Austin American-Statesman: It started with a seemingly off-the-wall question in a 2004 global change biology class at Southwestern University. The discussion was about how increases in carbon dioxide, a contributing cause of global warming, lead to a decline in the amount of proteins in some plants. "How would rising CO2 levels affect the Atkins diet?" asked Holly Allen, then an undergraduate majoring in environmental studies. The Atkins diet, still en vogue then, emphasizes proteins over …