Domestic Livestock and Its Alleged Role in Climate Change

3.1.1. Carbon dioxide (CO₂)

CO₂ emitted by human consumption of cereals, meat, and milk, by livestock respiration and forage digestion, does not increase atmospheric CO₂ levels, as this is part of the natural carbon cycle. Not a single human- or livestock-born CO₂ molecule is additionally released into the atmosphere, as it has previously been captured through photosynthesis. The amount of CO₂ released annually by humans and livestock is offset by regrowing CO₂-assimilating forages and crops. The only sources of additionalCO₂ emissions caused by agriculture and livestock husbandry, beyond the natural carbon cycle, are:

• fossil fuel consumption during production, processing, and marketing, such as transportation, soil tillage, harvesting, and fertilizer manufacturing,

• deforestation for reclamation of pasture and cropland, and

• soil organic matter decomposition from degrading grasslands and arable lands, as determined by the difference of ecosystemic carbon stocks before and after certain human interventions.

Usage of fossil fuels is considerable in industrial livestock production systems which rely on forage cropping and feed transportation to the confined animals. In grazing systems, however, fuel consumption is rather low. Fossil fuel-related emission intensity of feed is less than 0.05 CO₂ kg⁻¹ of dry matter intake in grazing systems and around 0.3 in feedlots [4]. The widespread perception that only feedlot intensification can reduce the overall GHG emission intensity (per kg of beef produced) was recently challenged by Paige et al. [5] who found considerable soil organic carbon sequestration in certain grazing systems which even offset methane emissions from enteric fermentation. However, after any sort of land use change, the rate of soil carbon sequestration or of carbon loss is changing over time until a new equilibrium level is reached for each kind of land management [6].

Deforestation for pasture establishment causes a unique one-time CO₂ release from burning and decomposition of woody vegetation. For emission intensity calculations, deforestation-born emissions have to be shared out over the accumulated animal products generated during the total utilization period of the very pasture, which replaced the forest. This may easily be hundreds of years (as in the case of European grasslands). In the long run, total production accumulates to huge quantities and the deforestation part of the emission intensity (CO₂ emitted per kg of carcass weight) approaches zero (Figure 2).

Unfortunately, in published literature, emissions from deforestation are treated inconsistently. They are either neglected or charged entirely to the year of their appearance onto a product which is not necessarily related to the ongoing deforestation, such as total beef production in South America (e.g., Figure 1). For Europe, however, these emissions are usually ignored as they took place 500 years and longer ago.

In spite of ongoing deforestation, world vegetation cover, particularly in (semi-)arid regions, has improved in the past 30 years due to rising CO₂, as a satellite image-based analysis by CSIRO Australia [7] and Geoscience Institutes in Denmark and Spain [8] has shown. Another study of 32 authors from 24 institutions from 8 countries, published on the NASA website, found a significant increase in the leaf area index on most of the earth’s vegetated surface, during the past 35 years, for which increasing CO₂ emissions are considered responsible at a 70% level [9, 10].

In the Northern Hemisphere with big landmasses covered with vegetation, the annual oscillation of CO₂ rose considerably in the past decades. In 2013, 36% more CO₂ was captured in spring and summer and released again in wintertime than 45 years ago. The growing annual amplitude with more CO₂ in the air is a clear indicator of a tremendous vegetation response to increased CO₂ levels [11]. Fully in line with this finding is another paper published in Natureproviding evidence that twentieth-century CO₂ emissions caused an over 30% increase in Global Terrestrial Gross Primary Production [12].

Former IPCC author and reviewer Indur Goklany [13] estimated the global fertilization value of manmade CO₂ in the atmosphere to 140 billion US$ every year. Therefore, anthropogenic CO₂ contributes considerably to global food security. There are dozens of studies corroborating the efficiency of CO₂ as a fertilizer of our crops, pastures, and forests [14]. Nevertheless, UNEP projects (United Nations Environmental Program) such as the initiative TEEB (The Economy of Ecosystems and Biodiversity for Agriculture and Food) categorically ignore the obvious beneficial effects of manmade CO₂ emissions in their economic assessments. So do the authors of a recent assessment of potential economic damages under UN mitigation targets [15]. The well-established desirable effects of manmade CO₂ are entirely disregarded, whereas the global warming thresholds of future emission scenarios, as proposed by the IPCC, are fully accepted and related to potential economic losses, differentiated by regions. However, this widely accepted approach does not represent an objective and trustworthy method (see Chapter 3.2).

During most of the geological eras, atmospheric CO₂ concentrations were higher than today. At the last glaciation maximum, however, 18,000 years ago, CO₂ concentration reached as little as 180 ppm, low enough to stunt plant growth [16]. Therefore, quite a number of authors celebrate the recirculation of CO₂ by fossil fuel burning to secure long-time survival of life on earth. Taking into account that CO₂ is essential nutrient for life, is the only carbon source of all biomass, is fertilizing our crops and pastures, and is greening our deserts as it improves water use efficiency and therefore drought resistance of plants [17], this trace compound in the air (0.04% vol.) qualifies for being the most important, however limiting, nutrient for life. It is not the air pollutant as which it is seemingly exposed in the media and even by members of the scientific community. CO₂ is a transparent and odorless trace gas of which we are respiring about 5 kg every day.

