Past Temperature Variations Inferred from a 400-Year Tree-Ring Chronology from Yukon Territory, Canada

A time series of ring-width indices from 27 cores of 13 white spruce trees (Picea glauca [Moench] Voss) from Yukon Territory shows growth response to summer temperatures and other climatic variables. The correlations with various temperature parameters are high enough that past temperature information can be inferred for the last 400 yr. The highest simple correlation is between tree growth and total degree-days above 100C for June and July. A substantial moisture stress in the trees towards the end of the growing season is also indicated. The chronology shows effects of the Little Ice Age, of the subsequent Northern Hemisphere warming, and of a recent cooling trend. A second timeseries of the first amplitude from a principal component analysis of the ring widths yields a better climatic signal than the time series of ring-width indices. These and other temperature-sensitive trees from near the northern tree line are