Malcolm K. Hughes: Regents' Professor of Dendrochronology and Director Emeritus, Laboratory of Tree-Ring Research, University of Arizona is a paleoclimatologist specializing in the use of tree rings and other annual records to reconstruct and understand the past behavior of the climate system on geographic scales from local to global, and from time scales ranging from years to millennia. He has carried out research in Europe, North America, Russia, China, India and the Eastern Mediterranean region. Professor Hughes is a Fellow of the American Geophysical Union and Chair-Elect of the Section on Geology and Geography of the American Association for the Advancement of Science. Thomas W. Swetnam, Professor of Dendrochronology and Director of Laboratory of Tree-Ring Research, University of Arizona, is a forest ecologist and dendrochronologist specializing in the study of forest fires, insect outbreaks, and forest demography and the climatic and human causes of variations in forest ecosystems; graduate training in forestry, watershed management, and dendrochronology at the University of Arizona; has carried out extensive research in western North America, and in areas of South America and Siberia, Russia. Henry F. Diaz is a research climatologist with the Cooperative Institute for Research in Environmental Sciences at the University of Colorado-Boulder. He is a recognized expert on the El Nino phenomenon, modern and paleo-climate changes, climate impacts, and other topics, and has published dozens of scientific journal articles on various topics related to the subject of climatic variations. He has edited several books, on topics such as El Nino, Climate Change and Water Resources, Climate Change in Mountains, and Climate Extremes and Society. He retired from the National Oceanic and Atmospheric Administration (NOAA) in 2007 after a distinguished 33 years career in the federal civil service. Dr Diaz is a Fellow of the American Meteorological Society.