The Keeling Curve: Tracking Atmospheric Carbon Dioxide

Explore the Keeling Curve, a critical tool in understanding our planet's rising CO2 levels and its implications for climate change.
The Keeling Curve: Tracking Atmospheric Carbon Dioxide
Explore the Keeling Curve, a critical tool in understanding our planet's rising CO2 levels and its implications for climate change.
The Keeling Curve: Tracking Atmospheric Carbon Dioxide
Explore the Keeling Curve, a critical tool in understanding our planet's rising CO2 levels and its implications for climate change.
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The Keeling Curve shows the accumulation of carbon dioxide in the atmosphere since 1958. This curve, created by Dr Charles David Keeling, has become essential in understanding the impact of human activities on our planet’s climate.

Carbon Dioxide (CO2) is a greenhouse gas which captures and holds heat within the Earth’s atmosphere. The Keeling Curve demonstrates a steady increase in carbon dioxide emissions.  The data supports scientific and public concerns about climate change and global warming.

Illustration titled 'Keeling Curve' showcases the iconic graph developed by Charles David Keeling."  The illustration depicts the Keeling Curve, a graph that tracks the concentration of carbon dioxide (CO2) in the Earth's atmosphere over time. The graph was pioneered by Charles David Keeling and is an important tool in understanding the rise of CO2 levels and its implications for climate change.  The illustration visually represents the Keeling Curve with a line graph, showing the increasing trend of CO2 concentration over the years. The x-axis represents time, while the y-axis represents the concentration of CO2 in parts per million (ppm).  The curve typically shows a regular oscillation, indicating seasonal variations in CO2 levels due to natural processes like plant photosynthesis. However, the overall trend of the curve demonstrates a steady rise in CO2 concentrations, primarily driven by human activities such as burning fossil fuels and deforestation.  The purpose of the illustration is to highlight the significance of the Keeling Curve in illustrating the long-term trend of increasing atmospheric CO2 levels and its connection to global climate change. It serves as a visual representation of the ongoing impact of human activities on the Earth's atmosphere and underscores the importance of taking action to mitigate carbon emissions and address climate change.

The graph also highlights the influence of natural seasonal fluctuations on atmospheric CO2 levels, offering invaluable insights into complex interactions between human activities and natural phenomena.

Many scientists and policymakers rely on the Keeling Curve to understand the real-time state of Earth’s atmospheric CO2. The curve highlights the urgent need for effective measures to reduce greenhouse gas emissions and mitigate the impacts of climate change.

The Keeling Curve has been crucial in:

  • Demonstrating the increasing levels of CO2 in the atmosphere
  • Establishing a link between human activities and rising CO2 levels
  • Raising awareness of the impact of CO2 on climate change

By promoting awareness and drawing attention to the connections between CO2 levels and global warming, the Keeling Curve plays a pivotal role in the ongoing conversation around environmental conservation and sustainable living.

Visual by Sketchplanations showing the rising CO2 levels in the earth's atmosphere - known as the Keeling Curve. An accompanying chart shows the seasonal variation of carbon dioxide emissions.
Source: Sketchplanations

The sawtooth pattern of seasonal variation

The Keeling Curve isn’t just a smooth, upward trend. If you look closely, it has a sawtooth pattern, with CO2 levels rising and falling each year. This sawtooth pattern gives us more insights into how our planet breathes.

Why does this pattern occur? It’s primarily because of plants. During the Northern Hemisphere’s spring and summer, plants absorb lots of CO2 for photosynthesis, which helps them grow. This uptake of CO2 by plants causes a temporary drop in global CO2 levels, creating the downward part of the sawtooth.

However, in the fall and winter, plants decay, releasing the CO2 they stored into the atmosphere. Most of Earth’s land mass is in the Northern Hemisphere, so the global CO2 levels rise again, creating the upward part of the sawtooth.

This pattern repeats every year, but despite these seasonal falls, the overall trend of CO2 levels is still upward due to human activities.

Atmospheric CO2 levels continue to exceed historical records

Understanding the current state of atmospheric CO2 levels is crucial in appreciating the significance of the Keeling Curve. As of today, the data collected paints a sobering picture of the ongoing increase in greenhouse gases. This current data provides a tangible connection to the broader trends that the Keeling Curve has charted over the decades.


