Methane emissions generated by manure and ruminants such as cattle and sheep as well as those produced by fossil fuel extraction and refining are much higher than estimates reported by the EPA, according to a study published in the Proceedings of the National Academy of Sciences.
Methane emissions produced by agriculture could be twice as high as EPA estimates, according to the Anthropogenic Emissions of Methane in the United States study. The discrepancy in methane source estimates is particularly pronounced in the south-central United States, where researchers found total emissions 2.7 times greater than other estimates.
Methane emissions from fossil fuel extraction and refining activities in the same south-central US region are nearly five times higher than previous estimates.
Overall, total methane emissions in the US appear to be 1.5 times and 1.7 times higher than amounts previously estimated by the EPA and the international Emissions Database for Global Atmospheric Research (EDGAR), respectively.
Researchers contend that the discrepancy lies in the methodology. The EPA and EDGAR use a so-called bottom-up approach, calculating total emissions based on emissions factors, such as the amount of methane typically released per cow or per unit of coal.
This study took a different top-down approach and measured what was actually present in the atmosphere. Then, using meteorlogical data and statistical analysis, the researchers traced it back to regional sources, according to Harvard University, which was involved in the study.
Research released in November by the Climate Accountability Institute says just 90 companies including Chevron, ExxonMobil and BP are responsible for causing almost two-thirds of all man-made global emissions during the industrial era.
These “carbon majors” include 50 investor-owned companies, 31 state-owned companies, and nine government-run industries in the former Soviet Union, China and other countries, according to the study.
Photo Credit: cattle via Shutterstock/branislavpudar