Cows are not the primary cause of recent increase in methane

Atmospheric methane concentration has reached a record, but the exact reason has been difficult to determine. Atmospheric methane concentration increased 8 ppb per year during the 1980s, 6 ppb per year in the 1990s, then the trend was static from 2000 to 2007, but now increasing at 9 ppm per year since 2007 (Figure 1). The reason for the increased accumulation of methane in recent years is likely due to several factors. The methane budget includes both sources of emissions and sinks that remove methane from the atmosphere. The primary sources include agriculture, natural wetlands, fossil fuels, biomass burning, and other natural sources (oceans, lakes, termites). The primary sinks are chemical reactions in the atmosphere and soils. The increase in atmospheric methane concentrations means that emissions were larger than sinks, but which source has been the cause of the recent increase.

Ruminant animals account for the largest proportion of man-made methane emissions and cattle are by far the largest contributor. Estimated enteric methane emissions have increased since 2000, but the global cattle population has remained constant questioning the reason for the increased enteric methane emissions (Figure 1). Wetlands are the largest natural source of methane emissions and methane emissions from wetlands have also been increasing since 2000. Methane leakage during oil extraction is also a source of methane emissions into the atmosphere and was thought to possibly be the cause of increased methane due to the increase in shale oil extraction.

Based on the change in radio isotope ratio of atmospheric methane, the increase in methane emissions is likely from microbial sources which rules out fossil fuel extraction leaving enteric and wetland methane emissions. The largest increases in atmospheric methane coincide with the largest increases in global temperature. The largest methane growth rates (> 10 ppb) occurred in the tropics and subtropics through 2014 to 2017, which had average temperatures > 1°C warmer than the 1880-1909 baseline. Methane emissions from wetlands increase with increasing temperature because of increased microbial activity, but microbes in the rumen of cattle are at a constant 38°C such that global temperature would not be affecting microbial activity in the rumen. Additionally, the largest increases in methane emissions have come from the tropical and subtropical latitudes, where increased precipitation, flooding and temperature coincided between 2014 – 2017. Wetlands are the largest global source of methane emissions (Figure 2) and are a major driver of atmospheric methane especially with increasing global temperature.

Removal of methane through chemical reactions in the atmosphere can have a dramatic effect on methane lifetime. Hydroxyl, which is the chemical with which methane reacts in the atmosphere, concentrations in the atmosphere increased 10% between the late 1990s and mid-2000s coinciding with the plateau in methane concentrations from 2000 to 2007. But hydroxyl concentrations have decreased approximately 10% from mid-2000s to 2014 coinciding with the renewed increase in atmospheric methane concentrations.

The methane budget is not as simple as once thought and changes in relative amounts of sources and sinks can readily change the atmospheric concentration. Enteric emissions from ruminants is not always the primary driver and is not the largest emissions source. As global temperatures increase, wetland emissions may become a larger proportion of global methane emissions.

Figure 1. Global atmospheric methane (NOAA) and hydroxyl (Rigby et al., 2017) concentration, methane emissions from enteric fermentation (FAO) and wetlands (Zhang et al. 2017), and cattle population (USDA).
Figure 2. Contribution to global methane emissions by various sources. Adapted from the Environmental Change Institute, University of Oxford.

Food, Innovation, Service, & Hospitality Talk

The Association of Healthcare Food Service hosted their first ever Food, Innovation, Service, Hospitality (FISH) Talks – Live Panel at the 2019 national conference.   The broad subject of the panel was to provide healthcare leaders with information surrounding food and climate change that would help them purchase more sustainably.   The below clip shares improvements in ranching and farming over the decades thru the eyes of a dietitian, who was once in their food service shoes trying to make similar thoughtful choices.  

Thinking Beyond Food Waste to Food Recovery

As we listen to conversations about supply issues, food waste and providing food to the hungry, people not familiar with our beef commodity markets have asked why the U.S. exports beef as well as the ethics of feeding human edible beef to our pets. Here are some thoughts and facts to consider. You might think these concepts are common knowledge, and they probably are among your circle of agriculture friends. Sustainable food production questions rarely have simple answers, but try these to help us all have dialogue together and reach the common goal of a more sustainable food supply.

Why do we export beef to other countries?

The majority of beef variety meats are commonly exported as opposed to finding a home in the U.S.  Diets are cultural and ours does not typically include variety meats, but we respect that they are of value to others. In the U.S., they are mainly used as pet food ingredients.

Annual exports are generally 9 to 11 percent of total domestic beef production and are a critically important source of revenue.  U.S. beef producers receive about $300/head in additional premiums as a result of export values in fed cattle according to Oklahoma State University livestock economist, Derrell Peel.  Foreign markets are willing to pay much higher premiums for variety meats than the U.S. consumer and are also purchasing premium cuts as their economies improve.  

Why do we feed edible beef to our pets instead of feeding ourselves?

Twenty-five to 30% of the meat eaten in the U.S. is fed to dogs and cats, according to a recent UCLA study. There are 157+ million pets in the U.S. as of 2014 ,which is triple the number since the 1970’s.  

