What Is the Carbon Footprint of Ethanol? A Life-Cycle Assessment

What Is the Carbon Footprint of Ethanol? A Life-Cycle Assessment

Grace Smoot

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Gasoline and diesel fuel may still be the two most common fuel sources in the modern transportation industry, but ethanol has emerged as a promising alternative that boasts lower levels of greenhouse gas emissions. So, we had to ask: What is the carbon footprint of ethanol?

On a life-cycle basis, ethanol has a lower carbon footprint than gasoline. One gallon of ethanol emits 18.92 pounds (8,595 grams) of CO2 when combusted, and driving one mile on average emits 315 grams of CO2. It has various environmental benefits but also comes with some drawbacks.

Keep reading to learn about the overall carbon footprint of ethanol, its carbon footprint throughout its life-cycle, and how environmentally friendly it is.

Here’s What the Carbon Footprint of Ethanol Is

The carbon footprint is one of the ways we measure the effects of human-induced global climate change. It primarily focuses on the GHG emissions associated with consumption, but also includes other emissions such as methane (CH4), nitrous oxide, and chlorofluorocarbons.

Carbon footprint: the amount of greenhouse gases and specifically carbon dioxide emitted by something (such as a person’s activities or a product’s manufacture and transport) during a given period”

Merriam Webster

Basically, it is the amount of carbon emitted by an activity or an organization. This includes GHG emissions from fuel that we burn directly (e.g., heating a home, driving a car) and GHG emissions from manufacturing the products that we use (e.g., power plants, factories, and landfills).

Ethanol, also known as ethyl alcohol, grain alcohol, and EtOH, is a clear and colorless liquid that can be used as a vehicle fuel in gasoline-powered vehicles. It is a subset of biofuels (ethanol and biodiesel) that is made from biomass. Biomass is renewable organic material from plants and animals that can be used to produce a wide range of products including energy, everyday products that contain plastics, and fuel. Ethanol is most commonly made from corn but can also be made from crop residues and wood (cellulosic biomass).

Ethanol: a colorless volatile flammable liquid C2H5OH that is the intoxicating agent in liquors and is also used as a solvent and in fuel”

Merriam-Webster Dictionary

Like gasoline, ethanol is used in engines that use a spark to ignite the fuel. Ethanol can be blended with gasoline in any percentage up to 83% to produce finished ethanol fuel. Pure ethanol is referred to as E100, and E10 (10% ethanol and 90% gasoline) is the most common blend. Other common forms of ethanol include E15 and E85. 

One gallon of ethanol produces 4% fewer emissions than gasoline, 8,595 grams of CO2 (gCO2) compared to 8,887 gCO2. And the average ethanol (E85) emission rates for all vehicle models are 22% lower compared to gasoline.

Burning of ethanolCarbon footprint
Burning one gallon8,595 grams of CO2 emitted (when E10 is combusted)
Driving one mile (on average)315 grams of CO2 emitted (when E85 is combusted)
Per million British thermal units (Btu)150.88 pounds of CO2 emitted (when E100 is combusted)

Global ethanol production in 2019 was 115 billion liters, and this number is expected to increase to 119 billion in 2025. 

Illustration of lobal biofuel production in 2019 and forecast to 2025
International Energy Agency: Global biofuel production in 2019 and forecast to 2025

Oil (including gasoline and diesel fuel) is the world’s primary fuel source for transportation. But since the turn of the century, there has been a push towards a cleaner-burning transportation fuel with less negative effects on the environment. This is one major reasons the market for ethanol is expected to increase from $93.7 billion in 2020 to $155.6 billion by 2030.

To understand the total carbon footprint of ethanol, we must assess its life-cycle and each stage’s carbon footprint. This life-cycle assessment (LCA) is a method to evaluate the environmental impacts of products and materials. Over the years, companies have strategically used LCA to research and create more sustainable products. So, let’s have a look at the LCA of ethanol!

The life-cycle stages of ethanolEach stage’s carbon footprint
Building of ethanol production facilitiesCO2 emissions from building the components of the ethanol power plant
Extracting of ethanolCO2 emissions from the milling and fermentation processes
Transportation of ethanolCO2 emissions from transporting ethanol by barges, tankers, pipelines, trucks, and railroads across distances
Building back of ethanol production facilitiesCO2 emissions from utilizing construction equipment to demolish the buildings and construct new buildings in the old ethanol plant’s place

The total carbon footprint of ethanol would equal the carbon footprint from building + the carbon footprint from extracting + the carbon footprint from transportation + the carbon footprint from building back.

What Is the Carbon Footprint of Building Ethanol Production Facilities

Ethanol is made in ethanol production facilities, which convert biomass material into fuel. Ethanol production facilities have many components, and constructing these components requires machinery that emits CO2

What Is the Carbon Footprint of Extracting Ethanol

In this stage, ethanol feedstocks (corn) are grown, harvested, and transported to an ethanol production facility. In these facilities, biomass sources are converted to ethanol via biological conversion, specifically the process of fermentation. Fermentation converts sugars (glucose, fructose, sucrose) into ethanol and produces CO2 as a byproduct.

