The likelihood that continuing greenhouse-gas emissions will lead to an unmanageable degree of climate change (1] has stimulated the search for planetary-scale technological solutions for reducing global warming  ("geoengineering"), typically characterized by the necessity for costly new infrastructures and industries . We suggest that the existing global infrastructure associated with arable agriculture can help, given that crop plants exert an important influence over the climatic energy budget [4, 5] because of differences in their albedo (solar reflectivity) compared to soils and to natural vegetation . Specifically, we propose a "bio-geoengineering" approach to mitigate surface warming, in which crop varieties having specific leaf glossiness and/or canopy morphological traits are specifically chosen to maximize solar reflectivity. We quantify this by modifying the canopy albedo of vegetation in prescribed cropland areas in a global-climate model, and thereby estimate the near-term potential for bio-geoengineering to be a summertime cooling of more than 1 degrees C throughout much of central North America and midlatitude Eurasia, equivalent to seasonally off setting approximately one-fifth of regional warming due to doubling of atmospheric CO2 . Ultimately, genetic modification of plant leaf waxes or canopy structure could achieve greater temperature reductions, although better characterization of existing intraspecies variability is needed first.