--- title: "Keeling Curve | Intro to Climate Science" description: "The Keeling Curve tracks atmospheric carbon dioxide at Mauna Loa, showing the long-term rise and seasonal cycle that climate science uses to measure human impact." canonical: "https://fiveable.me/introduction-climate-science/key-terms/keeling-curve" type: "key-term" subject: "Intro to Climate Science" unit: "Unit 10" --- # Keeling Curve | Intro to Climate Science ## Definition The Keeling Curve is the long-running graph of atmospheric carbon dioxide measured at Mauna Loa, showing both seasonal swings and a steady rise since 1958. In Intro to Climate Science, it is one of the clearest records of human-driven CO2 increase. ## What It Is The Keeling Curve is the famous record of atmospheric carbon dioxide measured over time, usually shown from Mauna Loa Observatory in Hawaii. In Intro to Climate Science, it is the cleanest visual proof that CO2 has not only risen, but risen steadily since direct measurements began in 1958. The graph works because scientists take repeated CO2 measurements from the same place under consistent conditions. That matters a lot. If you only looked at one year, you might miss the pattern. By measuring continuously, the record shows short-term ups and downs on top of a long-term climb. Those short-term wiggles are the seasonal cycle. When plants in the Northern Hemisphere grow during spring and summer, they pull more CO2 out of the air through photosynthesis, so the atmospheric concentration dips. In fall and winter, plant decay and reduced photosynthesis let CO2 rise again. The seasonal cycle is natural, but it sits on top of a much larger human-caused trend. The bigger story is the upward line. Since the Industrial Revolution, fossil fuel burning and deforestation have added extra carbon to the atmosphere faster than natural sinks can remove it. The Keeling Curve shows that imbalance directly. It is not just a record of carbon dioxide, it is a record of the carbon cycle being pushed out of balance. A lot of students first read the curve as just a climate graph, but it is also a measurement story. It depends on careful sampling, consistent instrumentation, and long-term observation. That is why it shows up so often in climate science, it turns an invisible gas into something you can actually track over decades. ## Why It Matters The Keeling Curve gives you a real-world way to see atmospheric concentration trends instead of just memorizing that greenhouse gases are increasing. In Intro to Climate Science, that matters because the course keeps linking causes, measurements, and consequences: human emissions change the atmosphere, the atmosphere traps more heat, and climate patterns respond. It also helps you separate natural variation from long-term change. The seasonal cycle in CO2 can look dramatic if you zoom in, but the long-term trend is what tells you the climate system is shifting. That distinction shows up again and again when you read graphs, compare time scales, or explain why one hot year is not the same thing as a persistent warming trend. The Keeling Curve is also a model for how climate evidence is built. A single measurement is a snapshot, but a long record becomes a dataset that can support arguments about fossil fuels, deforestation, sinks, and feedbacks. If you can read this graph well, you are already practicing one of the main skills in climate science: turning observations into an explanation of the carbon cycle and greenhouse warming. ## Connections ### Carbon Dioxide The Keeling Curve is specifically a record of CO2 concentration, usually reported in parts per million. If you understand what carbon dioxide is and why it absorbs infrared radiation, the graph stops being just a line and starts being evidence of a warming influence in the atmosphere. ### Greenhouse Gases CO2 is one of the major greenhouse gases, so the Keeling Curve sits inside the bigger greenhouse gas story. It shows one gas with especially clear long-term measurements, which makes it a useful stand-in when you are discussing how greenhouse gases accumulate and affect Earth’s energy balance. ### Mauna Loa Observatory Mauna Loa is the site most closely associated with the Keeling Curve. The high, remote location helps reduce local pollution effects, so the data better reflect background atmospheric CO2 rather than a city or factory plume. That makes the record more useful for global climate analysis. ### [historic co2 levels](/introduction-climate-science/key-terms/historic-co2-levels) The Keeling Curve is one of the main ways scientists compare modern CO2 with historic CO2 levels. Ice cores and other proxies tell you what the atmosphere was like before direct monitoring, while the Keeling Curve gives precise modern measurements. Together, they show how unusual the recent rise is. ## On