Methane: A Powerful Greenhouse Gas

Methane bubbles from lake sediment trapped in ice.
Methane bubbles from lake sediment trapped in ice. Piriya Photography / Getty Images

Methane is a major constituent of natural gas, but its chemical and physical characteristics also make it a powerful greenhouse gas and worrisome contributor to global climate change.

What Is Methane?

A methane molecule, CH4, is made of a central carbon atom surrounded by four hydrogens. Methane is a colorless gas usually formed in one of two ways:

  • Biogenic methane is produced by microorganisms breaking down certain types of sugars in conditions where oxygen is absent. This biologically-produced methane can be released to the atmosphere immediately upon being produced, or it can be accumulated in wet sediment only to be released later.
  • Thermogenic methane was formed when organic matter was buried deeply under geological layers and over millions of years, and then broken down by pressure and high temperatures. This type of methane is the primary constituent of natural gas, making up 70 to 90% of it. Propane is a common by-product found in natural gas.

Biogenic and thermogenic methane may have different origins but they have the same properties, making them both effective greenhouse gases.

Methane as a Greenhouse Gas

Methane, along with carbon dioxide and other molecules, contributes significantly to the greenhouse effect. Reflected energy from the sun in the form of longer wavelength infrared radiation excites methane molecules instead of traveling out into space. This warms up the atmosphere, enough that methane contributes to about 20% of the warming due to greenhouse gases, second in importance behind carbon dioxide.

Because of the chemical bonds within its molecule methane is much more efficient at absorbing heat than carbon dioxide (as much as 86 times more), making it a very potent greenhouse gas.

Fortunately, methane can only last about 10 to 12 years in the atmosphere before it gets oxidized and turns into water and carbon dioxide. Carbon dioxide lasts for centuries.

An Upward Trend

According to the Environmental Protection Agency (EPA) the amount of methane in the atmosphere has multiplied since the industrial revolution, growing from an estimated 722 parts per billion (ppb) in 1750 to 1834 ppb in 2015.

Emissions from many developed parts of the world have now appeared to have leveled off, however.

Fossil Fuels Once Again to Blame

In the United States, methane emissions come primarily from the fossil fuel industry. Methane is not released when we burn fossil fuels, like carbon dioxide does, but rather during the extraction, processing, and distribution of fossil fuels. Methane leaks out of natural gas well heads, at processing plants, out of faulty pipeline valves, and even in the distribution network bringing natural gas to homes and businesses. Once there, methane continues to leak out of gas meters and gas-powered appliances like heaters and stoves.

Some accidents occur during the handling of natural gas resulting in the release of large amounts of gas. In 2015 very high volumes of methane were released from a storage facility in California. The Porter Ranch leak lasted for months, emitting almost 100,000 tons of methane into the atmosphere.

Agriculture: Worse than Fossil Fuels?

The second largest source of methane emissions in the United States is agriculture. When evaluated globally, agricultural activities actually rank first. Remember those microorganisms that produce biogenic methane in conditions where oxygen is lacking?

Herbivorous livestock guts are full of them. Cows, sheep, goats, even camels have methanogenic bacteria in their stomach to help digest plant material, which means they collectively pass very large quantities of methane gas. And it is not a minor issue, as a full 22% of methane emissions in the United States are estimated to come from livestock.

Another agricultural source of methane is the production of rice. Rice paddies contain methane-producing microorganisms as well, and the soggy fields release about 1.5% of global methane emissions. As the human population grows and with it the need to grow food, and as temperatures rise with climate change, it is expected that methane emissions from rice fields will continue to increase. Adjusting rice-growing practices can help alleviate the problem: temporarily drawing down water mid-season, for example, makes a big difference but for many farmers, the local irrigation network cannot accommodate the change.

From Waste to Greenhouse Gas – to Energy?

Organic matter decomposing deep inside a landfill produces methane, which is normally vented out and released into the atmosphere. It’s an important enough problem that landfills are the third largest source of methane emissions in the United States, according to the EPA. Fortunately, an increasing number of facilities capture the gas and route it to a plant that uses a boiler to produce electricity with that waste gas.

Methane Coming from the Cold

As Arctic regions warm up quickly methane is released even in the absence of direct human activity. The Arctic tundra, along with its numerous wetlands and lakes, contains large amounts of peat-like dead vegetation locked in ice and permafrost. As those layers of peat thaw, microorganism activity picks up and methane is release. In a troublesome feedback loop the more methane there is in the atmosphere, the warmer it gets, and more methane is released from the thawing permafrost.

To add to the uncertainty, another worrying phenomenon has the potential to further disrupt our climates very rapidly. Under Arctic soils and deep in oceans large concentrations of methane exist entrapped in an ice-like mesh made of water. The resulting structure is called a clathrate, or methane hydrate. Large deposits of clathrate can be destabilized by changing currents, underwater landslides, earthquakes, and warming temperatures. The sudden collapse of large methane clathrate deposits, for whatever reason, would release lots of methane in the atmosphere and cause rapid warming.

Reducing Our Methane Emissions

As a consumer, the most effective way to lower methane emissions is by reducing our fossil fuel energy needs. Additional efforts include choosing a diet low in red meat to reduce the demand for methane-producing cattle, and composting to reduce the amount of organic waste sent to landfills where it would produce methane.