The Global Methane Budget

Lead Research Organisation: University of Leeds
Department Name: Sch of Geography


Methane is the second most important greenhouse gas contributing to human-induced global warming. Atmospheric methane concentrations have increased sharply since 2007, and dramatically in 2014, for reasons that are not understood.

The overall increase since 2007 is comparable to the largest growth events over the past 1000 years. The recent rises have occurred worldwide, but after an Arctic pulse in 2007, the growth has been primarily in the tropics and southern hemisphere. 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, coal mining and so on) playing a subordinate 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 currently not well understood. "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 known.

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 greenhouse gas monitoring network and much better knowledge of the global methane budget.

Planned Impact

This project will produce a much better understanding of the global methane budget, and the role of climate feedbacks in driving emissions. The sharp increase of atmospheric methane since 2007 will be of major public interest.. Simultaneously, there has been a shift in its carbon isotopes implying the increase is primarily biogenic, not driven by fossil fuel emissions. A better knowledge of the global methane budget is vital if we are to understand what is driving climate change and predict future emissions. This work will have impact on a very wide range of beneficiaries, from scientists to policy-makers.

Measurement: The project will create an Observation network as a long-term outcome, to sustain and improve global methane mole fraction and isotopic measurement, especially in the tropics where data gathering is presently very weak. In particular, the project will continue the greenhouse gas measurement on Ascension Is., one of the very few tropical background stations globally, and currently unfunded from 2017. The data will be invaluable to modellers.

Policymakers: With the Paris Climate Conference later this year, policy makers and governmental bodies are strongly focussed on climate change. 195 nations participate in the United Nations Framework Convention on Climate Change (UNFCCC). This commits signatory countries to assess their greenhouse gas emissions. For methane, there is a major discrepancy between global total emissions as assessed by atmospheric measurement ('top-down' measurement) and the sum of national emissions declared under UNFCCC (the 'bottom-up' inventory). This project will make major advances towards resolving this problem.

Space: When Sentinel 5P, GOSAT-2 and MERLIN satellites are launched, this project's in-situ observation of equatorial and Southern Hemisphere methane will make a significant contribution to analysis of the satellite measurements and will help validate the TCCON station at Ascension Island, a key equatorial site for satellite ground-truthing.

In the modelling component of the project, interpretation of the observations will help ecologists and geographers understand the impact of climate change globally and especially in less developed nations. There will be strong impact on those carrying out global security studies, benefitting from the significant improvement the work will bring to greenhouse gas emissions inventories in tropical nations, where methane is very poorly constrained at present. The work will support marked improvements in emissions estimate for these nations.

In the private sector, a direct beneficiary will be Isoprime Ltd. (Cheshire: Queen's Award 2013), who will partner the development of the D/H analysis system at Royal Holloway. Wider beneficiaries include the gas, coal and oil industries, as the strong improvement of isotopic work, especially in D/H, will facilitate leak identification and location. Cutting leaks will improve efficiency and productivity as well as help compliance with regulatory frameworks.

Education: The project will support a number of younger staff, who will sustain the UK's key skills in greenhouse gas measurement and modelling, especially in the use of isotopes to characterise emissions. Career development will come through skills learned, publications, conferences, and training opportunities.

Public/Media: The results of this work will also be of interest to the wider public. Greenhouse gas, global warming and climate change are high on the political and media agenda, especially with the Paris climate conference later this year. Decisions made there will have implications for all.

Methane and its feedbacks rank among the most important and the most poorly understood problems in the global climate system. In wide global constituencies, from specialist scientists to policy makers, there is great need for better knowledge. Thus this project will have unusually strong and very wide impacts worldwide.


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Description Methane (CH4) is a potent greenhouse gas. Amongst the anthropogenically emitted greenhouse gases its contribution to greenhouse warming is only second to carbon dioxide . Compared to pre-industrial level CH4 concentration levels in the atmosphere have nearly tripled. Based on the atmospheric CH4 records pre 2006 it seemed that sources and sinks of methane began to balance each other and thus a stationary state of CH4 in the atmosphere being approached. However atmospheric CH4 growth resumed again thereafter. The MOYA project aims to understand better what the reasons for stalling of growth pre 2006 and resumption of growth post 2006 are. The Leeds component used atmospheric transport inverse modelling as well lower troposphere CH4 measurements over the largest seasonally flooded savannah, the Pantanal, in tropical South America to contribute to resolve this question. We found a CH4 'hotspot' the Eastern Amazon based both on regular vertical profile measurements in this region as well as inverse modelling using surface atmospheric data and air-column CH4 retrievals using satellite. These emissions are increasing over time. We also quantified CH4 emission from the Pantanal and found interesting seasonality of CH4 release to the atmosphere.
Exploitation Route We are interested to pin down why there is a large East-West gradient in CH4 fluxes to the atmosphere from the Amazon Basin and what causes an upward trend of CH4 emissions in this region. A variety of approaches could be used including measurements of CH4 isotopes and targeted measurements with aircraft of lower troposphere CH4 concentrations over this region.
Sectors Agriculture, Food and Drink,Environment

Description The project in general has contributed to increased awareness that the increasing trend of CH4 in the atmosphere is a major concern. It is one of the burning problems society will need to solve.
First Year Of Impact 2019
Sector Environment
Impact Types Societal,Policy & public services

Title Atmospheric transport inversion estimator of Methane sources and sinks using atmospheric concentration data of methane and methane isotopes 
Description Atmospheric transport inversion estimator of Methane sources and sinks using atmospheric concentration data of methane and methane isotopes. The primary tool used is the atmospheric chemistry and transport model TOMCAT which calculates expected concentration elevations at greenhouse gas observation sites given localized and temporary sources. A least square estimator is then being used to find the best linear combination of sources and sinks to match atmospheric greenhouse gas observations. A main element of the tool is the inclusion of both 12CH4 and 13CH4 data. The 13CH4 isotope data add an additional constraint on nature of sources - like biogenic versus thermogenic origin. 
Type Of Material Improvements to research infrastructure 
Year Produced 2018 
Provided To Others? Yes  
Impact We are in the process of publishing the first study based on the tool. It is freely accessible on request (as will be stated in the publication).