It is the second biggest contributor to global warming. Methane occurs naturally and is the primary component of natural gas. It constitutes 1.8ppm, or 0.00018% of the atmosphere, much less than carbon dioxide.
Compared to carbon dioxide, methane is:
- 20 times more potent over 100 years
- 100 times more potent over 10 years
The difference in these numbers is partly because methane has a relatively short lifespan in our atmosphere. All told, methane is responsible for 20% of the current warming trend.
Sources of Methane
Methane is released:
- In the production of coal, oil, and natural gas
- From landfills, wetlands, and rice paddies, and
- From the stomachs of grazing animals such as cows, sheep and goats.
The largest source of methane in the U.S. is cattle, according to the Environmental Protection Agency.
Methane is also stored in clathrates, which are deposits of methane that lie on the ocean floor, frozen in lumps of ice. Changes in ocean temperatures and currents could cause a sudden release of methane from these clathrates. Some scientists believe that past releases of methane from clathrates caused warming trends in the Earth’s history.
Current Methane Levels
- Methane levels fell from 1990 to 2004, perhaps due to droughts in wetland areas, as well as better management of landfills, gas wells and oil wells
- Methane levels began climbing again in 2007, which may be the result of the thawing of the arctic tundra
Abrupt Climate Change
A positive feedback loop may occur if the thawing of the arctic tundra causes a rapid release of methane. This would in turn accelerate global warming.
Author: Brown, Nathan. A Cooler Climate, 2008.