The ongoing global warming debate has convinced some people that human activity is seriously impacting climate change while others are sceptical and dismissive. Whether you believe global warming is real or imagined, scientists do know that the atmospheric concentrations of certain gases are increasing rapidly to levels that we have not seen before (Figure 1). While the impacts of these increased concentrations on climate is less certain, it is believed that these gases will trap heat in the atmosphere and could lead to global warming.

Agriculture and other industries are under increasing public pressure to reduce emissions of these gases. Therefore, knowing your carbon footprint or energy use can help you reduce the amount of energy you use and improve your bottom line.

Figure 1. Changes in atmospheric concentrations of GHGs
(IPCC, 2006)

The Consolidated Appropriations Act of 2008 (H.R.2764) included a provision that directed the United States Environmental Protection Agency (EPA) to require mandatory reporting of greenhouse gas (GHG) emissions from all sources in all sectors in the US economy. Even though the EPA (2008) estimated that only 6.4 per cent of US GHG emissions come from agriculture, this law has raised the collective attention of the agricultural sector (Figure 2). Of this 6.4 per cent, beef cattle accounted for about 37 per cent, dairy cattle 11.5 per cent, swine 4.4 per cent and poultry 0.6 per cent, according to the USAF Greenhouse Gas Inventory, 1990-2005 (Figure 2). While the figures for poultry production appear to be low, understanding how these GHG are generated and what we in the poultry industry can do to further reduce our impact remains important.

Figure 2. Relative contribution to greenhouse gas emission by major emitters in the United States

Figure 3. Distribution of greenhouse gas emissions
*High global warming potential (GWP) gases include hydroflorocarbons, sulphur hexafluoride and per-fluorocarbons
(US EPA, 2010).

What are Greenhouse Gases?

Human activities, including modern agriculture, contribute to GHG emissions. Greenhouse gasses are defined by their radiative forces – defined as the change in net irradiance at atmospheric boundaries between different layers of the atmosphere – which change the Earth’s atmospheric energy balance. These gases can prevent heat from radiating or reflecting away from the Earth and thus may result in atmospheric warming. A 1996 report published by the International Panel on Climate Change showed that GHG levels have increased since the Industrial Revolution (Figure 1). GHGs of particular concern (Figure 3) include carbon dioxide (CO₂), nitrous oxide, methane, hydroflorocarbons and sulphur hexafluoride. Billions of tons of carbon in the form of carbon dioxide are absorbed by oceans and biomass and are emitted into the atmosphere naturally. The concentrations of global atmospheric carbon dioxide have risen by about 36 per cent since the Industrial Revolution. This increase is primarily due to the combustion of fossil fuels. In 2008 in the US, fossil fuel combustion accounted for 94.1 per cent of carbon dioxide emissions (US EPA, 2010).

Changes in land use and forestry practices can also emit carbon dioxide or act as a sink for carbon dioxide. Within the agricultural sector, nitrous oxide and methane are of primary concern; most of the other gasses are not typically associated with agricultural sources. Nitrous oxide is mainly emitted as a by-product of nitrification (i.e. aerobic transformation of ammonium to nitrate) and de-nitrification (i.e. anaerobic transformation of nitrate to nitrogen gas), which commonly occurs when fertilisers are used. Methane is emitted when organic carbon compounds break down under anaerobic conditions. These anaerobic conditions can occur in the soil, in stored manure, in an animal’s gut during enteric fermentation (mainly in ruminants) or during incomplete combustion of burning organic matter.

Several other gasses are also of interest because they may be converted into GHG, including nitrogen oxide, ammonia, non-methane volatile organic compounds and carbon monoxide. In another report, the IPCC stated that these precursor gases are considered indirect emissions and are usually associated with leaching or run-off of nitrogen compounds applied to the soil (IPCC, 2006). The EPA estimated that in 2008 about 15 per cent of total GHG emissions were methane and nitrous oxide, of which 36 per cent and 77 per cent, respectively, were directly attributable to agriculture (US EPA, 2010).

What Does ‘Carbon Footprint’ Mean?

Over the past several years, the term ‘carbon footprint’ has often been used in conversation as public debate centres on responsibility and mitigation practices that can be used to stem the threat of global climate change. In general, the term refers to the sum of gaseous emissions that are relevant to climate change associated with any given human activity. A 2007 ISO Research Report defined ‘carbon footprint’ as the measure of the exclusive total amount of carbon dioxide emissions that are directly or indirectly caused by an activity or accumulate over the life stages of a product. In other words, your carbon footprint is a measure of the amount of GHG emitted to the atmosphere because of your activity or product.

