Gary Funkhouser

Twentieth-century summer warmth in northern Yakutia in a 600-year context

We report unusual twentieth-century early-summer warmth recorded by larch tree-rings at the north ern tree-line in far northeastern Eurasia (Yakutia). The tree-ring series are strongly replicated and well suited to the detection of fluctuations on interannual to century timescales. They are strongly correlated with local instrumental temperature data. Mean early-summer temperature in the twentieth century significantly exceeds that of any period of the same length since ad 1400. A century-scale trend, which commences in the midnineteenth century, is superimposed on interannual and decadal fluctuations, for example a marked cooling since 1978. While many of the 20 coolest early summers in the reconstruction occur within a few years after major explosive volcanic eruptions from low-latitude volcanoes, several of the 20 warmest early summers followed major explosive eruptions from high-latitude volcanoes.

Frequency-dependent climate signal in upper and lower forest border tree rings in the mountains of the great basin

We examine the relationships, over the past millennium, between tree-ring chronologies from long-lived pines at their upper and lower limits in four mountain ranges in and near to the semi-arid Great Basin. We confirm LaMarches (1974a) finding, based on a single mountain range in this same region, and a much shorter period of comparison, that climate responses are frequency dependent. In particular, upper and lower forest border chronologies in each mountain range are strongly coherent at decadal periods and less, with particular strength in the 3–7 year band. Thisvariability is significantly correlated with precipitation. Conversely, we find no significant correlation between the low frequency fluctuations (60 years and longer) of upper and lower forest border chronologies. There are, however, significant correlations between the low-frequency components of the upper forest border chronologies in the different ranges, consistent with their containing a growing season temperature signal on decadal time scales. The four upper forest border chronologies all show an anomalous increase in growth since the late 19th century, and an apparent change in climate control of ring growth.