Estimated land area increase of agricultural ecosystems to sequester excess atmospheric carbon dioxide

An estimated 3.3 Pg carbon (C) is accumulating in the atmosphere annually, with carbon dioxide (CO2) concentrations increasing approximately 1.5-2.0 ppm per year. The conversion of land to agroforestry, rangeland, and cropping systems has been identified as a possible option to offset rising CO2 levels. The objective of this work was to estimate the increase in land area for the leading global cereal crops (maize, rice, wheat), temperate rangeland, and temperate forest ecosystems to sequester the surplus atmospheric C. Based on calculations and previously published data, maize cropping systems are the most efficient at sequestering C. An additional 6.7-7.6 X 10(8)ha of maize would be required to assimilate the 3.3 Pg C yr(-1), a 477-543% increase in global corn production. Agroforestry appears to be the only agricultural system that could realistically be implemented to reduce global CO2 levels with a calculated increase of 4.6-4.6 X 10(8)ha (a 52-66% growth in worldwide area). Also, the estimated net productivity of 6.7-7.1 Mg C ha(-1) for temperate forests is significantly greater than the productivity of maize, rice, or wheat cropping systems, which ranged from 2.7-4.3 Mg C ha(-1). Increasing land area for agricultural production may not be the answer to the global C dilemma, but intensive management systems that result in increased soil organic matter are a significant part of the solution.