Carbon cycle

The carbon cycle is the biogeochemical circulation of carbon among the atmosphere, the biosphere, the hydrosphere, and the geosphere — a loop without beginning or end, driven by photosynthesis, respiration, decomposition, weathering, and volcanic outgassing. It is the thermostat of the Earth system on geological timescales: when CO₂ concentrations rise, chemical weathering of silicate rocks accelerates, drawing carbon down into the ocean and eventually into sedimentary rock. This negative feedback stabilizes climate over millions of years — but it is too slow to buffer the anthropogenic carbon pulse, which is altering the cycle on timescales a hundred times faster than the geostat can respond. The carbon cycle does not care about our deadlines.