The Global Methane Budget

自2007年以来，大气中甲烷的浓度急剧增加，原因尚不完全清楚，在未来的气候项目中如何处理甲烷的不确定性也越来越大。总的来说，自2007年以来的增长与全新世最大的增长事件相当。浓度上升幅度最大的是热带和南半球，2014年是迄今为止增幅最大的一年。2015年将继续保持强劲增长。碳同位素证据表明，增加的原因主要是生物源，而人为源（如天然气泄漏、水力压裂等）的变化起了较小的作用。考虑到热带的生长轨迹，这表明这种增长主要是由气象变化驱动的。然而，全球甲烷预算并没有得到很好的描述。通过汇总排放清单（例如气体泄漏、火灾、垃圾填埋场、奶牛、湿地等）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评估的“自上而下”估算有很大不同。为什么会出现这种差异还不清楚。该项目有四个组件，每个组件都有一些工作包。需要更好的观测来支持区域和全球大气模型，从而得出排放的估计。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。瓶或袋取样（甲烷、13C和D/H同位素）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，并在英国进行离线测量。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岛。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。热带活动将在亚马逊、非洲、印度和东南亚的湿地以及C4稀树草原生物质燃烧地区开展。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。区域排放的特征同位素特征将通过廉价的基林图研究来确定，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。主要的汇过程将在热带大气中进行研究，FAAM飞机将进行垂直和纬度上的OH和Cl收支研究，并对热带甲烷营养物进行量化。将利用模型计算区域和全球通量，并利用原位和遥感综合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UKCA等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的响应。该项目将在项目结束后投资英国最先进的温室气体监测网络作为遗产。

Atmospheric methane has been increasing in concentration sharply since 2007, for reasons that are not fully understood, with ever-increasing uncertainty in how it should be treated in future climate projects. Overall, the increase since 2007 is comparable to the largest growth events in the Holocene. The largest rises in concentration have been seen 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, with changes in anthropogenic sources (for example natural gas leakage, fracking and so on) playing a more minor role. This, taken with the tropical locus on growth, suggests that the increase has primarily been driven by meteorological change. However, 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, wetlands, etc) balanced with known loss processes, are significantly different from '"top-down" budgets assessed by direct measurement of the atmosphere. Why this discrepancy occurs is not known.The project has four components, each with a number of work packages.1. Better Observations are needed, to support regional and global atmospheric modelling 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 (methane, 13C and D/H isotopes) will be at these stations and at a number of continental stations in S. America, Africa and S, SE and E Asia, with offline measurement 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. Tropical campaigns will be in 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 by inexpensive Keeling plot studies, 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 latitudinal resolved OH and Cl budget studies by the FAAM aircraft, and quantification of tropical methanotrophy.3. 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 like UKCA 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 as it responds to climate change. The project will invest in a state of the art UK greenhouse gas monitoring network as a legacy after the project has ended.