Tropical deforestation has been responsible, in part, for the increasing concentrations of CO2 in the atmosphere. In 1980, the amount of carbon released to the atmosphere (as CO2) from deforestation was 10 to 50% of the annual emission from fossil fuels. If current trends continue until tropical forests are eliminated, about as much carbon will be released to the atmosphere in the next 50 to 100 years as has been emitted from worldwide combustion of fossil fuels since the start of the industrial revolution. If, on the other hand, deforestation is halted and replaced with massive reforestation, the net flux of carbon will be reversed. Establishment of forests on tropical lands formerly forested and not currently in either agriculture or human settlements could withdraw almost as much carbon from the atmosphere as will be released if current trends continue unchecked. While such a strategy of reforestation would help stabilize the concentration of CO2 in the atmosphere, the solution is temporary. Once regrown, forests no longer accumulate carbon from the atmosphere. If the halting of deforestation is accompanied by the substitution of sustainably harvested wood fuels for fossil fuels, however, and if use of fossil fuels does not increase above current rates, the total net release of carbon to the atmosphere from both fossil fuels and deforestation could be eliminated indefinitely.