Meghan Hodges
Carbon dioxide (CO2) is a chemical compound made up of molecules, each containing one carbon atom covalently double-bonded to two oxygen atoms. It is found in a gaseous state at room temperature and is odorless at normally encountered concentrations. CO2 emissions from human activities are now higher than at any other point in history. In 1938, British physicist G.S. Callendar suggested that higher CO2 levels were causing warmer temperatures in America and Europe. This view has since been confirmed by modern scientists, who have also identified other causes of rising carbon dioxide levels, such as deforestation. The understanding of carbon dioxide as a pollutant was evident in the 1960s, as congressional hearings from that era reveal. The Clean Air Act of 1970, signed by Republican President Richard Nixon, authorized the federal government to regulate harmful air pollutants, including carbon dioxide.
| Characteristics | Values |
|---|---|
| Year carbon dioxide was discovered as a pollutant | 1970 |
| Country that emitted the most CO2 in 1850 | United Kingdom |
| US ranking in CO2 emissions in 1850 | Second |
| Year when the US became the top CO2 emitter | 1887 |
| Year when CO2 and human-caused climate change were discussed in congressional hearings | 1960s |
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What You'll Learn
CO2 as a pollutant in the Clean Air Act
The Clean Air Act is a federal law that gives the US Environmental Protection Agency (EPA) the authority to regulate air pollutants and polluting industries. The Act was signed by Republican President Richard Nixon in 1970. It was well understood at the time that one of those pollutants was climate-warming carbon dioxide (CO2).
Naomi Oreskes, a professor of the history of science at Harvard University, reviewed government documents from the 1960s and found more than 100 congressional hearings in which CO2 and human-caused climate change were discussed. Oreskes states that the inclusion of the words "weather" and "climate" in the text of the law demonstrates that lawmakers intended for the statute to apply to carbon dioxide.
The Clean Air Act has been amended several times since its enactment, with major amendments in 1977 and 1990. These amendments have helped to reduce the country's air pollution dramatically over the past few decades. For example, the carbon pollution standards for power plants that were tightened under the Clean Air Act were predicted to deliver $480 billion in total climate and health benefits over two decades.
The EPA has also issued rules and guidance to address CO2 emissions, such as the GHG Tailoring Rule, which established initial emission thresholds for PSD and Title V permitting based on carbon dioxide equivalent (CO2e) emissions. The EPA has also announced plans to treat biogenic CO2 emissions from stationary sources, such as energy production facilities, under its air regulatory programs.
However, there have been debates about whether the Clean Air Act applies to carbon dioxide and other greenhouse gases. In 2003, the EPA denied a petition from the International Center for Technology Assessment (ICTA) and other parties to regulate greenhouse gases from new motor vehicles under the Act, stating that it did not have the authority to address global climate change.
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CO2 emissions from human activities
Carbon dioxide (CO2) emissions from human activities are now higher than at any point in our history. CO2 emissions in 2022 were 182 times higher than in 1850, around the time the Industrial Revolution began. The COVID-19 pandemic caused the largest annual drop in CO2 emissions in recorded history, with global emissions falling by 1.5 billion metric tons in 2020. However, emissions quickly bounced back as countries resumed their economic activities, with 2021 surpassing 2019 levels.
The build-up of atmospheric CO2 is primarily caused by burning fossil fuels, and this build-up is accelerating. Fossil fuels like coal and oil contain carbon from millions of years of photosynthesis, and we are returning that carbon to the atmosphere in just a few hundred years. Since the middle of the 20th century, annual emissions of CO2 from burning fossil fuels have increased every decade, from close to 11 billion tons per year in the 1960s to an estimated 37.4 billion tons in 2024. If global energy demand continues to grow and we meet it mostly with fossil fuels, human emissions of CO2 could reach 75 billion tons per year or more by the end of the century.
Human CO2 emissions upset the natural balance of the carbon cycle. While natural land and ocean carbon have remained in balance for a long time, human activities release additional CO2 outside of this natural cycle. About 40% of this additional CO2 is absorbed, with the rest remaining in the atmosphere. As a result, atmospheric CO2 levels are at their highest in 15 to 20 million years. Every year, we add more CO2 to the atmosphere than natural sinks like plant growth and ocean absorption can remove, causing atmospheric CO2 levels to rise.
While CO2 emissions from burning fossil fuels are the most significant contributor to human-caused climate change, other human activities also contribute to CO2 emissions. For example, human and livestock respiration can be a substantial source of CO2 emissions in densely populated areas like Manhattan or Beijing. Additionally, activities such as electricity generation, deforestation, and cement production also contribute to human-induced CO2 emissions.
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CO2 emissions from burning fossil fuels
Carbon dioxide (CO2) is a heat-trapping gas, also known as a greenhouse gas, that is released into the atmosphere when fossil fuels are burned. Fossil fuels include coal, oil, and natural gas, which are hydrocarbons formed from the remains of plants that grew on Earth millions of years ago. These plants absorbed CO2 from the atmosphere, and when they died, their biomass was buried and transformed over time into the fossil fuels we extract and burn today.
The burning of fossil fuels for energy is the largest source of CO2 emissions. This includes the combustion of oil, natural gas, and coal to power vehicles, generate electricity, and support industrial processes. In 2022, the United States emitted 5,053 million metric tons of CO2 into the atmosphere, with 93% of these emissions attributed to the combustion of fossil fuels. Transportation accounted for about 35% of these emissions, while the generation of electric power contributed approximately 30%. Industrial, residential, and commercial buildings were responsible for 16%, 7%, and 5%, respectively.
