1998: Global Methane Inventory

Researchers: Harvey Augenbraun, Elaine Matthews, and Teresa Smith

Atmospheric concentrations of greenhouse gases have increased substantially in the last two centuries. Increases in these gases, including methane (CH₄), carbon dioxide (CO₂) and nitrous oxide (N₂O), are most likely due to anthropogenic (human) activities. The scientific objectives of this research are to understand the global methane cycle, including how its sources and sinks have changed over the last ten years, how they might change in future decades, and what the implications are for climate. The objective of this project is to compile a current, complete, and internationally-recognized inventory of sources of methane and methane emissions. These data contribute to measuring, understanding, and predicting changes in atmospheric chemistry and climate.

Project Goal for 1998-99

The goal of this research is to assess the potential contribution of several anthropogenic sources of methane to the recent trend of declining growth rates in atmospheric methane concentrations. The present rate of increase in the concentration of atmospheric methane is slowing down. Studies suggest that this decline is not due to increased destruction of methane in the atmosphere. Therefore, we need to look at methane sources to see how they are changing. We chose to look at these large anthropogenic methane sources: irrigated rice cultivation, domestic animals, and landfills. Data for rice harvested area, number of domestic animals, and human populations need to be collected. These data will be used to calculate methane emissions from the three sources using the Intergovernmental Panel on Climate Change (IPCC) methodologies for single years at 5-year increments from 1965 to 1995. This will yield a crude approximation of methane emissions from anthropogenic sources from which we may identify trends.

Science Questions

1. What are the atmospheric concentrations of methane over the last two decades?
2. What are the major anthropogenic sources of methane?
3. How have these sources varied over the last 2 decades?
4. What sources are candidates to explain the declining growth rate of atmospheric methane?

Hypotheses

Rice: Since the rice-harvest area has increased very modestly over last 20 years, methane emissions from rice are relatively stable. Domestic animals: Methane emissions have increased with the increase in domestic animal populations. Landfills: Methane emissions in developed countries are declining and will continue to decline in the future; emissions in developing countries are increasing, and will continue to increase in the future.

Research Tasks

1. Complete the inventory of animal populations for 1990 by obtaining data for subnational units of Australia, India, and Canada; develop the geographic distribution of animal populations from these data; carry out the IPCC methodology to estimate 1990 emissions of methane from animals.
2. Gather national statistics for animals, rice harvest, and trash disposal for single years at 5-year increments from 1965 to 1995; carry out country-specific estimates of methane emissions for these three sources over the study's time period using the IPCC methodology.

Data

Annual (global, by political unit) estimates at 5-year increments from 1965 to 1995 from:

• Food and Agriculture Organization
• United States Department of Agriculture
• Statistical yearbooks for China, India, Brazil, Canada, and Australia

Using consistent data sources over time allows assessment of the trend in emissions even if the absolute numbers are not exact. Weaknesses of the data include: no seasonality, large political units, no consideration of management practices that can influence emissions.

References

Chappellaz, J.A., I.Y. Fung, and A.M. Thompson 1993. The Atmospheric CH₄ Increase since the Last Glacial Maximum: (1) Source estimates. Tellus, 45B, 228-241.

Chappellaz, J.A., J.M. Barnola, D. Raynaud, Y.S. Korotkevich, and C. Lorius 1990. Ice-core record of atmospheric methane over the past 160,000 years, Nature, 345, 127-131.

Franzen, L.G. 1994. Are Wetlands the Key to the Ica-Age Cycle Enigma?, Ambio, 23, 300-308.

Lorius, C. and H. Oeschger 1994. Paleo-perspectives: Reducing Uncertainties in Global Change, Ambio: A Journal of the Human Environment, 23, 30-36.

Sinisalo, J. and I. Savolainen. Radiative Forcing Caused by Anthropogenic Greenhouse Gas Emission Histories of the Nordic Countries, Ambio: A Journal of the Human Environment, 25,185-190.

Lerner, J., E. Matthews and I. Fung 1988. Methane emission from animals: A global high-resolution database. Global Biogeochemical Cycles, 2, 139-156.

Matthews, E., I. Fung and J. Lerner 1991. Methane emission from rice cultivation: Geographic and seasonal distribution of cultivated areas and emissions. Global Biogeochemical Cycles, 5(1), 3-24.

Food and Agriculture Organization 1991. 1990 FAO Production Yearbook, vol. 43, Food and Agriculture Organization of the United Nations, Rome.

Matthews, E. 1994. Assessment of methane sources and their uncertainties. In J.P. Slanina, P. Warneck, N.M. Bazhin, H. Akimoto, W.M. Kieskamp (eds.), Assessment of uncertainties in the projected concentrations of methane in the atmosphere, Technical Report, Pure Appl. Chem., 66, 137-200.

Matthews, E. 1993. Wetlands. In M.A.K. Khalil (ed.) Atmospheric Methane: Sources, Sinks, and Role in Global Change, pp14-61, NATO ASI Series, I 13, Springer-Verlag, Berlin.