How much do direct livestock emissions actually contribute to global warming?

Abstract

Agriculture directly contributes about 10%-12% of current global anthropogenic greenhouse gas emissions, mostly from livestock. However, such percentage estimates are based on global warming potentials (GWPs), which do not measure the actual warming caused by emissions and ignore the fact that methane does not accumulate in the atmosphere in the same way as CO . Here, we employ a simple carbon cycle-climate model, historical estimates and future projections of livestock emissions to infer the fraction of actual warming that is attributable to direct livestock non-CO emissions now and in future, and to CO from pasture conversions, without relying on GWPs. We find that direct livestock non-CO emissions caused about 19% of the total modelled warming of 0.81°C from all anthropogenic sources in 2010. CO from pasture conversions contributed at least another 0.03°C, bringing the warming directly attributable to livestock to 23% of the total warming in 2010. The significance of direct livestock emissions to future warming depends strongly on global actions to reduce emissions from other sectors. Direct non-CO livestock emissions would contribute only about 5% of the warming in 2100 if emissions from other sectors increase unabated, but could constitute as much as 18% (0.27°C) of the warming in 2100 if global CO emissions from other sectors are reduced to near or below zero by 2100, consistent with the goal of limiting warming to well below 2°C. These estimates constitute a lower bound since indirect emissions linked to livestock feed production and supply chains were not included. Our estimates demonstrate that expanding the mitigation potential and realizing substantial reductions of direct livestock non-CO emissions through demand and supply side measures can make an important contribution to achieve the stringent mitigation goals set out in the Paris Agreement, including by increasing the carbon budget consistent with the 1.5°C goal.

The role of non-CO2 mitigation options within the dairy industry for pursuing climate change targets

“…We emphasize that our result could be an underestimate since dairy emissions from the FAO-STAT lack full life cycle assessment, and only account for a selection of CH 4 and N 2 O dairy practices. While this may be the case, our results agree with a recent analysis looking at the contribution of livestock (combined beef, dairy, poultry, etc) to past and future warming [20]. Under a low emissions scenario (RCP2.6) with an additional 50% reduction in CH 4 and N 2 O from livestock, 0.08°C is reduced by 2100.…”

“…However, several modeling studies look at net livestock emissions, in which emissions from beef production and dairy production are aggregated together [18,19]. Using a simple carbon-climate model, a recent study determined that global livestock emissions caused about 23% of the total warming in 2010 and could potentially lead to an additional 0.23°C of warming by 2100 [20].…”

Methane Mitigation: Methods to Reduce Emissions, on the Path to the Paris Agreement

“…Methane emissions from hard-to-mitigate sources, such as enteric fermentation, are very large (Rogelj et al, 2015;Reisinger & Clark, 2018), too important to ignore as intractable. For example, high methane mole fractions, often 10-100 ppm can occur in air around feed lots (Figure 19), cattle pens (Grainger et al, 2007), manure heaps, agricultural biodigesters (Flesch et al, 2011), and near active faces of landfills (Riddick et al, 2017;Zazzeri et al, 2015).…”

Climate Change Impact, Adaptation, and Mitigation in Temperate Grazing Systems: A Review

“…Livestock systems are also significant contributors (about 12-19%) to the global greenhouse gas emissions budget [18]. This occurs through emissions of enteric methane (44% of the sectoral emissions), nitrous oxide (N 2 O) (29% from excreta and feed-crops), and CO 2 (27%) via land clearing, soil carbon (C) loss and fossil fuel use [4,19].…”