Five-box carbon cycle: atmosphere, surface ocean, deep ocean, terrestrial biosphere, and sediments. Fluxes between reservoirs follow first-order kinetics. Perturb with anthropogenic emissions and watch multi-timescale carbon equilibration.
The ~50% airborne fraction of anthropogenic CO₂ is well-established (Canadell et al. 2007). Atmospheric perturbations decay on multiple timescales: fast (land/ocean, decades), intermediate (deep ocean, centuries), slow (carbonate compensation, millennia). About 20% of fossil CO₂ persists for >10,000 yr.