the AP Exam A graph-analysis question may ask you to identify the long-term trend, describe the seasonal cycle, or explain why the curve rises over time. You should be able to read the slope, connect the increase to fossil fuel combustion and deforestation, and distinguish short-term fluctuations from the bigger upward pattern. On a quiz or short-answer response, you might also be asked why Mauna Loa is a good measurement site or what the ppm values mean. In a lab write-up, the Keeling Curve can show up as evidence that atmospheric CO2 is increasing and that the increase is not just a random variation in the data. ## Key Takeaways - The Keeling Curve is the long-term graph of atmospheric CO2, best known from measurements at Mauna Loa Observatory. - It shows two patterns at once, a repeating seasonal cycle and a strong upward trend since 1958. - The seasonal dips and rises come mostly from plant growth and decay, especially in the Northern Hemisphere. - The long-term increase reflects human activities such as fossil fuel combustion and deforestation adding carbon to the atmosphere. - In climate science, the curve is one of the clearest records showing that atmospheric CO2 is rising and that the rise is accelerating. ## FAQs ### What is the Keeling Curve in Intro to Climate Science? It is the long-running graph of atmospheric carbon dioxide measurements, showing how CO2 has increased since direct observations began in 1958. In climate science, it is a standard piece of evidence for the buildup of greenhouse gases in the atmosphere. ### Why does the Keeling Curve go up and down every year? The yearly up-and-down pattern is the seasonal cycle of plant growth, especially in the Northern Hemisphere. Plants pull CO2 out of the air during the growing season and release less of it when growth slows, so the graph wiggles even while the long-term trend keeps rising. ### How is the Keeling Curve different from historic CO2 levels? Historic CO2 levels come from proxies like ice cores, which estimate ancient atmosphere conditions. The Keeling Curve is direct modern measurement, so it gives a precise record of recent atmospheric CO2 rather than a reconstruction. ### Why is Mauna Loa used for the Keeling Curve? Mauna Loa is high and remote, which helps the measurements represent background atmospheric CO2 instead of local pollution. That makes the record better for tracking the global trend rather than a nearby source or sink. ## Related Study Guides - [10.2 Atmospheric concentration trends of greenhouse gases](/introduction-climate-science/unit-10/atmospheric-concentration-trends-greenhouse-gases/study-guide/T9bjaYQr01x7aUxj) ## About This Document Canonical Fiveable pages are available as Markdown at the same path plus `.md`. - [llms.txt](https://fiveable.me/llms.txt): index of Fiveable's sections and URL patterns - [llms-full.txt](https://fiveable.me/llms-full.txt): complete subject and unit listing - [MCP server](https://fiveable.me/mcp): call Fiveable as tools instead of fetching pages (`https://fiveable.me/api/mcp`) - [MCP server for AP teachers](https://fiveable.me/mcp/teachers): a teacher's classes, assignments and AP-rubric grading (`https://fiveable.me/api/mcp/teacher`) ## Structured Data ```json {"@context":"https://schema.org","@graph":[{"@type":"LearningResource","@id":"https://fiveable.me/introduction-climate-science/key-terms/keeling-curve#resource","name":"Keeling Curve | Intro to Climate Science","url":"https://fiveable.me/introduction-climate-science/key-terms/keeling-curve","learningResourceType":"Concept explainer","educationalLevel":"AP® / High School","about":{"@id":"https://fiveable.me/introduction-climate-science/key-terms/keeling-curve#term"},"audience":{"@type":"EducationalAudience","educationalRole":"student"},"dateModified":"2026-07-03T02:22:54.414Z","isPartOf":{"@type":"Collection","name":"Intro to Climate Science Key Terms","url":"https://fiveable.me/introduction-climate-science/key-terms"},"author":{"@type":"Organization","@id":"https://fiveable.me/editorial#content-team","name":"Fiveable Content Team","url":"https://fiveable.me/editorial","parentOrganization":{"@id":"https://fiveable.me/#organization"},"member":[{"@type":"Person","name":"Amanda DoAmaral","sameAs":["https://www.linkedin.com/in/adoamaral"]},{"@type":"Person","name":"Becky Bahr","sameAs":["https://www.linkedin.com/in/becky-bahr-b52743132"]}]},"publisher":{"@type":"Organization","name":"Fiveable","url":"https://fiveable.me"}},{"@type":"DefinedTerm","@id":"https://fiveable.me/introduction-climate-science/key-terms/keeling-curve#term","name":"Keeling Curve","description":"The Keeling Curve is the long-running graph of atmospheric carbon dioxide measured at Mauna Loa, showing both seasonal swings and a steady rise since 1958. 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