By Paul Homewood
I was sent this article from two years ago, and it is relevant to the debate on agriculture’s impact on GHGs:
The way the public and the media perceive animal agriculture’s environmental impact can, and should, change. New research from Oxford University and the University of California, Davis have recently debunked some of the most critical and long-standing myths surrounding animal agriculture. But can this breakthrough overcome animal agriculture’s bad reputation?
The current narrative about animal agriculture says that ruminant livestock animals (e.g., beef cattle, dairy cattle, etc.) produce methane. Methane is a potent greenhouse gas. Thus, animal agriculture is bad for the environment.
During a keynote presentation for the Alltech ONE Virtual Experience, Dr. Frank Mitloehner, professor at the University of California, Davis and air quality specialist, boldly proclaimed a path for animal agriculture to become climate-neutral.
Yes, “you heard me right — climate-neutral,” said Dr. Mitloehner. He said he would like to, “get us to a place where we have the impacts of animal agriculture that are not detrimental to our climate.”
3 myths about animal agriculture’s environmental impact debunked
Myth #1: Methane (the most common greenhouse gas, or GHG, in animal agriculture) acts just like other GHGs in the environment.
Fact: The three main greenhouse gases, carbon dioxide, methane and nitrous oxide, all impact the environment in critically different ways, especially as it relates to their source, life span in the atmosphere and global warming potential.
Carbon dioxide and nitrous oxide are known as “stock gases.” Stock gases are long-lived gases and once emitted will continue to build up in the atmosphere. Carbon dioxide, for example, has an estimated lifespan in the atmosphere of 1,000 years, meaning carbon dioxide emitted from the year 1020 may still be in the atmosphere today. Methane, on the other hand, is a “flow gas.” Flow gases are short-lived gases and are removed from the atmosphere at a more rapid pace. Methane’s lifespan in the atmosphere is approximately 10 years. This means a flow gas like methane would impact the environment for a duration that is nearly 100 times shorter than the stock gas carbon dioxide.
What causes these gases in the first place? Carbon dioxide is created by the burning of fossil fuels. Fossil fuels are used as the energy source to power most homes, vehicles and industry globally. As the graph below depicts, Dr. Mitloehner refers to stock gases like carbon dioxide as a “one-way street” because they only accumulate in the environment over time due to their long lifespan.
Methane can be produced in a variety of methods, but most commonly, it’s produced through the rumination process in beef and dairy livestock (i.e., belching). As a short-lived flow gas, “The only time that you really add new additional methane to the atmosphere with the livestock herd is throughout the first 10 years of its existence or if you increase your herd sizes,” explained Dr. Mitloehner. Methane levels do not increase if herd sizes remain constant because methane is being broken down at the same rate it is being produced.
“What I’m saying here by no means (is) that methane doesn’t matter,” he continued. “While that methane is in the atmosphere, it is heat-trapping, it is a potent greenhouse gas. But the question really is, do our livestock herds add to additional methane, meaning additional carbon in the atmosphere, leading to additional warming? And the answer to that question is no. As long as we have constant herds or even decreasing herds, we are not adding additional methane, and hence not additional warming. And what I just said to you is a total change in the narrative around livestock.”
Alternatively, carbon dioxide is created from extracting fossil fuels that are millions of years old and are trapped under the Earth’s surface.
“These long-lived climate pollutants are only emitted,” said Dr. Mitloehner. “They are put into the atmosphere, but there’s no real sink for it in a major way.”
This demonstrates that carbon dioxide and methane are very different types of gases (stock versus flow) and have very different lifespans in the environment (1,000 years versus 10 years), but what about their global warming potential?
Myth #2: The current method for assessing the global warming potential (GWP100) of greenhouse gases properly accounts for all important variables.
Fact: The initial method for calculating GWP100 misrepresents the impact of short-lived flow gases, like methane, on future warming. The new “GWP*” is an improved and more representative measurement.
The initial GWP100 measures produced by the Kyoto Protocol nearly 30 years ago marked a very positive step for assessing global warming. The initial documents included many footnotes and caveats to account for variability and unknown values. “But the footnotes were cut off, and people ran with (it),” said Dr. Mitloehner. “And in my opinion, that was a very dangerous situation that has really gotten animal agriculture into a lot of trouble, actually, quite frankly.”
The current GWP100 measurement generates an over-assessment of methane’s contributions to global warming. Currently, in short, GWP100 measurements are all standardized to a billion tonnes of carbon dioxide equivalent. So, all non-carbon dioxide emissions are converted by multiplying the amount of the emissions of each gas by its global warming potential over 100 years value. Methane has a GWP100 value of 28, meaning it is 28 times more potent than carbon dioxide in the atmosphere.
Unfortunately, this type of calculation completely omits the fact that flow gases, like methane, are destroyed after approximately 10 years and would not continue for the entire 100-year duration as described in the GWP100 formula. Additionally, it underestimates the impact that stock gases, like carbon dioxide, would have that persist in the environment for 1,000 years.
Dr. Mitloehner cited Dr. Myles Allen from Oxford University as the pioneer of a new calculation called “GWP*.” The new GWP* calculation better accounts for both gas intensity and gas lifespan in the atmosphere in its measurements of global warming. This is a new narrative to explain global warming emissions and, Dr. Mitloehner said, “you will see it will gain momentum, and it will become the new reality” soon.
Myth #3: To keep up with increasing demand and global population growth, the United States has continued to increase its numbers of beef and dairy cattle, thus increase methane emissions.
Fact: The United States reached peak beef and dairy cattle numbers in the 1970s and has reduced its number of animals every decade since, resulting in 50 million fewer cattle in total.
Over the last half-century, the United States has made tremendous progress to improve efficiency and increase productivity while also reducing total beef and dairy cattle numbers. For example, in 1950, the U.S. dairy cow herd peaked at 25 million cattle. Today, the dairy herd is approximately 9 million cows, yet it is producing 60% more milk — that’s significantly more milk with 14 million fewer cows!
Though cattle numbers have continued to increase in countries such as India and China, this means the United States has not increased methane output — thus not increasing GHG contributions from livestock — over the last five decades.
This first myth of the article really goes to the heart of the issue. As Dr Mitloehner explains, the global stock of methane in the atmosphere will not increase unless herds increase around the world. And even if you do away with all cattle, the reduction in methane levels is only ten years’ worth.
There are of course other factors not taken into account here. If we do abolish all livestock, how do we replace that food? All types of food production, whether arable or not, involve the emission of GHGs, not least in the use of fertilisers, which would inevitably increase without the availability of manure.
via NOT A LOT OF PEOPLE KNOW THAT
October 10, 2022
3 myths debunked: Animal agriculture’s real impact on the environment | NOT A LOT OF PEOPLE KNOW THAT (wordpress.com)
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