The term “carbon footprint” is important when discussing human-induced climate change because it refers to greenhouse gas emissions. Different energy types have different carbon footprints, with some of these values being higher than others. So we had to ask: Which energy sources have the highest carbon footprint?

Fossil fuels and biomass have the four highest carbon footprints. Per kWh produced, oil emits 970, coal 820, natural gas 490, and biomass 230 or 740 grams of carbon dioxide on a life-cycle basis. They directly contribute to climate change and have various negative environmental effects.

Fossil fuels and biomass make up a significant portion of our total energy consumption and have various environmental implications. Keep reading to learn about the overall carbon footprints of these energies, their carbon footprints throughout their life cycles, and their environmental benefits and drawbacks. 

Here’s How We Assessed the Carbon Footprint of All Energy Types

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

To understand the carbon footprint of all energy types, we must assess their 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, we had a look at the LCA for all of the energy types! (No worries, we’ll link back to each throughout this article.)

These 4 Energy Sources Have the Highest Carbon Footprint

When discussing the carbon footprint of certain energy types, we must take into account carbon emissions across the energy’s building, operating, and building back phases.

Have a look at the illustration below to see the average life-cycle CO₂ equivalent emissions of the four energy sources with the highest carbon footprint and how they compare to the other energy types.

Fossil fuel (coal, oil, NG) consumption began with the Industrial Revolution, and consumption has increased exponentially over the past 70 years. The type of fuel we consume has shifted from solely coal, to coal and oil, and lastly to coal, oil, and NG. 

Biomass continues to be a major fuel in developing countries, especially for heating and cooking. This is known as traditional biomass. Countries that rely heavily on traditional biomass include Niger, Kenya, Tanzania, Nigeria, the Democratic Republic of Congo, and Haiti.

In developed countries, it has been used increasingly as a transportation fuel and to reduce CO₂ emissions from fossil fuels like coal and oil. These countries include the US, Brazil, Indonesia, Germany, and China. 

Oil Energy Has the Highest Carbon Footprint at 970 grams of CO₂/kWh on a Life-Cycle Basis

Oil energy comes from the combustion of petroleum, a fossil field also known as crude oil. Oil was formed millions of years ago when plant and animal remains gradually built up on the earth’s surface and the ocean floor, mixing with sand, silt, and calcium carbonate. Under immense heat and pressure, some of these remains were converted into oil depending on the combination of organic matter present, how long it was buried, and pressure conditions. 

“Oil: petroleum (= the black oil obtained from under the earth’s surface from which gasoline comes)”

Cambridge Dictionary

On a life-cycle basis, oil emits 970 grams of carbon dioxide (CO₂) equivalent per kWh of electricity produced. Which is the highest carbon footprint of all energy types – and higher than all the other ones.

The top 10 largest oil producers in the world account for 72% (67 million barrels per day (mb/d)) of global oil global production, which is approximately 94 mb/d total.

Here are the life-cycle stages of oil energy and each stage’s carbon footprint:

• Building of oil: CO₂ emissions from oil extraction and refinement, construction of oil-fired plants, and transportation of oil to refineries and plants
• Operating of oil: CO₂ emissions from oil combustion and operation of mechanical equipment at plants
• Building back of oil: CO₂ emissions from plugging wells and decommissioning power plants; CH₄ seepage from unplugged wells

The world collectively emitted 12.36 billion tons (bt) of CO₂ from oil in 2019, and because oil has been one of the most in-demand global fuel sources since the 1920s, it is important to understand what its carbon footprint is and how its carbon emissions affect the global climate change process.

Coal Energy Has the Second Highest Carbon Footprint at 820 grams of CO₂/kWh on a Life-Cycle Basis

Coal energy is produced via the combustion of black or brownish-black sedimentary rock containing energy stored by plants that lived in swampy forests over a hundred million years ago. The 4 main types, or ranks, of coal depend on the type and amount of carbon the coal contains and the amount of heat energy the coal can produce. The ranks are anthracite, lignite, subbituminous, and bituminous coal. 

“Coal: a combustible black or dark brown rock consisting mainly of carbonized plant matter, found mainly in underground deposits and widely used as fuel.”

Cambridge Dictionary

On a life-cycle basis, coal emits 820 grams of carbon dioxide (CO₂) equivalent per kWh of electricity produced, which is the second-highest out of all of the fuel types. 

