Linking a global terrestrial biogeochemical model and a 2-dimensional climate model: implications for the global carbon budget

Abstract

We used the terrestrial ecosystem model (TEM, version 4.0) to estimate global responses of annual net primary production (NPP) and total carbon storage to changes in climate and atmospheric CO2, driven by the climate outputs from the 2-dimensional MIT L-O climate model and the 3-dimensional GISS and GFDL-q atmospheric general circulation models (GCMs). For contemporary climate with 315 ppmv CO2, TEM estimates that global NPP is 47.9 PgC/yr and global total carbon storage is 1658 PgC: 908 PgC of vegetation carbon and 750 PgC of reactive soil organic carbon. For climate change associated with a doubling of radiative forcing and an atmospheric level of 522 ppmv CO2, the responses of global NPP are + 17.8% for the MIT L-O climate, + 18.5% for the GFDL-q climate and + 20.6% for the GISS climate. The responses of global total carbon storage are + 6.9% for the MIT L-O climate, + 8.3% for GFDL-q climate and + 8.7% for the GISS climate. Among the three climate change predictions, the changes in latitudinal distributions of cumulative NPP and total carbon storage along 0.5° latitudinal bands vary slightly, except in high latitudes. There are generally minor differences in cumulative NPP and total carbon storage for most of the 18 biomes, except for the responses of total carbon storage in boreal biomes for the 2-D MIT L-O climate change. The results demonstrate that the linkage between the TEM and the 2-D climate model is useful for impact assessment and uncertainty analysis within an integrated assessment framework at the scales of the globe, economic regions and biomes, given the compromise between computational efficiency in the 2-D climate model and more detailed spatial representation of climate fields in 3-D GCMs.