These pages describe the work being done as part of the Natural Environment Research Council project, SISLAC (2017-2020).


Atmospheric methane (CH4) accounts for ~20% of the total direct anthropogenic radiative forcing by long-lived greenhouse gases making it the second largest contributor after CO2. In addition to direct radiative forcing effects methane breaks down to form CO2 and water vapour. As a major contributor to stratospheric water vapour CH4 indirectly contributes to the degredation of the ozone layer.

Since the pre-industrial era human activities have accelerated the growth of CH4 and the atmospheric concentration now measures at ~1850 ppb, which is approximately a 150% increase since 1750. Methane has a relatively short atmospheric lifetime compared to CO2 of ~10 years, this means any changes to the sources or sinks can be detected in the trends in atmospheric concentration. As a result, CH4 is a suitable target species for short-term climate change mitagation strategies.


It is not only human activities that produce CH4; approximately half of all emissions are natural in origin. These include emissions from wetlands, wildfires, oceans and even termites. Determining the cause of changes in global atmospheric methane is often difficult because of the multiple different sources and sinks.




Global CH4 emissions based on IPCC estimates.


Global CH4 concentration measured from NOAA surface sites.


Atmospheric measurements taken since the mid-1980s show a steady growth in global CH4 with large interannual variability. During the 1990s the growth rate slowed and in 1999 a period of near-zero growth began which continued until 2007. This balancing in the methane budget indicated one of two things, either an approach to steady state or interannual variability in the sources/sinks. Since 2007 the growrth rate has resumed and the atmospheric concentration of CH4 continues to rise. The reasons for this remain poorly understood.

Typically measurements of CH4 are made from surface sites, either in-situ or using flask samples, other sources of CH4 data include ground based Fourier Transform Spectrometers (e.g. TCCON) and satellite retrivals (e.g. GOSAT).

Isotopic measurements of δ13CH4 provide an additional tool in attributing sources and sinks to observed trends in atmospheric CH4. In 2007 their was a shift in isotopic signature to a light δ13CH4 depleted CH4 concentration, which coincided with the observed increase in CH4. Possible explanations for these two trends include :

  • a decrease in δ13CH4 enriched fossil fuel emissions (this alone would not explain the rise in CH4).
  • an increase in δ13CH4 depleted microbial emissions (e.g. wetlands, agriculture).
  • a decrease in the atmospheric sink, which enriches δ13CH4.
  • a combination of all three.
Global δ13CH4 overlayed onto CH4 measured from NOAA surface sites.

By using CH4 and isotopic measurements combined with forward and inverse model simulations we can gain a better understanding of changes in methane sources and sinks.


Here is a list of recent relevant publications related to short-lived atmospheric chlorine species and a brief comment on their importance.


Hossaini, R., M.P. Chipperfield, S.A. Montzka, A.A. Leeson, S.S. Dhomse, and J.A. Pyle,
The increasing threat to stratospheric ozone from dichloromethane,
Nature Communications, 8, 15962, doi:10.1038/ncomms15962, 2017.
This paper...

Oram, D., M.J. Ashfold, J.C. Laube, L.J. Gooch, S. Humphrey, W.T. Sturges, E. Leedham-Elvidge, G.L. Forster, N.R.P. Harris, M. Iqbal Mead, A. Abu Samah, S. Moi Phang, C.-F. Ou-Yang, N.-H. Lin, J.-L. Wang, A.K. Baker, C.A.M. Brenninkmeijer and D. Sherry,
A growing threat to the ozone layer from short-lived anthropogenic chlorocarbons,
Atmos. Chem. Phys, 17, 11929, doi:10.5194/acp-17-11929-2017, 2017.
This paper...












Moya @ Leeds Website 2017