In 2020, 477 million tonnes (432.7 million tons)  of coal were consumed in the United States (US) alone, which represents around 10% of total US energy consumption. While consumption has decreased in the US and European Union (EU), consumption continues to increase in some Asian countries such as China and India.

Here are the life-cycle stages of coal energy and each stage’s carbon footprint:

• Building of coal: Mining, construction, and transportation
• Operating of coal: Operation of the coal power plant
• Building back of coal: Shutdown, decommissioning, remediation, and redevelopment

In 2019, the world collectively emitted 14.36 billion tons of CO₂ from coal alone, higher than that from all other industries. Because coal remains an important fuel source for the global economy, it is important to understand what its carbon footprint is and how its carbon emissions affect the global climate change process.

Natural Gas Energy Has the Fourth Highest Carbon Footprint at 490 grams of CO₂/kWh on a Life-Cycle Basis

Commonly referred to as the world’s cleanest fossil fuel, natural gas (NG) is a flammable gas composed of mostly methane (CH₄), some hydrocarbon gas liquids (HGLs), and nonhydrocarbon gases (CO₂ and water vapor). When burned it produces mostly CO₂, water vapor, and some nitrogen oxides. NG is acquired in one of two ways, either by conventional (vertical) drilling or by hydraulic fracturing. 

“Natural Gas: flammable gas, consisting largely of methane and other hydrocarbons, occurring naturally underground (often in association with petroleum) and used as fuel”

Oxford Dictionary

On a life-cycle basis, NG emits 490 grams of CO₂ equivalent per kWh, the third-highest amount out of all of the fuel types, but the lowest out of the three fossil fuels. 

In 2020, 30.5 trillion cubic feet (Tcf) of NG were consumed in the US alone. This represents around 34% of total US energy consumption. And since 2010, 80% of NG growth has been concentrated within the US, China, and the Middle East. 

Here are the life-cycle stages of NG energy and each stage’s carbon footprint:

• Building of NG: CO₂ emissions from extracting and processing NG, transportation of NG through pipes and on ships, construction of NG power plants 
• Operating of NG: CO₂ emissions from NG combustion, operation of equipment at NG power plants, and leakage of CH₄ from in-service wells
• Building back of NG: CO₂ emissions from plugging wells and decommissioning power plants, CH₄ seepage from unplugged wells

The world collectively emitted 7.62 billion tons (bt) from NG in 2019, the fewest amount out of the three fossil fuels (i.e. coal, oil, NG). Because NG is the world’s fastest-growing fossil fuel that accounts for around 23% of primary energy demand and 25% of electricity generation, it is important to understand what its carbon footprint is and how its carbon emissions affect the global climate change process.

Biomass Energy Has the Third and Fifth Highest Carbon Footprint at 740 and 230 grams of CO₂/kWh on a Life-Cycle Basis

Biomass is renewable organic material that comes from plants and animals. It is incredibly versatile and can be used to produce fuel, energy, and everyday products that contain plastics.  Sources of biomass energy include wood and wood processing wastes, agricultural crops and waste materials, municipal solid waste, animal manure, and human sewage. To harvest biomass energy, these sources are burned or are converted to release the stored chemical energy from the sun. 

“Biomass: natural materials from living or recently dead plants, trees and animals, used as fuel and in industrial production, especially in the generation of electricity”

Oxford Dictionary

On a life-cycle basis, regular biomass energy emits 230 grams of CO₂ equivalent per kWh (gCO₂ per KWh), the fourth-highest amount out of all of the fuel types, and the highest amount out of all of the renewable fuel types. However, co-firing biomass energy, where biomass is added as a partial substitute fuel in coal boilers, emits 740 gCO₂ per KWh, the second-highest amount out of all fuel types and second only to coal. 

In 2018, 637 Terawatt hours (TWh) of electricity were produced globally from biomass. Solid biomass accounted for 66% (420 TWh), municipal and industrial waste 19% (121 TWh), and biogas 14% (89 TWh) of total biopower. Also 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. 

