Interest in natural and man-made carbon dioxide production is stirred because it resides after formation in critical atmospheric zones. To determine the oncoming “greenhouse” effect, indeed to determine whether there will be a greenhouse effect, investigators have tried to sum up the global carbon cycle. In accounting for the sources and sinks of carbon dioxide produced at the earth's surface, it has been postulated that most of the unbalanced sources can be identified with the earth's biomass and not so much with man's combustion of fossil fuels (Ecol. Monogr., 53, 235, 1983). New figures on the calculated areas of tropical forests suggest otherwise.