Contrary to what the word implies, a carbon footprint involves not only carbon dioxide emissions but also includes other GHG emissions that are expressed in carbon dioxide equivalents (CO₂e). A carbon dioxide equivalent is the concentration of carbon dioxide that would give the same levels of radiative properties as a given amount of carbon dioxide. The global warming potential (GWP) is a measure of how much a given mass of GHG is estimated to contribute to global warming. This is calculated over a specified time period and must be stated whenever a GWP is stated. For example, the GWP over 100 years for nitrous oxide is 298. This means that the emission of one million tons of nitrous oxide is equivalent to 298 million tons of carbon dioxide over 100 years. The GWP over 100 years for methane is 25. Therefore, a gas like methane has 25 times as much GWP as carbon dioxide and nitrous oxide has 298 times as much GWP as carbon dioxide.

Carbon Dioxide, Nitrous Oxide and Methane: Their Relationship with the Poultry Industry

Much of the carbon dioxide equivalent that the poultry industry generates is primarily from the utilisation of fossil fuels in the form of purchased electricity, propane use in stationary combustion units such as furnaces or incinerators, and diesel use in mobile combustion units such as trucks, tractors and generators that are used on the farm. In the animal industry, the consumption of plants (feed) by animals eventually results in the division of the carbon into either animal biomass (meat and eggs) or carbon dioxide respired by animals and fecal deposition of carbon in unutilised co-products (manure).

Aside from the fossil fuel emissions on poultry farms, nitrous oxide and methane gases are also emitted from manure during handling and storage. Nitrous oxide and methane emissions depend on management decisions about manure disposal and storage, as these gases are formed in decomposing manures as a by-product of nitrification / de-nitrification and methanogenesis, respectively. Stored manure will only emit nitrous oxide if nitrification occurs, which is likely to take place provided there is an adequate oxygen supply. Indirect GHG emissions of ammonia and other nitrogen compounds also occur from manure management systems and soils.

In animal agriculture, the greatest contribution to methane emissions is enteric fermentation (21 per cent) and manure management (eight per cent). Enteric fermentation is the most important source of methane in dairy production, while most of the methane from poultry and swine production originates from manure. When comparing the distribution of methane emissions from enteric fermentation among animal types (Figure 4), poultry produces the lowest amount with 0.57 pounds of methane per animal per year compared to dairy cattle, which produces 185 to 271 pounds of methane per animal per year and swine, which produces 10.5 pounds of methane per animal per year (Monteny, et al., 2001).

Figure 4. Methane emissions from enteric fermentation in pounds (lbs.) based on animal type.
The figure represents emissions per animal per year.

Of course, one must consider the size (weight) of the livestock and the number of each type of livestock grown each year. Larger animals produce more methane than smaller animals. The amount of methane emitted increases with the number of animals grown. The type of digestive system will also determine the amount of methane produced. Cattle are poly-gastric animals with a four-compartment stomach. Their digestive tract is designed for microbial fermentation of fibrous material. One of the by-products of microbial fermentation is methane. Poultry and swine are monogastric animals with a simple stomach where little microbial fermentation takes place; therefore they produce less enteric methane.

Methane emissions may be generated as a result of the decomposition of manure under anaerobic conditions. These conditions occur readily when large numbers of animals are managed in a confined area. The main factor affecting methane emissions is the amount of manure produced and the portion of the manure that decomposes anaerobically. The amount of manure produced depends on the number of animals and the rate of waste production. Anaerobic decomposition depends on the type of manure storage. The majority of poultry production systems handle manure as a solid and the manure thereby tends to decompose under aerobic conditions, generating less methane than under anaerobic conditions.

The main cause of agricultural nitrous oxide emissions is from the application of nitrogen fertilisers and animal manures. Application of nitrogenous fertilisers and cropping practices are estimated to account for 78 per cent of total nitrous oxide emissions, according to Johnson et al., 2007. The EPA (2005) reported that manure from all livestock is a contributor to nitrous oxide emissions, with poultry accounting for nine per cent of manure nitrogen.

Nitrous oxide can be produced directly or indirectly through nitrification or denitrification of the nitrogen in the manure. Sixty-five per cent of all nitrous oxide emissions from stored manure result from soil microbial nitrification and denitrification. The loss of nitrogen from manure as gaseous emissions depends on how the manure is stored and applied to the land. Indirect emissions result from volatile nitrogen losses primarily in the form of ammonia and nitrogen oxide compounds. The amount of excreted organic nitrogen mineralised to ammonia during manure collection and storage depends on time and temperature. In the case of poultry, uric acid is quickly mineralised to ammonia nitrogen, which, due to its volatility, is easily diffused into the surrounding air. On the other hand, injecting or incorporating manure into the top layer of soil reduces ammonia emissions but can increase emissions of other nitrogen compounds.

