2.5.1 Global carbon budget

Carbon on the earth is stored in the atmosphere, oceans, biosphere and lithosphere and carbon components are exchanged among these stores in gas phase (CO2), and in organic or inorganic phase. According to the IPCC 4th Assessment Report, 2007, the global fossil-fuel emission including fossil-fuel use and cement industry is 6.4 GtC/yr in 1990s, and emission by land use changes is 1.6 GtC/yr. On the contrary, the estimated accuracy of net land and ocean uptakes are 2.6 GtC/yr and 2.2 GtC/yr, respectively. The net carbon balance of the atmosphere in 1990s is 3.2 GtC/yr (=8.0-2.6-2.2) as shown in Table 1. These values of carbon balances have been assessed thorough comparative check of many results related carbon cycle. The global fossil-fuel emissions of CO2 and the net carbon balances of the atmosphere are now rather well established, the others in the Table 2.5.1 are less accurate. And also, there are carbon cycles in the land and ocean-biosphere, the net carbon balances are related to the activities of them. The status of carbon cycle in each store is controlled by forest management and climatic changes. The Kyoto Protocol, which accounts for offsetting reduced targets of CO2 emission by carbon sequestration in forests through forest management, became effective in February 2005. The rules for the effective management have focused attention on the role of the terrestrial biosphere in global scale carbon cycles. Therefore, accurate data are required for carbon stocks and cycle over various terrestrial ecosystems. However, uncertainty remains about the change in carbon stock from forest management and the response of the ecosystem CO2 exchange to climate change.