大気中のメタンの変動性に対する人為的および自然発生源の貢献
P Bousquet1, P Ciais, J B Miller
1Laboratoire des Sciences du Climat et de l'Environnement, IPSL-LSCE, CEA-CNRS-UVSQ, F-91191, France. philippe.bousquet@cea.fr
Nature
|September 29, 2006
まとめ
大気中のメタンのレベルは,人類による排出量が減少したため,1990年代以降安定した. しかし,最近の人為的なメタン排出量の増加は,湿地のメタン排出量の減少によってマスクされ,将来の上昇につながる可能性があります.
科学分野:
- 大気化学 大気化学
- 気候科学 気候科学
- 環境科学 環境科学
背景:
- メタンは強力な温室効果ガスで,工業化以前の時代から大気中の濃度がほぼ3倍になった.
- 大気中のメタンの増加率は,地表からの排出と,ヒドロキシルラジカルによる破壊の影響を受けています.
- メタンの増加率は1990年代以降減少しており,世界の気温予測に影響を与えています.
研究 の 目的:
- 1984年から2003年にかけてのメタン排出量の変動を制御するプロセスを定量化する.
- 大気中のメタンの増加率の年次変動の要因を理解する.
- メタンの予算の変化における湿地,火災,および人為的な排出量の役割を評価する.
主な方法:
- 大気輸送と化学の逆転モデルを利用した.
- 1984年から2003年までのメタン排出量の変動を分析した.
- トップダウンの推定値とリモートセンシングと生地化学モデルのデータを比較した.
主要な成果:
- 湿地の排出量は,年次メタンの変動の主な要因でした.
- 1997年から1998年のエルニーニョを除き,火災による排出はほとんどなかった.
- 人為的な排出量の減少が1990年代のメタンの増加の減速を引き起こし,その後1999年以来増加した.
結論:
- 湿地と火災の排出量のトップダウン推定値は,独立したデータと一致しています.
- 最近の人為的なメタン排出量の増加は,湿地の排出量の減少によって相殺されています.
- 湿地の排出が回復すれば,将来の大気メタン増加は可能である.
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