Earth's carbon doesn't sit still — it continuously moves between four great reservoirs, or "spheres". Plants and phytoplankton pull carbon out of the atmosphere via photosynthesis and lock it into biomass; the biosphere returns it just as fast through respiration and decomposition. The ocean surface dissolves atmospheric CO₂ (ocean uptake) and releases it back through outgassing. Slower still, dead organic matter and dissolved minerals settle to the sea floor (sedimentation), buried carbon returns to the surface through volcanism, and atmospheric CO₂ is slowly locked back into rock by silicate weathering — the slow inorganic counterpart to volcanic outgassing.
d(atmosphere)/dt = -photo + resp - oceanUptake + outgas + volcanism - weathering + anthropogenic
d(biosphere)/dt = +photo - resp
d(hydrosphere)/dt = +oceanUptake - outgas - sedimentation
d(lithosphere)/dt = +sedimentation - volcanism + weathering
- Photosynthesis intensity — scales how fast the biosphere draws carbon from the atmosphere. Lowering it (as deforestation would) leaves respiration unmatched, so the biosphere shrinks and the atmosphere reservoir grows.
- Anthropogenic CO2 emissions — an external source injecting carbon straight into the atmosphere, standing in for burning fossil fuels: carbon that was locked in the lithosphere on geological timescales, released in decades.
- Ocean uptake rate — scales how quickly the ocean surface absorbs atmospheric CO₂. A faster ocean cushions atmospheric growth, but the carbon has to go somewhere — hydrosphere content rises instead.
- At default settings (photosynthesis 1×, emissions 0×, ocean 1×) every flow is paired with a near-equal counter-flow — the system sits close to a steady state. Push any one slider and watch the reservoirs drift as the balance breaks.
The glowing particles streaming between spheres represent carbon moving along each pathway; the thickness of each ribbon scales with that pathway's current flow rate, so a thick photosynthesis ribbon and a thin respiration ribbon means the biosphere is a net carbon sink right now — and vice versa.