Methane from herbivores: Impact on modern and ancient climate change

Methane is the second most important anthropogenic greenhouse gas and as such makes a major contribution to climate change. It has been increasing in the atmosphere for the past 5000 years, but the reasons for both past increases and recent increases are not fully understood. In addition, predictions of future atmospheric methane levels require an accurate knowledge of all sources.

Herbivorous animals, particularly ruminants and other foregut fermenters, make a significant contribution to global methane emissions, but estimates of this contribution are poorly constrained for the present and the archaeological past. Existing methods can be used to measure the amount of methane produced by domesticated ruminants such as cows and sheep. However, these methods cannot be readily applied to wild animal populations, for animal welfare and logistical reasons.

Archaeol is a lipid produced by archaea including the methane-producing methanogens, such as those found in the digestive tract of herbivores. Previous studies have shown that archaeol is present in the faeces of foregut-fermenting herbivores and that for cows on contrasting diets, the concentration of archaeol in the faeces co-varies with the amount of methane produced. However, details of the quantitative relationship between archaeol and methane production are currently poorly understood. This project seeks to address this knowledge gap by quantifying archaeol and measuring methane in several key suites of samples. This will improve understanding of the controls on faecal archaeol concentration, allowing a quantitative proxy for methane emissions in herbivores to be developed. Such a proxy could be used to generate methane estimates to be incorporated into existing atmospheric models of methane sources. This project will also produce new estimates of the impact of livestock on prehistoric methane levels, through the use of the global climate models with changes in atmospheric methane levels across the last 5000 years.

In this project, you will work with leading scientists at the University of Leeds and elsewhere to:

1. Carry out in vitro fermentation experiments on a range of herbivore feeds and quantify the methane and archaeol produced.
2. Quantify archaeol in samples from the digestive tract of herbivores and compare with PCR data on methanogens where available.
3. Quantify archaeol from an extensive range of herbivore faecal samples, spanning multiple taxa and digestion types, and compare with methane emission data where available.
4. Integrate results to develop a faecal lipid proxy for methane emissions.
5. Test the proxy at a local and regional scale.
6. Simulate the dispersion of methane from herbivores in the atmosphere using numerical models, and compare the simulations with recent in-situ methane observations.
7. Assess the role of herbivore methane emissions in present-day climate change and test its potential role in climate changes of the past 5000 years.

Applicants should have a background in a relevant subject, such as biology, chemistry, Earth or environmental science, with an interest in global environmental problems.