TY - JOUR
T1 - Evolution of Uncertainty in Terrestrial Carbon Storage in Earth System Models from CMIP5 to CMIP6
AU - Wei, Ning
AU - Xia, Jianyang
AU - Zhou, Jian
AU - Jiang, Lifen
AU - Cui, Erqian
AU - Ping, Jiaye
AU - Luo, Yiqi
N1 - Publisher Copyright:
© 2022 American Meteorological Society.
PY - 2022/9/1
Y1 - 2022/9/1
N2 - The spatial and temporal variations in terrestrial carbon storage play a pivotal role in regulating future climate change. However, Earth system models (ESMs), which have coupled the terrestrial biosphere and atmosphere, show great uncertainty in simulating the global land carbon storage. Here, based on multiple global datasets and a traceability analysis, we diagnosed the uncertainty source of terrestrial carbon storage in 22 ESMs that participated in phases 5 and 6 of the Coupled Model Intercomparison Project (CMIP5 and CMIP6). The modeled global terrestrial carbon storage has converged among ESMs from CMIP5 (1936.9 6 739.3 PgC) to CMIP6 (1774.4 6 439.0 PgC) but is persistently lower than the observation-based estimates (2285 6 669 PgC). By further decomposing terrestrial carbon storage into net primary production (NPP) and ecosystem carbon residence time (tE), we found that the decreased intermodel spread in land carbon storage primarily resulted from more accurate simulations on NPP among ESMs from CMIP5 to CMIP6. The persistent underestimation of land carbon storage was caused by the biased tE. In CMIP5 and CMIP6, the modeled tE was far shorter than the observation-based estimates. The potential reasons for the biased tE could be the lack of or incomplete representation of nutrient limitation, vertical soil biogeochemistry, and the permafrost carbon cycle. Moreover, the modeled tE became the key driver for the intermodel spread in global land carbon storage in CMIP6. Overall, our study indicates that CMIP6 models have greatly improved the terrestrial carbon cycle, with a decreased model spread in global terrestrial carbon storage and less uncertain productivity. However, more efforts are needed to understand and reduce the persistent data–model disagreement on carbon storage and residence time in the terrestrial biosphere.
AB - The spatial and temporal variations in terrestrial carbon storage play a pivotal role in regulating future climate change. However, Earth system models (ESMs), which have coupled the terrestrial biosphere and atmosphere, show great uncertainty in simulating the global land carbon storage. Here, based on multiple global datasets and a traceability analysis, we diagnosed the uncertainty source of terrestrial carbon storage in 22 ESMs that participated in phases 5 and 6 of the Coupled Model Intercomparison Project (CMIP5 and CMIP6). The modeled global terrestrial carbon storage has converged among ESMs from CMIP5 (1936.9 6 739.3 PgC) to CMIP6 (1774.4 6 439.0 PgC) but is persistently lower than the observation-based estimates (2285 6 669 PgC). By further decomposing terrestrial carbon storage into net primary production (NPP) and ecosystem carbon residence time (tE), we found that the decreased intermodel spread in land carbon storage primarily resulted from more accurate simulations on NPP among ESMs from CMIP5 to CMIP6. The persistent underestimation of land carbon storage was caused by the biased tE. In CMIP5 and CMIP6, the modeled tE was far shorter than the observation-based estimates. The potential reasons for the biased tE could be the lack of or incomplete representation of nutrient limitation, vertical soil biogeochemistry, and the permafrost carbon cycle. Moreover, the modeled tE became the key driver for the intermodel spread in global land carbon storage in CMIP6. Overall, our study indicates that CMIP6 models have greatly improved the terrestrial carbon cycle, with a decreased model spread in global terrestrial carbon storage and less uncertain productivity. However, more efforts are needed to understand and reduce the persistent data–model disagreement on carbon storage and residence time in the terrestrial biosphere.
KW - Ecological models
KW - Model comparison
KW - Model evaluation/performance
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U2 - 10.1175/JCLI-D-21-0763.1
DO - 10.1175/JCLI-D-21-0763.1
M3 - Article
AN - SCOPUS:85137722803
SN - 0894-8755
VL - 35
SP - 5483
EP - 5499
JO - Journal of Climate
JF - Journal of Climate
IS - 17
ER -