Dr. Roberts asks, could the U.S. become a grain import nation by the middle of the next century? The trigger for this change, if it occurs, will be the "greenhouse effect" of increased atmospheric carbon dioxide gas coming largely from fossil fuel burning. Dr. Roberts interest in this particular ... Show moreDr. Roberts asks, could the U.S. become a grain import nation by the middle of the next century? The trigger for this change, if it occurs, will be the "greenhouse effect" of increased atmospheric carbon dioxide gas coming largely from fossil fuel burning. Dr. Roberts interest in this particular topic is influenced by an upcoming trip to Russia. Walter Orr Roberts informal series, "Provocations." Each issue consists of provocative comments related to scientific issues that mostly focus on weather, climate the sun, or near space, with the aim of creating a forum for discussion. Show less