Research press release




メタンは、地球の大気を温暖化させる温室効果ガスとして、二酸化炭素に次いで2番目に重要だ。メタンには天然の発生源と人為的発生源が数多くあるが、それぞれの場所と生成量の正確な理解はあまり進んでいない。今回、Stefan Schwietzkeたちは、全球メタン放出量の長期データとメタン炭素同位体比の記録という詳細なデータセットを用いて、全球メタン収支の再評価を行った。その結果、化石燃料(化石燃料関連産業による放出と自然の地質学的発生源からの漏出)によるメタン放出量が、過去の推定値より60~110%多いことが判明した。特に地質学的漏出を除外すると、天然ガス・石油・石炭の生産と使用によるメタン放出量は、現在の排出目録から示唆される値から20~60%多くなっている。


Methane emissions from fossil fuel industry and natural geological leakage are up to 110 per cent greater than current estimates, according to a detailed analysis of methane sources published in Nature this week. These results imply a greater potential than previously thought for fossil fuel industry efficiency improvements to mitigate the effects of human activity on the climate. Moreover, the research indicates that fossil fuel methane emissions do not seem to be increasing over time.

Methane is the second-most important greenhouse gas (after carbon dioxide) that has warming effects in Earth’s atmosphere. Our understanding of exactly where and how much of this gas is being produced from many different natural and anthropogenic sources is currently limited. Stefan Schwietzke and colleagues re-evaluate the global methane budget, using a detailed data set of long-term global methane emissions and methane carbon isotope records. They find that total fossil fuel methane emissions (from industry and leakage from natural geological sources) are 60 to 110 per cent greater than previously estimated. Notably, after accounting for geological seepage, methane emissions from the production and use of natural gas, oil and coal are 20 to 60 per cent higher than current emission inventories suggest.

The authors also report that the fraction of leaked methane from natural gas production may have declined from around 8 per cent to around 2 per cent over the past three decades. This finding indicates that improvements in the natural gas industry may have already helped to reduce methane emissions, but more needs to be done to offset the increase in natural gas production.

doi: 10.1038/nature19797

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