This data is a real-time representation of the CO2 concentration in our atmosphere. It’s a live testament to the observations made by Dr Charles David Keeling more than half a century ago, and it confirms the continuation of the trend he first identified. Today, his work is more relevant than ever as we grapple with the realities and consequences of climate change.


Charles David Keeling

Charles David Keeling was an American scientist who began monitoring program atmospheric carbon dioxide concentration at Mauna Loa Observatory. He developed a precise instrument for measuring the concentration of carbon dioxide and started collecting air samples.

Keeling laid the foundation for understanding the atmospheric carbon dioxide growth rate. His work revealed increasing CO2 levels and their link to human activities, raising awareness of the potential impact of climate change.

Ralph Keeling

Ralph Keeling, the son of Charles David Keeling, followed in his father’s footsteps and continued studying CO2 levels in the atmosphere.

He expanded the research to include other greenhouse gases and maintained the time series of data that his father had started. Ralph’s work has furthered our understanding of the consequences of rising CO2 levels on climate and helped identify strategies to mitigate these effects.

Scripps Institution of Oceanography

The Scripps Institution of Oceanography at UC San Diego played a significant role in developing and continuing the Keeling Curve. Charles David Keeling was a scientist at this institution when he started measuring atmospheric CO2.

The institution continues to support climate research, including the ongoing monitoring of CO2 levels at the Mauna Loa Observatory in Hawaii.

The continued climate research at Scripps, led by Ralph Keeling, provides valuable information regarding the drive to mitigate climate change and understand its consequences.

Keeling’s other research

While the Keeling Curve remains his most famous contribution, Charles David Keeling also conducted other necessary climate research. This included studying the ocean’s role in the carbon cycle and investigating the effect of fossil fuels on atmospheric oxygen levels. His wide-ranging research has provided valuable insights into many aspects of climate science.

Controversies and challenges

While the Keeling Curve is a cornerstone of climate science, it has faced its share of controversies and challenges. Funding for the ongoing CO2 monitoring has sometimes been uncertain, and there has been climate scepticism about the scientific evidence of rising CO2 levels. However, most scientists agree on the importance of the Keeling Curve and the urgent need to address rising CO2 emissions.

Keeling’s quality control in CO2 measurements

Charles David Keeling’s work produced more than just a groundbreaking curve. It also set new standards for scientific measurements. Keeling insisted on rigorous quality control in his CO2 measurements. This principle of his work was vital for the Keeling Curve’s accuracy and reliability.

Illustration titled 'Keeling's Quality Control in CO2 Measurements' showcases two slopes of graphs with hands representing meticulous monitoring and calibration of CO2 measurements."  The illustration depicts two graph slopes representing the measurement of carbon dioxide (CO2) concentrations over time. Each slope is accompanied by a hand symbol placed on it.  The first slope shows an upward trend, indicating an increase in CO2 concentration. A hand symbol is positioned on this slope, representing the careful monitoring and data collection process pioneered by Charles David Keeling. The hand signifies the continuous measurement and tracking of CO2 levels, ensuring the accuracy and reliability of the data.  The second slope shows a more precise and calibrated curve, indicating the quality control aspect of Keeling's work. Another hand symbol is placed on this slope, representing the meticulous calibration and validation process conducted by researchers. This process involves comparing the measurements with reference standards, performing data validation, and ensuring the accuracy of the recorded CO2 concentrations.  The purpose of the illustration is to showcase Keeling's commitment to quality control in CO2 measurements. It emphasizes the ongoing monitoring and measurement of CO2 levels, as well as the rigorous calibration and validation processes that Keeling implemented. These efforts are essential for maintaining the integrity of CO2 data and providing reliable information for climate change research and understanding the long-term trends in atmospheric CO2 concentrations.

Keeling used precise instruments to measure CO2 concentrations and established strict procedures for collecting and analysing air samples. These procedures ensured the data was not influenced by local sources of CO2, like human or plant activity near the measurement sites. Because of his meticulous methods, Keeling’s measurements were accurate to within 0.2 parts per million (ppm).

Keeling’s quality control also involved regularly recalibrating his instruments. He used reference gas mixtures with known CO2 concentrations for this. By comparing these known values with the readings from the tools, Keeling could correct any inaccuracies.

