Rising atmospheric methane: 2007-2014 growth and isotopic shift
Rising atmospheric methane: 2007-2014 growth and isotopic shift
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DOI：
10.1002/2016gb005406
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发表时间：
2016-09-01
影响因子：
5.2
通讯作者：
Ganesan, A. L.
中科院分区：
文献类型：
--
作者：
Nisbet, E. G.;Dlugokencky, E. J.;Ganesan, A. L.
从2007年到2013年，大气中甲烷的全球平均摩尔分数增加了5.7 +/- 1.2 ppb/年（-1）。与此同时，自2007年以来，δ C-13（CH 4）（甲烷中C-13/C-12同位素比率的测量值）已经转向更负的值。2014年的增长是极端的，为12.5 +/- 0.4 ppb，在大多数纬度上观察到进一步转向更负的值。这里提出的同位素证据表明，甲烷的上升主要是生物甲烷排放量的显着增加，特别是在热带地区，例如，热带湿地在降雨异常或反刍动物和稻田等农业来源增加排放量的年份扩大。在大气化学的其他示踪剂中没有发现OH自由基对甲烷去除率的变化，似乎也不能解释甲烷的短期变化。化石燃料的排放量也可能增加，但碳-13消耗值的持续变化及其显著的年际变化，以及2007年后增长的热带和南半球地区，都表明化石燃料排放量并不是推动增加的主要因素。热带湿地和热带农业甲烷排放量增加的一个主要原因可能是它们对气象变化的反应，而甲烷排放量可能是增长的主要贡献者。
From 2007 to 2013, the globally averaged mole fraction of methane in the atmosphere increased by 5.7 +/- 1.2 ppb yr(-1). Simultaneously, delta C-13(CH4) (a measure of the C-13/C-12 isotope ratio in methane) has shifted to significantly more negative values since 2007. Growth was extreme in 2014, at 12.5 +/- 0.4 ppb, with a further shift to more negative values being observed at most latitudes. The isotopic evidence presented here suggests that the methane rise was dominated by significant increases in biogenic methane emissions, particularly in the tropics, for example, from expansion of tropical wetlands in years with strongly positive rainfall anomalies or emissions from increased agricultural sources such as ruminants and rice paddies. Changes in the removal rate of methane by the OH radical have not been seen in other tracers of atmospheric chemistry and do not appear to explain short-term variations in methane. Fossil fuel emissions may also have grown, but the sustained shift to more C-13-depleted values and its significant interannual variability, and the tropical and Southern Hemisphere loci of post-2007 growth, both indicate that fossil fuel emissions have not been the dominant factor driving the increase. A major cause of increased tropical wetland and tropical agricultural methane emissions, the likely major contributors to growth, may be their responses to meteorological change.