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The United States is a global grain supplier. Agriculture uses 22% of all US transported tonnage with grain being the largest component. Crop mix shifts are an often cited consequence of climate change and such shifts may change the demands grain places on the transport system. Studies also find that climate change could decrease Great Lakes water levels, shorten the duration of ice cover in the winter and alter grain supplies in grain-exporting countries. This study investigates the effects of such phenomena on US grain transportation movements both in volumes and modes. Specifically we examine the effects of possible shifts in: crop production patterns; Great Lakes water levels; winter navigation possibilities; and foreign grain production. We find that crop mix shifts reduce the importance of Lower Mississippi River ports, but increase the role of Pacific Northwest ports, Great Lakes ports and Atlantic ports. We also find a shift from barge to rail and truck transport. Conversely, a longer navigation season or a reduction in Great Lake water levels increases grain shipments to the ports in the Lower Mississippi River. Higher use of Great Lakes ports occurs under a reduction of grain production in European exporting countries that compete with Great Lakes ports. [ABSTRACT FROM AUTHOR]