This simulation shows how carbon flows between the atmosphere, ocean, land biosphere and fossil fuel reserves. Set a fossil fuel emission rate and watch a simplified but genuine box model update every reservoir year by year, while a live graph tracks atmospheric CO2 in parts per million.
Carbon reservoirs and fluxes: photosynthesis and respiration, ocean-atmosphere exchange, fossil fuel combustion, deforestation, and a natural sink that grows stronger as atmospheric CO2 rises above equilibrium.
Drag the emissions slider to set GtC/yr burned, adjust simulation speed, and watch the atmosphere box grow and the CO2-ppm graph climb. Pause anytime to read the exact numbers, or reset to start fresh.
Natural sinks (ocean plus land) currently absorb only about half of human CO2 emissions — the rest accumulates in the atmosphere, which is exactly why CO2 concentration keeps climbing year after year.
This simulation renders a simplified box model of Earth's carbon cycle. Carbon is tracked across four reservoirs — the atmosphere, the ocean, the land biosphere (vegetation and soil), and underground fossil fuel reserves — with box sizes drawn roughly proportional to how many gigatons of carbon (GtC) each one holds. Animated particles along the connecting arrows represent real carbon fluxes: photosynthesis and respiration exchange carbon between land and air, the ocean trades roughly 90 GtC per year with the atmosphere in each direction, and burning fossil fuels injects carbon directly into the atmosphere at the rate set by the emissions slider.
Each simulated year, the model updates every reservoir using real relationships rather than fixed numbers: a natural sink flux is computed as proportional to how far the atmosphere sits above its pre-industrial equilibrium of 590 GtC, so the sink strengthens as CO2 rises, closely tracking how the real ocean and land absorb roughly half of today's human emissions. Atmospheric carbon mass is converted to a live parts-per-million reading using the standard factor of 2.13 GtC per ppm, anchored at 280 ppm for the pre-industrial baseline, and a running graph plots that CO2 curve over simulated time so you can watch decades or centuries of accumulation unfold at your chosen simulation speed.
What are the four reservoirs shown in the diagram?
The atmosphere holds roughly 870 GtC today, the ocean holds by far the most carbon at around 38,000 GtC (shown at a compressed visual scale since it dwarfs the others), the land biosphere (plants and soil combined) holds about 2,000–2,500 GtC, and fossil fuel reserves underground hold roughly 5,000 GtC that shrinks as it is burned.
What do the arrows and moving particles represent?
Each arrow is a carbon flux — a flow of carbon between two reservoirs measured in gigatons per year. The thickness of the arrow and the speed and density of the particles flowing along it scale with the size of that flux, so a thick, fast-moving stream means a much larger annual carbon transfer than a thin, slow one.
How does the natural carbon sink work in this model?
The sink flux is computed as k times the difference between the current atmosphere GtC and the pre-industrial equilibrium of 590 GtC, so it is a genuine feedback rather than a fixed fraction of emissions. The constant k is tuned so this relaxation absorbs roughly half of realistic present-day emissions, matching observed ocean and land uptake.
How is atmospheric carbon converted to CO2 parts per million?
The model uses the standard conversion of about 2.13 gigatons of carbon per part per million of atmospheric CO2, anchored so 590 GtC corresponds to the pre-industrial baseline of 280 ppm. Every simulated year the current atmosphere GtC is converted through this formula to produce the live ppm readout and graph.
The fossil fuel emissions slider sets how many gigatons of carbon are burned into the atmosphere each simulated year, from 0 to 12 GtC/yr. The simulation speed slider sets how many simulated years pass per real second. The pause button freezes simulated time so you can read exact values, and reset restores every reservoir and the year counter to their starting state.
Every gigaton of carbon burned for energy is permanently removed from the underground fossil fuel reserve and added to the atmosphere, so the reserve box visibly shrinks the longer emissions continue. At higher emission rates and faster simulation speeds you can watch centuries of depletion play out in seconds.
Roughly half of what humans emit is absorbed by natural sinks — mostly the ocean surface and land plants and soil — through the same relaxation mechanism modelled here. The remainder accumulates in the atmosphere, which is why CO2 concentration has been rising steadily for over a century even though the sinks are working continuously.
It is a genuine, simplified box model with real reservoir magnitudes, real flux directions, and a real feedback mechanism for the natural sink and the ppm conversion — but it merges the ocean into a single box and treats fluxes as simple linear relationships rather than the full coupled carbonate chemistry and biosphere dynamics used in research-grade Earth system models.