At The Conversation, Frank M. Mitloehner explains how a flawed statistic — comparing numbers derived from non-parallel bases — evolved into one of the most widely quoted arguments for governments forcing people to give up meat in their diet:
As the scale and impacts of climate change become increasingly alarming, meat is a popular target for action. Advocates urge the public to eat less meat to save the environment. Some activists have called for taxing meat to reduce consumption of it.
A key claim underlying these arguments holds that globally, meat production generates more greenhouse gases than the entire transportation sector. However, this claim is demonstrably wrong, as I will show. And its persistence has led to false assumptions about the linkage between meat and climate change.
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Global livestock production by region (milk and eggs expressed in protein terms).
Source: United Nations Food and Agriculture Organization.Setting the record straight on meat and greenhouse gases
A healthy portion of meat’s bad rap centers on the assertion that livestock is the largest source of greenhouse gases worldwide. For example, a 2009 analysis published by the Washington, D.C.-based Worldwatch Institute asserted that 51 percent of global GHG emissions come from rearing and processing livestock.According to the U.S. Environmental Protection Agency, the largest sources of U.S. GHG emissions in 2016 were electricity production (28 percent of total emissions), transportation (28 percent) and industry (22 percent). All of agriculture accounted for a total of 9 percent. All of animal agriculture contributes less than half of this amount, representing 3.9 percent of total U.S. greenhouse gas emissions. That’s very different from claiming livestock represents as much or more than transportation.
Why the misconception? In 2006 the United Nations Food and Agriculture Organization published a study titled “Livestock’s Long Shadow,” which received widespread international attention. It stated that livestock produced a staggering 18 percent of the world’s greenhouse gas emissions. The agency drew a startling conclusion: Livestock was doing more to harm the climate than all modes of transportation combined.
This latter claim was wrong, and has since been corrected by Henning Steinfeld, the report’s senior author. The problem was that FAO analysts used a comprehensive life-cycle assessment to study the climate impact of livestock, but a different method when they analyzed transportation.
For livestock, they considered every factor associated with producing meat. This included emissions from fertilizer production, converting land from forests to pastures, growing feed, and direct emissions from animals (belching and manure) from birth to death.
However, when they looked at transportation’s carbon footprint, they ignored impacts on the climate from manufacturing vehicle materials and parts, assembling vehicles and maintaining roads, bridges and airports. Instead, they only considered the exhaust emitted by finished cars, trucks, trains and planes. As a result, the FAO’s comparison of greenhouse gas emissions from livestock to those from transportation was greatly distorted.