How Can the Industry Address Carbon Footprints?

As the poultry industry moves toward becoming more energy efficient and sustainable, it is important to perform a complete evaluation of the carbon footprint of each segment of the poultry industry. Reducing poultry production’s carbon footprint will require identifying and adopting on-farm management practices and technological changes in production and waste management that can result in positive net changes for producers and the environment.

The results from a University of Georgia study evaluating the carbon footprint of poultry farms in the US indicate that the utilisation of fossil fuels, specifically propane gas, for heating poultry houses generated the most GHG on broiler and pullet farms. In this study about 68 per cent of the emissions from the broiler and pullet farms were from propane use, while only 0.3 per cent of the total emissions from breeder farms were from propane use. Propane is used mainly for heating during brooding and the colder times of the year.

On breeder farms, about 85 per cent of GHG emissions were the result of electricity use, while the pullet and broiler grow-out farms had 30 per cent and 29 per cent emissions, respectively, from electricity use.

Results from studies looking at energy audits from poultry farms indicate that a large amount of energy in the form of electricity is utilised primarily for lighting and ventilation. These results put the poultry industry in a favourable light when compared to other protein production sources. It was recently reported in Germany that producing one pound of chicken meat resulted in the emission of 7.05 pounds of carbon dioxide equivalents (ThePoultrySite, 2010). A higher proportion (48.3 per cent) of the emissions came from production farms than breeders and hatcheries.

A similar report on swine production indicates that 8.8 pounds of carbon dioxide equivalents were emitted to produce one pound of pork. In this swine study, 53 per cent of the emission burden was attributed to the nursery through finish stages of production as compared to the sow and gestation stages (Miller, 2007). In both of these studies, it is clear that the growing stages of production are where most of the emissions occur.

Reducing Fossil Fuel Use

Improvements in energy use on poultry farms have to be approached on an individual farm basis. Any savings in fossil fuel use will reduce emissions and thus the farm’s carbon footprint. There are a number of actions that can be taken to reduce the use of fossil fuel, specifically propane, on poultry farms, including:

• enclosing and insulating curtain openings in houses without solid walls to reduce heat loss and thus propane use
• installing attic inlets to allow the utilisation of the attic area as a solar energy collector
• adding insulation to the walls and ceilings to reduce heat loss
• installing circulatory fans to reduce temperature stratification and using radiant heaters instead of gas heaters for brooding
• choosing efficient exhaust fans for new buildings and replacing worn out fans in older/existing houses
• selecting energy-efficient generators and incinerators that will pay for themselves quickly with the amount of energy they conserve, and
• replacing incandescent lights with compact fluorescent lights to help reduce electricity use and costs.

Although many farms have already implemented some of these upgrades, there are still a number of poultry houses that have a lot of room for improving the efficiency of their heating systems and electricity use. It is not uncommon to see projected reductions of 40 per cent to 60 per cent. For more ideas on reducing energy use, click here.

Alternative Energy

Currently, there are a number of alternative energy sources that could be considered for poultry production. The most common are solar, wind and biomass. While these alternatives may eventually prove effective, they remain in the proving stage and are expensive to implement. Even though solar energy is readily available, it has a high cost of recovery when compared to fossil fuels. Wind energy is not as accessible as solar energy and is not practical in all areas. Biomass has a low power density and while it could not practically be used to power a poultry farm, it could be used to provide heat in poultry houses.

Approximately 10.2 million tons of poultry litter is generated annually in the US. A large amount of this litter is applied to crop land and pastures as a means of soil amendment. Alternatively, the litter in poultry houses could be used as renewable energy source, such as biomass for pyrolysis to produce liquid biofuels (which would be considered carbon-neutral) to power equipment on the farm. Replacing fossil-fuel energy with biofuel to operate equipment is considered carbon neutral because the contemporary carbon cycle produces and consumes this liquid fuel.

A co-product from biomass pyrolysis is bio-char, which can be used as a soil amendment that can sequester the carbon in soils for centuries. Bio-char has the capacity to reduce carbon dioxide emissions, thereby making the system carbon-neutral or in some instances carbon-negative.

