The Global Methane Budget

Lead Research Organisation: NERC Centre for Ecology and Hydrology
Department Name: Hydro-climate Risks

Abstract

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.

Planned Impact

This project will produce a much better understanding of the global methane budget, and the role of climate feedbacks in driving emissions. Atmospheric methane has increased sharply since 2007. 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 a UK Observation network available as a long-term legacy from the work. The observation network will 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 sustain the greenhouse gas measurement on UK Ascension Is. station, one of the very few tropical background stations globally and currently unfunded from 2017.

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. Specifically, the work will help validate the TCCON station at Ascension Island, a key equatorial site for satellite ground-truthing.

Interpretation of the observations by the modelling component of the project will help ecologists and geographers to 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, in which methane is very poorly constrained at present. The work will support marked improvements in emissions estimate for less developed 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.

Publications

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

 
Description Wetland flux measurements in collaboration with the Okavango Research Institute 
Organisation University of Botswana
Department Okavango Research Institute
Country Botswana 
Sector Academic/University 
PI Contribution CEH will measure methane fluxes from a permanent and seasonal wetland in the Okavango delta, one of the largest global wetlands. This project will provide the first field scale methane flux measurements from this delta, using the eddy covariance (EC) method over a one year period.
Collaborator Contribution The Okavango Research Institute will be responsible for site selection and logistical support for the eddy covariance measurements. The Okavango Research Institute will also make plot scale chamber measurements in the footprint of the EC tower, thus providing information on the spatial heterogeneity. The combined data will improve our understanding of the magnitude and seasonality of methane emissions from this inland delta and will feed into global methane models.
Impact None at present
Start Year 2016