甲烷 – 全球變暖的二號元凶
甲烷 – 全球變暖的二號元凶
陳敏儀
2022年4月
甲烷是三大主要溫室氣體之一,它是繼二氧化碳後第二個導致全球變暖的主要因素。與二氧化碳相比,甲烷的溫室效應更強,但其大氣濃度則顯著較低,而且逗留在大氣中的時間較短。根據政府間氣候變化專門委員會《第六次評估報告》,2010-2019年全球表面平均溫度較工業化前水平高出約1.1℃,當中約0.5℃的升溫是源自甲烷(圖一)。
甲烷的最大天然來源包括濕地和淡水湖的缺氧水和沉積物、石油和天然氣滲漏,以及泥火山;最大的人為排放源是畜牧業生產過程中牛羊的腸道發酵、糞肥處理、堆填區、廢物處理、種植水稻,和開採化石燃料。
甲烷的排放量在過去兩個世紀幾乎增加一倍,自1900年起,其排放主要是人為的。現時甲烷的大氣濃度是最少80萬年來所未見(圖二)。在全球持續變暖的背景下,預料冰凍圈的凍土會繼續升溫和融化,釋放甲烷和二氧化碳到大氣中,加強溫室效應,繼而造成惡性循環。
在2021年的聯合國氣候變化會議,超過一百個國家承諾到2030年將全球甲烷排放量減少30%。要達至《巴黎協定》的目標,提升減排力度實在刻不容緩。
參考資料:
[1] Figure SPM.2 from IPCC, 2021: Summary for Policymakers. In: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson- Delmotte, V., P. Zhai, A. Pirani, S. L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M. I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J. B. R. Matthews, T. K. Maycock, T. Waterfield, O. Yelekçi, R. Yu and B. Zhou (eds.)]. Cambridge University Press. In Press.
[2] Figure 5.4 from Josep G. Canadell, J. G., P. M.S. Monteiro, M. H. Costa, L. Cotrim da Cunha, P. M. Cox, A. V. Eliseev, S. Henson, M. Ishii, S. Jaccard, C. Koven, A. Lohila, P. K. Patra, S. Piao, J. Rogelj, S. Syampungani, S. Zaehle, K. Zickfeld, 2021, Global Carbon and other Biogeochemical Cycles and Feedbacks. In: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S. L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M. I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J. B. R. Matthews, T. K. Maycock, T. Waterfield, O. Yelekçi, R. Yu and B. Zhou (eds.)]. Cambridge University Press. In Press.
[1] Figure SPM.2 from IPCC, 2021: Summary for Policymakers. In: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson- Delmotte, V., P. Zhai, A. Pirani, S. L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M. I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J. B. R. Matthews, T. K. Maycock, T. Waterfield, O. Yelekçi, R. Yu and B. Zhou (eds.)]. Cambridge University Press. In Press.
[2] Figure 5.4 from Josep G. Canadell, J. G., P. M.S. Monteiro, M. H. Costa, L. Cotrim da Cunha, P. M. Cox, A. V. Eliseev, S. Henson, M. Ishii, S. Jaccard, C. Koven, A. Lohila, P. K. Patra, S. Piao, J. Rogelj, S. Syampungani, S. Zaehle, K. Zickfeld, 2021, Global Carbon and other Biogeochemical Cycles and Feedbacks. In: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S. L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M. I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J. B. R. Matthews, T. K. Maycock, T. Waterfield, O. Yelekçi, R. Yu and B. Zhou (eds.)]. Cambridge University Press. In Press.