Manure Management

Proper management of bedding and manure stores will reduce GHG emissions since substantial amounts of the methane and nitrous oxide are produced under sub-optimal conditions. Several factors affect methane and nitrous oxide emissions from manure, including temperature, moisture content and oxygen. Methane production from animal manures increases with increased temperature. This is where the majority of the methane is emitted during poultry production. The following mitigation strategies can help to reduce GHG emissions:

• handle manure as a solid or spread it on land where it decomposes aerobically and produces little or no methane
• avoid prolonged litter storage, which can increase methane emissions
• ensure manure heaps are covered to keep them dry
• add nitrification inhibitors to the poultry litter to reduce nitrous oxide emissions
• add high-carbon substrate to manure heaps, and
• compact solid manure heaps, which tends to reduce the oxygen entering the heap and therefore maintains an anaerobic condition in the heap. However, there is a drawback in that the anaerobic condition is favourable for methane production and one GHG would be swapped for another, i.e. reducing nitrous oxide but increasing methane emission.

What about Carbon Credits?

An international cooperation of 190 countries, including the United States, formed the Kyoto protocol, which has guided the global plan to reduce GHG emissions and invest in renewable technologies in developing countries. This global, compliance-driven market was valued at $120 billion in 2009 and estimates indicate that by 2020 it could be worth more than a trillion dollars.

The US has a total voluntary carbon credit market that was estimated to be worth about $400 million in 2009 (Ecosystem Marketplace, 2010). It is voluntary in the US because there are currently no limits on the amount of GHG that can be emitted. In the US, private trades are made between buyers and sellers. While these trades are not regulated, there are several credible registries such as the Chicago Climate Exchange (which ceased to exist after 2010) and the California 'Cap and Trade System'. A ‘carbon credit’ unit represents a certified reduction in GHG emissions equal to one metric ton of carbon dioxide equivalent. These carbon credits can be generated when producers voluntarily take action to reduce emissions that would have been emitted under normal production operations. Since the costs of verifying these reductions and facilitating these trades are quite high, it is usually only feasible to obtain carbon credits when significant reductions can be made.

From all indications, the majority of GHG gases generated by the poultry industry occur during the production stage (i.e. at the grow-out, pullet and breeder farms) and specifically come from propane and electricity use. It is therefore important that the poultry industry continues to work on improving efficiency when using fossil fuels in an effort to reduce GHG emissions. Engineering approaches will be necessary to address heating strategies and electricity use in poultry houses, and agricultural engineers and poultry scientists are constantly working on ways to make these houses more efficient. Through genetic selection and improved nutrition, the poultry industry has consistently improved growth rate and feed efficiency, and when compared to other animal production systems, the modern broiler, layer and turkey are considered to be very efficient. However, the scale of the US poultry sector is vast and even small impacts can add up; therefore, we must be vigilant and continue working to reduce emissions and make the industry more sustainable.

References

Ecosystem Marketplace. 2010. State of the voluntary carbon markets report.

Intergovernmental Panel on Climate Change (IPCC). 2006. Guidelines for national greenhouse gas inventories.

ISO 14040, 2007. Carbon footprint - What it is and how to measure it. JRC European Commission.

Johnson, J.M., A.L. Franzluebbers, S.L. Weyers and D.C. Reicosky. 2007. Agricultural opportunities to mitigate greenhouse gas emissions. Environ. Pol. 150:107-124.

Miller, D. 2010. Peeling away the layers of pork’s carbon footprint. National Hog Farmer. March 2010.

Monteny, G.J., C.M. Groenestein and M.A. Hilhorst. 2001. Interaction and coupling between emission of methane and nitrous oxide from animal husbandry. Nutr. Cycl. Agroecosyst. 60:123-132.

ThePoultrySite. 2010. Wiesenhof reports its first carbon dioxide footprint.

US Agriculture and Forestry Greenhouse Gas Inventory: 1990-2005. Global Change Office, Office of the Chief Economist, US Department of Agriculture. Technical Bulletin No. 1921. Chapter 2: pp 11-18. August 2008.

US EPA. 2005. US Greenhouse Gas Inventory Reports: Inventory of US greenhouse gas emissions and sinks: 1990-2004. USEPA #430-R-06-002, United States Environmental Protection Agency, EPA 430-R-06-002 April 2006, Office of Atmospheric Programs (6207J) Washington, DC 20460, updated 19 October 2006.

US EPA. 2008. 2007 Draft US Greenhouse Gas Inventory Report: DRAFT inventory of US greenhouse gas emissions and sinks: 1990-2005. United States Environmental Protection Agency, 11 April, 2007, 27 February, 2007.

US EPA. 2010. Inventory of the US greenhouse gas emissions and sinks: 1990-2008. Executive summary, April 2010.