Investigation of the Southern Methane Anomaly: causes, implications, and relevance to past global events.

Lead Research Organisation: University of Cambridge
Department Name: Chemistry

Abstract

Methane is the second most important greenhouse gas and contributes to the atmospheric chemistry affecting ozone. Southern tropical methane sources and sinks constitute a significant component of the global methane budget. The current major anomaly in southern methane growth rate is among the largest on record. Yet despite its importance, tropical methane variability has received relatively little study. This proposal is to investigate the southern tropical methane budget. The work will improve quantification of southern tropical sources and the understanding of the mechanisms of sudden growth events.

Southern tropical methane sources are varied, each having their own isotopic signature in the methane they produce. Wetlands are very extensive in southern tropical S. America and in western parts of southern sub-equatorial Africa, but data on methane emissions from these wetlands are very sparse. Fires in savanna grasslands in Africa and S. America are also significant sources, as are the large ruminant animal populations. Anthropogenic sources are also increasing, with major recent hydrocarbon discoveries. Tropical OH is the major global methane sink.

Ascension Is. is a uniquely located, UK-administered, experimental site for studying the methane budget. At surface the air is almost always SE Trade wind, which arrives from the South Atlantic middle latitudes, and, after Ascension, becomes the background air for Amazonia. Above the trade wind inversion, the air over Ascension is tropical, its origin switching regularly between Africa and S. America. Currently Royal Holloway sustains continuous high-precision CH4 and CO2 measurement (CRDS instrument) and also flask measurement of d13C in CH4 on Ascension, as well as on E. Falkland Is. and on RRS JC Ross.

Methodologically, the project will focus on the measurement of methane in the southern tropics, carrying out campaign studies, especially on Ascension, and modelling the results. Measurement will include continuous measurement by CRDS in Ascension, E. Falklands, bi-annual Atlantic transects by RRS JC Ross, and Tedlar bag sample collection for CH4 and d13C of CH4 in Uganda, Peru and Bolivia. Campaign studies will include installation of a CRDS instrument in Peru and use of an unmanned aerial system (UAV) to sample above the Trade Wind Inversion on Ascension, as well as source campaigns to characterise d13C signatures of CH4 emissions in Africa and S. America. The proposed helicopter UAV deployment exploits new expertise and would represent an important UK deployment of a substantial UAV for atmospheric sampling. This deployment therefore addresses one of the key science challenges set out in the NERC scoping study for next-generation platforms for Earth & Environmental Science. Modelling studies are also state-of-the-art, and will include regional trajectory analysis to assess source inputs across Africa and S. America, and global modelling of d13C of CH4, tested against the measurements made in the project.

The results will be used to assess the importance of southern tropical methane in the global budget, the causes of rapid past changes, and the possibility of future rapid growth in emissions.

Planned Impact

This work will have impact for scientists, development thinkers, and policy makers. Better measurement of tropical emissions is vital for the scientific community who model greenhouse gas budgets, providing data in a globally important yet very little studied region, and quantifying regional CH4 fluxes. The work will provide understanding of the environmental health of wetland and savanna regions of southern tropical Africa and S. America. Such work feeds into policy, both in greenhouse gas negotiations and in development policy in Africa.

The Ascension and Falklands continuous high precision CH4 and CO2 measurement forms a contribution to UK national capability in greenhouse gas monitoring. These high-precision greenhouse gas measurement time series, which will otherwise be unfunded, will provide a vital input to global CH4 modelling. There is very limited greenhouse gas measurement in the southern tropics worldwide, and global greenhouse budget models are badly hampered by this lack. If the continuous Ascension and Falklands greenhouse gas time series are lost, global modelling as a whole will be made more difficult.

The data will input to global CH4 measurement, supporting the UN Global Atmosphere Watch (GAW), and will meet the UK's moral obligation in this large area in which the islands are UK owned. Data will be submitted to primary databases used by global greenhouse gas modellers, including the World Data Centre for Greenhouse Gases (WDCGG), one of the WDCs under the GAW programme.

Scientifically, sustaining improved CH4 budgets in the Southern Tropics and specific information for the South Atlantic will inform IPCC. UK government policy makers will be helped the better knowledge of global greenhouse gas budgets. More generally, installation of high-precision measurement capability on the JCR and the Atlantic network of stations will contribute greatly to NERC's charter task of measurement. Commercially the work will be of benefit to firms such as Earth Networks, that are building global greenhouse gas networks.

In terms of public benefit, we will work in collaboration with the National Schools Observatory (NSO) to promote understanding of greenhouse gas science in UK schools. The NSO currently has ~2000 registered schools engaging with young people at Key Stage 3 and 4. NSO will host a Greenhouse Gas Monitoring website that will (i) present Near-Real-Time CO2 and CH4 data from Ascension and Falklands monitoring stations, (ii) serve that data to registered school users and (iii) provide online tutorials to various public domain back-trajectory tools, information, and news that will enable schools to get the best use out of the data. NSO and Project partners will populate the website with background, historical plots, images, news, interviews etc. See: http://www.schoolsobservatory.org.uk/astro/tels/weather. This collaboration will support GCSE curriculum modules from various examination boards.

More generally, we will engage with journalists using our excellent existing links: for example, a recent paper by the PI on methane emission by dinosaurs was reported worldwide, and, more profoundly, a Royal Society Discussion meeting on Greenhouse Gases led to sustained media interest at the highest level not only in the UK but in the EU, US and worldwide.

Publications

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