Open AccessEarth System Models Are Not Capturing Present‐Day Tropical Forest Carbon Dynamics
Author(s) -
Koch Alexander,
Hubau Wannes,
Lewis Simon L.
Publication year - 2021
Publication title -
earth's future
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.641
H-Index - 39
ISSN - 2328-4277
DOI - 10.1029/2020ef001874
Subject(s) - carbon sink , coupled model intercomparison project , sink (geography) , environmental science , tropics , atmospheric sciences , carbon cycle , climate change , climatology , earth system science , tropical forest , tropical climate , climate model , geography , ecology , geology , biology , ecosystem , cartography
Tropical forests play a key role in absorbing carbon from the atmosphere into the land surface. Recent analyses of long‐term (1985–2014) forest inventory plots across the tropics show that structurally intact tropical forest are a large carbon sink, but that this sink has saturated and is projected to be in long‐term decline. Here we compare these results with estimates from the two latest generations of Earth System Models, Climate Modelling Intercomparison Project 5 (CMIP5) (19 models) and CMIP6 (17 models). While CMIP5 and CMIP6 are of similar skill, they do not reproduce the observed 1985–2014 carbon dynamics. The “natural” pan‐tropical carbon sink from inventory data is 0.99 Pg C yr −1 (95% CI 0.7–1.3, n = 614) between 2000 and 2010, the best sampled decade, double the CMIP6 multimodel‐mean of 0.45 Pg C yr −1 (95% CI 0.35–0.55). The observed saturating and declining sink is not captured by the models, which show modest increases in sink strength. The future (2015–2040) “natural” pan‐tropical sink from a statistical model driven by extrapolating past trends of its putative environmental drivers decreases by 0.23 Pg C per decade (95% CI 0.09–0.39) until the 2030s, while the CMIP6 multimodel‐mean under the climate change scenario closest to the statistical model project an increasing carbon sink (0.54 Pg C per decade; 95% CI 0.25–0.67). CMIP multimodel‐means reproduce the response of carbon gains from tree growth to environmental drivers, but the modeling of carbon losses from tree mortality does not correspond well to the inventory data. The model‐observation differences primarily result from the treatment of mortality in models.