John Kutzbach

The 2001 Milutin Milanković Medal is awarded to John Kutzbach for his pioneering and outstanding contributions towards the understanding of the response of the climate system to astronomical forcing using three dimensional ocean-atmosphere models.

John E. Kutzbach was one of a small group of individuals who began, in the early 1980’s to use general circulation climate models (GCM) as a tool to explore possible causes of climate change. Over the past twenty years, and with various collaborators, he was focused on four major climatic problems:

1. understanding the role of earth’s orbital variations in causing glacial-interglacial cycles, and monsoon cycles, with an emphasis on the past one hundred thousand years;
2. understanding the role of the uplift of mountains and plateaus in causing major onset of the Asian monsoon systems, and changes in mid-latitude climates, with an emphasis on the past 10 million years;
3. understanding the role of plate-tectonic shifts of the continents in causing major changes of climate, with an emphasis on the period around 250 million years ago – the time of Pangea;
4. understanding the role of future increases in atmospheric concentration of carbon dioxide, and land-use changes, in changing climate, and climate variability.

His studies started with models of limited degrees of freedom (for example, atmospheric models with prescribed ocean and land surface boundary conditions), and advanced to use of coupled atmosphere-ocean models, or models with coupled biospheres, in order to exam feedbacks and biosphere feedbacks. As computers increased in power, he began to conduct studies of climate variability at interannual to decadal time scales. He works in close collaboration with geologists and paleoecologists in order to develop realistic hypotheses for climate change and to test the accuracy of the climate simulations by comparing them to observations; in the process, he helped to develop and nurture strong interdisciplinary collaboration among climate, geological, and ecological sciences. Approximately 100 of his publications relate directly to climate, paleoclimate modeling or model/data comparisons.

All numerical experiments made by John Kutzbach in relationship to the astronomical theory, mountain uplift and tectonics gave him more confidence to finally study the response of coupled atmosphere-ocean models to tropical deforestation and to carbon dioxide increases, including possible changes in the strength and frequency of El Nino and other natural short-term climate oscillations.

John Kutzbach is not only a pioneer in modelling paleoclimate with comprehensive ocean-atmosphere models, he is also a leader who succeeded to build a strong American group of high reputation and to work with many scientists in the world, in particular with Europeans. He is an active member of the Paleoclimate Modeling Intercomparison Project lead by S. Joussaume of Laboratoire des Sciences du Climat et de l’Environnement in Paris and has very recently spent a sabbatical in Jena at the Max Planck Institute for Biogeochemistry.

Response
Dear Prof Berger. Jensen, Colleagues, guests

It is a great honour to receive the Milankovitch medal. I have admired three characteristics of his work that I have also tried to follow. First, Milankovitch tackled broad, interdisciplinary earth science questions. Second, he pioneered using climate models to answer these questions. Third. he sought quantitative explanations for climate change.

In my work I have tried to follow similar paths. First, I have enjoyed collaborations with geologists and ecologists who helped me develop interdisciplinary perspectives —COHMAP. Second, I have used coupled atmosphere-ocean-biosphere models to study climate change. Third. I’ve linked monsoon changes to orbital changes much as Milankovitch linked glacial changes to orbital changes.

On a personal note, I became interested in climate changes exactly 40 years ago when visiting Lascaux in the Dordogne and saw those marvelous paintings of mammoths and bisons. I began to ask what caused those environmental changes so long ago. Then, this topic was mainly of intellectual interest. Now, it is of urgent practical interest because we humans are changing the climate- and studies of the past may provide insights for the future.

So, it is special for me to return to France today, not so far from the Dordogne, to receive this award and to share this moment with Gisela, my wife, and with friends and colleagues who have helped me along the way. Thank you.

John Kutzbach (25 March 2001)