Many questions remain to be answered regarding the real significance of anthropogenic carbon dioxide as a climate forcing factor and related rising sea level consequences projected by the I.P.C.C. First, there is no incontrovertible evidence to support contentions that pre-industrial carbon dioxide levels were consistently lower than the 380 ppm recorded now. More than 90,000 published measurements carried out between 1812 and 1961 indicate that atmospheric levels were actually rising before the Industrial Revolution. They reached about 440 ppm in 1820, dropped to about 390 ppm by 1855, and rose back to about 440 ppm by 1940.