Change in potential natural vegetation (PNV) distribution associated with climate change due to the doubling atmospheric carbon dioxide (2×CO2) was estimated with a global natural vegetation mapping system based on the modified Kira scheme to the globe and the continents. With an input of widely-distributed global climate data, the system interpolates data onto a 1° latitude by 1° longitude grid over the globe, generates estimates of vegetation type, and produces a composite PNV map. The input climate data corresponding to the 1×CO2 and 2×CO2 consists of observations prior to AD 1958 at 2,001 weather stations worldwide and the 2×CO2 simulation output from the Japan Meteorological Research Institue's General Circulation Model, respectively. As a result of the simulated global warming, the vegetation zones expanded mostly from the tropics toward the poles. PNV area changed by 6.98 billion (G) ha of the total land area (15.04 Gha) and potential forest area corresponding to the closed forest and open forest (woodland) reached 9.74 Gha with the increase of 1.29 Gha. The potential forest area in Europe had obvious advantages to the climate change accompanied with the increase of actual forest area. Although the actual forest area has decreased in North America and Asia, the potential forest area in these continents also benefitted from the climate change. In the end, the remaining continents tended to bear the brunt of the climate change.