Keith showed great breadth of scientific understanding, creativity, rigor, willingness and ability to collaborate and unflinching intellectual honesty. These attributes are clearly evident in all his work, from his Ph.D. dissertation to the most recent of his more than 130 publications. He has been a central figure in the elaboration and testing of new and improved approaches to dendrochronology in general and to dendroclimatology in particular. Especially indispensable contributions include methods for evaluating common signal strength in tree-ring collections, including Expressed Population Signal (EPS) and Subsample Signal Strength (SSS). Keith also investigated methods of tree-ring standardization based on Gaussian filters, and later the groundbreaking Regional Curve Standardization (RCS) method. His identification of apparent reduced sensitivity of tree-ring records to temperature at high latitudes in recent decades (“divergence”) stimulated much critical examination and improvement in dendroclimatology. Keith's research contributed greatly to the analysis of tree-ring networks on regional to global scales and their use in the rigorously tested reconstruction of climate fields based on the method of ‘Orthogonal Spatial Regression’ (OSR) developed in his thesis. He was at the very forefront of expanding the use of networks of tree-ring chronologies in climate reconstruction across the Northern Hemisphere and as far south as New Zealand.
In making these advances, Keith showed not only willingness and ability to collaborate with colleagues from many countries but also intellectual courage and leadership. This resulted in multiple large-scale climate reconstructions and important advances in understanding of the climate system, its variability in recent millennia and the context of recent and ongoing climate change. Those who had the good fortune to work with Keith know that he carried his talents and achievements with great good grace and humor.
—Contributed by Malcolm K. Hughes, Edward R. Cook, Timothy J. Osborn, Thomas M. Melvin