John E. Kutzbach

2006 Roger Revelle Medal Winner

Center for Climatic Research, University of Wisconsin, Madison

John E. Kutzbach was awarded the Roger Revelle Medal at the AGU Fall Meeting honors ceremony, which was held on 13 December 2006 in San Francisco, Calif. The medal recognizes outstanding contributions in atmospheric sciences, atmosphere-ocean coupling, atmosphere-land coupling, biogeochemical cycles, climate, or related aspects of the Earth system.


John Kutzbach’s career contributions to climate science are broad and deep. After a distinguished early career in atmospheric sciences, he shifted into paleoclimate during the 1970s. His subsequent research used general circulation models to explore several problems, including insolation and icesheet forcing of regional climates during the last deglaciation and in the late Holocene, the megamonsoon climates on the supercontinent Pangaea, and the climatic impacts of uplift of Tibet. These and other studies are characterized by an impressive economy of design, clarity of interpretation, and depth of insight into the operation of the climate system. Together, this body of work forms a large part of the framework of our current understanding of past climates.

One contribution stands out above all: John’s 1980 hypothesis on orbital forcing of monsoons. Prior radiocarbon dating had discredited the ‘glacial-pluvial’ idea that ice sheets caused southward shifts of moist westerly winds into the tropics and produced glacial climates wetter than today. In 1981, John proposed a simple but elegant alternative: that the overhead Sun accounts for these wetter intervals. He invoked the same mechanism that produces wet summer monsoons today—strong summer insolation heating of the land, but operating at higher levels in the past because of greater solar radiation levels every 22,000 years.

This hypothesis has been widely tested in time and space. Dozens of general circulation model experiments have confirmed that higher summer insolation drives stronger monsoons in the northern tropics. The hypothesis has also been confirmed by an array of ground-truth evidence: lake levels in Africa and Southeast Asia, carbon-rich sapropels in the Mediterranean, oxygen-isotopic data from caves in China, and methane variations in Antarctic ice cores. Isotopic data from speleothems in Brazil also show 22,000-year changes in monsoon strength, but opposite in phase to those in the north, just as John’s hypothesis predicts.

Having passed all these tests, John’s hypothesis deserves to be called a theory. Indeed, his orbital monsoon theory has been more completely verified than the Milankovitch ice-age theory, which is valid to a point but fails to explain the dominance of particular orbital cycles during almost three million years of ice-sheet variations. The orbital monsoon theory is especially relevant to human evolution in the tropics and subtropics over the same interval of time. Scientists studying early human sequences in East Africa use dated volcanic deposits to constrain the general age ranges of the intervals they study but then examine lake-level changes driven by the summer monsoon as a 22,000-year metronome to further tune their timescales.

Those who study past climates love their work and have the continual satisfaction of pushing into new areas of knowledge, in steps large and small. But down deep I think that most of us hope to discover something so important that it dazzles the scientific community and ends up in the textbooks as a form of scientific immortality. John’s orbital monsoon theory has guaranteed him that kind of immortality, and the Revelle Award is further testimony to that fact.



Mr. President, Bill, friends, thank you. I am both humbled and delighted to receive the Roger Revelle Medal. I met Roger Revelle once, at a meeting of the Climate Dynamics Panel and the Climate Research Board of the National Research Council held in Washington, D.C., in the late 1970s. I was new to the affairs of science panels, and Revelle was a wise and senior member of the Climate Board. The Board’s report on “Carbon Dioxide and Climate” was short but very much to the point. Thirty years later, we have the much longer and much more detailed reports on greenhouse gases and climate prepared by the Intergovernmental Panel on Climate Change (IPCC). The encouraging difference between those days 30 years ago, and today, is that now, both here and around the world, concerned citizens are beginning to give this topic the attention it deserves.

There is a long tradition of environmental studies and environmental stewardship at the University of Wisconsin, where John Muir was a student and Aldo Leopold was a professor. I am proud to be a small part of that tradition and to have had the privilege of digging deep into the amazing processes and forces that bring about climate change: changes in Earth’s orbit, changes in elevation of mountains and plateaus, changes in greenhouse gases, and changes in position of the continents. And, through work with colleagues, I’ve enjoyed being part of an interdisciplinary tradition, synthesizing information from many disciplines: geology, geochemistry, paleoecology, glaciology, archeology, hydrology, and of course climate.

Why do we use climate models to study past climate? First, we help solve puzzles about Earth’s history. Second, we learn about climate processes and feedbacks that have implications for estimating future climates. If climate models simulate accurately the climate changes of the past, then we have increased confidence that these models can simulate accurately the possible climate changes of the future, changes caused by human activities. The most recent IPCC reports document the accuracy of past climate simulations as a measure of climate model performance.

At the University of Wisconsin, Reid Bryson and Heinz Lettau provided special mentoring that has stuck with me: Reid’s passion for interdisciplinary climate studies; Heinz’s physical insights on all aspects of geophysics. Program managers at the U.S. National Science Foundation and other agencies provided financial support for my research. Gene Bierly got me involved in international aspects of climate research. My closest colleagues in interdisciplinary research, dating from the 1970s, have been Tom Webb, Bill Ruddiman, Warren Prell, Alayne Street-Perrott, and Herb Wright. I owe so much to them. Colleagues at the National Center for Atmospheric Research in Boulder, Colo., helped introduce me to the use of climate models: Warren Washington and Steve Schneider in early years, and also Jerry Meehl and Bette Otto-Bliesner. Faculty at the University of Wisconsin, Madison have encouraged and helped me as well, including John Young and Zhengyu Liu. And undergraduates and graduate students have kept me fresh with questions and ideas.

As many of you know, Gisela and I have enjoyed, for over 40 years, our mutual love of science and history of science, and our long association with the University of Wisconsin. One characterization of university life that we fondly recall came long ago when one of our children answered her second grade teacher’s question—“What does your father do?”—with the confident answer, “He works at the Universe.” Thank you to all of you who have indeed helped me work in the universe of ideas these many years.

—JOHN E. KUTZBACH, Center for Climatic Research, University of Wisconsin, Madison