Keeling’s quality control methods set the standard for later CO2 monitoring efforts. Even today, scientists follow his methods to maintain the accuracy and reliability of the Keeling Curve. The continued quality control ensures the curve remains a powerful tool for understanding our changing climate.

Monitoring atmospheric CO2 on Earth

Mauna Loa Observatory

The data for the Keeling Curve is collected at the Mauna Loa Observatory in Hawaii. Mauna Loa is situated at a high altitude and provides an ideal location to collect data unaffected by local emissions.

Continuous measurement has provided a reliable and long-term record of atmospheric CO2 levels. However, daily measurements were disrupted by an eruption of the local volcano in November 2022.

Antarctica and the South Pole

Atmospheric CO2 monitoring also occurs in the remotest parts of the globe, such as Antarctica and the South Pole. The pristine environment and lack of human influence make these locations valuable for monitoring global trends in CO2 concentrations.

Data from these locations is vital in backing up findings from the Mauna Loa Observatory. It provides a broader picture of global atmospheric CO2, showing consistency across different regions and environmental conditions.

National Oceanic and Atmospheric Administration

The National Oceanic and Atmospheric Administration (NOAA) plays a significant role in monitoring atmospheric CO2 through multiple observation sites worldwide. They collect data on greenhouse gas concentrations, supporting the ongoing study of climate change.

NOAA’s efforts are essential in validating and supplementing the data collected at Mauna Loa and the South Pole. This reliable and consistent monitoring of CO2 is critical for understanding our planet’s changing climate and the steps needed to mitigate its impact.

Other observatories and measurement systems

Besides Mauna Loa and the South Pole, CO2 measurements are taken at other observatories worldwide as part of the Global Greenhouse Gas Reference Network. This network provides a comprehensive view of global CO2 levels and trends.

Illustration titled 'CO2 Emissions and Climate Change' depicting industrial emissions of carbon dioxide (CO2) and the negative impact on human health."  The illustration portrays two elements: industrial CO2 emissions and the adverse effects on human health.  On the right side of the image, there are visual representations of industries emitting CO2. This can include factories, smokestacks, or other sources of significant CO2 emissions. The emphasis is on showcasing the scale and impact of industrial activities contributing to CO2 levels in the atmosphere.  On the left side of the image, there is a girl depicted outside who appears unwell and struggling to breathe. This visual element represents the negative consequences of increased CO2 concentrations on human health. It aims to convey the idea that high levels of CO2 in the atmosphere can contribute to respiratory problems, discomfort, and adverse health effects.  The illustration highlights the link between industrial CO2 emissions and their detrimental impact on human well-being. It serves as a visual reminder of the urgent need to reduce CO2 emissions to mitigate the effects of climate change and safeguard human health.

CO2 emissions and climate change

Fossil fuels and combustion

The Keeling Curve shows Earth’s increased atmospheric carbon dioxide (CO2) levels. A primary driver of this increase is the combustion of fossil fuels like coal, oil, and natural gas. Burning these fuels releases CO2, resulting in more greenhouse gas emissions, which trap heat in the atmosphere.

  • Fossil fuels provide most of the world’s energy
  • Their combustion produces high levels of CO2

Photosynthesis and respiration

Plants are natural carbon sinks. They absorb CO2 from the atmosphere through photosynthesis and transform it into energy. Conversely, animals and plants release CO2 during respiration. A balanced cycle between photosynthesis and respiration maintains stable CO2 levels.

  • Plants use CO2 for growth and energy
  • Respiration in animals and plants emits CO2

Role of the oceans

Oceans play a critical role in the global carbon cycle by absorbing significant CO2 emissions. However, as CO2 levels rise, the oceans absorb more CO2, leading to ocean acidification.

This change in ocean chemistry can harm marine life, particularly species with calcium carbonate shells or skeletons. An increased understanding of the oceans’ role in the carbon cycle is crucial for predicting and mitigating the impacts of rising CO2 levels.

Impact on global warming

As CO2 levels rise due to human activity, the balance between photosynthesis and respiration is disrupted. The increasing CO2 concentrations in the atmosphere contribute significantly to global warming, causing climate change and affecting ecosystems.

