The impact of managing biomass specifically for the conservation or production of. energy can become a significant factor in the global management of atmopsheric CO2 over the next century. This paper evaluates the global potential for: (1) conserving energy by using trees and wood for shading, shelterbelts, windbreaks, and construction material; and (2) increasing the use of biomass and improving its conversion. efficiency for producing heat, electricity, and liquid biofuels. The potential reduction in CO2 emissions possible by the anticipated time of atmospheric CO2 doubling was. estimated to be up to 50 x 106 t C yr-1 for energy conservation and as high as 4 x 109 C yr-1 for energy production. Of the many opportunities, two stand out. Through afforestation of degraded and deforested lands, biomass energy production offers the potential of 0.36 to 1.9 x 109 t C yr-1 emission reduction. Dedicated energy crops, which include short-rotation woody crops, herbaceous energy crops, halophytes, some annual crops, and oilseeds, offer the potential of 0.2 to 1.0 x 109 t C yr-1 emission -reduction. Also addressed in the paper, but not quantified, were establishment of new forests, increasing the productivity of existing forests, or protecting forests to sequester C as an offset against CO2 emissions from burning fossil fuels or forest destruction. Also addressed are uncertainties, gaps in scientific knowledge about ecosystems and their management, and policy considerations at the international and national levels.