3.1.2. Non-CO₂ GHGs: methane (CH₄) and nitrous oxide (N₂O)

Other agricultural GHGs such as methane (CH₄) and nitrous oxide (N₂O) also form part of natural cycles, just like CO₂. An easily understandable overview on methane and nitrous oxide dynamics in the atmosphere has been worked out by Stephen Zwick in LA Chefs Column [18]. There are natural and manmade sinks and sources for CH₄ and N₂O (Figure 3); there is, however, some confusion in the quantification of the manmade part of their emissions from agro-ecosystems. The IPCC Guidelines for National Greenhouse Gas Inventories [19] meticulously provide instructions, emission factors, and formulas to estimate the emissions from the various sources in managed ecosystems. Emissions from pristine or native ecosystems are explicitly not taken into account, as they are not manmade. However, all managed agro-ecosystems replaced native ecosystems at some stage in history which also had been sources of considerable methane and nitrous oxide emissions.

In order to get the effective manmade part of the emissions from managed ecosystems, one has to subtract the baseline emissions of the respective native ecosystems or of the pre-climate change-managed ecosystems from those of today’s agro-ecosystems (Figure 4). Omitting this correction leads to a systematic overestimation of farm-born non-CO₂ GHG emissions. Scientific publications generally do not take this consideration into account, as farm-born CH₄ and N₂O emissions are consistently interpreted at a 100% level as an additionalanthropogenic GHG source, just like fossil fuel-born CO₂. As the mentioned IPCC guidelines [19] are taken for the ultimate reference, this severe methodological deficiency propagated through scientific literature.

Temporarily waterlogged or flooded pristine ecosystems or those with a high density of wild ungulates might have emitted the same amount or even more methane per hectare and year than they did after land reclamation and utilization. So net anthropogenic methane emissions from certain agro-ecosystems could be zero or even assume a negative value.

The same applies to nitrous oxide, particularly in farming systems where no or little synthetic nitrogen fertilizer is used such as most pastoral systems: ecosystem management and herbage consumption by livestock might increase somewhat the turnover rate of nitrogen but does not increase the quantity of nitrogen in circulation from which N₂O is emitted as a by-product from nitrification and denitrification.

Dung patches concentrate the nitrogen ingested from places scattered across the pasture. Nichols et al. [20] found no significant differences between emission factors from the patches and the rest of the pasture, which means the same amount of nitrous oxide is emitted whether or not the herbage passes livestock’s intestines. However, the IPCC and FAO do consider mistakenly all nitrous oxide leaking from manure as livestock-born and therefore manmade.

Comparing, for instance, sown grassland with native bushland in the Gran Chaco, which contains many leguminous species, it becomes evident that nitrogen stocks are higher and more nitrogen is circulated annually in native bushland than in sown pasture (Figure 5). Therefore, in spite of the presence of grazing animals in the grassland, there is likely more nitrous oxide produced from bushland than from grassland after bush clearing and pasture establishment.

Hence, instead of charging the emission intensity of South American Beef with 23 kg of CO₂-equ. kg⁻¹ of CW (carcass weight) for nitrous oxide emissions from animal feces (Figure 1), there should rather be a negative value when corrected for the emissions from the respective pre-land use pristine ecosystem. Similar thoughts can be made for the enteric fermentation and deforestation part of emission intensity charges.

3.1.3. Global methane emissions and livestock

The rise of methane emissions beginning around 1850 coincides perfectly with the progressive use of fossil energy. But the methane growth rate fell to zero at the turn of the millennium as shown by Quirk [21], cited from [22]. The stabilization of methane emissions in the 1990s is very likely associated with the adoption of modern technology in fossil fuel production and use, particularly the replacement of leaking pipelines in the former Soviet Union [21].

Between 1990 and 2005, the world cattle population rose by more than 100 million head (according to FAO statistics). During this time, atmospheric methane concentration stabilized completely. These empirical observations show that livestock is not a significant player in the global methane budget [23]. This appreciation has been corroborated by Schwietzke et al. [24] who suggested that methane emissions from fossil fuel industry and natural geological seepage have been 60–110% greater than previously thought.

When looking to the global distribution of average methane concentrations as measured by ENVISAT (Environmental Satellite) [25] and the geographical distribution of domestic animal density, respectively [1], no discernible relationship between both criteria was found [22].

Although the most recent estimates of yearly livestock-born global methane emissions came out 11% higher than earlier estimates [26], we still cannot see any discernible livestock fingerprint in the global methane distribution (Figure 6). The idea of a considerable livestock contribution to the global methane budget relies on theoretical bottom-up calculations. Even in recent studies, e.g., [27], just the emissions per animal are measured and multiplied by the number of animals. Ecosystemic interactions and baselines over time and space are generally ignored [28]. Although quite a number of publications, such as the excellent most recent FCRN report (Food Climate Research Network) [29], do discuss extensively ecosystemic sequestration potentials and natural sources of GHGs, they do not account for baseline emissions from the respective native ecosystems when assessing manmade emissions of non-CO₂ GHGs from managed ecosystems. This implies a systematic overestimation of the warming potential, particularly when assuming considerable climate sensitivity to GHG emissions. However, even LA Chefs Column [18], in spite of assuming a major global warming impact of methane, came to the conclusion: “When methane is put into a broader rather than a reductive context, we all have to stop blaming cattle (‘cows’) for climate change.”