  • Imbalance in the CO2 cycle contributes to global warming
  • Ecosystems are impacted by climate change

By understanding the Keeling Curve and the factors contributing to increased CO2 emissions, society can work towards reducing fossil fuel consumption and sustaining a healthier environment.

Other greenhouse gases

CO2 is not the only gas that warms up our planet. Other gases like methane, nitrous oxide, and fluorinated gases also contribute to climate change. Each of these gases comes from different sources and has unique properties.

Methane (CH4)

Methane is a potent greenhouse gas. Although less prevalent, it is more efficient at trapping atmospheric heat than CO2. Methane comes from natural sources like wetlands and human activities like farming livestock. Like the Keeling Curve for CO2, scientists track methane levels over time with a ‘Methane Curve’.

Nitrous Oxide (N2O)

Nitrous oxide is released when we burn fossil fuels and biomass. It also comes from some types of farming. It’s also a potent greenhouse gas and can stay in the atmosphere for over 100 years. Scientists track atmospheric concentration trends with a ‘Nitrous Oxide Curve’.

Fluorinated Gases

Fluorinated gases are synthetic, potent greenhouse gases that are emitted from a variety of industrial applications. They are less common but are very potent when released into the atmosphere. Curves for these gases are also tracked, although their impact is significantly less compared to CO2, methane, and nitrous oxide.

All these gases contribute to global warming by trapping heat on Earth, a process called the ‘greenhouse effect’. Although carbon dioxide is the main driver of climate change due to its large concentrations, understanding the role of other gases is essential for mitigating climate change.

Global CO2 monitoring

Illustration titled 'Global CO2 Monitoring' featuring a globe emitting CO2 and two people monitoring it with graphs and technology."  The illustration depicts a central element, a large globe emitting CO2, symbolizing global carbon dioxide emissions. Surrounding the globe, there are two individuals engaged in monitoring and analyzing CO2 levels using various tools and technologies.  The two people are shown using graphs and technology to track and analyze the CO2 emissions. They may be observing data on screens, interacting with sensors or instruments, or studying charts and graphs related to CO2 levels. This signifies their role in monitoring and assessing the global CO2 situation.  The illustration aims to represent the importance of monitoring CO2 emissions on a global scale and the utilization of advanced technology and data analysis in this process. It emphasizes the significance of understanding and tracking CO2 levels to address climate change and make informed decisions about mitigation strategies.

Air samples and ice cores

The Keeling Curve involves taking air samples to measure carbon dioxide concentration in Earth’s atmosphere. By comparing current measurements with air bubbles trapped in ice cores, scientists get valuable insights into CO2 levels in the past.

Ice cores serve as a window into Earth’s climatic history. They contain air bubbles from various periods, reflecting the atmosphere of ancient ice ages. By studying ice cores, researchers can identify trends in carbon dioxide levels and observe the impact of human activities on the greenhouse effect.

Long-term studies and international collaboration

The Keeling Curve’s CO2 data dates back to the International Geophysical Year (IGY) of 1957-1958, highlighting its long-term significance. Authoritative records are ensured through international collaboration. Institutions like the Scripps Institution of Oceanography work together to provide a reliable understanding of atmospheric carbon dioxide levels and trends.

To further enhance global CO2 monitoring, various research groups and government agencies work together, sharing data and insights. This international collaboration is essential to comprehend the magnitude of human-induced climate change and identify potential solutions.

The Keeling Curve is pivotal to global CO2 monitoring. Air samples and ice cores enable a better understanding of past and present carbon dioxide levels, while international collaboration ensures the continuity of this critical long-term study.

Human activities and environmental impact

Greenhouse gases and global temperature

Human activities, such as burning fossil fuels and deforestation, release greenhouse gases into the atmosphere. These gases, including CO2, trap heat from the sun, causing increased temperatures and climate change.

The Keeling Curve has revealed that CO2 concentrations have risen significantly since its first measurements.

Factors contributing to greenhouse gas emissions:

  • Burning fossil fuels for transportation, electricity, and industry
  • Deforestation reduces the planet’s ability to absorb CO2
  • Agricultural practices emitting methane and nitrous oxide

Consequences of rising greenhouse gas emissions:

  • Increased global temperatures
  • Melting ice caps and rising sea levels
  • More frequent and severe weather events
  • Loss of biodiversity
  • Negative impacts on agriculture and human health

The Keeling Curve links modern CO2 concentrations and those from the past. It can be compared to CO2 concentrations from ice-core samples.

