Paris Agreement targets to limit climate change to 1.5-2oC require the reduction of anthropogenic emissions of important greenhouse gases such as methane.
Wetlands are the largest natural source of methane. To improve emission budget estimates to meet the Paris agreement we need to understand wetland emissions further. Important interactions between wetland emissions and several key atmospheric pollutants have been largely omitted from the Earth System modelling of the CH4 cycle. For example, atmospheric sulphate (causing so-called “solar dimming”) and biomass burning aerosols impact on vegetation through the amount of solar radiation reaching the surface. These processes impact on vegetation productivity, and can therefore alter wetland CH4 production by changing the carbon available to methane-generating microbes. Moreover deposition of sulphur and nitrogen on the land result in other interactions in wetland soil, which can strongly modulate the amount of methane emitted
The aim of this project is to answer the following questions:
- How much have atmospheric pollutants modulated historical wetland CH4 emissions?
- Can this be used to help constrain the current CH4 wetland budget?
- To what extent has recovery from past pollution affected the current global CH4 budget?
This work will contribute to the newly developed Met Office capability in fully coupled methane cycling, where the UK Earth System Model has recently been extended so that dynamical wetlands CH4, full stratospheric-tropospheric CH4 chemistry, and CH4 surface deposition are fully interactive.
The JULES land surface scheme describes the main drivers of wetland CH4 emissions. The latest version of JULES includes improvements in hydrology, including representating tropical soils, and inundation. The recent discovery of significant CH4 transfer through tropical trees has also been parameterised in JULES. We will also utilise any JULES developments from the NERC Hydro-JULES program that further improve terrestrial water cycle modelling. The latest JULES terrestrial carbon and nitrogen parameterisations will also be used.
Methodology:
The student will develop a soil biogeochemistry model which encompasses the impact of sulphur and nitrogen on CH4 production and emission in the soil. The parameterisation will be incorporated into the latest version of the JULES model, which includes the latest carbon and nitrogen cycle descriptions, and hydrology and CH4 wetland models.
The impact of these pollutants on CH4 generation through changes in soil biogeochemistry, and direct and diffuse surface radiation will then be incorporated and assessed with JULES. This will include evaluation of both long-term trends and inter-annual variability. Validation will include comparisons against: field data; estimated large-scale emissions, such as from atmospheric inversion models; and historical atmospheric CH4 concentrations by using a simple model of atmospheric CH4 lifetime.
There is the potential to run the model off-line for future socio-economic scenarios such as how it affects estimates of allowed anthropogenic emissions consistent with Paris climate targets.
Training and skills:
Students will be awarded CENTA2 Training Credits (CTCs) for participation in CENTA2-provided and ‘free choice’ external training. One CTC equates to 1⁄2 day session and students must accrue 100 CTCs across the three years of their PhD.
This project will give the student direct experience of high-performance computing and using the Met Office/NERC land surface model JULES. During the project the student will receive training in understanding and evaluating complex systems, land surface modelling and coding. Further, they will be given training in the issues surrounding the global methane cycle and the emission of pollutants. There remains scope for the student to engage with lab and field experiments (COVID-19 permitting).
Partners and collaboration (including CASE):
The project benefits for collaboration with our CASE partner Dr Nicola Gedney of the UK Met Office, world leaders in modelling all aspects of the Earth system including the exchange of greenhouse gases between ecosystems in the Earth surface and the atmosphere. The CASE partner is based at the Joint Centre for Hydro-Meteorology Research in Wallingford, Oxfordshire along with the Centre for Ecology and Hydrology.
COVID-19 Resilience of the Project:
This is a modelling project that will not require field or lab access and contingencies can be put in place for computer/server access as necessary. We foresee limited scope for disruption to the project.
Possible timeline:
Year 1: Develop schemes for impact of pollutants on wetland biogeochemistry within JULES and evaluate against site measurements and atmospheric inversion models. Present a poster of work.
Year 2: Further develop schemes for sensitivity to diffuse/direct radiation interception and integrate improvements with latest wetland methane emissions schemes, including emission through trees. Present at a UK conference.
Year 3: Evaluate the influence of historical, present-day, and (time permitting) projected future emissions of pollutants on the wetland biogeochemistry and methane emissions. Present at an international conference.
Please email potential supervisor Prof Gauci ([Email Address Removed]) for more information.
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