Global Warming: Cars, Cows, and Everything In Between

Wyatt Pontius
December 13, 2018

Submitted as coursework for PH240, Stanford University, Fall 2018

Introduction to Global Warming

Fig. 1: Carbon Dioxide Concentration - The measured CO2 in the atmosphere, showing the value increasing as time progresses, resulting in global warming. [9-11] (Source: Wikimedia Commons)

Global warming, also known as climate change, is the increase in global average temperatures in Earth's climate system. In today's usage, the term refers to theorized anthropogenic warming that has occurred on Earth since the industrial revolution, as well as the projected continuation of these temperature increases into the future. Though past debate existed (and to some extent continues) regarding the existence of climate change, the Intergovernmental Panel on Climate Change Working Group 1 indicated that it was extremely likely that global warming existed and that humans were the dominant cause of said warming. [1] Primarily, the emission of greenhouse gases - notably nitrous oxide, methane, and carbon dioxide - was to blame. [1]

Sources of Global Warming and Their Energy Traits

There are a multitude of sources of global warming. In particular, this report will specifically focus on sources which have contributed to global warming through the emission of greenhouse gases, such as carbon dioxide (see Fig. 1). Though not typically thought of as a primary contributor to global warming, livestock - and in particular, cattle - are actually an interesting part of the problem. Cows are tremendous sources of methane, one of the greenhouse gases which has caused a great deal of damage to the atmosphere. In the United States alone, there is a bovine population of over 1.3 billion, responsible for producing significant methane emissions. Worldwide, the cattle population is much greater, including cattle which are much less "efficient" in terms of beef output per methane output. [2] In sum, it is estimated that cattle methane production can account for approximately 2% of the global warming over the course of the next century. [3] Though this does not sound like a large amount, cattle are an interesting source to explore because they are hardly thought about (in contrast to vehicles) yet contribute a non- insignificant amount of greenhouse gases to the atmosphere. Though carbon dioxide is the most prevalent greenhouse gas in the atmosphere by far, methane is estimated to be twenty-six times as potent when it comes to global warming potential. [4] The potential from damage is measured in terms of something called the global warming potential (GWP), which is a relative measure of how much heat a given greenhouse gas traps in the atmosphere.

GWP is commonly calculated over a set time period, such as 20, 100, or 500 years and is expressed as a factor with the GWP of carbon dioxide normalized to a value of 1. The radiative forcing capacity (RF) of a gas, which is the amount of energy per unit area per unit time absorbed by that gas, is a principal component of the GWP formula. The RF formula calculates the sum of integrated infrared absorbances of gas over the course of the pathlength of heat in the gas. GWP, meanwhile, is the ratio of RF of the specified substance to the RF of the reference gas (carbon dioxide) over the specified time period. [4]

Ruminant animals such as cattle produce methane because of their special digestive tracts. Cows are capable of digesting fibrous plants, but often digest things multiple times due to indigestion. Methanogenic bacteria result in methane being expelled whenever a cow spits out its cud, in a process known as enteric fermentation. [2]

Another more obvious source of greenhouse gases which cause global warming are vehicles. In particular, automobiles account for nearly 20% of US-generated greenhouse gases, emitting approximately 24 pounds of carbon dioxide into the air for each gallon of gas consumed. Increasing vehicle miles traveled (VMT) year to year has led to an increasing quantity of pollution attributable to vehicle traffic in the US. [5]

In addition to livestock and vehicles, there are a number of sources of greenhouse gases which contribution to global warming. Industry, for example, contributes 22% of direct ghg emissions. Buildings contribute an addition 6.4%. Though much could be said about these sources, cows and cars (in addition to sounding cool together) epitomize sources of two of the most dangerous greenhouse gases contributing to global warming today: methane and carbon dioxide, respectively. [6]

Addressing The Heat-Trapping Issues

Fig. 2: Global Warming Projections - Increasing concentrations of greenhouse gases such as carbon dioxide in the atmosphere contribute to increasing temperatures on the surface of the Earth. [12] (Source: Wikimedia Commons)

Though some cow breeds, such as those found in the United States, are highly efficient, some - such as Brazilian cattle - are much less so. Brazil, home to the second largest cattle population in the world, would be able to survive with a herd one-tenth the size of its current herd if they had the more efficient breed of cattle. Furthermore, introducing molasses-urea products (MUPs) has the potential to reduce methane emissions by as much as 70%. Just like electric vehicles to cars, ensuring the most efficient cattle are maintained around the world has the potential to make a huge difference on their contribution to global warming. [2]

When comparing internal-combustion engine vehicles to electric vehicles, a standardizing unit must be used. Scientists created the mpgghg for this purpose. Though EVs which receive their power from coal power plants only achieve 30 mpgghg, other forms of electricity generation are much more efficient. Natural gas achieves 54 mpgghg, solar achieves 500 mpgghg, and the most efficient form of energy generation in terms of mpgghg, geothermal, achieves a whopping 7,600.

Though improving our energy infrastructure to focus on clean power is one great solution, another potential solution is reducing reliance on private automobiles for transportation. The average private passenger vehicle today generates 0.96 pounds of carbon dioxide per passenger mile. Meanwhile, light rail generates just 0.36 pounds of carbon dioxide per passenger mile. This represents a 62% reduction in the amount of emissions, which - when taking into account the proportion of greenhouse gas emissions attributable to transportation in the US - would reduce overall emissions by approximately 11%. [7]

Global Warming Going Forward

Since 1980, the average temperature has increased by nearly 0.15°C per decade. Since 2000, sixteen of the seventeen warmest years on record have occurred. [8] Emissions of greenhouse gases continue to rise due largely to the industrialization of the developing world as well as continually increasing usage by developed nations.

While scientific work toward efficiency improvements such as increasing the population of "efficient cattle" and the introduction of electric vehicles - is resulting in progress, more must be done to prevent the surface temperature from increasing by devastating amounts (see Fig. 2). Anything related to the production or consumption of energy in any form is relevant, ranging from reductions in the amount of electricity consumed, to changes in dietary patterns which are less energy-intensive, to increases in the proportion of energy produced through clean, renewable methods will have an impact on this trend.

© Wyatt Pontius. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.


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[11] "Four Hundred Parts Per Million," The Economist, 11 May 13.

[12] D. J. Wuebbles et al., "Climate Science Special Report," U.S. Global Change Research Program, 2017.