PHYS/ASTR Colloquium: "What do tree rings tell us about the history of Earth’s climate?" - Dr. Zan Stine (Professor, SF State U)

Physics and Astronomy Colloquium

What do tree rings tell us about the history of Earth’s climate?

Most of our records of Earth’s surface temperature in the 1000 years preceding widespread thermometer measurements come from measurement of annual variation in the width of tree rings. Tree growth responds to many things other than local climate variation, and received techniques average over many records in an attempt to minimize other influences. Here we present an alternative approach for recovering climate signals from tree rings based on an ecological principle known as Liebig’s Law of the Minimum. We demonstrate that this method results in improved recovery of temperature and moisture climate history across a global dataset. Such local operation of Liebig’s Law implies that standard methods for compositing tree-ring records into climate reconstructions introduces a temperature-dependent bias. Reconstruction of Arctic-wide temperature using a reconstruction method that takes advantage of the law of the minimum increases the squared cross-correlation with instrumental records from 0.14 to 0.42, eliminating the so-called "divergence problem" in tree-ring density reconstructions of arctic temperature.