Agriculture has significantly transformed the face of the planet -- in particular, croplands have replaced natural vegetation over large areas of the global land surface. To cultivate the land, humans take advantage of the resource provided by climate – optimum temperature and precipitation. However, land clearing for cultivation 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 study, we used global 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 land suitability might have occurred. Our study showed that the major changes in suitability occurred in Canada, Eastern Europe, the Former Soviet Union, and Mexico and Central America. Our study also showed that local land cover changes may very likely cause changes in climate elsewhere through changing the general circulation of the atmosphere. Therefore, similar to climate problems related to fossil-fuel emissions, local land use changes have the potential to become a global climate problem. 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.