Comment Log Display

Dear Members of the California Air Resources Board,

I am writing to submit my comments on the Scoping Plan Amendments
for AB 32, the California Global Warming Solutions Act.
Specifically, I would like to remark on your recommended actions
and next steps for the agriculture sector, which comprises a
significant portion of California’s economy. 

The agriculture sector is a $45 billion dollar industry that
generates about $100 billion in related economic activity (1).
Given its substantial scale and the impending threats to
agriculture from climate change (as evidenced by the crippling
drought the state is currently experiencing), as well as
California’s unique position as a leader in innovative technologies
that may be adopted nation-wide, there is much to be gained by
farmers, ranchers, and the state as a whole from reducing overall
greenhouse gas emissions (GHG) within this sector. 

The current proposed updates to the Scoping Plan include voluntary
measures to reduce GHG emissions, such as the adoption of manure
digesters, soil management practices, improvements to water and
fuel use practices, land use planning, and others. However, as a
whole, the Scoping Plan is lacking in specificity, and is missing
detailed information on actionable solutions that can be
incorporated into farming and ranching practices. 

In the short term, farmers and ranchers can adopt immediate,
low-tech, and cost-effective measures that will reduce GHG
emissions. In particular, measures could focus on reducing methane
gas from livestock production and nitrous oxide from the usage of
nitrogen-based chemical fertilizers. Together, methane and nitrous
oxide comprise approximately 80 percent of GHG emissions from
agriculture in the US (2). Below, I outline possible strategies for
reducing both methane and nitrous oxides through simple adaptations
of farming and ranching practices.

Methane Gas (CH4)
Methane is the second most prevalent GHG emitted from human
activities in the US. Although methane has a relatively short
lifetime in the atmosphere, its comparative impact pound for pound
is over 20 times greater than carbon dioxide over a 100-year period
(3). After natural gas and petroleum systems, methane from domestic
livestock constitutes the second largest source of emissions from
all other sectors including landfills, mining, wastewater
treatment, and others (3). Domestic livestock naturally produce
large amounts of methane as part of their normal digestive process.
Methane is also produced when animal manure is kept or stored in
lagoons or holding tanks. 

The Scoping Plan Update highlights the use of manure digesters—a
voluntary measure—as its main strategy for reducing methane
emissions. Manure digesters capture methane from storage ponds or
lagoons and subsequently use this captured methane to produce
energy or renewable fuel. In the long term, the use of manure
digesters represents an innovative and valuable solution. However,
as acknowledged in the Scoping Plan Update, there are many
obstacles to implementing their use on a wide scale (4). For one,
as a voluntary strategy, purchasing and installing the technology
is extremely cost prohibitive – manure digesters often cost as much
as three million dollars – and actually obtaining one entails a
lengthy and often confusing permitting process (5). One livestock
producer stated that “getting a digester in [California] takes an
act of God" (5). The California Air Resources Board (CARB) has
committed to incentivizing and removing obstacles to digester
installation. However, in the interim, greater focus should be
placed on low-tech fixes and improved feed and land use management
practices that reduce methane gas emissions from livestock. 

One simple fix that CARB can and should highlight for farmers and
ranchers is the improvement of livestock diets. Supplementing
cattle feed with grains, high quality fats, and more digestible
fodder such as silage (a fermented feed) and legume hay can help to
reduce methane production in the animals’ digestive processes (5).
Livestock producers can also complement cattle feed with high
quality fats (such as edible vegetable oils) in order to reduce
methane emissions. According to one study, supplemental high
quality fats may reduce emissions by almost 4 percent by inhibiting
the rumen bacteria in the animals’ gut (6). 

Another approach is to ensure that cattle have access to
high-quality pasture as opposed to mature grass – one study found a
50 percent reduction in methane emissions from livestock that
grazed high-quality pasture grasses (7). One technique that ensures
livestock have access to high-quality pasture grasses that have not
been overgrazed is a practice known as Managed Intensive Rotational
Grazing (MIRG). Adopted by many farmers globally, MIRG is a grazing
management system in which pasturelands are divided into numerous
paddocks or cells, and selectively grazed. This practice allows
ranchers to selectively manage the timing and intensity of
defolitation (8). Lastly, incorporating legume grasses into
pastures can also have significant effects on methane
emissions—cattle raised on legume-grass pastures emitted 25 percent
less methane than animals raised on grass-only pastures (9).
Through a variety of low-cost, low-tech feed supplementation and
pasture management strategies, long-term methane reductions may be
achieved starting immediately. 

