The Global Methane Budget

Lead Research Organisation: University of Bristol
Department Name: Chemistry


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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France JL (2022) Very large fluxes of methane measured above Bolivian seasonal wetlands. in Proceedings of the National Academy of Sciences of the United States of America

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Ganesan A (2018) Spatially Resolved Isotopic Source Signatures of Wetland Methane Emissions in Geophysical Research Letters

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Merbold L (2021) Opportunities for an African greenhouse gas observation system in Regional Environmental Change

Description We have derived methane emissions from India using in situ and satellite atmospheric observations. Our estimates are consistent with India's National Inventory Report, and show no statistically significant trend between 2010 and 2015.

Using data from the UK's GHG monitoring network, we found that the reported decline in the UK's methane emissions is consistent with our findings from atmospheric data (Lunt et al., 2021).

We derived the first atmospheric data-based estimate of methane emissions from North Africa, and discovered a new major seasonal source in the Nile delta (Western et al., 2021).

Also using satellite data, we estimated emissions from China, and hypothesised that emissions were continuing from abandoned coal mines (Sheng et al., 2021).
Exploitation Route We will share the code used in this work with researchers interested in estimating greenhouse gas flux using atmospheric observations.
Sectors Environment

Description Our research on India's methane emissions (Ganesan, et al., 2017) have led to us contributing to the Indian government's Biennial Update Report to the United Nations Framework Convention on Climate Change (UNFCCC). As far as we know, this represents the first time that atmospheric observation-based emissions estimates have been included in a UNFCCC inventory report from a developing country.
First Year Of Impact 2017
Sector Environment
Impact Types Policy & public services

Description National Oceanic and Atmospheric Administration (NOAA) Earth System Research Laboratory (ESRL) 
Organisation National Oceanic And Atmospheric Administration
Department Earth System Research Laboratory (ESRL)
Country United States 
Sector Public 
PI Contribution Modelling of greenhouse gases.
Collaborator Contribution Provision of greenhouse gas data and expertise
Impact Several publications have resulted from this collaboration.
Start Year 2012
Description University of Wollongong 
Organisation University of Wollongong
Country Australia 
Sector Academic/University 
PI Contribution Model runs, data provision and processing, expertise in atmospheric modelling and statistics.
Collaborator Contribution Expertise in statistics
Impact Several publications, with further work in the pipeline.
Start Year 2013
Title ACRG-Bristol/acrg: ACRG v0.2.0 
Description ACRG standardisation and inversion code v0.2.0 Added Ability to convert calibration scale in get_obs New "defaults" file that specifies inlets and instruments to use for particular time periods An obs.db SQLite database that specifies the location of all obs files and basic details about their contents (species, inlet, time range, etc.) notebooks directory for Jupyter notebooks notebooks/tutorials directory for notebook based tutorials a tmp directory to store random job script output files added a dev environment that includes spyder and a lighter environment that does not Changed get_single_site now returns a list of xarray datasets, one for each combination of inlet and site. If defaults are specified, the list will contain the default instruments and inlets for each period get_obs now returns a dictionary containing lists of datasets calibration scale and inlet are now attributes to obs datasets (e.g. ds.attrs["scale"]) fp_data_merge now works with new get_obs object The flux function will now look for named files first and then look for files. This will not be able to read both files. This can still accept an more explicit source such as co2-ff_*.nc as an alternative to this. arviz package version pinned to prevent conflict with pymc3 version 
Type Of Technology Software 
Year Produced 2022 
Open Source License? Yes  
Impact This software is used to evaluate emissions of greenhouse gases for the UK and other countries. 
Description Schools and Public Science Outreach Event (Futures Event) 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact Purpose: To educate and inspire school children and adults to learn more about greenhouse gases, what they do in their lives that could change their consumption of these and the kinds of instrumentation we use to measure greenhouse gases.
Activities: Quizzes about greenhouse gas emissions from different animals and rating the carbon equivalent emissions of everyday activities; measuring CO2 in their breath; and making play dough greenhouse gas molecules.
Daytime event: Four researchers engaged with 400+ primary and secondary school students over one day. Half the students attending were from schools in the top 30% most deprived decile.
Quotes from students following the event " I am inspired to keep learning and not be afraid to ask questions", "It makes you have bigger dreams for the future"
Evening Event: Three researchers engaged with 500+ adults .
Quotes from the Event "Great to see researchers taking time out to connect with young people and the public"
"It was so lovely seeing so many researchers excited to talk about their work. Especially those who made it interactive"
Year(s) Of Engagement Activity 2019