Emissions of methane (CH4) are the 2nd largest contributor to global climate change, but the attribution of emissions to specific sources, such as natural gas leaks, landfills or livestock, currently has large uncertainties. This project advanced the state-of-the-art for characterisation of anthropogenic sources of CH4 with the use of radiocarbon and it created new directions in atmospheric methane research, with the potential to impact global climate policy and industrial practices over the next 10-20 years.
We developed an innovative new technique to sample atmospheric CH4 for radiocarbon analysis that simplifies and improves upon previous methods (WP1). Radiocarbon measurements in atmospheric CH4 (14CH4) can identify fossil fuel emissions because radiocarbon is absent in fossil fuel CH4 (from natural gas, coal) but present in biogenic CH4 (waste, livestock). However, it is challenging to perform 14CH4 measurements using current techniques. Our new technique has been proven and applied to measure 14CH4 in London, providing the first quantitative regional assessment of fossil CH4 emissions using 14CH4 and showing strong fossil CH4 emissions in London. The technique is now being developed into a portable, automatic system that can be easily used by other researchers, as part of a Marie Curie fellowship by one of the team members.
By close examination of nuclear reactor design and operation, we have produced improved estimates of 14CH4 emissions from nuclear power plants, which can interfere with the 14CH4 tracer technique (WP2). We have developed the first 3-dimensional modelling of 14C in CH4 at regional and global scales to enable the application of 14CH4 observations to estimate the fossil fraction of global and regional CH4 emissions (WP3 and WP4). We have conducted a multi-tracer analysis of the global CH4 budget that incorporates multiple constraints as well as uncertainties that have previously been neglected, leading to biases in prior work.
Major outcomes of this project are the introduction and deployment of new approaches to identify fossil vs biogenic CH4 emissions, validate CH4 emissions mitigation policies and understand the response of wetland ecosystems to climate change.
