AGRICULTURAL ECONOMICS Agricultural Economics 45 (2014) 85–101 Agriculture and climate change in global scenarios: why don’t the models agree Gerald C. Nelson a,b, ∗ , Dominique van der Mensbrugghe c , Helal Ahammad d , Elodie Blanc e , Katherine Calvin f , Tomoko Hasegawa g , Petr Havlik h , Edwina Heyhoe d , Page Kyle f , Hermann Lotze-Campen i , Martin von Lampe j , Daniel Mason d’Croz a , Hans van Meijl k , Christoph M ¨ uller i , John Reilly e , Richard Robertson a , Ronald D. Sands l , Christoph Schmitz i , Andrzej Tabeau k , Kiyoshi Takahashi g , Hugo Valin h , Dirk Willenbockel m a International Food Policy Research Institute, Washington, DC 20006, USA b University of Illinois, Urbana-Champaign, Champaign, IL 61801, USA c Agricultural Development Economics Division, Food and Agriculture Organization of the United Nations, I-00153 Rome, Italy d Australian Bureau of Agricultural and Resource Economics and Sciences, Canberra, ACT 2601, Australia e Joint Program on the Science and Policy of Global Change, Massachusetts Institute of Technology, Cambridge, MA 02142, USA f Joint Global Change Research Institute, Pacific Northwest National Laboratory, College Park, MD 20740, USA g National Institute for Environmental Studies, Center for Social and Environmental Systems Research, Tsukuba, Ibaraki, 305-8506, Japan h Institute for Applied Systems Analysis, Ecosystems Services and Management Program, A-2361 Laxenburg, Austria i Potsdam Institute for Climate Impact Research, 14473 Potsdam, Germany j Trade and Agriculture Directorate, Organisation for Economic Cooperation and Development, 75775 Paris, Cedex 16, France k Agricultural Economics Research Institute (LEI), Wageningen University and Research Centre, 2585 DB, The Hague, The Netherlands l Resource and Rural Economics Division, Economic Research Service, US Department of Agriculture, Washington, DC 20250, USA m Institute of Development Studies, University of Sussex, Brighton BN1 9RE, United Kingdom Received 31 January 2013; received in revised form 8 August 2013; accepted 31 August 2013 Abstract Agriculture is unique among economic sectors in the nature of impacts from climate change. The production activity that transforms inputs into agricultural outputs involves direct use of weather inputs (temperature, solar radiation available to the plant, and precipitation). Previous studies of the impacts of climate change on agriculture have reported substantial differences in outcomes such as prices, production, and trade arising from differences in model inputs and model specification. This article presents climate change results and underlying determinants from a model comparison exercise with 10 of the leading global economic models that include significant representation of agriculture. By harmonizing key drivers that include climate change effects, differences in model outcomes were reduced. The particular choice of climate change drivers for this comparison activity results in large and negative productivity effects. All models respond with higher prices. Producer behavior differs by model with some emphasizing area response and others yield response. Demand response is least important. The differences reflect both differences in model specification and perspectives on the future. The results from this study highlight the need to more fully compare the deep model parameters, to generate a call for a combination of econometric and validation studies to narrow the degree of uncertainty and variability in these parameters and to move to Monte Carlo type simulations to better map the contours of economic uncertainty. JEL classifications: Q10, Q11, Q16, Q21, Q54, Q55 Keywords: Climate change impacts; Economic models of agriculture; Scenarios ∗ Corresponding author. Tel.: +1-217-390-7888. E-mail address: nelson.gerald.c@gmail.com (G. C. Nelson). Data Appendix Available Online A data appendix to replicate main results is available in the online version of this article. 1. Introduction Agriculture is unique among economic sectors in the na- ture of impacts from climate change. Its production processes involve direct use of weather inputs (solar radiation available to the plant, temperature, and precipitation). Climate change C  2013 International Association of Agricultural Economists DOI: 10.1111/agec.12091