Cows put it out there. So do mines and landfills. On a molecular level, methane gas is elegantly simple, just four tiny hydrogen atoms surrounding a single carbon atom.
Zoom out, however, and the picture is more complex, particularly when it comes to climate change. Methane, the main component in natural gas, is both a rich source of energy and a powerful greenhouse gas.
Our atmosphere allows solar energy to reach and warm the Earth's surface. However, greenhouse gases in the atmosphere trap the heat emitted from the Earth's surface and prevent it from escaping to space. To a point, the greenhouse effect is beneficial to life on Earth. Greenhouse gases in the atmosphere keep surface temperatures warm enough for life on Earth to flourish. Without them, Earth would be an inhospitable ice ball.
Since the start of the industrial revolution, human activity has added greatly to the amount of carbon dioxide, methane, and other greenhouse gases in the atmosphere. While carbon dioxide is the most abundant and has a much longer life span, methane is more potent at trapping heat.
Where's all this methane coming from?
Mining and the processing of fossil fuels are the principal sources of methane. Livestock emit large quantities of the gas as they digest grain and grasses. Landfills also give off lots of methane as garbage decays.
NOAA scientists have been measuring the levels of these gases for many decades. The changes in the levels are summarized yearly in the NOAA Annual Greenhouse Gas Index.
Their measurements have tracked startling increases in greenhouse gases over time, as well as increases in average surface temperature. As the atmosphere warms, NOAA scientists expect that alterations in climate will bring more intense storms, heat waves, droughts, flooding and rising sea levels.
Methane levels, however, have not shown a consistent upward trend. From the late 1970s through the late 1990s, methane levels in the atmosphere rose but then flattened until they began increasing again in 2007. Methane emissions from wetlands found mainly in the tropics, with some in the Arctic, are the likely reason for the increase.
As global temperature rises, scientists have been keeping their eyes on another source of methane - permafrost. As soil that has remained at or below freezing for two or more consecutive years, permafrost resides near the poles and at high altitudes. Permafrost in the Northern Hemisphere holds vast amounts of carbon equal to the amount of carbon in known coal reserves. The Southern Hemisphere, having relatively less land area, has less permafrost.
As temps rise, so does methane
Thawing of permafrost would liberate a great quantity of methane: As the soil warms, microbes digest vegetation contained in this frozen ground, releasing methane as the byproduct. Potentially, this process could set a feedback cycle into motion, amplifying atmospheric warming, increasing permafrost thaw and promoting the release of more methane.
"NOAA's Earth System Research Lab analyzes methane in air samples collected around the world," says Ed Dlugokencky, Ph.D., a NOAA research chemist who leads the methane monitoring program. "The data we generate from these samples helps us understand global trends and details of the methane cycle. We do not see signs of a feedback cycle yet, but continued monitoring is very important."
A new study led by Kevin Schaefer, Ph.D., and a team of scientists from NOAA-funded Cooperative Institute for Research in Environmental Sciences and the NOAA Earth System Research Lab now predicts a 29 to 59 percent decrease in permafrost by 2200. Published in the journal Tellus B, the study estimates a large release of carbon - in the form of carbon dioxide and methane - from thawing permafrost over the next century, though much is still unknown about how these emissions will accelerate climate warming.
Scientific climate projections do not currently account for carbon emissions from permafrost, but the study concludes that the effect is "strong enough to warrant inclusion in all projections of future climate."
NOAA's mission is to understand and predict changes in the Earth's environment, from the depths of the ocean to the surface of the sun, and to conserve and manage our coastal and marine resources. Visit us on Facebook.