To stabilize and reduce atmospheric CO2 concentrations, global efforts are necessary to reach net-zero emissions. This involves offsetting any remaining emissions with carbon sinks, such as forests, which absorb CO2 during plant growth in spring and release it back into the atmosphere during decomposition in autumn. While there have been downward trends in CO2 emissions in some countries, overall emissions continue to rise, emphasizing the urgency of transitioning to renewable energy sources and reducing the burning of fossil fuels.
Historically, the understanding of CO2 as a pollutant has evolved over time. In the 1960s, during the era of Congressional hearings, climate change and carbon dioxide were recurring discussion topics. This led to the passing of the Clean Air Act in 1970, which authorized the federal government to regulate harmful air pollutants, including climate-warming carbon dioxide.
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CO2 levels in the atmosphere
Carbon dioxide (CO2) is a greenhouse gas that has been recognised as a pollutant since at least the 1960s. It was discussed in over 100 congressional hearings during that decade, and the Clean Air Act of 1970, which authorised the federal government to regulate harmful air pollutants, was aimed at reducing CO2 emissions.
CO2 emissions have been measured since 1850, and they have increased significantly over time. In 2022, global CO2 emissions were 182 times higher than they were in 1850, when the Industrial Revolution was underway. The COVID-19 pandemic caused a temporary decrease in emissions in 2020, but they quickly rebounded as countries resumed their economic activities.
The increase in CO2 levels has had a significant impact on the Earth's climate. Greenhouse gases trap heat in the atmosphere, leading to an increase in global temperatures. The Annual Greenhouse Gas Index (AGGI) shows that increases in carbon dioxide are responsible for about 81% of the increase in the heat-trapping capacity of the atmosphere over the past decade. The concentration of CO2 in the atmosphere is measured by organisations such as the National Oceanic and Atmospheric Administration (NOAA) Global Monitoring Laboratory and the United States Environmental Protection Agency (EPA), which use data from ice core studies and air monitoring sites around the world.
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CO2 emissions reduction strategies
Carbon dioxide was first discovered by heating calcium carbonate, which produced a gas denser than air and could not sustain fire or animal life. This gas was called "fixed air" then, but we now know it as carbon dioxide or CO2.
CO2 is the primary gas responsible for trapping heat in the lower layers of the atmosphere, and it is released by burning different types of fuels. It is a major contributor to global warming and climate change. While CO2 is not the only greenhouse gas, it represents about three-quarters of annual emissions. Global CO2 emissions in 2022 were 182 times higher than in 1850, the earliest year for which data is available.
To reduce CO2 emissions, individuals, organizations, and governments can take several measures and strategies. Here are some critical CO2 emissions reduction strategies:
Reforestation and Nature-Based Solutions
Reforestation is an accessible and economical way to offset greenhouse gas emissions. Trees can eliminate between 330 and 7,700 pounds of CO2 throughout their life cycle. Other nature-based solutions include wetlands and grasslands, which can absorb and sequester carbon.
Energy Efficiency and Renewable Energy
Increasing energy efficiency and transitioning to renewable energy sources are crucial. Individuals can choose energy-efficient appliances, improve home insulation, and set recommended temperatures to reduce energy consumption and associated emissions. Organizations and governments can invest in renewable energy technologies, such as solar and wind power, and promote energy conservation through initiatives like the U.S. EPA's ENERGY STAR Program.
Sustainable Transportation
Transportation is a significant source of CO2 emissions. Individuals can reduce their carbon footprint by driving less, opting for walking, public transportation, carpooling, or biking. When driving, maintaining proper tire inflation and consistent driving habits can improve fuel efficiency. Organizations and governments can promote sustainable transportation through initiatives like the U.S. EPA's SmartWay program, which improves fuel efficiency in the freight transportation industry.
Dietary Choices
Livestock and dairy production contribute about 14.5% of global greenhouse gas emissions. Individuals can reduce their carbon footprint by eating lower on the food chain, choosing organic and local seasonal produce, and reducing food waste. Organizations can support sustainable agriculture and promote plant-based diets.
Waste Reduction and Recycling
Waste reduction and recycling programs can help decrease methane emissions from landfills and waste management processes. The U.S. EPA's resources provide guidance on starting recycling programs and reducing waste in the workplace.
Carbon Offsets and Capture
Individuals and organizations can purchase carbon offsets to compensate for carbon emissions. These funds support climate protection projects, such as tree planting, renewable energy initiatives, and energy efficiency programs. Additionally, technologies are being developed to capture and utilize CO2 as a raw material in various industrial processes.
These strategies provide a comprehensive approach to reducing CO2 emissions and mitigating the impacts of climate change. By implementing these measures, individuals, organizations, and governments can contribute to global efforts to create a more sustainable future.
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Frequently asked questions
Carbon dioxide was recognized as a pollutant in the 1960s, during the time of the Clean Air Act of 1970.
Carbon dioxide (CO2) is a chemical compound made up of molecules, each containing one carbon atom covalently double-bonded to two oxygen atoms.
Carbon dioxide emissions are primarily due to human activities, such as burning fossil fuels, deforestation, and industrialization.
Carbon dioxide acts as a greenhouse gas, absorbing infrared radiation in the Earth's atmosphere, leading to the warming of the planet and causing climate change.
Carbon dioxide emissions can be reduced through reforestation, afforestation, improved land management practices, and transitioning to renewable energy sources.
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