The Global Methane Budget

甲烷是造成人类引起的全球变暖的第二大温室气体。大气甲烷浓度自2007年以来急剧增加，原因尚不完全清楚，导致未来气候预测的不确定性不断增加。自2007年以来的总体增长可与过去1000年来的最大增长事件相媲美。最近的上升发生在热带和南半球，到目前为止最大的同比增长发生在2014年。2015年将继续保持强劲增长。碳同位素证据表明，这种增加主要是由生物源引起的，化石碳和燃烧（如天然气泄漏、水力压裂等）引起的人为源的变化起着次要作用。考虑到热带生长轨迹，这表明增加主要是由气象变化（如温度、降雨）驱动的。此外，全球甲烷预算没有得到很好的描述。通过汇总排放清单（如气体泄漏、火灾、垃圾填埋场、奶牛等）或过程模型（如湿地）与已知损失过程相平衡而得出的“自下而上”估算，与通过直接测量大气中甲烷而得出的“自上而下”估算有显著不同。为什么会出现这种差异还不清楚。该项目有四个组成部分：1。需要更好的观测来估算排放量。该项目将支持英国的甲烷及其同位素观测网络。在挪威的Kjolnes、Weybourne、泽西岛、NERC的RRS JC Ross船、佛得角、阿森松岛、福克兰群岛、哈雷湾、香港设有连续的站点，在加拿大、斯皮次卑尔根岛、玻利维亚、南非、印度、卢旺达和马来西亚设有合作站点。还将在这些站点以及南美洲、非洲和南亚、东南亚和东南亚的一些大陆站点进行瓶或袋取样（甲烷、13C和D/H同位素），并在英国进行离线分析。设置温湿度测量设备。英国FAAM飞机将执行横跨大西洋热带地区的航班，从亚速尔群岛到佛得角再到阿森松。过程研究将解决全球预算中最大的信息缺口。热带排放通量和同位素特征没有得到很好的约束。将在亚马逊河流域、非洲、印度和东南亚的热带湿地以及C4稀树草原生物质燃烧区开展实地活动。将在科威特和南亚、东南亚和东南亚研究尚不清楚的人为来源。将确定区域排放的特征同位素特征，以支持全球和区域模拟。陆地表面模拟和卫星研究将研究排放以及对温度和降水变化的反应。将调查热带大气中的主要汇过程，FAAM飞机将进行垂直和纬度分解的OH和Cl收支研究，并对土壤的热带吸收进行量化。将利用大气模拟计算区域和全球通量，并利用综合原位和遥感观测系统按来源类型和地理进行分配。我们将利用NAME等模式开展区域轨迹研究，评估区域排放。使用3D模型的全球建模将测试甲烷摩尔分数和同位素记录的合成估计。4.将使用摩尔分数、13C和D/H的全球逆模拟，按地理来源和来源类型估计通量，包括对利用所有现有观测资料后仍存在的不确定性进行全面评估。综合研究将利用该项目的结果来检验自上而下和自下而上的排放估算，并评估全球甲烷预算对气候变化预测的响应。该项目将提供最先进的英国温室气体监测网络，并减少全球甲烷预算的不确定性。

Methane is the second most important greenhouse gas contributing to human-induced global warming. Atmospheric methane concentrations have increased sharply since 2007, for reasons that are not fully understood, resulting in ever-increasing uncertainty for future climate projections. The overall increase since 2007 is comparable to the largest growth events over the past 1000 years. The recent rises have occurred in the tropics and southern hemisphere, with the sharpest year-on-year increase thus far occurring in 2014. Strong growth continues in 2015. Carbon isotopic evidence suggests that the increase is due to sources that are predominantly biogenic in origin, with changes in the anthropogenic sources from fossil carbon and burning (e.g., natural gas leakage, fracking and so on) playing a minor role. This, taken with the tropical locus on growth, suggests that the increase has primarily been driven by meteorological change (e.g., temperature, rainfall). Moreover, the global methane budget is not well described. "Bottom-up" estimates, made by aggregating inventories of emissions (e.g. from gas leaks, fires, landfills, cows, etc) or from process models (e.g., wetlands) balanced with known loss processes, are significantly different from '"top-down" budgets assessed by direct measurement of methane in the atmosphere. Why this discrepancy occurs is not understood.The project has four components:1. Better Observations are needed to derive estimates of emissions. The project will support a UK observation network for methane and its isotopes. Continuous stations will be at Kjolnes (Norway), Weybourne, Jersey, NERC ship RRS JC Ross, Cape Verde, Ascension, Falklands, Halley Bay, Hong Kong, with partner stations in Canada, Spitsbergen, Bolivia, S. Africa, India, Rwanda and Malaysia. Flask or bag sampling (for methane, 13C and D/H isotopes) will also be undertaken at these stations and at a number of continental stations in S. America, Africa and S, SE and E Asia, with offline analysis in the UK. A D/H measurement facility will be set up. The UK FAAM aircraft will carry out flights across the Atlantic tropics, from Azores to Cape Verde to Ascension.2. Process Studies will address the largest information gaps in the global budget. Tropical emission fluxes and isotopic signatures are not well constrained. Field campaigns will be undertaken in tropical wetlands in Amazonia, Africa, India and SE Asia, and C4 savanna biomass burn regions. Poorly understood anthropogenic sources will be studied in Kuwait and S, SE and E Asia. Characteristic isotopic signatures of regional emissions will be determined, to support global and regional modelling. Land surface modelling and satellite studies will study emissions and responses to change in temperature and precipitation. Major sink processes will be investigated in the tropical atmosphere, with vertically and latitudinally resolved OH and Cl budget studies by the FAAM aircraft, and quantification of tropical uptake by soils.3. Atmospheric modelling will be used to derive regional and global fluxes, apportioned by source type and geography using integrated in situ and remote sensing observing systems. We will carry out regional trajectory studies using models like NAME to assess regional emissions. Global modelling using 3D models will test synthetic estimates of the methane mole fraction and isotopic record. Global inverse modelling for mole fraction, 13C and D/H will be used to estimate fluxes by geographic source and source type, including a comprehensive assessment of the uncertainties that remain once all available observations have been used.4. Integrative studies will use the results from the project to test top-down and bottom-up emission estimates, and evaluate the responses of the global methane budget to projections of climate change.The project will deliver a state of the art UK greenhouse gas monitoring network and reduced uncertainty of the global methane budget.