (age band decomposition) designed to preserve greater long-timescale variability than in previous analyses. We provide time-dependent and timescale-dependent uncertainty estimates for all of the reconstructions. The new regional estimates are generally cooler in almost all precalibration periods, compared to estimates obtained using earlier processing methods, particularly during the 17th century. One exception is the reconstruction for northern Siberia, where 15th century summers are now estimated to be warmer than those observed in the 20th century. In producing a new Northern Hemisphere series we demonstrate the sensitivity of the results to the methodology used once the number of regions with data, and the reliability of each regional series, begins to decrease. We compare our new hemisphere series to other published large-regional temperature histories, most of which lie within the 1s confidence band of our estimates over most of the last 600 years. The 20th century is clearly shown by all of the palaeoseries composites to be the warmest during this period.


Plate 2. Reconstructions of nine regional April-September temperature series

Plate 2. Reconstructions of nine regional April-September temperature series, all with decadal smoothing. Observed temperatures are shown in red, Hugershoff-standardized reconstructions are shown in dark blue, age-banded reconstructions are shown in black (with 1 and 2 sigma errors indicated by the yellow and orange shading). The vertical red lines in some reconstructions indicate how far back the age-banded reconstructions are considered to be reliable (see text for further details). Download the data from this figure and data description from the WDC Paleo archive.


Plate 3. Comparison of six large-scale reconstructions

Plate 3. Comparison of six large-scale reconstructions, all recalibrated with linear regression against the 1881-1960 mean April-September observed temperature averaged over land areas north of 20N. All series have been smoothed with a 50-year Gaussian-weighted filter and are anomalies from 1961-1990 mean. Observed temperature for 1871-1997 (black) from Jones et al. (1999); circum-Arctic temperature proxies for 1600-1990 (yellow) from Overpeck et al.(1997); northern hemisphere temperature proxies for 1000-1980(red) from Jones et al. (1998); global temperature and non-temperature proxies for 1000-1980 (purple) from Mann et al. (1998, 1999); and three northern Eurasian tree ring width chronologies for 1000-1987 (green) from Briffa and Osborn (1999); 13 Northern Hemisphere temperature proxies for 1000-1987 (orange) from Crowley and Lowery (2000), but excluding the two low-resolution records used by them; and the NH reconstruction from the age-banded analysis presented in this study for 1402-1960 (blue), bounded by the 1 and 2 sigma standard errors. Download the data from this figure and data description from the WDC Paleo archive.


To read or view the full study, please visit the AGU website. It was published in Journal of Geophysical Research 106 D3 (16-Feb-2001) 2929-2941.

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