Although further research is required to identify optimal livestock
diets and supplements, these relatively simple first steps aimed at
livestock producers should be included in the Scoping Plan in order
to reduce methane emissions. To be effective, these strategies must
be widely communicated and financially incentivized. If these
suggestions rely solely on voluntary action, it is likely that
farmers and ranchers will not change their feed practices.  

Nitrous oxide (N2O)
Agricultural soil management is the largest source of nitrous oxide
emissions in the United States and accounted for almost 70 percent
of total US nitrous oxide emissions in 2011 (10). The impact of 1
pound of nitrous in terms of atmospheric warming is over 300 times
that of 1 pound of carbon dioxide (10). Nitrous oxide is emitted
when farmers add nitrogen to the soil through the use of synthetic
fertilizers. Farmers can use a variety of fertilizer and soil
management practices to reduce these emissions. Most farmers
routinely over-fertilize their crops hoping to increase yields,
fearing that under-use will lessen overall crop production (5).
However, when farmers over-fertilize, the unused nitrogen in the
soil can form nitrous oxide. In order to reduce the formation of
nitrous oxide from over-fertilized fields, farmers can time
fertilizer applications for key growth phases of the crop, reduce
reliance on synthetic fertilizers through the use of nitrogen
fixing crops such as legumes, and explore the adoption of new
tilling practices, including no-till methods. Reducing tillage has
been shown to decrease nitrous oxide emissions (11). Another
low-tech improvement that may be employed is the use of drip
irrigation practices in which liquid fertilizers are mixed with
water. This method decreases nitrous oxide emissions through a more
efficient delivery system of fertilizer to the plant roots through
the irrigation system (5). 

Conclusion
While the current Scoping Plan Update outlines promising future
research in the agricultural sector, there is a need to include
more immediately actionable next steps that farmers and ranchers
can adopt. The main strategies outlined for GHG emission reductions
are mainly voluntary practices, such as the adoption of a manure
digester, which is cost-prohibitive and logistically challenging.
Other approaches in areas such as nitrogen management, soil
management practices, water and fuel use, and land use planning, to
name a few, are lacking in detail. Farmers and ranchers should be
educated and financially incentivized to make use of low-cost,
low-tech, immediately actionable strategies to reduce emissions of
methane and nitrous oxide.

By focusing on so-called ‘low-hanging fruit,’ CARB has an
opportunity to strengthen recommendations and next steps for
reducing GHG emissions in California’s agricultural sector, as well
as demonstrating innovative leadership that may be followed
nation-wide and globally.

Respectfully yours,

Lila Rubenstein, MPH Candidate
School of Public Health; University of California, Berkeley
Environmental Health Sciences Division


Sources

1.	CDFA. California Department of Food and Agriculture History.
California Department of Food and Agriculture (2014). at

2.	Paustian, K., Antle, J. M., Sheehan, J. & Paul, E. A.
Agriculture’s role in greenhouse gas mitigation. (2006).
3.	US EPA. Methane Emissions. Overview of Greenhouse Gases (2013).
at 
4.	California Air Resources Board. Proposed First Update to the
Climate Change Scoping Plan: Building on the Framework. (2014). at

5.	Elkind, E. N. Room to Grow: How California Agriculture Can Help
Reduce Greenhouse Gas Emissions. (University of California,
Berkeley Law School, 2010). at

6.	Moate, P. J. et al. Influence of cold-pressed canola, brewers
grains and hominy meal as dietary supplements suitable for reducing
enteric methane emissions from lactating dairy cows. Animal Feed
Science and Technology 166–167, 254–264 (2011).
7.	National Sustainable Agriculture Coalition. Agriculture &
Climate Change: Impacts and Opportunities at the Farm Level.
(2009). at

8.	Badgery, W. B., Cranney, P., Millar, G. D., Mitchell, D. &
Behrendt, K. Intensive rotational grazing can improve profitability
and environmental outcomes. in Proceedings of the 27th annual
conference of the Grassland Society of NSW Inc.’. Wagga Wagga.(Eds
C Harris, G Lodge, C Waters) pp 85–91 (2012).
9.	Ominski, K. H., Boadi, D. A., Wittenberg, K. M., Fulawka, D. L.
& Basarab, J. A. Estimates of enteric methane emissions from cattle
in Canada using the IPCC Tier-2 methodology. Canadian Journal of
Animal Science 87, 459–467 (2007).
10. US EPA, C. C. D. Nitrous Oxide Emissions. Overview of
Greenhouse Gases (2014). at

11. Omonode, R. A., Smith, D. R., Gál, A. & Vyn, T. J. Soil Nitrous
Oxide Emissions in Corn following Three Decades of Tillage and
Rotation Treatments. Soil Science Society of America Journal 75,
152 (2011).