Shift Manure Management, Reduce Methane Emissions, Report Urges

Anaerobic digester from Regenis

by | Oct 22, 2018

When it comes to the agricultural sector in California and the state’s methane reduction goals, dairies must change the way they store and handle manure for the state to be successful, according to a new report. 

Methane emissions from manure come primarily from “wet storage,” the report, from the Dairy Cares coalition with support from the Environmental Defense Fund, found. Emissions differences between dairies in California appear to be linked to the amount of manure that is stored in anaerobic, or wet and airless, conditions. The study suggests that reducing the amount of manure stored in that manner, or the length of time manure is stored in liquid form, could significantly reduce methane emissions.

Agriculture is responsible for about 60% of California’s methane emissions, and the state’s dairies are the primary source of those emissions, according to the California Climate and Agriculture Network (CalCAN).

The study, which focused on methane emissions at two Central Valley dairies, also found that:

  • Direct methane emissions from ruminating animals, such as cow digestive gases or burps, tend to remain steady year-round;
  • Emissions from manure storage can be highly variable and weather dependent; they are three to six times higher in summer than in winter.

California managed to meet its original emissions reduction goals – reducing emissions below 1990 levels by 2020 – in 2016, largely due to advances in the state’s renewable energy sector. But emissions from cars and trucks, the state’s biggest source of GHGs, have been on the rise. “The deep reductions from electric power generation are compensating for lackluster performance in other sectors of the economy, including an uptick in the transportation sector where we know we have our work cut out for us,” said Alex Jackson, senior attorney at the Natural Resources Defense Council (via

On the other hand, methane comprises just 6% of the total GHG emissions generated in California, CalCAN says. Approximately equal levels of emissions come from dairy manure management systems and from the digestive process of enteric fermentation in dairy cattle rumens that generate methane exhaled by the animals.

With a law passed in 2016, California became the first dairy region in the world to set a goal for a 40% reduction of methane emissions from dairy manure by 2030.

The state’s current programs to incentivize emissions reductions target the exact emissions sources pinpointed by this study: liquid manure storage. California has made $260 million available for dairy methane reduction projects. These include digesters, which capture methane and convert it to clean renewable energy and fuel, and projects that change manure storage to avoid methane production from anaerobic conditions.

California is on its way to having 100 to 120 dairy digesters operating within the next four to five years. These digesters, one of California’s most cost-effective climate investments, are capturing methane and creating clean, renewable energy, says Dairy Cares.

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