This comparison shows that CO2 levels have fluctuated between 275 and 290 ppmv during most of the period between 1000 and 2000 CE. The slope of the curve indicates a rapid increase in CO2 levels since the Industrial Revolution, highlighting the consequences of human activities.

The role of vegetation and climate

Vegetation plays a vital role in balancing atmospheric CO2 levels. Plants absorb CO2, converting it into oxygen and biomass during photosynthesis. Land use changes and deforestation have reduced vegetation and, in turn, increased CO2 concentrations.

Climate conditions, such as temperature and precipitation, also affect vegetation growth and CO2 absorption.

Ways to reduce CO2 emissions and mitigate climate change

  • Adopting cleaner and sustainable energy sources
  • Implementing energy-efficient practices in transportation, industry, and agriculture
  • Reforestation and afforestation, increasing Earth’s ability to absorb CO2
  • Developing and adopting innovative technologies for carbon capture and storage

By understanding the relationship between human activities, vegetation, and climate conditions, we can develop innovative solutions to address the increasing environmental concerns.

Implications for policy and international agreements

The Keeling Curve’s continuous record of rising CO2 concentrations has significantly impacted policy and international agreements. It has provided compelling evidence of human-induced climate change, prompting nations worldwide to take action.

Recognising the increasing CO2 levels and their climate impact, global leaders have negotiated several international agreements to reduce greenhouse gas emissions. For instance, the 1997 Kyoto Protocol and the 2015 Paris Agreement were landmark treaties that committed countries to reduce emissions.

These agreements rely heavily on accurate data, like that provided by the Keeling Curve, to set targets and track progress. They also highlight the importance of transitioning to sustainable energy sources, improving energy efficiency, and protecting and restoring forests, which absorb CO2 from the atmosphere.

As the Keeling Curve continues to track atmospheric CO2, it remains a crucial tool for policy decisions. It helps scientists, policymakers, and the public understand the climate crisis’s urgency and the effectiveness of measures to address it.

Future projections

Suppose the trends indicated by the Keeling Curve continue. In that case, scientists predict that we could see even more pronounced impacts of climate change, including higher global temperatures, more frequent and severe weather events, and greater disruption of ecosystems.

This poses a significant risk to both the planet and human societies.

Innovation and technological developments

However, the future is not set in stone, and there are ways we can act to change this trajectory. One of the most promising areas lies in innovation and technological advancements.

Scientists and engineers are developing new technologies and methods to monitor and reduce CO2 emissions, and these could play a crucial role in our response to climate change.

For instance, there’s growing interest in carbon capture and storage (CCS) technologies. These technologies aim to capture CO2 emissions at their source, such as power plants, and store them underground so they don’t enter the atmosphere. This could significantly reduce the amounts of carbon dioxide we’re currently adding to the atmosphere.

Other innovative approaches include the development of renewable energy technologies, energy-efficient appliances and vehicles, and sustainable agricultural practices. Each of these areas presents opportunities to reduce our carbon footprint and mitigate the impacts of climate change.

While these technological developments are promising, they are not a silver bullet. We also need systemic changes in our economies and societies. This will require political will and widespread public support. The Keeling Curve underscores the scale of our challenge and the potential for human ingenuity and determination to overcome it.

Frequently asked questions

The carbon cycle refers to the process through which carbon compounds move through Earth’s atmosphere, oceans, biosphere, and geosphere. This cycle is central to life on Earth. The Keeling Curve shows how human activities, like burning fossil fuels, disrupt the carbon cycle by adding more carbon dioxide to the atmosphere than natural processes can remove, leading to a rise in atmospheric CO2 levels and, consequently, global warming.

The Keeling Curve can be used to project future climate scenarios. It suggests that if CO2 emissions continue to rise, global warming will accelerate, informing strategies for climate change mitigation.

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Rob Boyle
Rob built Emission Index to collect and share data, trends and opportunities to reduce our greenhouse gas emissions and expedite the energy transition.

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