While it is not recommended that your dog and cat give up meat, it is good to know that the by-products from beef are an important nutritious ingredient as you do your research on the ingredient label. Veterinary nutritionists tell us that feeding by-products to pets not only is safe and healthy, but it is better for the environment and dramatically reduces food waste.  The pet food aisle has seen an influx of brands made with “human-grade” ingredients to lead us to believe they are better than those that contain animal by-products.  

The Environmental Protection Agency has developed the “Food Recovery Hierarchy” that demonstrates the most valuable use of food waste down to the last resort — the landfill. Wholesome, edible food should be kept in the human food supply whenever possible. When food is no longer edible for humans but still safe and wholesome for animals, the hierarchy recommends diverting these food scraps to feed animals, including pets.

Shifting gears, there is renewed interest in feeding food scraps to livestock as a way to reduce organic waste in landfills and the methane gas it generates.  After disease outbreaks were linked to animal feed back in the 1980’s, there are state laws that regulate the process of converting food waste to animal feed.  The Food and Drug Administration’s Bovine Spongiform Encephalopathy/Ruminant Feed Ban Rule also prohibits the use of animal tissue in feeds for ruminant animals such as cattle. Consumers are asking questions about how companies handle their waste, and more research and technology will be needed to overcome some of the barriers of re-feeding people leftovers to food animals. Cattle have demonstrated they can upcycle a variety of products into safe, quality food and can be a part of the environmental solution.   

Mitigating Ruminant Methane Emissions

Last month we evaluated data indicating that only 35% of current methane emissions from domestic ruminants is contributing to increased atmospheric methane. With reductions in methane emissions ranging from 10 to 50%, feed additives could almost eliminate the 35% contributing to atmospheric methane.  Many feed additives have potential adverse effects on the animal, but 3-nitrooxyproponal reduces methane emissions without negatively affecting animal performance and is in the process of commercialization. Furthermore, 3-nitrooxypropanol shifts rumen VFA profile toward higher proportions of propionate making the ruminant animal more feed efficient and the compound very attractive to economically include in livestock rations.

Reassessing Ruminant Methane Contribution

The environmental impact of livestock production, especially ruminants, has received a lot of attention in both the scientific community and popular media. One of the most discussed aspects of ruminants’ environmental impact is the production of the greenhouse gas, methane. Methane is produced as a natural byproduct of fermentation in the ruminant stomach during the process of feed digestion. The production of methane is not a man-made process and occurs naturally in all wild and domestic ruminant animals.

Wild ruminants in North America include deer, moose, elk, big horn sheep, antelope and bison with bison having the largest population. Estimates of the bison population prior to European settlement of North America varies greatly ranging from 21 to 88 million. And estimates of the total wild ruminant population prior to settlement ranges from 83 to 133 million. Due to lots of factors chief among them the growth in human population, the wild ruminant population has decreased to 30.5 million today and have been replaced by 90 million domestic ruminants.

Do domestic ruminants produce more methane than wild ruminants? Methane emissions factors for bison are similar to that of domestic cattle when fed the same diet, and both are greater than deer and elk. However, diets of wild and domestic ruminants are not necessarily similar. Diets of domestic ruminants are managed by humans and are typically of greater nutritive value than wild ruminants consume, especially during the winter months when vegetation is dormant.

Attempting to account for differences in methane emissions from wild and domestic ruminants, recent research compared the amount of methane from wild ruminants prior to European settlement of North America and current wild and domestic ruminant populations (Figure 1). Due to the wide variation in estimates of bison population, results were computed for low, medium and high bison populations. Based on these data, the amount of methane from domestic ruminants contributing to the increase in global atmospheric methane concentration is less than 100% because a fraction of that methane is replacing naturally produced methane from pre-settlement wild ruminant populations. Doing the math, the proportion of methane emissions from domestic ruminants in North America that is contributing to atmospheric methane concentrations ranges from 50 to -19% depending upon the pre-settlement bison population with an average of 35%.

Several feed additives have been investigated for their ability to reduce enteric methane emissions from domestic ruminants; the most effective include methane inhibitors, electron acceptors, hydrogen sinks, and plant extracts. These feed additives can reduce enteric methane emissions from 10 to 50% depending upon domestic ruminant species and diet, indicating that implementation could mitigate the 35% of domestic ruminant methane emissions that is new to North America since the European settlement. Although most of these feed additives have adverse effects that may hinder their use, one, 3-nitrooxyproponal, reduces methane emissions without negatively affecting animal performance and is in the process of commercialization. 3-nitrooxypropanol also shifts rumen VFA profile toward higher proportions of propionate making the ruminant animal more feed efficient, which is very similar to another feed additive, monensin, which has been widely adopted in ruminant livestock production. Thus, the use of 3-nitrooxypropanol looks very attractive for producers to economically include in livestock rations and could significantly mitigate enteric methane emissions from domestic ruminants.

In conclusion, the extent of domestic ruminants’ contribution to greenhouse gas emissions is not as great as once thought, although livestock production has more environmental impact than methane alone. It appears that we are on the verge of balancing the methane scale as far as domestic ruminant emissions are concerned.

Estimated methane emissions from wild ruminants prior to European settlement of North American Continent based on 3 estimates of the American bison herd (30, 50 and 75 million bison) compared with methane emissions from current population of wild and domestic ruminants. Adapted from Hristov, 2012