Feedbacks between agriculture and climate: An illustration of the potential unintended consequences of human land use activities Navin Ramankutty ⁎ , Christine Delire 1 , Peter Snyder 2 Center for Sustainability and the Global Environment (SAGE), Gaylord Nelson Institute for Environmental Studies, University of Wisconsin, 1710 University Avenue, Madison, Wisconsin 53726, USA Received 29 April 2005; received in revised form 21 September 2005; accepted 21 October 2005 Available online 11 July 2006 Abstract Agriculture has significantly transformed the face of the planet. In particular, croplands have replaced natural vegetation over large areas of the global land surface, covering around 18 million km 2 of the land surface today. To grow crops, humans have taken advantage of the resource provided by climate — optimum temperature and precipitation. However, the clearing of land for establishing croplands might have resulted in an inadvertent change in the climate. This feedback might, in turn, have altered the suitability of land for growing crops. In this sensitivity study, we used a combination of land cover data sets, numerical models, and cropland suitability analysis, to estimate the degree to which the replacement of natural vegetation by croplands might have altered the land suitability for cultivation. We found that the global changes in cropland suitability are likely to have been fairly small, however large regional changes in cropland suitability might have occurred. Our theoretical study showed that major changes in suitability occurred in Canada, Eastern Europe, the Former Soviet Union, northern India, and China. Although the magnitude, sign, and spatial patterns of change indicated by this study may be an artifact of our particular model and experimental design, our study is illustrative of the potential inadvertent consequences of human activities on the land. Moreover, it offers a methodology for evaluating how climate changes due to human activities on the land may alter the multiple services offered by ecosystems to human beings. © 2006 Elsevier B.V. All rights reserved. Keywords: land use; land cover; agriculture; climate; modeling 1. Introduction Over the last few decades, numerous studies have highlighted the importance of considering the interactions between terrestrial vegetation and climate (Bonan et al., 1992; Prentice et al., 1992; Woodward et al., 1995; Brovkin et al., 1998; Foley et al., 2003). Climate influences the types of vegetation that can grow in a given location (Holdridge, 1947; Box, 1981; Woodward, 1987). In turn, the vegetation types, by modifying land surface characteristics such as albedo, the partitioning of sensible heat and latent heat, and surface roughness, Global and Planetary Change 54 (2006) 79 – 93 www.elsevier.com/locate/gloplacha ⁎ Corresponding author. Department of Geography, McGill Univer- sity, Room 627, Burnside Hall 805 Sherbrooke St. W., Montreal, QC H3A 2K6, Canada. Tel.: +1 514 398 8428; fax: +1 514 398 7437. E-mail address: navin.ramankutty@mcgill.ca (N. Ramankutty). URL: http://landuse.sage.wisc.edu/~navin/pub/Navin_Ramankutty/ (N. Ramankutty). 1 Current address: Institut des Sciences de l'Evolution (UMR CNRS 5554), Université Montpellier II - pl. E. Bataillon, case postale 61, 34095 Montpellier cedex 05 France. 2 Current address: Department of Atmospheric Sciences, University of Illinois at Urbana-Champaign, 105 South Gregory Street, Urbana, IL 61801, USA. 0921-8181/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.gloplacha.2005.10.005