Dairy digester in California. (Image courtesy of Dairy Cares)

By Natalie Willis, Reporter, Valley Ag Voice 

Wetlands are the Earth’s largest natural source of methane — a potent greenhouse gas roughly 30 times more powerful than carbon dioxide at warming the atmosphere — according to the Department of Energy’s Larence Berkeley National Laboratory.  

Methane is a key point of controversy among dairy producers and the environmental justice community given that dairy and livestock are responsible for over half of California’s methane emissions, according to the California Air Resources Board.  

However, a peer-reviewed paper recently published by CABI Biological Sciences argues that the state’s dairy sector can reach climate neutrality in the coming years through aggressive methane mitigation which almost no other sector can achieve.  

“If the dairy sector can continue to decrease methane, it can reduce its warming contribution,” Frank Mitloehner, director of the CLEAR Center at UC Davis said. “Other sectors of society can’t do that as easily, but dairy can because the main greenhouse gas it produces is methane. If we reduce that methane, not only can we reach climate neutrality, but we can also chip away at historical emissions, and the sector can become part of a climate solution.” 

The dairy industry’s commitment to reducing methane emissions is evidenced by several initiatives such as dairy digesters which reduce greenhouse gas emissions by roughly 2 million metric tons per year according to CARB. Yet, environmental groups such as the Center for Food Safety, claim that digesters are false climate solutions. 

In a CFS article, authors Rebecca Spector, West Coast Director, and Dashel Murawski, Communications and Development Associate, stated that digesters incentivize increased herds and thereby increase emissions.  


On the other hand, wetlands preservation and restoration have been championed through both political and environmental initiatives as a way to combat climate change. According to the United States Geological Survey within the Department of Interior, wetlands capture large quantities of carbon dioxide and other greenhouse gasses from the atmosphere to store in its soil and plants — commonly known as carbon sequestration.  

A 2015 study from the U.S. Geological Survey found that restored wetlands can release large amounts of methane that reduce or negate carbon sequestration benefits. USGS looked into restored wetlands in the Sacramento-San Joaquin Delta in 2010-2011 to inform the study.  

“The anaerobic conditions that promote CO2 sequestration also make wetlands the largest natural source of [methane] emissions to the atmosphere,” according to the study.  

Wetlands are known as carbon sinks — meaning they hold the capacity to store large amounts of carbon — but they are also one of the largest emitters of methane. A research team from Berkeley Lab studied wetland sites in the Arctic-Boreal region and found that from 2002 to 2021, wetlands released an average of 20 teragrams of methane — equivalent to the weight of about 55 Empire State buildings. 

While the study focused on wetlands in high latitudes, roughly one-third of total methane emissions came from wetlands, according to NASA. This is a result of waterlogged soils and permafrost — which make them carbon sinks — but when wetland soils warm or flood, carbon is released into the atmosphere as methane.  


The California dairy industry is projected to reach climate neutrality as early as 2027 according to the CABI Biological Sciences study. Forty-five percent of California’s annual methane is produced by dairy farms and, as a result, Senate Bill 1383 was instilled to mandate a 40% reduction in dairy emissions by 2030. 

Since then, the industry has generally taken an aggressive approach to reducing its footprint including 236 dairy digesters that collect and harvest methane from 254 farms. According to the study, digesters will achieve 42.6% of SB 1383’s goals, and in order to meet the remaining reduction goals, 420 additional projects will be necessary.  

“Given the success observed to this point, there is the potential for the industry to achieve its 2030 climate goals and these scenarios to be accomplished,” the study explained. “For additional consideration, it is important to note that approximately one-fifth of all California dairies have either constructed or are planning to build a privately financed or public-private partnership digester.” 

The study also notes that while the state’s dairy industry plays a large role in GHG emissions, the majority of emissions fall outside the scope of California’s dairy industry as roughly 80% of the national herd is located in other states. 

Increasing dairy digester projects, improving manure management, and utilizing feed additives are all necessary to reach climate neutrality by 2027, according to the study.  

“This will require widespread adoption of methane-reduction projects by California’s dairy farmers,” the study concluded.  


While both the dairy industry and wetlands are significant sources of methane emissions, they are equally important to components of California’s ecosystem and economy. The dairy industry’s commitment to reducing methane emissions through dairy digesters and other mitigation strategies demonstrates a proactive approach to environmental sustainability as well as the potential to reach climate neutrality as early as 2027.  

Additionally, dairy is the top commodity in the state, generating over $7.4 billion out of California’s nearly $50 billion agriculture industry, according to the California Department of Food and Agriculture. 

Despite arguments that the dairy industry cannot be sustainable, most producers in California are invested in reducing emissions, and taking an aggressive approach, according to the CABI study, will likely lead to the achievement of California’s 40% methane reduction goal.  

Comparatively, while wetlands are major emitters of methane, they also provide habitat and food sources. According to USGS atmospheric scientist Frank Anderson, not all restored wetlands are necessarily GHG emission sources, but they should be continually monitored. 

Against politics and environmental initiatives, both California’s dairy industry and wetlands have a place in the state’s climate goals. 

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