Scientists at Pennsylvania State University say there
could be significant errors in the estimates of how much methane livestock are
giving off and contributing to global warming.
The say current estimates rely on outdated factors and
do not fully consider feed intake, differences in animal diets or the
facilities used to store manure.
Buy they also say the global totals are relatively
accurate; it’s the specifics for various regions and types of farming that
vary.
Published in the American Chemical society’s
peer-reviewed journal Environmental Science & Technology, the Penn State
researchers analyzed feed intake data for cattle and manure storage practices
for cattle, pigs and poultry at the county and state levels in the United
States.
A total of 3,063 counties in the contiguous U.S. were
included in the cattle methane emission database with inventories from the 2012
Census of Agriculture (latest Census available).
The study found total livestock methane emissions
comparable to current U.S. Environmental Protection Agency estimates, and to
the estimates from the global gridded Emission Database for Global Atmospheric
Research (EDGAR) inventory.
However, methane estimates by location varied
significantly from those reported by EDGAR. For example, Texas
and California were significantly different.
The U.S. EPA says livestock production is responsible
for 36 per cent of human-related methane production in the U.S.
That’s second to
the energy sector, which includes natural gas, petroleum systems and coal
mining and accounts for 40 per cent but ahead of landfill methane production at
18 per cent.
The researchers said there is a large uncertainty in
both enteric (farts and belches) and manure methane emissions from livestock.
“Work around the world has shown that variability in
enteric methane emissions can be largely explained with variability in feed dry
matter intake.
Nutrient composition of the feed is also important but
has a lesser impact on enteric methane production than DMI.”
