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Frank Mitloehner University of California, Davis • United States
- What are the most challenging environmental problems related to agriculture?
- What is the contribution of ruminant livestock to climate change?
- Can dietary change moderate climate change?
Take home messages
Global warming is due to increases in the levels of greenhouse gases (GHG). The extraction and burning of fossil fuels is the major culprit, as this releases CO2 which remains in the atmosphere (for 1000+ y). Any future use of oil, coal, and gas will add extra CO2 and, thus, more warming.
Livestock is said to cause global warming because ruminants produce methane, which is a potent GHG. This picture is simplistic because – in contrast to CO2 – methane from ruminants does not accumulate in the atmosphere and produces no new warming, provided that herd sizes do not increase. Well-managed ruminants are even able to sequester carbon in the soil, thereby also improving soil health.
Methane from livestock is part of the carbon cycle. Plant growth is based on photosynthesis, which consumes CO2. Ruminant animals will upcycle human-inedible plant material into high-quality animal food, thereby releasing methane. The latter will be rapidly destroyed in the atmosphere (10 y) and converted into CO2, which then goes once more to plant growth.
The reason why atmospheric methane has been increasing during the last years despite stable emissions from cattle is because part of it originates from fossil fuel production and use, agriculture and waste, biomass burning, wetlands and other natural emissions.
The main environmental issue around the food supply chain worldwide and in the US concerns food waste. Both in the US and globally, 40% of all food does not get eaten by humans but ends up in landfills.
Globally, livestock causes 14.5% of the total GHG emissions but there are vast regional differences. US animal agriculture, for instance, represents only 4% of the country’s total GHG emissions.
In the US, in 1950, there were 25 million dairy cows, versus 9 million today. With 16 million fewer cows (1950 vs 2018), milk production nationally has increased 60%. The carbon footprint of a glass of milk is 2/3 smaller today than it was 70 years ago.
Going vegan represents a decrease of 0.8 tons CO2e per year, which is half of one transatlantic flight per passenger (1.6 tons CO2e). Generalizing ‘Meatless Mondays’ in the US would represent a reduction in GHG emissions of merely 0.3% for the country, whereas 2.6% would be obtained if the entire country removed livestock. Moreover, this would result in a trade-off in nutritional outcomes.
Developing countries display high GHG emission levels per unit of animal source food. This can be tackled by improvement of fertility rates, animal health, genetics and feeding. If the global average emissions intensity of developed countries was achieved worldwide, GHG emissions could be 45% lower and still produce the same amount of beef as we do today.
Marginal lands, which represent 70% of total agricultural lands, are mostly unsuitable for crop growth but can be used for grazing livestock. Ruminants livestock has therefore a critical role to play in meeting the 2050 challenge.