Changes in soil organic carbon storage predicted by Earth system models during the 21st century

[摘要] Soil is currently thought to be a sink for carbon; however, the response ofthis sink to increasing levels of atmospheric carbon dioxide and climatechange is uncertain. In this study, we analyzed soil organic carbon (SOC)changes from 11 Earth system models (ESMs) contributing simulations to theCoupled Model Intercomparison Project Phase 5 (CMIP5). We used a reducedcomplexity model based on temperature and moisture sensitivities to analyzethe drivers of SOC change for the historical and high radiative forcing (RCP8.5) scenarios between 1850 and 2100. ESM estimates of SOC changed over the21st century (2090–2099 minus 1997–2006) ranging from a loss of 72 Pg C toa gain of 253 Pg C with a multi-model mean gain of 65 Pg C. Many ESMssimulated large changes in high-latitude SOC that ranged from losses of37 Pg C to gains of 146 Pg C with a multi-model mean gain of 39 Pg Cacross tundra and boreal biomes. All ESMs showed cumulative increases inglobal NPP (11 to 59%) and decreases in SOC turnover times (15 to28%) over the 21st century. Most of the model-to-model variation in SOCchange was explained by initial SOC stocks combined with the relative changesin soil inputs and decomposition rates (R² = 0.89, p < 0.01). Betweenmodels, increases in decomposition rate were well explained by a combinationof initial decomposition rate, ESM-specific Q₁₀-factors, and changes insoil temperature (R² = 0.80, p < 0.01). All SOC changes depended onsustained increases in NPP with global change (primarily driven by increasingCO₂). Many ESMs simulated large accumulations of SOC in high-latitudebiomes that are not consistent with empirical studies. Most ESMs poorlyrepresented permafrost dynamics and omitted potential constraints on SOCstorage, such as priming effects, nutrient availability, mineral surfacestabilization, and aggregate formation. Future models that represent theseconstraints are likely to estimate smaller increases in SOC storage over the21st century.

[学科分类] 地球化学与岩石