On a two-dimensional energy balance climate model coupled interactively to a land carbon cycle model

A two-dimensional (latitude-height) climate/global carbon cycle model has been developed to investigate the interactive climate/biogeochemical response of a land biosphere to a linearly increasing input of carbon totalling 1000 Gtons C into the atmosphere over a 150-years period. With no fertilization response to the increasing CO₂ content in the atmosphere (fertilization factor = 0.0), the land biosphere acts as a net source of CO₂ for the atmosphere. This is mainly due to the soil carbon response to increasing surface temperatures, resulting in a greater soil release than the uptake of carbon by NPP. At the end of 150 years, globally averaged NPP has increased by about 2.3 Gtons C yr^-1, while the soil respiration has increased by 3.9 Gtons C yr^-1. When the land biosphere is allowed to respond to the increasing atmospheric CO₂ (fertilization factor = 0.3), NPP increases at a much faster rate than the soil release, causing the land biosphere to become a net sink for the excess CO₂ in the atmosphere. In this case, NPP has increased by about 15.4 Gtons C yr^-1, while the soil release has increased by around 12.9 Gtons C yr^-1.