There are two main ways to produce ethanol from sugar or starch-based crops: dry and wet mill; plus there’s a distant third: cellulosic biomass. The difference between the two is the initial treatment of the grain. 

  1. Dry mill: In dry milling, the grain kernel is first ground before being mixed with water to form a “mash”. Enzymes are then added to the mash to convert starch into sugar. The mash is cooked, cooled, and sent to fermenters where yeast is added and the sugars begin to convert to alcohol. After fermentation, the ethanol is distilled, dehydrated, and blended with a small percentage of gasoline before it is transported to gas pumps.
  1. Wet mill: In wet milling, the grain is first soaked to separate it into its basic parts. Grinders separate the corn germ from the fiber, gluten, and starch components, which are then further separated to isolate the starch. The remaining starch is sent to fermenters where yeast is added and the sugars begin to convert to alcohol. After fermentation, the ethanol is distilled, dehydrated, and blended with a small percentage of gasoline before it is transported to gas pumps. 
  1. Cellulosic biomass: Converting cellulosic feedstock (grass, wood, crop residue) to ethanol is a more involved process with two pathways, biochemical and thermochemical. In the former, biomass is pretreated to release hemicellulose sugars. Hydrolysis then breaks cellulose into sugar which is fermented into ethanol. In the latter, heat and chemicals are added to biomass to produce syngas, a mix of hydrogen and carbon monoxide. Syngas is then mixed with a catalyst and reformed into ethanol. 

Approximately 90% of today’s ethanol is produced via dry milling, with the remainder largely via wet milling. 

What Is the Carbon Footprint of Transportation of Ethanol

In 2018, 160 billion liters (bl) of biofuels were produced globally from biomass. North and South America account for 75% and Europe 14% of global biofuel production. 

Illustration of biofuel energy production
Our World in Data: Biofuel Energy Production

The six largest biofuel-producing countries (amount per year) in the world are: 

  1. United States – 374 billion kilowatt-hours (bKWh)
  2. Brazil – 245 bKWh
  3. Indonesia – 78 bKWh
  4. Germany – 40 bKWh
  5. China – 39 bKWh
  6. Thailand – 27 bKWh

Overall, global ethanol production has continued to increase since 2007. Together, the United States and Brazil produce 84% of the world’s ethanol. The former produces it from corn, and the latter produces it from sugarcane.

Illustration of global ethanol production
US Department of Energy – Alternative Fuels Data Center: Global Ethanol Production by Country or Reason

Calculating the carbon footprint of ethanol transportation involves knowing where the ethanol is produced, where it is being consumed, and the distance between the two. 

The United States exports 40% of its ethanol to Brazil and Canada. Transporting ethanol from the US to Brazil, for example, is an approximate 6,790 kilometer (km) (4,219 mile) transportation distance. Likewise, there is only approximately 2,262 km (1,406 mile) distance between the United States and Canada. The carbon footprint of transportation for the former circumstance would be high because it is a long distance that would require multiple modes of transportation. The latter circumstance would have a lower carbon footprint because it is across a shorter distance. 

On the flip side, if ethanol is produced in one country and is consumed in that same country, the transportation distance is much shorter and would require fewer modes of transportation, leading to a lower carbon footprint for this stage. 

What Is the Carbon Footprint of Building Back Ethanol 

Although ethanol was first used to power an engine in 1826, the modern ethanol industry didn’t come about until the 1970s. Since it is a relatively new industry, there is not much historical data available on the life expectancy of ethanol production facilities. Experts estimate that dry-mill ethanol production facilities can last anywhere from 30-60 years if maintained properly. CO2 emissions at this stage occur when utilizing construction equipment to demolish the buildings and construct new buildings in the old plant’s place. 

What Role Does Ethanol Play in Combating Climate Change

Ethanol can reduce GHG emissions by 32-62% percent when compared with gasoline, and fuel made from cellulosic biomass can reduce GHG emissions by more than 100%. A study done by Swiss Federal Laboratories compared E10, E85, and gasoline (E0) and found that E10 produced 67-96% less and E85 82-96% less hydrocarbon emissions. E10 and E85 also reduced particulate matter emissions by 95%.

Climate Change: changes in the world’s weather, in particular the fact that it is believed to be getting warmer as a result of human activity increasing the level of carbon dioxide in the atmosphere:”

Cambridge Dictionary

Climate change is arguably the most severe, long-term, global impact of fossil fuel combustion. Every year, approximately 36 bt of CO2 are emitted from burning fossil fuels. 12 bt (34%) of this comes from oil. The carbon found in fossil fuels reacts with oxygen in the air to produce CO2 which warms the earth by acting as a heating blanket.

