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Assessing causes of global methane changes during 1979--2007 using measurements and models of mixing ratios and stable isotopes.

机译：使用混合比和稳定同位素的测量值和模型评估1979--2007年全球甲烷变化的原因。

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摘要

Atmospheric methane (CH4) is a major greenhouse gas and plays a critical role in the chemistry of the atmosphere. Rapid increases in CH 4 from the pre-industrial period (-700 ppb) to the 1970s contribute substantial to global warming. Since the early 1980s, however, the growth rate of CH4 has declined, implying that sources and sinks are becoming increasingly balanced. Superimposed on the multi-decadal slowdown are large year-to-year variations that have been linked with El Nino-Southern Oscillation. The factors contributing to the CH4 slowdown and interannual variability in the CH4 growth rate are incompletely understood. This research applied long-term records of CH4 mixing and its isotope ratios, estimates of fire emissions, and decadal histories of rice cultivation to assess the causes of multi-decadal changes in the CH 4 growth rate with the help of modeling techniques. First, the mechanisms contributing to the interannual variations in the global CH4 growth rate were evaluated using CH4, delta13C-CH 4, satellite-derived estimates of fire emissions, and a three-dimensional chemical transport model (GEOS-CHEM). Previous competing hypotheses related to the increase in CH4 anomaly during the 1997/1998 El Nino were tested using stable isotope observations and simulations from the GEOS-CHEM model. Next, the causes of the multi-decadal CH4 slowdown were assessed using synchronous time series of atmospheric CH4 (mixing ratio and both 13C/12C and D/H ratios). As a part of this study, changes in the interhemispheric differences of CH 4 and its isotopic ratios (delta13C, deltaD) were quantified using long-term time series from the University of California, Irvine (UCI) and National Institute of Water and Atmospheric Research (NIWA). A 2-box atmospheric model was developed to examine various hypotheses formulated to explain the overall decline in the CH4 growth rate. Finally, an empirical process-based biogeochemical model was developed to estimate the global CH4 flux from rice paddies, one of the largest uncertainties among anthropogenic emissions. In this analysis, I used multi-national histories of rice cultivation to assess changes in CH4 emissions from rice paddies. The impacts of changes in agricultural practices in rice fields were represented using the empirical process-based model. Overall, I concluded that the major high CH4 anomaly events (i.e. the 1998 increase, the 2003 increase, and the 2007 increase event) were linked closely to major fire events around the world. For the slowdown in CH4 mixing ratio, I found that a reduction in an isotopically depleted source, such as agricultures, was needed to explain the atmospheric observations. Agricultural intensification (such as the practices of mid-season drainage, and reductions in organic amendments in rice fields) is consistent with isotope observations and has reduced CH 4 emissions from rice agriculture during the past 3 decades.
机译：大气甲烷（CH4）是一种主要的温室气体，在大气化学中起着至关重要的作用。从工业化前时期（-700 ppb）到1970年代，CH 4的快速增加为全球变暖做出了重要贡献。但是，自1980年代初以来，CH4的增长率下降了，这意味着源和汇的平衡越来越大。与年代际变慢叠加的是与厄尔尼诺-南方涛动有关的逐年较大变化。导致CH4减慢和CH4增长率年际变化的因素尚未完全了解。这项研究利用CH4混合及其同位素比率的长期记录，火排放的估算以及水稻种植的十年历史来借助建模技术评估CH 4增长率多年代际变化的原因。首先，使用CH4，delta13C-CH 4，卫星衍生的火灾排放估算值和三维化学迁移模型（GEOS-CHEM），评估了导致全球CH4增长率年际变化的机制。使用稳定同位素观察和来自GEOS-CHEM模型的模拟，检验了与1997/1998年厄尔尼诺现象期间CH4异常增加有关的先前竞争假设。接下来，使用大气CH4的同步时间序列（混合比以及13C / 12C和D / H比）评估了十年年代CH4减慢的原因。作为这项研究的一部分，使用加州大学尔湾分校（UCI）和美国国家水与大气研究所的长期时间序列，对CH 4的半球间差异及其同位素比率（delta13C，deltaD）的变化进行了定量。 （NIWA）。开发了一个2箱式大气模型，以检查为解释CH4增长率总体下降而制定的各种假设。最后，建立了一个基于经验过程的生物地球化学模型，以估算稻田产生的全球CH4通量，这是人为排放中最大的不确定性之一。在此分析中，我使用了跨国的水稻种植历史来评估稻田CH4排放量的变化。使用基于经验过程的模型来代表水稻田中农业实践变化的影响。总的来说，我得出的结论是，重大的高CH4异常事件（即1998年的增加，2003年的增加和2007年的增加）与世界各地的重大火灾事件密切相关。对于CH4混合比的降低，我发现需要减少同位素贫乏源（例如农业）来解释大气观测。农业集约化（如季中排水做法，以及减少稻田中有机物的含量）与同位素观测结果一致，并在过去30年中减少了稻米农业中的CH 4排放。

著录项

  • 作者

    Kai, Fuu Ming.;

  • 作者单位

    University of California, Irvine.;

  • 授予单位 University of California, Irvine.;
  • 学科 Biogeochemistry.;Atmospheric Sciences.;Environmental Sciences.
  • 学位 Ph.D.
  • 年度 2009
  • 页码 167 p.
  • 总页数 167
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 生物地球化学、气体地球化学;环境科学基础理论;
  • 关键词

  • 入库时间 2022-08-17 11:38:24

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