concept

Net primary production

The carbon that plants and other photosynthesisers keep after subtracting what they respire away — the part that actually becomes leaf, wood, root and seed, and the entire budget every other organism in an ecosystem has to live on. The distinction from gross production is essential: on Earth, gross terrestrial photosynthesis runs about 120 gigatons of carbon a year, but the plants' own respiration takes roughly half of it back, leaving around 60. Those enormous two-way flows dwarf the small net imbalance — which is what makes the imbalance both hard to measure and decisive.