Methane as a Greenhouse Gas: Ask the Expert Question Answered

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Gas cooker

Methane is considered a “cleaner” fuel. Image by tranquillity

Methane is a powerful greenhouse gas present in the atmosphere, the second most abundant greenhouse gas, and it is mainly due to human activities.

This article describes the different methane sources and the possible measures to limit/decrease its emissions.

Methane

Methane is the simplest hydrocarbon, with the formula CH– it is often referred to as natural gas.

CH4 has several important uses; it is employed, for instance, as fuel in combustion processes to generate energy. It is generally considered a “cleaner” fuel when compared to oil or coal, since it rarely contains impurities such as sulfur or particulates.

CH4 is also used in industry, as a starting material to prepare larger/more complex molecules.

What Is Greenhouse Gas?

A greenhouse gas is a gaseous species which, if present in the Earth´s atmosphere, is capable of retaining/trapping some of the energy emitted from the sun.

The most abundant and known greenhouse gas is carbon dioxide, CO2. Although CO2 is naturally present in the atmosphere, its concentration has increased remarkably in recent years, since it is generated from the combustion of fossil fuels.

According to some people, the higher concentrations of greenhouse gases in the atmosphere due to human activities are the cause of global warming.

Methane Greenhouse Gas Potential

CH4 is the second most common greenhouse gas in the atmosphere. Scientists and environmentalists are concerned by this, since it is a much more powerful greenhouse gas than CO2. Methane’s greenhouse gas potential is in fact more than 80 times higher than CO2. This means that, considering the same molar amount, CH4 can trap 80 times more energy than CO2.

Plant of natural gas

Natural gas is often found with oil. Image by anita_starzycka

CH4 Sources

The majority of CH4 present in the atmosphere comes from human activity; in the US, for instance, about 60% of CH4 has an anthropogenic source.

CH4 can be leaked into the atmosphere during the various stages of its use as a fuel; for example, leaks can occur during the extraction, storage or transportation of the gas.

Similarly, leaks can take place during oil processing (i.e. extraction, refining, etc.), since CH4 can be often found together with oil.

CH4 is also formed in landfills, as the organic matter generally present in landfill gets converted into CH4 through anaerobic processes. This conversion can be more or less rapid, depending on the landfill conditions.

Another important source of CH4 is agriculture; ruminant animals such as cattle, for instance, generate methane through their digestive process, which is then emitted through exhaling, belching or breaking wind. Moreover animal manure, if stored in anaerobic conditions, is also converted into methane.

CH4 Emissions Over Time

As stated above, anthropogenic activities are the main sources of atmospheric methane. It has to be highlighted, however, that in recent years overall CH4 emissions have decreased. According to the Environmental Protection Agency (EPA), in the US a 15% decrease was observed between 1990 and 2013 (from about 750 to 630 million tons of CO2 equivalent). In the United Kingdom in the same period, the decrease was even more enhanced, since the total CH4 emission were about 59% lower. Similar trends were observed in other developed countries.

However, despite the reduction in CH4 emissions already observed, some scientists think that further reductions are essential, considering its high greenhouse gas potential.

Improved Technology

An effective way to reduce CH4 atmospheric concentration is to minimize the leaks from both gas and oil industries; this can be achieved with better technology. Indeed, reduced leakage has already contributed to the decrease in the emissions observed in recent years.

In the US, in August 2015, the EPA decided to take this a step further, and proposed a series of measures to minimize CH4 leaks even more. According to the proposal, companies in the oil and gas industry should apply new technologies to new wells.

These proposals are not yet law, as the EPA expects to complete them in 2016, after a period of public debate and feedback from the industries. Up to now, there have been mixed responses: some industries welcomed the initiative; others, however, found it not very useful/helpful, as they thought it replicated the regulations already introduced in 2012 to limit the leakage of Volatile Organic Compounds (VOCs).

Cow.

Agriculture is a source of methane. Image by Keith Weller

Reduced Emissions from Agriculture

Scientists and environmentalists are currently studying possible strategies to reduce CH4 emissions from agriculture. One possible option is to reduce fermentation during the animals’ digestion process, so the amount of methane generated and emitted is lower. This could be done with appropriate food additives.

In a study published in July 2015, for instance, scientists showed the use of a methane inhibitor (3-nitrooxypropanol) in cattle’s diet led to a 30% decrease in CH4 emissions, without affecting milk production.

Researchers are also investigating more efficient ways to handle manure, to reduce methane formation from it, and/or to capture the formed methane, to reuse for industrial applications.

Future Perspectives

Methane presence in the Earth’s atmosphere is clearly a problem which needs to be addressed, due to its high greenhouse potential. Although some improvements have already been observed in recent years, more measures need to be implemented for CH4 emissions to be reduced.

Research in agriculture and improved technology are the keys which can lead to a significant decrease in the long term.

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