The Carbon Cycle

Activities to try

1. 1

   Follow one carbon atom and watch the CO₂ budget

   Why it works: Carbon is conserved and recirculated through reservoirs (atmosphere, living things, fossil fuels); the climate problem is not that carbon moves but that humans add it to the air faster than natural processes (mainly photosynthesis in this model) remove it, tipping a budget that was roughly balanced before.

   1. Trace a single carbon atom along its journey: drawn out of the air into a leaf by photosynthesis, eaten along a food chain (feeding), and breathed back out as CO₂ by respiration. Then follow it on a second trip: taken up again by a tree's photosynthesis, locked into wood that dies and is buried before decomposers can fully break it down, slowly turned into coal over millions of years (fossilisation), and finally released as CO₂ when the coal is burned (combustion). Note that if the dead wood had decomposed instead, the decomposers' respiration would have returned the carbon to the air much sooner.
   2. Watch an atmospheric-CO₂ meter while only natural processes run, and state whether removal and return are roughly in balance.
   3. Switch on fossil-fuel burning and deforestation, observe what the meter does, and write down what is actually changing (the rate of addition versus removal, not carbon appearing from nowhere).
   4. Try to steady the meter by dialling emissions down and replanting forests, then explain what each lever does to the budget (replanting restores removal; cutting emissions reduces addition).
   5. Tag each process with whether it ADDS atmospheric CO₂ (respiration, decomposition, combustion), REMOVES it (photosynthesis), or only moves carbon between stores without directly changing atmospheric CO₂ (feeding, fossilisation), and sort them into these groups.
2. 2

   Build and tag the carbon-cycle diagram

   Why it works: The canonical cycle diagram, with each process tagged by direction, is the representation pupils reason with; it establishes the processes and their +/− effect on atmospheric CO₂ before analysing the dynamic balance.

   1. Draw or label a carbon-cycle diagram showing photosynthesis, feeding, respiration, decomposition and combustion between the reservoirs atmosphere, living things, and fossil fuels.
   2. Arrow each process in its direction and tag it +CO₂ (adds to air), −CO₂ (removes from air), or 0 (moves carbon between other stores, e.g. feeding between living things).
   3. Add a human-activity layer (fossil-fuel burning, deforestation) and mark how it changes the arrows or the balance.
   4. Lift a flap or annotate photosynthesis and combustion to write the matter transformation each performs.
3. 3

   Check adds-vs-removes reasoning and why CO₂ is rising

   Why it works: Pupils can confirm the model and, crucially, articulate the flux-balance reason for rising CO₂ rather than reciting that carbon 'increases'.

   1. Categorise each process as adds-CO₂, removes-CO₂, or neither (moves carbon between other stores, e.g. feeding).
   2. Sequence a carbon atom's path through the processes.
   3. Match each process to the reservoir it moves carbon between.
   4. Answer 'why is atmospheric CO₂ rising?' and justify the answer in terms of additions outpacing removals, not carbon being created.