Journal of Climate, vol. 5, no. 7, July 1992

Tree-Ring Density Reconstructions of Summer Temperature Patterns across Western North America since 1600

K.R. Briffa, P.D. Jones, F.H.Schweingruber

Summer half-year (April-September) mean temperatures are reconstructed across western North America between 1600 and 1982. The reconstructions, ultimately in the form of gridpoint anomaly time series, are produced using a principal-components regression technique to relate variability in a network ofup to 53 high-elevation maximum latewood-density chronologies to a number of important temperature principal-component amplitude series. The reconstructions are of good quality over the area between 35° and 55°N but are subject to large uncertainty north of 55°N, particularly prior to 1750. Four regional time series, the average of between two and six gridpoint series - British Columbia and the Pacific Northwest, California, eastern Rockies and northern High Plains, and the Southwest deserts - plus one more-extensive western United States series are presented and described. Examples of individual-year and decadal-mean anomaly maps are illustrated, and the results of preliminary spectral analyses of the regional time series are described.

Quaternary Research 30, 36-52 (1988)

Summer Temperature Patterns over Europe: A Reconstruction from 1750 A.D. Based on Maximum Latewood Density Indices of Conifers

Keith R. Briffa, Philip D. Jones and Fritz H. Schweingruber

Temperature variations over Europe are reconstructed for a 6-month "summer" season from April to September for the period 1750-1850 using a network of maximum latewood density chronologies of coniferous trees. Around 44% of the variance of the whole temperature grid was explained in calibration. Independent verification indicates that over the reconstruction period the explained variance averaged over the whole grid should lie in the range 30 to 35%. The reconstructions are better in the north of the region (about 55% explained temperature variance based on comparison with independent climate data) than in the south (below 20%). The temperature reconstructions indicate cooler summers over Europe from 1812 to 1816 and during the 1830s. The summers of the 1820s were the warmest reconstructed. Decadal variations occur on a regional scale but no similar periods of anomalously cooler of warmer summers occurred between 1750 and 1810 throughout Europe.