The Carbon Cycle
Aligned to HS-ESS2-6 — Next Generation Science Standards.
What this lesson teaches
Carbon constantly moves among the atmosphere, oceans, rocks, and living things. Photosynthesis, respiration, ocean absorption, and volcanic eruptions shift carbon between these reservoirs, and the amounts can be tracked quantitatively.
Worked examples
Example 1
Each year plants pull about 120 billion tons of carbon from the air through photosynthesis, and respiration and decay return nearly the same amount. Burning fossil fuels adds an extra 10 billion tons that the natural cycle does not fully remove, so atmospheric carbon rises.
Example 2
The extra 10 billion tonnes is small next to the 120 that cycle, and it is the imbalance rather than the size that accumulates.
Example 3
About a quarter of the extra carbon dissolves into the ocean, which slows warming and acidifies the water instead.
Practice questions
- Observe: Plants remove carbon dioxide while burning fuel and decay release it. What determines whether atmospheric carbon goes up or down?
- Model: Draw the carbon cycle with boxes for atmosphere, ocean, plants, and rocks, and arrows showing carbon moving between them.
- Explain: Human emissions add carbon faster than oceans and forests remove it. Use a balance of inflows and outflows to explain why the atmosphere is gaining carbon.
Watch the lesson
Every lesson comes with a video taught in English and Spanish — the same video the QR code in the printed workbook opens.
▶ Watch this lessonEn español
El ciclo del carbono
El carbono se mueve constantemente entre la atmósfera, los océanos, las rocas y los seres vivos. La fotosíntesis, la respiración, la absorción oceánica y las erupciones volcánicas trasladan carbono entre estos depósitos, y las cantidades pueden medirse de forma cuantitativa.
Ejemplo 1: Cada año las plantas retiran unos 120 mil millones de toneladas de carbono del aire por fotosíntesis, y la respiración y la descomposición devuelven casi la misma cantidad. Quemar combustibles fósiles agrega 10 mil millones de toneladas extra que el ciclo natural no elimina por completo, así que el carbono atmosférico sube.
Ejemplo 2: Los 10 mil millones de toneladas extra son poco frente a los 120 que circulan, y lo que se acumula es el desbalance, no el tamaño.
Ejemplo 3: Cerca de una cuarta parte del carbono extra se disuelve en el océano, lo que frena el calentamiento y a cambio acidifica el agua.
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