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Greenhouse Gas Sources and Sinks on Dairy Farms

Greenhouse gas (GHG) emissions from dairy farms primarily come from enteric fermentation, manure management, feed production, and energy use. These emissions include methane  from cattle digestion and nitrous oxide  from manure and soil management, as well as carbon dioxide from energy consumption. Effective measurement and management of these GHGs are crucial for reducing their impact on climate change. Opportunities for reduction include increasing production efficiency, minimizing waste, improving soil health, and adopting new technologies. By enhancing carbon sinks and employing mitigation strategies, dairy farms can contribute to a more sustainable industry.

Learning HubIntroduction to Dairy Greenhouse Gases

CONTENT CURRENTLY UNDER DEVELOPMENT
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SPEAKER: Dr. Stephanie Masiello Schuette, Dairy Management Inc.

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Summary of Key Points from the Presentation

What Are GHGs?

GHGs are naturally occurring gases that retain some of the sun's warmth, making Earth a habitable planet. ​ While there are many types, the main GHGs emitted by agriculture are:

  • Carbon Dioxide (CO₂)

  • Methane (CH₄)

  • Nitrous Oxide (N₂O)

Elevated levels of GHGs in the atmosphere amplify the greenhouse effect, a natural process that traps heat and warms the Earth, leading to global warming and climate change. Human activities have increased the concentrations of GHGs in the atmosphere.

Biogenic and Fossil Carbon

Biogenic carbon and fossil carbon both contribute to the carbon cycle, but they differ significantly in their origins and impacts. Understanding the distinction between these two types of carbon is critical for evaluating agricultural practices and their impact on global warming.

  • Biogenic carbon: Biogenic carbon comes from natural processes, such as plant and animal respiration, decomposition, and the carbon stored in biomass. It is part of a short-term cycle where carbon is absorbed and released over relatively short timescales, such as within a few years or decades.

  • Fossil carbon: Meanwhile, fossil carbon originates from ancient organic matter that has been buried and transformed into coal, oil, or natural gas over millions of years. When fossil carbon is released through activities like burning fossil fuels, it introduces carbon that has been locked away for millennia into the atmosphere, significantly contributing to long-term GHG concentrations and climate change.

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Quantifying GHGs

Different GHGs can have different effects on the Earth's warming. Therefore, in order to quantify the impact of different gasses, each GHG has a different Global Warming Potential (GWP). GWP is a measure of how much heat a GHG traps in the atmosphere over a specific period compared to carbon dioxide.  

Global Warming Potentials

GWP values for different GHGs over various time horizons provided by the Intergovernmental Panel on Climate Change (IPCC).  The values for Global Warming Potential 100-Year Time Horizon, are presented below.

Carbon Dioxide

CO₂

GWP100 Value

1

Methane

CH₄

GWP100 Value

27

Nitrous Oxcide

N₂O

GWP100 Value

273

carbon dioxide equivalent

Carbon dioxide equivalent (CO₂e) is a metric measure to compare the emissions from GHGs on the basis of their GWP.  Carbon dioxide equivalents are used to standardize the effects of different GHGs. 

 

For example, if a gas has a GWP of 25 over 100 years, it traps 25 times more heat than carbon dioxide over that period. Thus, emitting one unit of that gas is equivalent to emitting 25 units of carbon dioxide in terms of its impact on global warming over 100 years.​

Carbon Dioxide

CO₂

Carbon dioxide is a colorless, odorless GHG released when fossil fuels (e.g., natural gas, oil, coal, etc.) burn. 

Carbon Dioxide Equivalent

CO₂e

In contrast, carbon dioxide equivalent is more accurate, as it contains all the molecules that will absorb heat and will warm our atmosphere. 

Understanding GHG Footprints

There are two basic ways to think about dairy GHG emissions:

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Absolute Emission

Total GHG emission over a defined period of time

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Emission Intensity

The volume of GHG emissions per unit of milk

 

Production efficiency gains have resulted in decreased GHG emissions intensity due to higher production per cow and a reduced need for replacement animals.

Estimating Dairy's GHG Footprint

The GHG impact or footprint of a farm is qualified via modeling. Many tools have been developed to estimate the GHG emissions of dairy farms, ranging from simple calculators to very sophisticated process models.​ To obtain an accurate estimate of all emissions related to producing milk on the farm, the tool must consider:

  • All direct emissions from the farm.

  • The emissions occurring in the production of resources (e.g., fuel, electricity, fertilizer, purchased feed, etc.) used on the farm. 

  • The indirect emissions from various forms of nitrogen lost from the farm.​​​

See Learning Hub Content for More Information

A Life Cycle Assessment (LCA) is a process for evaluating the environmental burdens associated with a product, process, or activity and helps to identify and quantify energy use, material use, and emissions. The U.S. dairy industry conducts nationwide LCAs to analyze the environmental impact of fluid milk production from farm to table, encompassing stages such as raw material extraction, processing, manufacturing, transportation, distribution, product use, recycling, and disposal.

Dairy Farm GHG: Sources 

Carbon sources release carbon dioxide into the atmosphere. Dairy farming GHG emissions primarily originate from cattle digestion, manure management, feed production, and energy use.​​​​​​

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COW EMISSIONS

The natural fermentation of forage by microbes in ruminants’ digestive system releases methane, primarily during belching and exhaling. Influential factors include animal health, ration composition, feed quality, and feed intake.

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MANURE STORAGE

Methane and nitrous oxide are released during manure collection, transport, storage, treatment, and application. Fuel used for manure transporting and spreading also contributes to carbon dioxide emissions. Influential factors include temperature, manure composition, and manure handling practices. 

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FEED AND FORAGE PRODUCTION

Soils release nitrous oxide when fertilizers and manure are applied.  Influential factors include high concentrations of fertilizers and manure combined with low oxygen, high moisture, warm temperatures, and low pH in soil.

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Soils can either store or release carbon as carbon dioxide.  Soil disturbance can release carbon dioxide. Influential factors include management practices that limit soil disturbance and support soil microbial activity to encourage soil carbon storage.​​

Emissions arise from fuel and electricity use.

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ENERGY

Burning fossil fuels (e.g., propane, diesel, and gasoline) for essential dairy operations such as electricity, heat, and transportation generates carbon dioxide.

How can we reduce emissions?

Opportunities for GHG emission reduction vary among farms, depending on emission sources, infrastructure, and management practices.

Some examples include:

  • Increase production efficiency: Producing more milk with fewer animals and less feed can reduce emissions per unit of milk.

  • Reduce waste: Steps toward reducing waste include minimizing feed shrinkage, using manure as fertilizer, and generating electricity from waste to lower external energy dependence.

  • Build soil resilience: Enhancing soil health through crop rotations, cover cropping, and reduced tillage can help sequester carbon (i.e., capturing carbon dioxide in stable forms within the soil).

  • Adopt new technologies: Using feed additives to reduce methane emissions from livestock can help mitigate GHG emissions​​​.

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