How does carbon move through Earth's systems, and how do humans change that flow?
Describe how carbon cycles among the atmosphere, biosphere, hydrosphere and geosphere through photosynthesis, respiration, decomposition and combustion, and explain how human activities alter the carbon cycle.
A Regents answer on the carbon cycle: how carbon moves among the atmosphere, biosphere, hydrosphere and geosphere through photosynthesis, respiration, decomposition and combustion, the role of carbon sinks (oceans, forests, fossil fuels), and how burning fossil fuels and deforestation move stored carbon into the air, with worked exam questions.
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What this topic is asking
The Regents (and especially the new Earth and Space Sciences exam) wants you to describe how carbon cycles among the four Earth systems through photosynthesis, respiration, decomposition and combustion, and to explain how human activities alter that cycle. The headline is carbon sinks and how burning fossil fuels moves long-stored carbon into the air.
What the carbon cycle is
The processes that move carbon
So the fast biological loop (photosynthesis taking carbon in, respiration and decomposition releasing it) is overlaid on a slow geological loop (burial into rock and fossil fuels, release by weathering and volcanism).
Carbon sinks
How humans alter the carbon cycle
Human activities shift carbon out of long-term storage and into the atmosphere:
- Burning fossil fuels takes carbon that was locked away in coal, oil and gas over millions of years and releases it as carbon dioxide in a matter of decades, far faster than natural processes can reabsorb it.
- Deforestation removes a major sink, so less carbon dioxide is taken up, and burning or decaying the cleared trees releases their stored carbon.
The result is a net rise in atmospheric carbon dioxide, which enhances the greenhouse effect and warms the climate, linking this topic directly to climate change.
Try this
Q1. Name the process that moves carbon from the atmosphere into plants. [1 point]
- Cue. Photosynthesis.
Q2. Explain why burning fossil fuels raises atmospheric carbon dioxide. [2 points]
- Cue. It releases carbon that was stored in coal, oil and gas over millions of years, adding carbon dioxide to the air faster than natural processes (photosynthesis, ocean uptake) can remove it.
Exam-style practice questions
Practice questions written in the style of NYSED exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Regents (style)1 marksPart A. During photosynthesis, plants remove which gas from the atmosphere and store its carbon? (1) oxygen (2) nitrogen (3) carbon dioxide (4) methane. Justify your choice.Show worked answer →
A 1-point multiple-choice question. The answer is (3).
In photosynthesis, plants take in carbon dioxide and use sunlight to build sugars, storing the carbon in their tissues and releasing oxygen. They do not store carbon from oxygen (1), nitrogen (2) or methane (4). The trap is confusing the gases: plants take in carbon dioxide and give off oxygen during photosynthesis (the reverse of respiration).
Regents (style)3 marksPart C. (a) Name two processes that move carbon from living things back into the atmosphere. (b) Explain how fossil fuels store carbon and how burning them affects the carbon cycle. (c) Explain why forests and oceans are called carbon sinks.Show worked answer →
A 3-point extended-response question.
(a) 1 point: respiration (organisms release carbon dioxide as they use energy) and decomposition (decomposers release carbon dioxide as they break down dead matter); combustion also counts.
(b) 1 point: fossil fuels are carbon stored from ancient organisms buried over millions of years; burning them releases that long-stored carbon as carbon dioxide into the atmosphere, adding to the air's carbon faster than natural processes remove it.
(c) 1 point: forests and oceans are carbon sinks because they absorb and store more carbon than they release, forests through photosynthesis and oceans by dissolving carbon dioxide and through marine life.
Markers reward respiration and decomposition, the fossil-fuel storage-then-release idea, and the sink definition for forests and oceans.
Related dot points
- Explain the greenhouse effect and the role of greenhouse gases, distinguish natural from human-enhanced climate change, and describe the evidence for and consequences of recent global warming.
A Regents answer on the greenhouse effect and climate change: how greenhouse gases (carbon dioxide, methane, water vapor) trap outgoing infrared energy and warm the surface, natural versus human-enhanced warming from burning fossil fuels, the evidence (rising carbon dioxide and temperature, melting ice, rising seas) and consequences, with worked exam questions.
- Explain how human activities (pollution, deforestation, land use, resource extraction) affect Earth's atmosphere, hydrosphere, geosphere and biosphere, and evaluate ways to reduce harm.
A Regents answer on human impact: how pollution, deforestation, land use and resource extraction affect the atmosphere, hydrosphere, geosphere and biosphere, examples such as air and water pollution, soil erosion and habitat loss, the idea of Earth's interconnected systems, and how to evaluate solutions, for the Earth and Space Sciences exam, with worked exam questions.
- Distinguish renewable from non-renewable energy resources, describe the main sources (fossil fuels, nuclear, solar, wind, hydro, geothermal) and weigh their advantages and environmental costs.
A Regents answer on energy resources: the difference between renewable and non-renewable resources, the main sources (coal, oil and gas, nuclear, solar, wind, hydroelectric, geothermal), how fossil fuels form over geologic time, and the advantages and environmental costs of each for the Earth and Space Sciences exam, with worked exam questions.
- Describe Earth's key natural resources (water, soil, minerals, air, forests) and explain how resource management, conservation and sustainability balance human needs against the limits of Earth's systems.
A Regents answer on natural resources and management: the difference between renewable and non-renewable resources, the key resources (fresh water, fertile soil, minerals, air, forests), the meaning of conservation and sustainability, why resources are unevenly distributed, and how management balances human needs against Earth's limits, with worked exam questions.
- Describe the water cycle and its processes, and explain the factors that control infiltration, runoff and groundwater storage (porosity, permeability, slope, saturation and the water table).
A Regents answer on the water cycle and groundwater: evaporation, transpiration, condensation, precipitation and runoff, the factors that control infiltration versus runoff (porosity, permeability, particle size, slope, saturation, vegetation), the water table and zones of saturation and aeration, and the energy that drives the cycle, with worked exam questions.
Sources & how we know this
- Earth and Space Sciences — New York State Education Department (2026)
- Regents Examination in Physical Setting/Earth Science — New York State Education Department (2026)