Carbon Dioxide

Environmental Stewardship Environmental and Regulatory Considerations Carbon Dioxide

Atmospheric carbon dioxide comes from both natural and man-made sources. Carbon dioxide (CO₂) is one of the main outputs of combustion, which can take the form of volcanic eruptions, forest fires, or the burning of fossil fuels. Carbon dioxide is also a byproduct of manufacturing (i.e., non-combustion related); for example, it is an intermediate product in cement manufacturing. Looking at natural processes on earth, we note that every living being produces CO₂ on the cellular level to produce usable cellular energy. The oceans’ capacity for absorbing CO₂ means that these bodies of water are the largest store of CO₂ on earth. Through a process known as upwelling, through which oceanic turbulence releases dissolved CO₂ back to the atmosphere, the oceans are the largest source of atmospheric CO₂.¹

Overall, atmospheric CO₂ levels are higher now than they ever have been. In a noteworthy move, carbon dioxide levels surpassed 400 parts per million (ppm) in 2013.² By 2021, the level was 414 ppm.³ Throughout history, levels hovered around 200 ppm during ice ages and 280 ppm during warmer periods.

Atmospheric rise in carbon dioxide from NASA. — *The rise of atmospheric CO₂. Data from NASA.*

Research supports that fossil fuel combustion is responsible for current levels of atmospheric CO₂, as about 60% of all fossil fuel emissions stay in the atmosphere. The National Oceanographic and Atmospheric Administration (NASA) estimates that if anthropogenic fossil fuel combustion continues at current rates until humans completely deplete the resource, then atmospheric CO₂ levels could rise as high as 1500 ppm. Projections of greenhouse gas emissions into the next century vary over a wide range, depending on both socioeconomic development and climate policy but the role of CO₂ in this process is now accepted by all major governments and most industries.⁴

CO₂ emissions and Human Activity

Anthropogenic or man-made sources also contribute to CO₂ in the atmosphere. As part of their national Carbon Storage Atlas project, the U.S. Department of Energy documented 6,358 stationary CO₂ sources with total annual emissions of approximatively 3,071 million metric tons of anthropogenic CO₂.⁵

1 U.S. customary ton (t) = 2,000 lbs whereas 1 metric ton (MT) (sometimes written as 1 tonne) = 1,000 kg.

Stationary sources of carbon dioxide compiled by the National Energy Technology Laboratory.

Carbon dioxide is the primary greenhouse gas

Carbon dioxide is the primary greenhouse gas emitted through human activities. In 2020, CO₂ accounted for about 79% of all U.S. greenhouse gas emissions from human activities. Human activities are altering the carbon cycle–both by adding more CO₂ to the atmosphere and by influencing the ability of natural sinks, like forests and soils, to remove and store CO₂ from the atmosphere. While CO₂ emissions come from a variety of natural sources, human-related emissions are responsible for the increase that has occurred in the atmosphere since the industrial revolution.⁶

CO₂ and the combustion of fossil fuels

The main human activity that emits CO₂ is the combustion of fossil fuels (coal, natural gas, and oil) for energy and transportation. Certain industrial processes and land-use changes also emit CO₂. The main sources of CO₂ emissions in the United States are shown below.⁷

2020 U.S. carbon dioxide emissions by source.

Carbon dioxide dominates gaseous emissions from the oil industry – contributing more than 99% of all releases to the atmosphere. Around 132 tonnes of CO₂ are released per thousand tonnes of oil and gas produced. Of this, around 60% is associated with the energy demands of oil and gas production – operating energy intensive equipment such as pumping. The remainder is dominated by flaring – the combustion of natural gas associated with oil production that cannot be economically captured, processed, and used on-site or sold. Only a small fraction, around 6%, is associated with venting of CO₂ dissolved within the oil and released as pressure drops.⁸,⁹

Earth’s natural capacity to absorb CO₂ is decreasing

Besides increase in anthropogenic CO₂ emissions, the natural capacity of the planet in absorbing CO₂ is decreasing. The oceans and forests play a vital role in capturing and storing CO₂ released into the atmosphere. Plants take up carbon dioxide through their leaves and stems, especially during their growth stage, and then store it. Trees have a very high storage capacity, with carbon accounting for 20% of their total weight on average. Forests and oceans combined capture more than half of annual emissions, helping to slow the rise in atmospheric CO₂ levels. However, the rapid eradiation of forests, especially the tropical rainforests, is depleting the Earth’s vegetation growth and diminishing its capability for absorbing CO₂. The unabsorbed CO₂ rises to the upper atmosphere and inhibits the reradiation of solar energy back into space. This trapped heat induces a global temperature increase resulting in global greenhouse effect, mainly carbon dioxide, from anthropogenic activities.¹⁰

Reduction in CO₂ emitted per unit volume of oil produced

In recent years there have been notable reductions in the amount of CO₂ emitted per unit volume of oil produced, dropping by some 10% in almost a decade.¹¹ This is a result of improvements in production processes including greater re-injection of unused gases into mature oil reservoirs to maintain pressure and boost production. The industry is making a strong push in reducing CO₂ emissions, with recent efforts focused on carbon capture utilization and storage (CCUS): the process of capturing waste CO₂, transporting it to a storage site, and injecting it deep underground in a geologic formation where it will not enter the atmosphere; or utilizing the CO₂ as a commodity to remove it from the atmosphere.

Images: “Coal power plant” by Kodda via Shutterstock; “Map” by National Energy Technology Laboratory

Previous Topic

Back to Lesson

Next Topic

Carbon Dioxide

CO2 emissions and Human Activity

Carbon dioxide is the primary greenhouse gas

CO2 and the combustion of fossil fuels

Earth’s natural capacity to absorb CO2 is decreasing

Reduction in CO2 emitted per unit volume of oil produced

CO₂ emissions and Human Activity

CO₂ and the combustion of fossil fuels

Earth’s natural capacity to absorb CO₂ is decreasing

Reduction in CO₂ emitted per unit volume of oil produced