Shutterstock | irin-k
The second most prevalent greenhouse gas emitted as a result of human activities is methane (CH4). In 2014, CH4 accounted for 11% of all US greenhouse gas emissions, and the majority of these emissions were the result of agriculture.
Methane is emitted from a wide range of natural sources including marshlands, livestock farming, and leakage from natural gas systems.1 Domestic livestock including sheep, goats, and cattle produce substantial amounts of CH4 due to the normal digestive processes in the ruminant stomach system.
Bacteria are present in gastrointestinal systems of ruminant animals, such as cattle, to help the breakdown of plant material. Some of the microorganisms (methanogens) use the acetate available from the plant material to produce methane.1,2
Whenever the animal defecates or eructates (burps), it simultaneously emits a substantial amount of methane. Rotting animal manure stockpiled for use by farms in fertilizing fields can be another potent source of the gas. From a global perspective, agriculture is the chief source of CH4 emissions, and methods to measure the effect and reduce the overall emissions are constantly being made.3
Methane is an active part of the carbon cycle but the natural processes in soil and chemical reactions in the atmosphere that help to remove it from the environment are being overtaken by gas production and industrial-scale farming activities.4
In the atmosphere, methane has a lifetime that is much shorter than carbon dioxide (CO2), which is the best known greenhouse gas and lasts for about 12 years. However, CH4 traps radiation more efficiently than CO2.5 Over a hypothetical 100-year period, the impact of CH4 on climate change is over 25 times more than CO2.
Methane produces a dominant greenhouse gas effect, and approximately 44% of anthropogenic livestock emissions (3.1 Gigatonnes CO2 equivalents in a year) are in the form of CH4.
The rest of the emissions are shared between nitrous oxide (N2O, 29%) and carbon dioxide (CO2, 27%). Methane is more devastating to the climate than CO2, although it doesn’t remain in the atmosphere for as long. For effective reduction of the impact of climate change, CO2 and CH4 emissions must be addressed.6
Methane has a 25 times greater impact on climate change than CO2. Shutterstock | JeffreyRasmussen
It is well known that dairy and beef herds are important producers of CH4. Protracted experiments involving a cow in a respiration chamber have to be conducted for several days to accurately determine the amount of the CH4 produced. One method being developed is the use of gas sensors in cow sheds and milking parlors to monitor the CH4produced by animals over a set time.
Although the respiration chamber is the benchmark, the gas sensor technique provides accurate and quick estimates of CH4 emissions which, in contrast to a respiratory chamber, do not disrupt agricultural activities.7
The emission measurements are generally made during ‘milking’, which is done 3 – 6 times daily. The data is invaluable for developing methane-reducing diets and identifying low emission cow species.
Cattle are a significant source of agricultural methane emissions. Shutterstock | andaq