報告書番号

U99043

タイトル（和文）

CO2排出削減による濃度安定化効果の検討 --CO2濃度推定モデルの適用と問題点--

タイトル（英文）

Investigation of CO2 concentrations under emission reduction scenarios: -Application of a carbon-cycle model and implication of model uncertainties.-

概要 （図表や脚注は「報告書全文」に掲載しております）

国際共同研究により、CO2濃度安定化による温暖化防止効果を予測した。この予測では、排出量から大気中CO2濃度の推定に、Wigley（1993）のモデルを使用した。このモデルの適用性を検討した結果、推定された濃度は、1990年代の観測データと良く一致することがわかった。しかし、海洋の吸収量は過大評価の可能性がある。また、植物吸収量は、土地利用変化によるネットの排出量Dnの不確実性の影響を受け、2100年時点の濃度に70ppmv程度の推定幅が生ずる。このモデルにより、京都議定書の削減による濃度安定化を試算した結果、削減効果は、濃度増加を約10年先送りする程度と試算され、先進国だけの削減では濃度安定化は困難であると推察された。今後の温暖化問題では、どのレベルで大気中濃度を安定化するかが重要な問題で、濃度推定の信頼性向上を目指し、モデルの改良に取り組む予定である。

概要 （英文）

Through an international research collaboration (ACACIA project), climate changes under a matchedset of CO2 stabilization and "business as usual (IS92.a, IPCC,1992)" scenarios were projected by the NCAR coupled climate system model (CSM). These results are reviewed briefly in this report. For these simulations the carbon-cycle model of Wigley (1993) (part of the MAGICC model) was usedto estimate atmospheric CO2 concentrations corresponding to both the "business as usual" scenario and the WRE550 stabilization scenario. This carbon-cycle model has been used in many investigationsregarding global warming issues, e.g., the IPCC second assessment report (1995). In this model, both the ocean and terrestrial biomass components of the CO2 cycle are simulated. Increases in atmospheric CO2 concentration are calculated by net balance between anthropogenic emission and estimated CO2 sinks including the effects of deforestation. Verification of the model is demonstratedby comparison of observational data from Mauna Loa and model calculations over the period of the 1990s.Future concentrations depend strongly on the value of Dn(1980s), which is the net CO2 emission from land use change in 1980s. In the long term, however, it is suggested that the ocean uptake in this model tends to be over estimated due to the use of linear response functions. We estimated CO2 concentrations following the Kyoto Protocol based on the IS92a emissions scenario. The model results reveal that the Kyoto reduction will delay the occurrence of any given concentrationby only a few decades. It is obvious that reductions by only advanced countries are not sufficient to stabilize the CO2 concentrations. We examine a new graduated reduction scenario where emissions are reduced at a cumulative rate of 5% every ten years, reaching a maximum reduction of 30%. If, in addition to the advanced countries, the developing countries adopt such reductions from the year 2030 forward then concentration at the end of the 21st century reach about 520 ppmv and the stabilization of concentration might be achieved. In future research on stabilization of carbon dioxide concentrations,which is the goal set by the UNFCCC, improvements in the carbon cycle model described above should be made in order to better estimate future limits on CO2 emissions more realistically.

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