Global warming and cattle production

Stories about global warming and cattle production in the popular media place often blame cattle for the increasing temperatures and changing climate, and the general perception is that cattle production is the major contributor to greenhouse gas (GHG) emissions.

The greenhouse effect

The natural greenhouse effect is an important part of the earth’s energy balance and in keeping the temperature in range to support life. The greenhouse effect is caused when gases in the atmosphere trap heat from the sun that would otherwise escape into space. The current problem is that the concentration of GHG in the atmosphere is increasing as a result of a variety of activities, including burning of fossil fuels, changes in land use, and both commercial production and agriculture.

Globally, the key GHG emitted by human activities are carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) and fluorinated gases. The global warming potential is the system that is used to standardise the potency of GHG based on CO2-equivalency based on the fact that carbon dioxide has a CO2-equivalence of one. The global warming potential of methane is 25 times that of CO2, but its atmospheric lifetime is only 12 years, compared with 100 to 200 years for CO2.

South Africa is the world’s 14th largest emitter of GHG and around 80% of the country’s CO2 emissions come from the burning of fossil fuel. Agriculture in South Africa contributes between 8% and 9% of the country’s GHG emissions, with livestock contributing between 5,5% and 6%. Beef cattle are the major contributor to livestock GHG emissions in South Africa, followed by sheep, dairy cattle, privately owned game, pigs, goats, ostriches, equines, and poultry. In South Africa, approximately 70% of the land surface is only suitable for extensive farming. Cattle are ruminants that have the unique ability to convert high-fibre vegetation, that is inaccessible to humans, to high-quality protein like meat and milk. Grasses, forages, and by-product feeds that cannot be used for human food are well-utilised by cattle.

Methane production

Methane is responsible for only 30% of the greenhouse effect and it is the primary GHG associated with cattle production. Other sources of methane production include coal mining or natural gas and petroleum systems, rice cultivation; biomass burning, landfills, and animal waste.

Cattle produce methane that is classified as anthropogenic, meaning that it originates from a living organism, and it is then further classified as either enteric or manure derived. Enteric methane is produced in the rumen and approximately 98% of this is actually exhaled by passive expiration through the nose and mouth. Anaerobic decomposition of manure, as found in feedlots and intensive dairy systems, produces methane as one of the major end-products. Under natural veld conditions, decomposition of manure is aerobic and leads to the production of CO2 and water as end-products. Part of the CO2 released as a result of aerobic digestion of manure is absorbed during the regrowth of the surrounding vegetation.

Methane production by cattle is part of a natural carbon cycle where the methane oxidises in the atmosphere over a period of years, converting the carbon to carbon dioxide (CO2) that can be fixed through plant growth to form carbohydrates in feed. (source: Rotz, C.A. & Hristov, A.N., Fact Sheet 21 in the Series: Tough Questions about Beef Sustainability. Beef Facts: Sustainability.)

The carbon cycle

Methane from cattle production is part of a natural carbon cycle that has been happening since the beginning of life on our planet. Cattle consume carbohydrates in plants. These carbohydrates contain carbon, the fundamental element of all living things, which is derived from CO2 in the atmosphere through photosynthesis. When cattle eat carbohydrates, some of the carbon gets converted to CO2 and methane by the rumen microbes. A series of rumen contractions releases this gas mixture from the animal’s mouth and nose through belching. If this natural belching process doesn’t occur, cattle can suffer from bloat. Over a period of 12 years, the methane emitted from a cow will be transformed through a series of photochemical reactions to CO2. That CO2 can then again be taken up by plants, and the cycle repeats.

Carbon in fossil fuels is different than the CO2 and methane that cattle emit, because it is not part of the natural carbon cycle. When carbon is released during the combustion of fossil fuels, we take carbon that has been stored in the earth since pre-historic times and convert it to CO2 that is released to the atmosphere. This emitted CO2 represents new carbon entering the system. Some of this CO2 is absorbed by plants, soil, and the oceans, but the rest accumulates in the atmosphere. We are releasing CO2 more rapidly than it can be absorbed and that is why we observe an increase in GHG causing global warming.

The increase in methane concentration in the atmosphere is caused by the greater demands of our global energy systems. We have seen an increase in methane released during extraction, refining, and transport of fossil fuels, as well as in the production of natural gas. Global estimates also indicate that the number of cattle on earth has increased by approximately 40% over the past 50 years.

Becoming climate-smart

When considering mitigation options are considered, it will be far more effective to have an 10% reduction in GHG emissions by the energy and mining sectors than a 10% reduction of GHG emissions from agriculture.

A simplified carbon cycle illustrating how methane (CH4) carbon is not additive to the atmospheric concentrations of carbon dioxide (CO2) as compared to fossil fuel combustion.(source: Place, S., 2019. Separating fact from fiction on farting cows. Beef Magazine.)

There are several climate-smart approaches that can be put in place to mitigate the effects of climate change and reduce GHG production. Improving productivity will generates less GHG emissions per unit of beef product, and this can quite easily be achieved through genetics, nutrition, and management. Enteric methane is essentially wasted energy escaping the rumen. Reducing this waste by increasing the efficiency of the rumen may provide a substantial benefit by producing more meat or milk for less feed consumed. Good management and production systems can have a significant effect on reducing the production of GHG. This includes reducing the time from conception to slaughter and carrying as few as possible non-productive animals.

Sustainable cattle production systems are also necessary to preserve and enhances natural veld ecosystems. If cattle don’t consume the vegetation, it could burn and produce CO2 that will be released into the atmosphere, or it will rot and produce nitrous oxide (N2O) with a global warming potential of almost 300 times more than CO2, or it will be consumed by other animals that will also emit methane.

Carbon sequestration has the potential to limit the carbon footprint by two to three times and this responsibility lies squarely in the hands of the agricultural sector. This means not disturbing the ecosystem and wetland areas on the farm, practising conservation agriculture, and implementing good veld and pasture management practices that will prevent erosion and supply good vegetation cover.

Humanity has depended on cattle production for the whole of civilisation and will continue to do so far into the future. It is true that cattle produce methane that are part of a natural carbon cycle with a short-term impact on GHG emissions compared to the burning of fossil fuels. Reducing any source of greenhouse gas emission will benefit our planet. Everybody needs to work together and a small change in the right direction can make a big difference in the future.

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