16 S. Solomon, G. K. Plattner, R. Knutti, and P. Friedlingstein, "Irreversible Climate Change Due to Carbon Dioxide Emissions,"Proceedings of the National Academy of Science of the United States of America (PNAS) 106, no. 6 (10 February 2009): 1704–1709. See www.pnas.org/content/early/2009/01/28/0812721106.full.pdf.