Revised methane emissions factors and spatially distributed annual carbon fluxes for global livestock

Abstract

BackgroundLivestock play an important role in carbon cycling through consumption of biomass and emissions of methane. Recent research suggests that existing bottom-up inventories of livestock methane emissions in the US, such as those made using 2006 IPCC Tier 1 livestock emissions factors, are too low. This may be due to outdated information used to develop these emissions factors. In this study, we update information for cattle and swine by region, based on reported recent changes in animal body mass, feed quality and quantity, milk productivity, and management of animals and manure. We then use this updated information to calculate new livestock methane emissions factors for enteric fermentation in cattle, and for manure management in cattle and swine.ResultsUsing the new emissions factors, we estimate global livestock emissions of 119.1 ± 18.2 Tg methane in 2011; this quantity is 11% greater than that obtained using the IPCC 2006 emissions factors, encompassing an 8.4% increase in enteric fermentation methane, a 36.7% increase in manure management methane, and notable variability among regions and sources. For example, revised manure management methane emissions for 2011 in the US increased by 71.8%. For years through 2013, we present (a) annual livestock methane emissions, (b) complete annual livestock carbon budgets, including carbon dioxide emissions, and (c) spatial distributions of livestock methane and other carbon fluxes, downscaled to 0.05 × 0.05 degree resolution.ConclusionsOur revised bottom-up estimates of global livestock methane emissions are comparable to recently reported top-down global estimates for recent years, and account for a significant part of the increase in annual methane emissions since 2007. Our results suggest that livestock methane emissions, while not the dominant overall source of global methane emissions, may be a major contributor to the observed annual emissions increases over the 2000s to 2010s. Differences at regional and local scales may help distinguish livestock methane emissions from those of other sectors in future top-down studies. The revised estimates allow improved reconciliation of top-down and bottom-up estimates of methane emissions, will facilitate the development and evaluation of Earth system models, and provide consistent regional and global Tier 1 estimates for environmental assessments.

Unmanned aerial vehicle observations of cold venting from exploratory hydraulic fracturing in the United Kingdom

“…Yacovitch et al (2015) For a contextualised UK comparison of instantaneous emissions, the fracking fluxes (from one sampling day) in figure 3 dwarf the maximum cattle emission flux (within uncertainty) of 3 g s −1 . The cattle fluxes are in broad agreement with inventory predictions (0.0042 g s −1 per animal) for enteric fermentation, from dairy cattle free to pasture in Western Europe (Wolf et al 2017). As the farm contained adult lactating cattle, young cattle and organic waste produced by the cattle, UAV sampling provides a unique opportunity to accurately quantify all methane emissions from the dairy farm, as a single facility.…”

Long‐Term Measurements Show Little Evidence for Large Increases in Total U.S. Methane Emissions Over the Past Decade

“…The new ONG trends are 3.2 ± 1.3%/year and 4.8± 1.0%/year for SGP‐s and WKT‐s, respectively, which are within the uncertainty ranges of our previous estimates. This is expected because both sites are dominated by ONG emissions and non‐ONG emissions account for less than 15% of the CH 4 enhancements (Wolf et al, ).…”

Enhanced response of global wetland methane emissions to the 2015–2016 El Niño-Southern Oscillation event

“…The atmospheric CH 4 growth rate is not exclusively a result of changes in wetland emissions, but rather due to a combined influence of anthropogenic and natural sources, and also due to a hydroxyl radical sink (Turner et al 2017, Rigby et al 2017. Recent studies have reported an increase in annual CH 4 emissions from global livestock (Wolf et al 2017) and an expansion of agricultural areas for rice paddies in southern Asia (Zhang et al 2017a), a region where precipitation has largely increased since 2007. Thus, we hypothesize that a combination of tropical wetlands and agricultural sources are likely responsible for the resumed growth rate of atmospheric CH 4 concentrations, which is consistent with the depletion in the global isotopic signature in 13 CH 4 (Schaefer et al 2016) and with regional measurements of 13 CH 4 in the tropics (Nisbet et al 2016).…”