Carbon Flux Calculator

Net Ecosystem Exchange (NEE) is the standard flux-tower metric for whether an ecosystem is pulling carbon out of the atmosphere or adding to it, and this calculator computes it the way micrometeorologists conventionally sign it: NEE = ecosystem respiration − gross primary production (GPP). That sign convention trips people up constantly — a negative NEE means the ecosystem is absorbing more CO₂ through photosynthesis than it's releasing through respiration, i.e. it's a net carbon sink, while a positive NEE means it's a net source. The calculator also reports Net Ecosystem Production (NEP = GPP − Rₑ), which is simply NEE with the sign flipped and often more intuitive since positive NEP reads naturally as "net carbon gained." From the per-square-meter flux, the calculator scales up to your entire site by converting hectares to square meters and multiplying through, then converts grams of carbon to tonnes and finally to CO₂-equivalent tonnes using the standard molecular-weight ratio of 3.664 (44 g CO₂ per 12 g C).

Two additional ratios help characterize the ecosystem's carbon economy: Carbon Use Efficiency (NEP/GPP) shows what fraction of gross photosynthesis actually ends up stored rather than respired back out, and the respiration ratio (Rₑ/GPP) shows how much of gross production is being burned off — healthy ecosystems typically respire 60-90% of GPP. Keep in mind this is a snapshot, single-period calculation: real NEE varies enormously by season, time of day, and disturbance history, so a single set of GPP/Rₑ inputs represents one measurement period (annual, seasonal, or otherwise) rather than a universal constant for the site — comparing flux across sites or seasons requires measuring under comparable conditions.