Methane (CH4) is the second most important greenhouse gas and its atmospheric concentration is increasing. However, in a period up to 2007 this growth stalled, but has since started to grow again. The abundance of the minor methane isotopologue 13CH4 was approximately constant pre 2008 and then started to decrease. These changes of the atmospheric CH4 cycle are poorly understood which limits our ability to make predictions of future levels of atmospheric CH4. The aims of this project are to deduce the causes of these causes using forward and inverse atmospheric transport modelling. The project will use a detailed 3-D atmospheric model and its 4D-Var inverse version. A novel element of this approach is to include 13CH4 into the modelling framework and to exploit the information which the combines 12CH4 and 13CH4.
Similar to atmospheric CO2, atmospheric CH4 levels have increased strongly over the last century. Since 1900 they have approximately doubled. However, unlike carbon dioxide methane reacts in the atmosphere with OH with a lifetime of approximate 9 years and, as a consequence, its levels are approximately 200 to 300 times lower than those of CO2. However CH4 is a much more effective greenhouse gas which makes the anthropogenic atmospheric methane perturbation the second largest contributor to anthropogenic greenhouse warming after CO2.
Methane is produced in various ways, including incomplete combustion of carbohydrates (fossil fuel and biomass burning), loss during recovery and transport of fossil methane, as well as methanogenesis of organic matter under anoxic conditions in wetlands, rice paddies and also guts of animals, predominantly cows.
The core of the project is to exploit not only the information in 12CH4 but also of 13CH4 to analyze the recent trends in atmospheric CH4 and what they may mean for future levels of CH4. This will involve:
(1) development of forward modelling of atmospheric 13CH4 and 12CH4,
(2) adaptation of the inverse modelling scheme developed for CH4 to include 13CH4
(3) estimation of spatially resolved surface fluxes and rough attribution to processes for the period from 1998 to 2012.
The project will thus combine data analysis, atmospheric transport modelling focussing on 13CH4, and inverse modelling development to include 13CH4 and its application to the CH4 and 13CH4 cycle.
This project is in competition for funding as part of the Leeds PICC studentships http://www.priestley.leeds.ac.uk/
The award will pay full fees and stipends. There is also a generous budget for travel and research expenses.
Nisbet, E. G., E. Dlugokencky, and P. Bousquet, Methane on the Rise—Again, Science, 343, 493-495, doi:10.1126/science.1247828, 2014.
Wilson, C., M.P. Chipperfield, M. Gloor, and F. Chevallier, Development of a variational flux inversion system (INVICAT v1.0) within the TOMCAT chemical transport model, Geosci. Model Dev., 7, 2485-2500, doi:10.5194/gmd-7-2485-2014, 2014.
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FTE Category A staff submitted: 79.20
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