Name: Life Cycle Assessment and Greenhouse Gas Emissions from Animal Agriculture
Uploaded: 2016-11-03T13:08:23.000Z
Duration: 20 min 43 s
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Scientists agree the major driver behind the rise in global greenhouse gas emissions is

human activity. How does farming fit it and,what is the contribution of animal agriculture

The consuming public is more and more interested in where their food comes from, what’s the

carbon footprint. What’s the carbon footprint, or the what’s

the environmental footprint, of a gallon of milk, or a pound of beef, or a pound of chicken meat?

My name is David Schmidt and I’m an agricultural engineer at the University of Minnesota and

Regional Coordinator for the national project, Animal Agriculture in a Changing Climate.

There is a significant amount of miscommunication about the role of agriculture

in climate change. Some say that animal agriculture is the largest contributor to greenhouse gas

emissions while others deny any contribution from animals. The answer lies somewhere in

between. The objective of this video is to provide you with a solid foundation of how

emission estimates are calculated and the real contributions of animal agriculture to

US and global greenhouse gas(GHG) emissions.

Carbon is all around us. It is the fourth most abundant chemical element in the universe,

behind hydrogen, helium and oxygen. The biggest reservoir of carbon is stored

in rocks- approximately 66,000 gigatons with one gigaton is equal to 1 trillion kilograms.

The second biggest reservoir is the deep ocean, and the third largest reservoir is in fossil

fuels. The atmosphere and the surface ocean are the smallest carbon reservoirs but possibly

the most important. Carbon is moving between these reservoirs constantly because of a variety

of chemical and biological processes. This is known as the carbon cycle.

The total amount of carbon that cycles in and out of the atmosphere naturally each year

is about 210 gigatons. The arrows and yellow numbers indicate this movement, or cycling

of carbon. Plants and oceans are referred to as net carbon “sinks” because they

absorb more carbon from the atmosphere than they emit. These carbon emissions occur in

the form of plant respiration and chemical exchanges with the ocean.

The red numbers indicate the human influence in the cycle, also known as “anthropogenic

emissions.” They can be mostly be attributed to the burning of fossil fuels and changes

in land use. Human activities contribute nine gigatons of carbon emissions annually. About

two gigatons of that carbon gets taken up or absorbed by the ocean. Three gigatons of

that carbon gets absorbed by plants through photosynthesis and taken up in plant soil

system. All this movement results in an annual net increase of about four gigatons of carbon

As you can see in this diagram, the amount of carbon dioxide in the atmosphere was relatively

stable for hundreds of thousands of years, at an average of around 230 parts per million.

Then about 100 years ago, the CO2 concentration in the atmosphere began climbing to where

it is right now, about 400 parts per million.

This animated diagram more dramatically illustrates the rise in carbon dioxide levels in the earth’s

atmosphere in more recent years, since 1979. The numbers on the left and right indicate

the CO2 concentration in parts per million. Again this indicates the current CO2 level

reaching up to and even beyond 400 parts per million.

While we do not intend to focus on all of the greenhouse gases in this lesson, it is

important to note that carbon dioxide is not the only greenhouse gas. The most common greenhouse

gas is water vapor, followed by carbon dioxide , methane , nitrous oxide and fluorinated

gases. Excluding water vapor, the combined sources of carbon dioxide, primarily from

fossil fuel use and land use change, make up about 77% of the global greenhouse gases.

Because these other gases trap different amounts of energy per molecule of gas, scientists

have normalized the data into something called Carbon Dioxide Equivalents, or CO2 equivalents.

This “equivalent” refers to the equivalent heating potential of the gas. This is also

known as radiative forcing or global warming potential. For instance, a single molecule

of methane will trap approximately 25 times the amount of energy as will a single molecule

of carbon dioxide. So methane has a CO2 equivalent of 25. Nitrous Oxide has a CO2 equivalent

of 298. This use of CO2 equivalents allows us to evaluate the impact of the gases on

the environment - not just the amount of these gasses in the atmosphere.

Anthropogenic greenhouse gases are emitted by many sources and from every country. Together

these nations contribute a world total of 45 thousand million metric tons of CO2 Equivalents.

This graph shows percentages of greenhouse gas emissions by country in 2012. The United

States is currently the second highest emitter of these gases, contributing about 15% of

the world total. The highest emitting country is China. However, this same information can

be evaluated based on emissions per capita. This breakdown shows the US at about 19 tons

CO2e per year per person vs China at 7.5 tons CO2e per year per person.

Taking a closer look at the sources of greenhouse gas emissions in the United States alone by

economic sector, we see that agriculture contributes 9 percent of total emissions in

the US. Total emissions in the US add up to approximately 6,673 million metric tons of

CO2 Equivalents. Agriculture’s 9% represents about 515 Million Metric Tons of that amount.

Looking at the agricultural sector itself, we can see that agricultural soil management

is the biggest source, it accounts for about 50% of total agricultural emissions. This

is followed by enteric fermentation at about 32% and manure management at 15%.

Now looking at the type of gases emitted, about 55% of the agricultural emissions are

from nitrous oxide, which is produced naturally through the the microbial process of nitrification

and denitrification of mineral nitrogen in the soil. The remaining 45% is from enteric

methane or from methane formed during the microbial breakdown of manure. Note that these

emissions are only the direct emissions of greenhouse gases occurring on the farm. Other

emissions that would occur off farm - like emissions from fertilizer production or electricity

used on the farm are not included in these numbers.

We can also look more closely at emissions by animal species. In this chart you can

see the comparisons between beef cattle, dairy cattle, swine, poultry and all other livestock.

These differences are primarily a function of total animal numbers and the contribution

of enteric fermentation. Again these are direct emissions for animal production and do not

include emissions from the production of things like animal feed.

Overall if you look at all animals in the united states for example – the beef sector

would have the greatest impact on carbon footprint of this nation but that’s only because there

are so much more beef animals than dairy animals. We have 90 million beef animals and 9 million

dairy animals, so 10 times more beef animals.

However, a better way to think about greenhouse gas emissions is in terms of emissions per

unit of production. We can look at kilograms of CO2 equivalents per kilogram of product

produced or product consumed. This evaluation includes not only direct emissions from the

farm, but also the emissions that occur after the products leave the farm. We will discuss

this further a little later in the video.This graph compares the greenhouse gas emissions

of several products on per kilogram basis. Of all the products, lamb is the highest emitter

per kilogram of product consumed, and beef is the second highest emitter at 27 kilograms

of CO2 equivalents per kilogram of beef consumed. Dairy is much lower in emissions, with 1.9

kilograms of CO2 equivalents per kilogram of milk consumed.

Before getting further into attributing emissions to different sectors of animal agriculture

or to different sources on the farm, we’ll look at the system used to measure and calculate

these emissions. There is a way to quantify greenhouse gases.

This quantification method is called LCA, life cycle assessment. It has been done for

many years and it has been done by many different groups using different methodologies.

The Life Cycle Assessment, or LCA, is an accounting method that tracks all of the greenhouse gas

emissions produced by a given process, product or system. Often this is called a ‘cradle