Reduced CO2 emissions from ethanol combat climate change in the following ways:

  • Melting of sea ice: Since 1979 arctic sea ice has declined by 30%. Sea ice plays a major role in regulating the earth’s climate by reflecting sunlight into space and providing habitat for animal species. If all of the glaciers on Earth melted, sea levels would rise by approximately 70 feet, effectively flooding out every coastal city on the planet. 
  • Changing precipitation patterns: Extreme weather events (e.g., hurricanes, floods, droughts) are becoming more common and more intense. Storm-affected areas will experience increased precipitation and flooding whereas areas located further from storm tracks will experience decreased precipitation and droughts.
  • Ocean acidification: The ocean absorbs 30% of the CO2 released into the atmosphere, which decreases the pH (increases the acidity) of the ocean. In the past 200 years, the pH of oceans has decreased by 0.1 pH units, which translates to a 30% increase in acidity. Aquatic life unable to adjust to this rapid acidification will die off. A prime example of this is coral bleaching, where coral expel the algae (zooxanthellae) living in their tissues as a result of changes in temperature, light, or nutrients. 

Climate change results in global warming, when CO2 and other air pollutants absorb sunlight and solar radiation in the atmosphere, thereby trapping the heat and acting as an insulator for the planet. Since the Industrial Revolution, Earth’s temperature has risen a little more than 1 degree Celsius (C), or 2 degrees Fahrenheit (F). Between 1880-1980 the global temperature rose by 0.07C every 10 years. This rate has more than doubled since 1981, with a current global annual temperature rise of 0.18C, or 0.32F, for every 10 years. 

Experts claim that to avoid a future plagued by rising sea levels, acidified oceans, loss of biodiversity, more frequent and severe weather events, and other environmental disasters brought on by the hotter temperatures, we must limit global warming to 1.5C by 2040

The more we reduce CO2 emissions, the more we slow the rate of temperature rise, sea-level rise, ice melting, and ocean acidification. When these rates are slowed, the earth’s biodiversity does not have to struggle to adapt to temperature and pH changes. People will not be displaced due to the flooding of coastal areas. And icebergs will continue to provide climate regulation. 

How Environmentally Friendly Is Ethanol

Ethanol is a biofuel that comes with lower levels of GHG emissions compared to gasoline.

Environmentally friendly: (of products) not harming the environment.”

Cambridge Dictionary

Both the environmental benefits and drawbacks of ethanol must be taken into consideration when discussing the issue of climate change.

What Are Environmental Benefits of Ethanol

The environmental benefits of ethanol include:

  1. Climate change mitigation: In 2020, the use of ethanol in gasoline reduced CO2 emissions from the transportation industry by 47.3 million metric tons. This is the equivalent of removing 10.1 million cars from the road for 1 year or negating the emissions from 12 coal-fired power plants for a year!
  1. Improves air quality: Blending ethanol into gasoline reduces tailpipe emissions from several pollutants including CO, hydrocarbons, air toxics (benzene), and particulate matter. These can reduce oxygen delivery to bodily organs, contribute to harmful ozone formation, and cause cancer and reproductive/birth defects.
  1. Employment Opportunities: Ethanol production creates jobs in many rural areas, and in 2019 the industry provided 68,600 jobs in the United States alone. Given that many other countries also produce ethanol, the total amount of jobs provided by ethanol is much higher. 

Ethanol benefits the environment by mitigating climate change, improving air quality, and creating jobs. 

What Are Environmental Drawbacks of Ethanol

Some research suggests that by 2050, bioenergy (biomass and biofuel) could meet 20% of the world’s total annual energy demand. But ethanol cannot replace gasoline and diesel fuel as the world’s primary transportation fuel because it would require using ALL of the world’s crop harvests, plant residues, timber, and grass consumed by livestock. 

The main drawback of ethanol is the amount of land needed to grow the biomass material. Some claim that ethanol is carbon neutral because the plants that are the source of the ethanol absorb CO2 as they grow, thereby offsetting the CO2 released when ethanol is burned. But in some parts of the world, large swaths of forests have been cleared and burned to plans needed to make ethanol. Dedicating land for the sole purpose of biofuel production leads to deforestation, which in turn expedites global climate change. 

Our forests absorb 2.6 billion tons of CO2 every year. The main threat to them is deforestation, which occurs at roughly 10 million hectares (~ 25 million acres) per year. The world has lost more than 1/3 of its forest since the last ice age, which occurred about 2.6 million years ago. Trees combat climate change, purify the air, provide housing for millions of plant and animal species, protect against floods and water pollution, and improve mental health. Chopping these trees to make space for crops has a devastating effect on the environment because it reduces the amount of trees that can capture our CO2 emissions. Protecting forest habitats increases carbon sequestration and decreases the effects of global climate change.

Final Thoughts

Ethanol emits slightly less CO2 than gasoline when burned but it also comes with lower levels of harmful air pollutants. It can be an effective alternative fuel source because it generally has a low carbon footprint across its building, extraction, transportation, and building back stages. Deforestation is the environmental drawback that must be taken into consideration when discussing using ethanol as a fuel source.

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