IMPROVING THE REALISM OF MODELING AGRONOMIC ADAPTATION TO CLIMATE CHANGE: SIMULATING TECHNOLOGICAL SUBSTITUTION WILLIAM E. EASTERLING 1 , NETRA CHHETRI 1 and XIANZENG NIU 2 1 Department of Geography, The Pennsylvania State University, University Park, PA 16802, U.S.A. E-mail: easter@gis.psu.edu 2 Department of Crop and Soils Science, The Pennsylvania State University, University Park, PA 16802, U.S.A. Abstract. The purpose of the paper is to propose and test a new approach to simulating farmers’ agronomic adaptation to climate change based on the pattern of adoption of technological innova- tion/substitution over time widely described as a S-shaped (or logistic) curve, i.e., slow growth at the beginning followed by accelerating and then decelerating growth, ultimately leading to saturation. The approach we developed is tested using the Erosion Productivity Impact Calculator crop model applied to corn production systems in the southeastern U.S. using a high-resolution climate change scenario. Corn is the most extensively grown crop in the southeastern U.S. The RegCM limited area model nested within the CSIRO general circulation model generated the scenario. We compare corn yield outcomes using this new form of adaptation (logistic) with climatically optimized (clairvoyant) adaptation. The results show logistic adaptation to be less effective than clairvoyant adaptation in ameliorating climate change impacts on yields, although the differences between the two sets of yields are statistically significant in one case only. These results are limited by the reliance on a single scenario of climate change. We conclude that the logistic technique should be tested widely across climate change scenarios, crop species, and geographic areas before a full evaluation of its effect on outcomes is possible. 1. Introduction In this research, we investigate how the procedure used by modelers to simulate adaptation to the impacts of climate change influences outcomes. The purpose of the paper is to propose and test a new approach to simulating farmers’ agronomic adaptation to climate change based on a well-known model of the adoption of technological innovation and technological substitution. Although economics and other social factors influencing adaptation are not considered, we assert that the approach is a robust test of the effect that the timing of adaptation, relative to the pace of climate change, has on outcomes. The approach is guided by the consider- able literature on varying rates at which individual decision makers in a population adopt new innovations or make technological substitutions (discussed by Ruttan, 1996). According to that literature not all farmers are likely to adopt changes in their operations in response to climate change at the same time. Some will adopt at the earliest indications of climate change, a great many will wait to see what others Climatic Change 60: 149–173, 2003. © 2003 Kluwer Academic Publishers. Printed in the Netherlands.