Methane (CH4) is a major source of greenhouse gas (GHG), it amounts to 23 times more potent than CO2 in trapping heat in the atmosphere and contributing to global warming, but is easier to control. Methane's brief atmospheric lifetime of about 12 years, coupled with its potency, make it attractive for near-term climate mitigation.

The natural byproduct of decomposition, methane emissions from landfills and agricultural wastes are abundantly available. These emissions represent an opportunity to significantly reduce greenhouse gas (GHG) emissions by capturing and destroying these emissions before they have a chance to enter the atmosphere. Landfill gas (LFG) is created as solid waste decomposes in a landfill. This gas consists of about 50% methane, the primary component of natural gas, and about 50% carbon dioxide. Instead of allowing LFG to escape into the air, it can be collected and combusted for energy or heat production, or simply destroyed by flaring. In the latter case, oftentimes the facility qualifies as a GHG emission reduction project that generates verified emission reductions (VERs) or carbon offsets. A key measure for determining this eligibility is whether the project is additional; in other words, the reductions must go beyond what would have happened anyway or in a "business as usual" scenario. LFG is extracted from landfills using a series of wells and a blower/flare (or vacuum) system. This system directs the collected gas to a central point for processing and treatment. From this point, the gas can be flared to destroy it. When combusted, each molecule of methane is converted to one molecule of CO2, thus reducing the global warming effect by 96%. Globally, livestock are the largest source of methane from human-related activities. This methane can be captured and destroyed by flaring, using a process akin to landfill gas flaring. Typically, livestock operations replace their conventional anaerobic manure management system with agricultural digesters, which combust manure gas. This methane collection and combustion is new on the agricultural scene, so most digester projects go beyond "business as usual" and are eligible as GHG offset projects producing verified emissions reductions.

What is methane?
 Methane (CH4) is a greenhouse gas that remains in the atmosphere for approximately 9-15 years. Methane is about 23 times more effective in trapping atmospheric heat than carbon dioxide (CO2) over a 100-year period and is emitted from various natural and human-influenced sources. Human-influenced sources include landfills, natural gas and petroleum systems, agricultural activities and coal mining. Methane is also a primary constituent of natural gas and an important energy source. As a result, efforts to prevent or utilize methane emissions can provide significant energy, economic and environmental benefits.

How much methane is now in the atmosphere?
 The historical record, based on analysis of air bubbles trapped in ice sheets, indicates that methane is more abundant in the Earth's atmosphere now than at any time during the past 400,000 years. Since 1750, global average atmospheric concentrations of methane have increased by 150 percent from approximately 700 to 1,745 parts per billion by volume (ppbv). Over the past decade, although methane concentrations have continued to increase, the overall rate of methane growth has slowed from approximately 20 ppbv per year to 9-13 ppbv per year.

Where does methane come from?
Methane is emitted from both human-related and natural sources. Human-related activities contribute about 60% of all methane emissions. The rest come from natural sources, including wetlands, permafrost and oceans.

What are the main human-related sources?
In the United States, the largest methane emissions come from the decomposition of waste in landfills. Livestock manure is another key source.

Landfills.
Landfills are the largest human-related source of methane in the U.S., accounting for 34% of all methane emissions. Methane is generated in landfills and open dumps as waste decomposes under anaerobic conditions. The amount of methane created depends on the quantity and moisture content of the waste and the site's design and management practices. Landfill gas is generated during the natural process of bacterial decomposition of organic material contained in landfills, organic compounds in the waste, and the moisture content and temperature of the waste.

Livestock.
Among domesticated livestock, ruminant animals (cattle, buffalo, sheep, goats, and camels) produce significant amounts of methane as part of their normal digestive processes. In the rumen, or large fore-stomach, microbial fermentation converts feed into products that can be digested and utilized by the animal. This microbial fermentation process, referred to as enteric fermentation, produces methane as a byproduct, which can be exhaled by the animal. Methane is produced during the anaerobic (i.e., without oxygen) decomposition of organic material in livestock manure management systems. Liquid manure management systems, such as lagoons and holding tanks, can cause significant methane production. Anaerobic digestion technologies recover and combust methane for odor control and energy production.

How can methane emissions from landfills be contained before entering the atmosphere?
Methane can be captured and used to generate energy, or it can be destroyed through a flaring process. Either method prevents methane emissions from entering the atmosphere. In the case of flaring, the facility may qualify as a GHG offset project. A key measure for determining the project's eligibility is whether the emissions reductions are actually additional; in other words, the reductions must go beyond what would have happened anyway or in a "business as usual" scenario. Methane capture and destruction at a landfill begins when landfill gas is extracted using a series of wells and a blower/flare (or vacuum) system. This system directs the collected gas to a central point where it can be flared and destroyed. When combusted, each molecule of methane is converted to one molecule of CO2, thus reducing the global warming effect by 96%.

What about controlling agricultural methane?
As with landfills, agricultural methane can be captured and used for energy, or it can be destroyed. When the objective is to destroy the methane, a common method for reducing GHG emissions from manure management systems is to replace conventional anaerobic manure management technology. Lagoons and liquid/slurry systems are superseded by an agricultural digester system that collects and combusts manure gas. To qualify as verified emissions reductions, such projects must pass a regulatory screen to ensure that the reductions would not have occurred anyway to satisfy government regulations. Today, most processes for manure management do not include methane collection and combustion. Therefore, digester projects can typically be considered beyond "business as usual". In other words, these projects are eligible GHG offset projects producing verified emissions reductions.

Real: Quantified GHG reductions represent actual emission reductions that have occurred.

Additional: Project-based GHG reductions go beyond what would have happened anyway or in a "business as usual" scenario.

Permanent: GHG reductions are permanent and can be backed by guarantees if reversed (e.g. re-emitted into the atmosphere).

Verifiable: GHG reductions result from projects whose performance can be readily and accurately quantified, monitored and verified.