Here are the life-cycle stages of biomass energy and each stage’s carbon footprint:

• Building of biomass: CO₂ emissions from extracting and processing biomass, transportation of biomass on trucks or by rail, construction of biomass power plants 
• Operating of biomass: CO₂ emissions from biomass combustion, operation of equipment at biomass power plants
• Building back of biomass: CO₂ emissions from utilizing construction equipment to demolish the buildings and construct new buildings in the old power plant’s place

Because biomass is still an important fuel source for the developing world and has become an important transportation fuel in the developed world, it is important to understand what its carbon footprint is and how its carbon emissions affect the global climate change process.

What Roles Do The Energy Sources With the Highest Carbon Footprint Play in Combating/ Contributing to Climate Change

Climate change is arguably the most severe, long-term, global impact of fossil fuel combustion. The carbon found in fossil fuels and biomass material reacts with oxygen in the air to produce CO₂. This warms the earth by acting as a heating blanket, and a warmer earth comes with a host of negative side effects. 

Every year, approximately 36 bt of CO₂ are emitted from burning fossil fuels. 44% (15.8 bt) of this comes from coal, 34% (12 bt) from oil, and 21% (7.5 bt) from NG. Also, per kWh,  biomass power plants emit 150% the CO₂ of coal and between 300% – 400% the CO₂ of natural gas, making them a major contributor to climate change. 

CO₂ emissions contribute to climate change in the following ways:

• Increasing temperatures: Earth’s atmosphere has warmed 1.5℃ since 1880. This may not seem like a lot, but these degrees create regional and seasonal temperature extremes, reduce sea ice, intensify rainfall and drought severity, and change habitat ranges for plants and animals.

• Rising sea levels: Global sea levels have increased approximately 8-9 inches since 1880, displacing people living along coastlines and destroying coastal habitats. Roads, bridges, subways, water supplies, oil and gas wells, power plants, sewage treatment plants, and landfills remain at risk if sea level rise goes unchecked. 

• 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. 

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 Are The Energy Sources With the Highest Carbon Footprint

Fossil fuels are our primary energy source and biomass is often referred to as a better option than coal, but their combustion produces a significant amount of CO₂ emissions annually which contributes to global climate change.

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

Cambridge Dictionary

Coal, oil, and NG are considered dirty fuel sources because of their high rate of CO₂ emissions, toxic heavy metals, and other chemicals that contribute to global climate change. Biomass power plants can emit more CO₂ from their smokestacks than coal plants. Because of this, the environmental benefits are scarce, and the environmental drawbacks are abundant. 

What Are Environmental Drawbacks of The Energy Sources With the Highest Carbon Footprint

Each of the main fossil fuels and biomass has its environmental drawbacks as well as collectively adding to atmospheric CO₂ levels and contributing to global warming. 

1. Oil: Oil spills cause serious environmental harm by contaminating water and soil, causing explosions and fires, and harming wildlife. Oil combustion also releases CO₂ and other particulates which can cause respiratory problems. In the case of fracking, large amounts of water and potentially hazardous chemicals are required, which can decrease water availability for people and aquatic life and can result in leaks and spills of fracking fluids. Fracking produces large amounts of wastewater which require treatment before disposal, and injecting it back underground can cause earthquakes that are large enough to be felt.   

2. Coal: The combustion of coal produces over 14 bt of CO₂ emissions every year which contributes significantly to global climate change. Air pollution can cause numerous health problems including asthma, breathing difficulties, brain damage, heart problems, and cancer. Leftover coal ash residue and toxic heavy metals can leach into surface (ponds, lakes) and groundwater ponds, lakes, landfills, and other sites which could eventually lead to the contamination of waterways and drinking water supplies. Methods to burn coal without adding to atmospheric CO₂ levels are often expensive and difficult to successfully implement.

3. NG: Drilling for NG can disturb vegetation and soil and may require clearing and leveling the area around a well pad. Drilling also produces air pollution and may contaminate water sources via erosion, fracking fluids, equipment runoff, and sedimentation. Erosion and fragmentation of wildlife habitat and migration patterns have also been documented. When NG is burned at well sites, it releases CO₂, carbon monoxide (CO), sulfur dioxide (SO₂), and nitrogen oxides into the atmosphere. Burning NG instead of releasing it directly into the atmosphere produces lower levels of GHG emissions because CO₂ is not as potent as methane, but it still contributes to the overall level of CO₂ in our atmosphere. 

