What the deep-sea and cows have in common

Abrupt climate change is a complex topic with many causes and numerous implications. But what do cows and deep-sea mud volcanoes have to do with the earth's changing climate? They both produce methane gas.

Why Methane is a Problem

This graph from NOAA shows how the methane concentration in the atmosphere has leveled off between the years 1984 and 2004, but is still at a very high level.
This image is in the public domain.

Methane (CH₄) is a greenhouse gas and contributes to climate change. A trace gas, methane makes up only 0.00017% of the total amount of atmospheric gases [1]. This may seem like a very small amount, but when we consider how one kilogram of methane has more than 20 times the greenhouse effects as the same amount of carbon dioxide [2], it becomes an important topic.

Since the industrial age began in the 1700s, the amount of greenhouse gases that have been produced and released into the atmosphere has steadily increased. Carbon dioxide, which makes up roughly 0.04% of the earth's atmospheric gases, is rapidly increasing and receives a lot of attention, but methane has also rapidly increased. Carbon dioxide has increased by 31% since 1750, but methane has increased by 149%! More than two-thirds of this increase can be attributed to human activities [3]. A major difference between the two gases is that carbon dioxide levels continue to climb drastically each year, while methane concentrations are, fortunately, leveling off [1]. Although atmospheric levels of methane are stabilizing, they are still extremely high and are contributing to abrupt climate change.

Global human -induced methane is released from a variety of sources. From public information distributed by the US Environmental Protection Agency.

Methane Gas Sources

Methane gas is released into the atmosphere from both natural and human sources. Natural sources include grazing animals, volcanic eruptions, and some land plants [4]. Bogs and mires naturally release methane gas as their bacterial communities breakdown organic material [5]. There is also evidence that methane is released when shifts in plate tectonics disrupt the ocean floor [6].

Methane is also released as a by-product by a number of different sources, mostly those involving human and animal waste. Landfills are a large source of methane gas as materials breakdown and release the methane to the atmosphere. Waste water and animal manure are also sizable sources of anthropogenic methane [7].

Domestic sheep grazing in a grassy meadow. Livestock worldwide have been estimated to contribute over 113 million metric tons of methane gas to the atmosphere each year[13].

Industrially produced methane comes from burning fossil fuels such as natural gas, which is the primary component of natural gas, which is burned to heat many homes and businesses. Methane is also released from active coal mines, and even abandoned coal mines that are no longer being used.

Remarkably, it is domestic hoofed-mammals like cows and sheep that are amongst the planet's major emitters of methane. By eating and digesting large quantities of grass, then burping and farting methane into the atmosphere, livestock contribute 21% of human-induced methane emissions. Currently, agricultural scientists are working to create special diets for cows that attempt to reduce this harmful waste, as beef and dariy cattle are responsible for 75% of the methane produced from livestock each year [8, 9].

Methane in the Oceans

There are also large amounts of methane gas below the ocean floors. Many kilometers underwater – where light never reaches – there are large stores of methane called clathrates frozen into the sediments along ocean margins. It has been estimated as much as 2000 to 4000 gigatons (Gt) of carbon are stored in these sediments. As a result of changing ocean chemistry caused by global warming, methane from clathrates may be released into the water and eventually the atmosphere [10]. With our current 6 Gt/year output of greenhouse gases worldwide this type of release would have devastating impacts on our climate. Melting of deep-sea methane stores has happened before, millions of years ago, when ocean acidity increased and the climate was affected for the next 100,000 years [10]. With atmospheric carbon dioxide making the oceans more acidic each year, the idea of frozen methane dissolving on the ocean floor is not so far fetched.

Methane gas bubbling into the water from the peak of a mud volcano in the Gulf of Mexico. Image courtesy of the Institute for Exploration.

Mud volcanoes are another source of deep sea methane. These form where gases and liquids are excreted out of the sediments. They are much cooler than igneous volcanoes where lava flows, but still have important impacts on the surrounding environment. Mud volcanoes are a source of methane found in every ocean around the world. These sea floor volcanoes release fluids and gases into the surrounding waters of the deep ocean. The released gases can have methane content as high as 99%. The rising methane accumulates in the surrounding sea floor mud and some escapes as free gas into the hydrosphere, and eventually into the atmosphere [11]. Unfortunately, knowing how to incorporate mud volcanoes into the global methane budget is not easy because we do not know how many mud volcanoes exist in the ocean [12].

How Methane is Different

One of the most important ways in which methane differs from carbon dioxide is that it only persists in the atmosphere for roughly 10 years after it is released, whereas carbon dioxide persists in the atmosphere for about 100 years. This means that actions we take today to reduce methane will provide results in just a decade.

" If one really tightens emissions, the amount of methane in the atmosphere 10 years from now could be less than it is today. We will gain some ground on global warming if methane is not as large a contributor in the future as it has been in the past century. ” Said by F. Sherwood Rowland, the Donald Bren Research Professor of Chemistry and Earth System Science at UC Irvine, and co-recipient of the 1995 Nobel Prize [3] .

Methane lesson plan

1. Alley, R., et al., Climate Change 2007: The Physical Science Basis, Summary for Policymakers . 2007, Intergovernmental Panel on Climate Change. p. 18.

2. Leifer, I., et al., Natural marine seepage blowout: contribution to atmospheric methane. Global Biogeochemical Cycles, 2006. 20 .

3. Level of important greenhouse gas has stopped growing. 2006, Physorg.com.

4. Keppler, F., et al., Methane emissions from terrestrial plants under aerobic conditions. Nature, 2006. 439 : p. 187-191.

5. Merila, P., et al., Methanogen communities along a primary succession transect of mire ecosystems. FEMS Microbiol Ecol, 2006. 55 : p. 221-229.

6. Jahren, A.H., et al., A plate tectonic mechanism for methane hydrate release along subduction zones. Earth and Planetary Science Letters, 2005. 236 : p. 691-704.

7. Methane: International Analyses. 2006, US Environmental Protection Agency.

8. DeRamus, A.H., et al., Methane emissions of beef cattle on forages: Efficiency of grazing management systems. Journal of Environmental Quality, 2003. 32 : p. 269-277.

9. Knight, M., The other greenhouse gas. 2007, Scienceline.

10. Overpeck, J.T. and J.E. Cole, Abrupt change in Earth's climate system. Annual Review of Environmental Resources, 2006. 31 : p. 1-31.

11. Markey, S., Methane-munching microbes take a bite out of warming. 2006, National Geographic News.

12. Niemann, H., et al., Novel microbial communities of the Haakon Mosby mud volcano and their rile as a methane sink. Nature, 2005. 443 : p. 854-858.

13. Stern, D. and R. Kaufman, Annual emissions of global anthropogenic methane emissions: 1860-1994.Trends Online: A compendium of data on global change. 1998, Carbon dioxide infomation analysis centre, Oak Ridge National Laboratory, US Department of Energy.