Carbon Cycle Simulator: Reservoirs & Fluxes
Set emissions, deforestation and uptake rates and watch carbon flow between the atmosphere, ocean, land biosphere and fossil reserves in a real mass-balance model.
How to use: set fossil-fuel emissions, deforestation and reforestation/uptake rates, then watch carbon flow between the atmosphere, ocean, land biosphere and fossil reserves as a real four-box mass-balance model.
Challenge 1: reach net-zero
Balance emissions with uptake and reforestation so the net atmosphere flux is within ±0.2 GtC/yr of zero.
Challenge 2: hold CO₂ below a target
Run the model for at least 50 simulated years while keeping atmospheric CO₂ below 500 ppm.
About the Carbon Cycle Simulator: Reservoirs & Fluxes
Free carbon cycle simulator: reservoirs & fluxes. Set emissions, deforestation and uptake rates and watch carbon flow between the atmosphere, ocean, land biosphere and fossil reserves in a real mass-balance model. Drag, change the sliders and see the result live. No sign-up, works on phone and computer. Built for environmental science, the carbon cycle simulator: reservoirs & fluxes runs instantly in your browser: change a setting or drag an object and the result updates at once, so you learn by trying things out rather than only reading about them.
Set emissions, deforestation and uptake rates and watch carbon flow between the atmosphere, ocean, land biosphere and fossil reserves in a real mass-balance model. Use it to explore environmental science ideas at your own pace, then check what you found against the key ideas further down this page.
How to use the Carbon Cycle Simulator: Reservoirs & Fluxes
- Use the controls to change Fossil fuel emissions (GtC/yr), Deforestation (GtC/yr), Reforestation / photosynthesis uptake (GtC/yr), Ocean uptake rate (GtC/yr). The simulation reacts instantly.
- Press "▶ Run 1 year/s", "Reset simulation", "🌿 Set pre-industrial (1850) fluxes", "Reset to defaults" to start, reset or change what is happening.
- Where you see a glowing handle, object, weight or atom, drag it with your mouse or finger. Everything responds in real time.
- Watch the readouts and graphs update as you experiment, and compare what you see with the key ideas below.
Things to try
- Set fossil emissions and deforestation to zero and watch CO₂ slowly fall as sinks keep absorbing.
- Try to hit net-zero with realistic non-zero fossil emissions by raising reforestation and ocean uptake.
- Run the simulation for 50 years at today's real-world emission rates and watch the ppm readout climb.
- Set every source to maximum and watch how fast the fossil reserve depletes.
Key ideas you can learn
- The carbon cycle moves carbon between four main reservoirs: the atmosphere, the ocean, the land biosphere (plants and soil) and long-buried fossil fuel deposits.
- Atmospheric CO₂ rises whenever the fluxes into it (burning fossil fuels, deforestation) exceed the fluxes out of it (photosynthesis uptake, ocean absorption).
- 1 part per million of atmospheric CO₂ corresponds to about 2.13 gigatonnes of carbon (GtC), which is how scientists convert between the ppm reported in the news and the GtC used in carbon budgets.
- Reaching net-zero means balancing carbon sources and sinks so the net flux into the atmosphere is zero - the atmosphere reservoir then stops growing, even though carbon keeps moving through the system.
Where this is used in the real world
Climate scientists build exactly this kind of multi-reservoir carbon-budget model - IPCC reports summarize sources and sinks in gigatonnes of carbon per year to track how close the world is to net-zero targets.
Who is this simulation for?
Students, teachers and curious learners of all ages.
For teachers: project it on the board, let students predict what will happen, then run it together. For students: change one thing at a time and write down what changes.
Frequently asked questions
Why does today's atmosphere keep rising even though land and ocean absorb roughly half of emissions?
Only about half of current fossil-fuel and deforestation emissions are being reabsorbed by land and ocean sinks; the remaining net surplus each year adds to the atmosphere reservoir, so its GtC (and ppm) total keeps climbing.
What does it actually take to reach 'net zero'?
Net zero means the total carbon flowing out of the atmosphere (via reforestation, restored ecosystems, ocean uptake, and any active removal) equals the total still flowing in from remaining fossil emissions and deforestation, so the atmosphere reservoir stops growing even if raw emissions are not literally zero.
Is the Carbon Cycle Simulator: Reservoirs & Fluxes free to use?
Yes. It is completely free, with no signup, no download and no ads inside the simulation. It runs in your web browser.
Does the Carbon Cycle Simulator: Reservoirs & Fluxes work on a phone or tablet?
Yes. It uses touch as well as the mouse, so you can drag objects with your finger. A larger screen makes the controls easier to see.