Reducing uncertainties in decadal variability of the global carbon budget with multiple datasets

Self Cite

To assess global carbon cycle variability, we decompose the net land carbon sink into the sum of gross primary productivity (GPP), terrestrial ecosystem respiration (TER), and fire emissions and apply a Bayesian framework to constrain these fluxes between 1980 and 2014. The constrained GPP and TER fluxes show an increasing trend of only half of the prior trend simulated by models. From the optimization, we infer that TER increased in parallel with GPP from 1980 to 1990, but then stalled during the cooler periods, in 1990–1994 coincident with the Pinatubo eruption, and during the recent warming hiatus period. After each of these TER stalling periods, TER is found to increase faster than GPP, explaining a relative reduction of the net land sink. These results shed light on decadal variations of GPP and TER and suggest that they exhibit different responses to temperature anomalies over the last 35 years.

Section: Resultssupporting

confidence: 87%

Recent Changes in Global Photosynthesis and Terrestrial Ecosystem Respiration Constrained From Multiple Observations

Ciais

Wang

et al. 2018

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“…Keenan et al () suggested that both a slower increase in terrestrial ecosystem respiration (TER) and a continued increase in global gross primary production (GPP) explain the increased S LAND and the pause in the CGR during 1998–2011. Like many previous studies, the land carbon sink in these studies was inferred as the residual land sink, which may be indirectly affected by uncertainties in estimation of E FF , ocean sink, and land use change (LUC) emissions (Arneth et al, ; DeVries et al, ; Li et al, ; Pongratz et al, ). The relative contributions of different ecological processes to the acceleration of S LAND remain uncertain.…”

Section: Introductionmentioning

confidence: 91%

“…Correspondence to: S. Piao, slpiao@pku.edu.cn Li et al, 2016;Pongratz et al, 2014). The relative contributions of different ecological processes to the acceleration of S LAND remain uncertain.…”

Section: Supporting Informationmentioning

confidence: 99%

The Accelerating Land Carbon Sink of the 2000s May Not Be Driven Predominantly by the Warming Hiatus

Zhu

Piao

Yan

et al. 2018

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Recent studies attributed the accelerating land carbon sink (SLAND) during the 2000s to respiration decrease induced by the warming hiatus. We used two long‐term atmospheric inversions, three temperature data sets, and eight ecosystem models to test this attribution. Our results show that the changes in seasonal SLAND trend between the warming (1982–1998) and hiatus (1998–2014) periods do not track evidently the changes in seasonal temperature trends at both global and regional scales. A conceptual model of the annual/seasonal temperature response of respiration suggests that changes in seasonal temperature during this period are unlikely to cause a significant decrease in annual respiration. The ecosystem models suggest that trends in both gross primary production and terrestrial ecosystem respiration slowed down slightly, but the resulting slight acceleration in net ecosystem productivity is insufficient to explain the increasing trend in SLAND. Instead, the roles of alternative drivers on the accelerating SLAND seem to be important.

“…With a third of CO 2 emissions absorbed by global terrestrial ecosystems, the buildup of atmospheric CO 2 is abated (Le Quere et al, 2015). Yet the magnitude and regional distribution of the terrestrial carbon (C) sink at elevated CO 2 levels remain uncertain, due to our limited knowledge on vegetation responses to increased CO 2 concentration and nutrient limitation (Bellassen & Luyssaert, 2014;Grassi et al, 2017;Le Quere et al, 2009;Le Quere et al, 2015;Li et al, 2016;Schimel et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

Nitrogen Availability Dampens the Positive Impacts of CO₂ Fertilization on Terrestrial Ecosystem Carbon and Water Cycles

Chen

Croft

et al. 2017

The magnitude and variability of the terrestrial CO2 sink remain uncertain, partly due to limited global information on ecosystem nitrogen (N) and its cycle. Without N constraint in ecosystem models, the simulated benefits from CO2 fertilization and CO2‐induced increases in water use efficiency (WUE) may be overestimated. In this study, satellite observations of a relative measure of chlorophyll content are used as a proxy for leaf photosynthetic N content globally for 2003–2011. Global gross primary productivity (GPP) and evapotranspiration are estimated under elevated CO2 and N‐constrained model scenarios. Results suggest that the rate of global GPP increase is overestimated by 85% during 2000–2015 without N limitation. This limitation is found to occur in many tropical and boreal forests, where a negative leaf N trend indicates a reduction in photosynthetic capacity, thereby suppressing the positive vegetation response to enhanced CO2 fertilization. Based on our carbon‐water coupled simulations, enhanced CO2 concentration decreased stomatal conductance and hence increased WUE by 10% globally over the 1982 to 2015 time frame. Due to increased anthropogenic N application, GPP in croplands continues to grow and offset the weak negative trend in forests due to N limitation. Our results also show that the improved WUE is unlikely to ease regional droughts in croplands because of increases in evapotranspiration, which are associated with the enhanced GPP. Although the N limitation on GPP increase is large, its associated confidence interval is still wide, suggesting an urgent need for better understanding and quantification of N limitation from satellite observations.