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The degree to which elevated CO2 concentrations (e[CO2]) increase the amount of carbon (C) assimilated by vegetation plays a key role in climate change. However, due to the short‐term nature of CO2 enrichment experiments and the lack of reconciliation between different ecological scales, the effect of e[CO2] on plant biomass stocks remains a major uncertainty in future climate projections. Here, we review the effect of e[CO2] on plant biomass across multiple levels of ecological organization, scaling from physiological responses to changes in population‐, community‐, ecosystem‐, and global‐scale dynamics. We find that evidence for a sustained biomass response to e[CO2] varies across ecological scales, leading to diverging conclusions about the responses of individuals, populations, communities, and ecosystems. While the distinct focus of every scale reveals new mechanisms driving biomass accumulation under e[CO2], none of them provides a full picture of all relevant processes. For example, while physiological evidence suggests a possible long‐term basis for increased biomass accumulation under e[CO2] through sustained photosynthetic stimulation, population‐scale evidence indicates that a possible e[CO2]‐induced increase in mortality rates might potentially outweigh the effect of increases in plant growth rates on biomass levels. Evidence at the global scale may indicate that e[CO2] has contributed to increased biomass cover over recent decades, but due to the difficulty to disentangle the effect of e[CO2] from a variety of climatic and land‐use‐related drivers of plant biomass stocks, it remains unclear whether nutrient limitations or other ecological mechanisms operating at finer scales will dampen the e[CO2] effect over time. By exploring these discrepancies, we identify key research gaps in our understanding of the effect of e[CO2] on plant biomass and highlight the need to integrate knowledge across scales of ecological organization so that large‐scale modeling can represent the finer‐scale mechanisms needed to constrain our understanding of future terrestrial C storage. [ABSTRACT FROM AUTHOR]

The degree to which elevated CO2 concentrations (e[CO2]) increase the amount of carbon (C) assimilated by vegetation plays a key role in climate change. However, due to the short‐term nature of CO2 enrichment experiments and the lack of reconciliation between different ecological scales, the effect of e[CO2] on plant biomass stocks remains a major uncertainty in future climate projections. Here, we review the effect of e[CO2] on plant biomass across multiple levels of ecological organization, scaling from physiological responses to changes in population‐, community‐, ecosystem‐, and global‐scale dynamics. We find that evidence for a sustained biomass response to e[CO2] varies across ecological scales, leading to diverging conclusions about the responses of individuals, populations, communities, and ecosystems. While the distinct focus of every scale reveals new mechanisms driving biomass accumulation under e[CO2], none of them provides a full picture of all relevant processes. For example, while physiological evidence suggests a possible long‐term basis for increased biomass accumulation under e[CO2] through sustained photosynthetic stimulation, population‐scale evidence indicates that a possible e[CO2]‐induced increase in mortality rates might potentially outweigh the effect of increases in plant growth rates on biomass levels. Evidence at the global scale may indicate that e[CO2] has contributed to increased biomass cover over recent decades, but due to the difficulty to disentangle the effect of e[CO2] from a variety of climatic and land‐use‐related drivers of plant biomass stocks, it remains unclear whether nutrient limitations or other ecological mechanisms operating at finer scales will dampen the e[CO2] effect over time. By exploring these discrepancies, we identify key research gaps in our understanding of the effect of e[CO2] on plant biomass and highlight the need to integrate knowledge across scales of ecological organization so that large‐scale modeling can represent the finer‐scale mechanisms needed to constrain our understanding of future terrestrial C storage. [ABSTRACT FROM AUTHOR]

