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植生改変・エアロゾル複合効果がアジアの気候に及ぼす影響の評価
須藤, 健悟;高田, 久美子;竹村, 俊彦;神沢, 博;安成, 哲三
Permalink : http://hdl.handle.net/2115/45172
Abstract
アジア域では, 土地利用変化などに伴う植生改変およびエアロゾルの増加が顕著であり, これらの変動は陸面過程, 大気放射, および雲・降水を変化させ, アジアモンスーンなどのアジア域気候に影響している可能性が大きい. 本研究では, 植生改変とエアロゾル変動の役割という観点から, 総合的に気候影響を検討している. 本論文では, 特に, 農地化などの土地利用変化が, 陸面, および硝酸塩や植生起源有機炭素などのエアロゾル成分の変動を通じて, どのように気候に影響するかについて, 全球化学・エアロゾル気候モデルを用いた最新の結果について紹介する.
This study assesses the roles of aerosols in the past/present changes in Asian climate and monsoon, isolating impacts of individual aerosol components in the framework of the CCSR/NIES/FRCGC climate model (MIROC). Many recent studies suggest that increases in anthropogenic aerosols such as black carbon and sulfate may play a crucial role in Asian climate change as observed. Our previous studies also demonstrate the significance of aerosol increases (sulfate and carbonaceous aerosols) in the simulated precipitation changes in Asia (e.g.,Arai et al., 2009). In this study, we particularly focus on the changes of nitrate and secondary organic aerosols (SOA) which are tightly linked to land use change in regions like Asia, but not treated in our previous aerosol studies. We newly introduced simulation of nitrate aerosol in our climate model. Our simulation shows that there are anomalously high concentrations of nitrate aerosol in South Asia (particularly around India and Bangladesh), coming from abundant ammonium and less sulfate components in this region. In India, free tropospheric mixing ratio and number concentration of nitrate in fine mode are both larger than those of sulfate in winter to early summer. Our study estimates large cooling (1-2 W m-2)in South Asia due to nitrate increase in terms of direct radiative forcing for 1850-2000. This result suggests nitrate aerosol may play an important role in the observed changes in Asian monsoon. In addition, we estimate changes in biogenic VOCs emissions associated with land use change during 1850-2000; biogenic VOCs like terpenes are important precursors of SOA. We estimate significant reduction (50-70%) in terpenes and other VOCs emissions in the central Eurasia, North America, and Asia due to intense cultivation and deforestation in these areas. Responding to the VOCs decreases during 1850-2000, our model calculates large reduction of SOA, leading to a positive direct radiative forcing (warming) of 0.5-1 W m-2 in South Asia. This warming from SOA and cooling from nitrate aerosol which are both linked to land use change may compensate for each other in Asia.
This study assesses the roles of aerosols in the past/present changes in Asian climate and monsoon, isolating impacts of individual aerosol components in the framework of the CCSR/NIES/FRCGC climate model (MIROC). Many recent studies suggest that increases in anthropogenic aerosols such as black carbon and sulfate may play a crucial role in Asian climate change as observed. Our previous studies also demonstrate the significance of aerosol increases (sulfate and carbonaceous aerosols) in the simulated precipitation changes in Asia (e.g.,Arai et al., 2009). In this study, we particularly focus on the changes of nitrate and secondary organic aerosols (SOA) which are tightly linked to land use change in regions like Asia, but not treated in our previous aerosol studies. We newly introduced simulation of nitrate aerosol in our climate model. Our simulation shows that there are anomalously high concentrations of nitrate aerosol in South Asia (particularly around India and Bangladesh), coming from abundant ammonium and less sulfate components in this region. In India, free tropospheric mixing ratio and number concentration of nitrate in fine mode are both larger than those of sulfate in winter to early summer. Our study estimates large cooling (1-2 W m-2)in South Asia due to nitrate increase in terms of direct radiative forcing for 1850-2000. This result suggests nitrate aerosol may play an important role in the observed changes in Asian monsoon. In addition, we estimate changes in biogenic VOCs emissions associated with land use change during 1850-2000; biogenic VOCs like terpenes are important precursors of SOA. We estimate significant reduction (50-70%) in terpenes and other VOCs emissions in the central Eurasia, North America, and Asia due to intense cultivation and deforestation in these areas. Responding to the VOCs decreases during 1850-2000, our model calculates large reduction of SOA, leading to a positive direct radiative forcing (warming) of 0.5-1 W m-2 in South Asia. This warming from SOA and cooling from nitrate aerosol which are both linked to land use change may compensate for each other in Asia.
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