Wednesday, December 6, 2017

Methane estimates may be faulty

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The say current estimates rely on outdated factors and do not fully consider feed intake, differences in animal diets or the facilities used to store manure.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.”