What it does
Carbon moves round the Earth all the time. Plants take carbon dioxide (CO₂) out of the air by photosynthesis; animals, plants and soil microbes put it back by respiration and decay. The ocean dissolves CO₂ from the air and lets some escape again, and slowly carries it down to the deep water. Coal, oil and gas are carbon locked away for millions of years, until we burn them.
This sandbox draws those five stores as boxes and the flows as arrows whose thickness shows their size. You choose three things that people do each year:
- burn fossil fuels (today about 10 gigatonnes of carbon a year),
- clear forest (about 1 a year),
- plant new forest that takes carbon in.
Then you run the years and watch the CO₂ in the air, in parts per million (ppm), change on a graph. It fits the Class 9 Science chapter on the Earth as a system of energy, matter and life, and the carbon cycle in Class 11 and 12 Biology (ecosystems and environmental issues).
Carbon enters living things through the photosynthesis lab and passes along the chains in the food web builder; what more CO₂ does to the planet’s temperature is in the climate balance model.
How to use it
- Pick a Level. Class 9 names the stores in words; Class 11 shows the amounts in gigatonnes of carbon (GtC) and every flow in GtC per year.
- Set the three sliders, or type a value in the box next to each.
- Press Run 1 year, Run 10 years or Run to 2100. Back to 2025 starts over.
- Read the big line (year and CO₂) and the note under it, which says where last year’s carbon went.
A worked example
The page starts in the model’s 2025 with CO₂ at about 428 ppm. With burning at 10 and clearing at 1, press Run 1 year in the Class 11 level. People released 11 GtC; the air gained about 5.6 GtC (2.6 ppm), plants and soil about 2.6 GtC and the ocean about 1.8 GtC. So roughly half of what people released stayed in the air. Run to 2100 with the same choices and CO₂ climbs past 600 ppm.
Now press Back to 2025, set burning and clearing to 0 and run to 2100: CO₂ falls only to about 385 ppm. The ocean and plants soak up the extra slowly, over decades to centuries.
Tips
- 1 ppm of CO₂ is about 2.12 GtC of carbon in the air. Divide GtC by 2.12 to get ppm.
- Planting forests helps, but a forest only takes in carbon while it is growing, and there is limited land.
- The total carbon in all five stores never changes: carbon only moves between them.
Check yourself
Four fresh questions: GtC to ppm, the share that stays in the air, how long new forests take, and adding up a year’s flows. Nothing is saved.
FAQ
Are these real numbers? They are rounded teaching values chosen so the model behaves like the real cycle in outline. Real measurements have uncertainty and change with warming, which this model leaves out. It is not a forecast.
Why does the ocean not take all the extra CO₂? Sea water’s chemistry pushes back: as it takes in carbon, the CO₂ pressure over it rises about ten times faster (the buffer factor), so it soon stops taking much more until the surface water mixes down to the deep.
Is this from the NCERT book? It covers the same topic with fibub’s own model and examples. fibub is not part of NCERT.
Where the numbers come from
- A teaching box model written for fibub with rounded, made-up values: five stores in gigatonnes of carbon, photosynthesis with a mild CO₂ fertilisation term, an ocean buffer (Revelle) factor of 10, slow mixing to the deep ocean, and a smooth made-up history of burning from 1850. Not data from any agency or paper.
- Conversion 2.12 GtC of carbon = 1 ppm of CO₂ in the air (from the mass of the atmosphere and the molar masses of air and carbon; a standard textbook figure).
- Checked by conservation of carbon over 500 model years, by the pre-industrial balance staying still, and by the airborne share of a year's emissions (about half) matching the size usually quoted in textbooks.
Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.
Last updated 2026-11-09.