4. Biomass: Existing biomass power plants emit more CO₂ from their smokestacks than coal plants. Developed countries that burn organic matter for heat and cooking release particulate matter (PM), carbon monoxide (CO), hydrocarbons, oxygenated organics, free radicals, and chlorinated organics, all of which are health hazards. Chopping trees to produce wood pellets that are burned for electricity speeds up deforestation and reduces the number of trees that can capture our CO₂ emissions (decreases carbon sequestration). It could take anywhere from decades to well over a century before we start receiving the climate benefits provided by biomass, which is well outside the timeframe of averting our current climate crisis. 

Overall, burning fossil fuels and biomass adds to the total level of CO₂ in our atmosphere and expedites global warming. 

• Atmospheric CO₂: Levels of CO₂ in our atmosphere have increased as a result of human emissions since the beginning of the Industrial Revolution in 1750. Emissions increased steadily to 5 bt per year in the mid-20th century before increasing exponentially to more than 35 bt per year at the end of the 20th century. The global average amount of CO₂ in the atmosphere was about 280 parts per million (ppm) in 1750 but today registers at over 400 ppm. By the end of the 21st century, this number is expected to exceed 900 ppm. Burning fossil fuels adds to this total, which in turn amplifies the greenhouse effect and causes global warming. 

• Global warming: This phenomenon occurs when CO₂ and other air pollutants absorb sunlight and solar radiation in the atmosphere, 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 easiest way to mitigate the environmental impact of fossil fuels and biomass is to simply not rely on either in the first place. Fossil fuel and biomass combustion releases toxic chemicals, heavy metals, and CO₂, while also directly contributing to global warming.

What Are Environmental “Benefits” of The Energy Sources With the Highest Carbon Footprint

Although fossil fuels do not benefit the environment, there are ways to possibly mitigate their environmental impact. Various methods to do so include:

1. Oil: To minimize environmental impacts, technological advances in drilling, production, and transportation of oil as well as strict safety and environmental laws and regulations must be enforced. For example, satellites, GPS, and remote sensing technology can detect oil reserves underground which negates the need to drill many exploratory wells. Also, horizontal and directional drilling allows a single well to produce oil from a much larger area, reducing the overall number of wells needed. 

2. Coal: Ways to possibly mitigate its environmental impact include desulfurization, carbon capture, and re-use and recycling. For desulfurization, scrubbers are installed in smokestacks to remove sulfur dioxide (SO₂) emissions before they enter the atmosphere. For carbon capture, CO₂ from coal emissions is separated and recovered in a concentrated stream for later injection underground (sequestration). For re-use, land used for coal mining is reclaimed and repurposed as airports, landfills, and golf courses. For recycling, waste emissions can be used to produce cement and synthetic gypsum for wallboard.

3. NG: This is considered the cleanest fossil fuel because it has lower levels of CO₂, CO, nitrogen oxides, and SO₂ than both coal and oil. However, these emissions and methane still contribute directly to global climate change. The best way to mitigate its environmental impact is to detect, fix, and repair methane leaks from well-pads, processing plants, compressor stations, and large distribution facilities. Doing this can reduce methane output by 1.70-1.80 million metric tons per year.

Biomass indirectly benefits the environment by promoting energy independence and creating jobs, but it does not benefit the fight against climate change because of its high carbon footprint.

1. Energy Independence: Being able to produce our own electricity in the U.S. without the aid of foreign countries is an important step to help us become more self-sufficient instead. Former President George W. Bush signed the Energy Independence and Security Act of 2007 to reduce U.S. dependence on oil, expand the production of renewable fuels (and confront global climate change). 

2. Employment Opportunities: The renewable energy sector employed 11.5 million people worldwide in 2019. Renewable energy jobs continue to increase as we start to realize just how beneficial renewable energy is for our environment.

Final Thoughts

Oil, coal, natural gas, and biomass have the four highest carbon footprints across their building, operating, and building back phases compared to all other energy sources. They contribute directly to global warming and have various other environmental drawbacks. Our atmosphere and Earth’s biota would all benefit if we reduce our consumption of these four energy sources.  

Carbon emissions have devastating effects on the environment. Reducing our carbon footprint is important because it mitigates the effects of climate change, which has a positive cascade effect on public health and plant and animal diversity. In addition, this boosts the global economy and leads to innovative, more environmentally-friendly solutions.

Stay impactful,

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