2001: Methane Emissions: A Fairer Accounting and Historical Trends from Fossil Fuel Consumption

The Methane Team will focus this summer on two general areas - research and education. In the following, we summarize our current status with respect to both of these efforts, and outline specifics of this summer's research goals for each effort.

1. Introduction

In situ measurements of atmospheric methane (CH₄) concentrations begun in the early 1980s exhibit decadal trends, as well as large interannual variations, in growth rate although the cause of these variations is not well understood. Since the atmosphere reflects the combined effect of inputs of CH₄ to the atmosphere from terrestrial sources and removal of CH₄ from the atmosphere via chemical destruction by OH (sinks), variations in concentrations are caused by changes in sources, changes in sinks, or a combination of the two. Recent research indicates that while wetlands can explain several of the large changes in concentration for individual years, the decadal trend may be the combined effect of increasing sinks (due to increases in tropospheric OH) and stabilizing sources.

Previous research by the Methane Team resulted in historical (1980-present) estimates of annual methane emissions from the major CH₄ sources including ruminant animals, rice cultivation, landfills, and wetlands. In addition, we assumed that several other sources, which remain extremely uncertain, produce constant emissions for each year of the history as follows: termites (20 Tg CH₄/yr) (1 Tg = 10¹² g), oceans (10 Tg CH₄/yr), and biomass burning (40 Tg CH₄/yr). Biomass burning is probably the most uncertain and the largest of these sources. In addition, because biomass burning is initiated by natural processes (lightening) and by human activities (land-improvement and clearing, domestic fuel consumption), it is controlled by climate and by people. In order to get a an initial sense of the trend and interannual variations in CH₄ emissions from fossil fuel production, processing, and transmission, we used the estimate of other researchers

In analyzing the history of methane emissions from these sources, we were able to identify wetlands as the major source for interannual variations in emissions and therefore in fluctuations in atmospheric concentrations of methane. Emissions from rice cultivation remained almost constant for the period while emissions associated with ruminant animals and landfills increased at very modest rates for the ~20 years. However, the simple fossil fuel history showed some interesting trends and interannual variations. Since emissions from fossil fuels account for about 20% of total emissions, it became clear to us that a more intensive effort to establish a reliable history of emissions was necessary in order to investigate the potential role of these fuels in the decadal observations of atmospheric methane concentrations.

The overall goal of the Methane Team's research is to understand the history of methane emissions from major methane sources individually in order to explain decadal trends and interannual variations in growth rates of atmospheric methane observed at a global network of measuring stations. The research goal of this summer is to focus on expanding and improving our understanding of emissions from production, processing, and transmission of fossil fuels including natural gas and coal.

Education

During the last five summers of ICP research, we have written a large body of background educational materials as well as a series of lessons for upper-middle and high-school students. These materials include the following:

• Introduction to the greenhouse effect
• Introduction to the global methane cycle
• Changes in greenhouse gas concentrations between pre- and post-industrial periods.
• A project-based unit using methane data to answer a real science question, "Why is the rate of increase in atmospheric methane concentration decreasing?"""
• Short- and long-term research projects related to methane emissions which students may do.

These materials and lessons have been evaluated (within ICP and in classroom environments) and have been incorporated as fundamental components of the Earth Science curriculum at the Mott Hall School during the last five years. In addition, Mott Hall students have undertaken the following research projects during the school years as follows:

• Estimating 1990 global methane emissions from landfills (1996-99)
• Estimating 1990 regional and global per capita profiles of methane emission from landfills, rice, and animals (1999-2000)
• Comparing production and exports of rice and cattle to see who should be responsible for methane emissions? - the producer or consumer (2000-01)

Guiding Science Questions

What is a sink? E.g., if everything else remains constant, does a sink increase or decrease atmospheric concentrations?

What is the relationship between CH₄ emissions and CH₄ concentrations in the atmosphere?

What is the general contribution of natural methane emissions versus anthropogenic (human generated) methane emissions in an average year?

What is the historical trend (general pattern of change) in CH₄ emissions for the period 1980-present for rice, for ruminant animals, for landfills, for fossil fuels, and for wetlands?

Which source emissions are relatively stable over time? which are increasing? which are declining?

What single source could have the largest impact on concentrations if it changed, for example, by 25%?

How variable are year-to-year changes in emissions from each of these sources? (Ignore oceans, termites, and biomass burning since they were set to constant values for all years.)

Which source varies the most from year to year (in absolute value of Tg), and therefore probably explains some of the large changes in atmospheric methane concentrations for individual years. For example, look at 1992 (this was a year with a small change in concentrations) and 1998 (this was a year of large changes in concentrations).

Hypothesize about what effect an increase or decline in temperature might have on methane emissions from wetlands? What effect might an increase or decrease in precipitation have on these emissions?

What may be causing the observed decrease in the rate of increase in the concentration of atmospheric of methane?

Plans

The major effort will be to identify and obtain the large amount of data required to estimate annual methane emissions from every country in the world. In particular, we need to collect information, by year and country, on production of natural gas (NG) (which is 95% methane), and amount of NG production that is flared or vented at production wells. For coal, we require production of hard coal (less methane released upon processing and use) and soft/brown coal (higher methane release rates) for all countries and years. Estimates of methane emission from these sources will follow the methodologies promoted by the Intergovernmental Panel of Climate Change as well as modifications of these methods proposed by expert groups assessing the methods. When completed, these new global historical inventories of methane emissions from this suite of fossil fuel sources and processes will be integrated into our analysis of the last ~20 years of emissions from all sources in order to identify the role of source changes in the observed variations in atmospheric methane.

The education work for this summer will focus on preparing and finalizing a packet of materials for teachers at the upper-middle school and high-school level which focuses on problem-solving activities involving methane. The packet will comprise background materials adapted for use by teachers, as well as lessons and a selection of prepared long- and short-term projects that students may select to undertake. All necessary materials, including the data necessary to carry out the investigations, will be placed on the ICP website for teacher use.

• H. Augenbraun - finalize teacher and student materials for web page; assist with integrative analysis of summer research
• A. Adams, L. Dorn, D. Sarma - identify, search for, and obtain data required for calculation of methane emissions from fossil fuel sources for 1980-2000; carry out calculations; analyze results; write individual paper sections on sources; contribute to integrated analysis

Basic Science Questions

What is the greenhouse effect?

Do greenhouse gases capture heat energy traveling downward through the atmosphere or upward through the atmosphere?

Explain the difference between the natural greenhouse effect and the perturbed or enhanced greenhouse effect?

Have greenhouse gas concentrations in the atmosphere varied over long time periods (e.g., hundreds of thousands of years?) By how much? Are there any cycles or trends in these changes? Is there any relationship between greenhouse gas concentrations in the atmosphere and temperature?

Which is more effective at trapping heat on a molecule basis - carbon dioxide or methane?

Which greenhouse gas has contributed most to the rise in temperature over the last 100 years?