CO2-model This Excel spreadsheet contains a simple yearly time step atmospheric CO2 budget model driven by yearly estimates of global anthropogenic CO2 emissions, a user-adjusable yearly CO2 sink rate, an "equilibrium" CO2 level that the CO2 sink rate uses in combination with the yearly CO2 value (the value the system is relaxing to), and an adjustable El Nino/Southern Oscillation (ENSO) term representing the effect of El Nino and La Nina on the yearly CO2 budget. The ENSO term uses 12-month averages of the Multivariate ENSO Index (MEI, both original and version 2, intercalibrated during their mutual period of overlap). From 2021 onward, Energy Information Administration (EIA) estimates of future global CO2 emissions are used.