My group’s research uses paleodata to improve our conceptual and physical understanding of climate change on interannual to millennial time scales. Our data extend the observational history of important climate systems and provide new information on the full range of natural variability. We also connect paleodata with climate models to improve understanding and evaluation of both.


We use a combination of modern cave system monitoring and multivariate paleoclimate methods to produce high-resolution reconstructions of past climate. With NSF support, we are making significant headway in the development of climate records from Arizona caves and in understanding how cave records form.  We have collected samples ranging in age from the recent millennium to nearly 275,000 years old. Some of these have been analyzed for stable isotopes, and we are beginning to collect elemental data as well. Stable isotopic analyses of glacial (isotope stage 2-3) samples show significant variations associated with deglaciation and millennial variability similar to patterns seen in the North Atlantic. Holocene and Last Interglacial data indicate a monsoonal response to insolation. We also see substantial multidecadal-multicentury variability over the Holocene. We are developing simple models that can help us identify scales of variability associated with processes internal to caves, vs variability that is likely climatic.

We have been collecting cave dripwater samples for geochemical analysis at multiple sites. Understanding the modern cave systems helps us unravel local cave hydrology and water budgets, and gives us a better understanding of modern climatic controls on speleothem formation to improve paleoclimate interpretations.

At right, recent Ph.D. graduate Toby Ault ascends D’s Climb in Cave of the Bells, to retrieve dripwater samples (above), and graduate student Sarah Truebe logs environmental conditions in the cave (below).

Our cave work is funded by NSF’s Paleo Perspectives on Climate Change program.


Our lab has longstanding experience in developing climate reconstructions from corals. Corals are uniquely valuable sources of information on tropical climate variability: in most of the tropical oceans, instrumental climate records don’t predate the mid-20th century. Our coral work emphasizes understanding how the tropical oceans respond to current and past changes in climate forcing and background conditions.

A major focus of our research is to determine the nature of the tropical Pacific’s response to recent changes in anthropogenic forcing, using multiple geochemical tracers of past climate. We are also developing fossil coral records to extend this view beyond recent centuries.

We are developing new ways to quantify comparisons of coral data with climate models to identify where models and coral data agree and where (and why) discrepancies exist. We work to extract temporal and spatial patterns of variability from large coral datasets. And we are exploring new geochemical tracers of reef environments in coral skeletons. At right, former graduate student Dr. Diane Thompson (U. of Arizona) works with Dr. Sandy Tudhope (Univ. Edinburgh) to sample modern and fossil corals in Galapagos.

Our Pacific work is funded by the NSF – most recently in Galapagos and Australia. We’ve also collected samples in Venezuela, East Africa, Kiribati, and the Marquesas.  


Drought is among the most costly and devastating of climate extremes. Most semiarid regions of the world, including our Southwest home, are expected to become even drier as climate warms, Moreover, we know from paleodata that prolonged (multidecadal) droughts, unlike any witnessed in the past century, occurred throughout the past millennium. What is the likelihood of a “megadrought” in the coming decades? Do climate models simulate megadroughts as a consequence of either natural variations or of greenhouse gas increases? We are exploring these questions by comparing the statistics of modeled drought with that observed in paleorecords. This work is a broad collaboration that includes colleagues at the University of Arizona, NCAR, and other institutions.

Our drought risk work is funded by NSF’s Climate and Large-Scale Dynamics program.