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News Article

Global methane emissions from livestock higher than estimated

Emissions predicted to be 11% higher due to “out-of-date” data

Livestock play an important role within the carbon cycle, through their emissions of methane (CH4) and consumption of biomass.  According to a recent study by researchers from the Joint Global Change Research Institute (JGCRI), global livestock methane emissions for 2011 are 11% higher than the estimates, based on the use of out-of-date data provided by the Intergovernmental Panel on Climate Change (IPCC) in 2006.  As a greenhouse gas, methane is much more potent than carbon dioxide, therefore, measuring and reducing its levels in the atmosphere is important for addressing climate change.

The researchers found that the difference between the original estimates and the revised figures included an 8.4% increase in the CH4 emissions from enteric fermentation in dairy cows and other cattle and a 36.7% increase in methane arising from manure management, compared to the IPCC-based estimate.  They revised the manure management CH4 emissions for 2011 in the US from this study and found that they were 71.8% higher than the IPCC-based estimates.

According to Dr. Julie Wolf, senior author of the study: “In many regions of the world, livestock numbers are changing and breeding has resulted in larger animals with higher intakes of food.  This along with changes in livestock management, can lead to higher methane emissions.  Methane is an important moderator of the Earth’s atmospheric temperature.  It has about four times the atmospheric warming potential of carbon dioxide. Direct measurements of methane emissions are not available for all sources of methane. Thus, emissions are reported as estimates based on different methods and assumptions. In this study, we created new per-animal emissions factors - that is measures of the average amount of CH4 discharged by animals into the atmosphere - and new estimates of global livestock methane emissions."

The researchers re-examined the data used to calculate the CH4 emission factors in the 2006 IPCC, resulting from digestion in dairy cows and other cattle, manure management from the dairy cows, other cattle and swine.  They found that estimating the livestock emissions with the revised emissions factors created in this study resulted in larger emission estimates compared to the calculations made using the IPCC 2006 emission factors for most regions, although emissions estimates varied substantially by region.

“Among global regions, there was notable variability in trends in estimated emissions over recent decades.  For example, we found that total livestock methane emissions have increased the most in rapidly developing regions of Asia, Latin America and Africa.  In contrast, emissions increased less in the US and Canada, and decreased slightly in Western Europe.  We found the largest increases in annual emissions to be over the northern tropics, followed by the southern tropics,” said co-author Dr. Ghassem Asrar of the JGCRI.

The revised estimates provided in the study are also 15% larger than the global estimates provided by the U.S. Environmental Protection Agency (EPA), slightly smaller than estimates provided by the EPA for the US, 4% larger than global estimates Emissions Database for Global Atmospheric Research (EDGAR), 3% larger than EDGAR estimates for the US and 54% larger than EDGAR estimates for California.  According to the authors, the EPA and EDGAR use IPCC 2006 information which could have contributed to their under estimations.

Further information on this topic is available to subscribers of the Environmental Impact database.  For example, by using the search string methane AND livestock AND “emissions” yields over 1,100 results. 

Journal Reference

Julie Wolf, Ghassem R. Asrar, Tristram O. West. Revised methane emissions factors and spatially distributed annual carbon fluxes for global livestockCarbon Balance and Management, 2017; 12 (1) DOI: 10.1186/s13021-017-0084-y

Article details

  • Author(s)
  • Stephanie Cole
  • Date
  • 05 October 2017
  • Source
  • BioMed Central
  • Subject(s)
  • Climate Change
  • Pollution