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Global climate models (GCM) investigating the effects of land cover on climate have found that replacing extra-tropical forest with cropland promotes cooling. We compared cropland and forest surface temperatures across the continental United States in 16 cells that were approximately 1°×2° using 1km² MODIS land surface temperature (LST) data and land cover from the 0.0009km² National Land Cover Database (NLCD). We found that forest surface temperatures tended to be cooler than cropland surface temperatures. This relationship held for spring, summer, fall, and annually. In winter, cropland surface temperatures were cooler than forest surface temperatures except in the southeastern United States, where forest surface temperatures were also cooler in winter. The difference between cropland and forest surface temperatures was driven by daytime maxima, which tended to be twice as large as differences in nighttime minima. The dominance of daytime maxima was influenced by the degree of continentality. For cells on coastal margins or with a high proportion of inland lakes, differences between cropland and forest nighttime minima tended to be very small. In more continental locations croplands were noticeably cooler at night which often led to insignificant differences between cropland and forest average surface temperatures.
