The Global Methane Budget

Lead Research Organisation: University of Cambridge
Department Name: Chemistry

Abstract

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.

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.
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. As a consequence tropical emissions are currently particularly poorly quantified. 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.
Scientists, both in atmospheric and climate studies, and in a wide range of other disciplines, will use the observations and the better global understanding of emissions and wetlands for much better modelling of ecosystem responses to climate change.
The work will help validate the TCCON station at Ascension Island, a key equatorial site for satellite ground-truthing. When TROPOMI and MERLIN satellites are launched, this project's in-situ observation of equatorial and Southern Hemisphere methane will make a significant contribution.
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 at present methane is very poorly constrained. The work will support marked improvements in emissions estimates for less developed nations.
In the private sector, the direct beneficiary will be Isoprime Ltd. (Stockport, 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.
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.
With the 2015 COP 21 Paris Climate Conference, policy makers and governmental bodies are currently strongly focussed on climate change. 195 nations, including the USA 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 UNFCC (the 'bottom-up' inventory). This project will make major advances towards resolving this problem.
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 specialists 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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Description Talks by me and team member Michelle Cain at NERC's Into the Blue event 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact T`lk on methane at Into the Blue, Manchester
Year(s) Of Engagement Activity 2016