Many institutions have substantial landholdings, but few consider soil carbon preservation and augmentation in their carbon management plans. A methodical framework was developed to analyse terrestrial carbon stocks (soil and tree biomass) for credible carbon offsetting strategies in institutional land. This approach was demonstrated at two farms (805 hectares) managed by Newcastle University. Soil carbon for three depths (0–30 cm, 30–60 cm and 60–90 cm) and above‐ground tree biomass were quantified. These data provided a terrestrial carbon baseline to evaluate future land management options and effects. Historical land‐use records enabled the following comparisons: (1) agricultural land vs. woodland; (2) arable land vs. permanent grassland; (3) organic vs. conventional farming; (4) coniferous vs. broadleaved woodland; and (5) recent vs. long‐established woodland. Carbon storage (kg/m2) varied with land usage and woodland type and age, but only agricultural land vs. woodland, and for agriculture, arable land vs. permanent grassland, significantly affected the 0–90 cm soil carbon. At the university‐managed farms, current terrestrial carbon stocks were 103,620 tonnes in total (98,050 tonnes from the 0–90 cm soil and 5,569 tonnes from tree biomass). These terrestrial carbon stocks were equivalent to sixteen years of the current carbon emissions of Newcastle University (6,406 tonnes CO2 equivalents‐C per year). Using strategies for alternative land management, Newcastle University could over 40 years offset up to 3,221 tonnes of carbon per year, or 50% of its carbon emissions at the current rate. The methodological framework developed in this study will enable institutions having large landholdings to rationally consider their estates in future soil carbon management schemes. [ABSTRACT FROM AUTHOR]

Here we examine the causal effects of El Niño–Southern Oscillation (ENSO) on the global carbon cycle over historical and future periods utilizing datasets from the Coupled Modeling Intercomparison Project Phase 6 models. Our results show that ENSO exhibits impact on terrestrial carbon fluxes and carbon storage over numerous regions of Asia, Oceania, and America. High consensus is found between models for the influences of ENSO over these regions. The results demonstrate that the effects of ENSO on carbon cycling over subtropics and high‐latitude regions may be more significant than previously understood. In historical simulation, the regions affected by ENSO account for approximately 8.5% land‐area and this proportion rises to approximately 11.7% in the future simulation, indicating an increase in ENSO influences on the gross primary productivity of terrestrial ecosystems. In addition, the results emphasize stronger response of seasonal carbon stocks to ENSO compared to that of seasonal carbon fluxes. Plain Language Summary: The global carbon cycle is an essential component of the Earth climate system. However, there is uncertainty in the response of future carbon cycling to El Niño–Southern Oscillation (ENSO) variations. Under warming environment and anthropogenic impacts, further understanding of ENSO and carbon cycle connections is important to accurately estimate future climate change and extremes. In the present study, we examine the causal effects of ENSO on the global carbon cycle over the future period 2015–2100 utilizing datasets from climate model simulations. Our results show that ENSO exhibits impact on carbon cycling over numerous regions of Asia, Oceania, and America. The results underscore that the impacts of ENSO on carbon cycling over subtropical and high‐latitude regions may be more significant than previously understood. We conclude that the future projections show an increase in ENSO influences on terrestrial carbon cycle compared to the historical period 1915–2000. In historical simulation, the regions with significant ENSO effects on gross primary productivity account for 8.5% land‐area and this proportion rises to 11.7% in the future simulation. This work might contribute to the forthcoming adaptation of global change and carbon neutrality policy. Key Points: El Niño–Southern Oscillation (ENSO) exhibits causal impact on carbon fluxes and terrestrial carbon storage over numerous regions of Asia, Oceania, and AmericaProjections over the future period show an increase in land‐area of regions affected by ENSO compared to the historical periodThe results emphasize that the response of seasonal carbon stocks to ENSO is stronger compared to the response of seasonal carbon fluxes [ABSTRACT FROM AUTHOR]

The knowledge of potential impacts of climate change on terrestrial vegetation is crucial to understand long-term global carbon cycle development. Discrepancy in data has long existed between past carbon storage reconstructions since the Last Glacial Maximum by way of pollen, carbon isotopes, and general circulation model (GCM) analysis. This may be due to the fact that these methods do not synthetically take into account significant differences in climate distribution between modern and past conditions, as well as the effects of atmospheric CO2 concentrations on vegetation. In this study, a new method to estimate past biospheric carbon stocks is reported, utilizing a new integrated ecosystem model (PCM) built on a physiological process vegetation model (BIOME4) coupled with a process-based biospheric carbon model (DEMETER). The PCM was constrained to fit pollen data to obtain realistic estimates. It was estimated that the probability distribution of climatic parameters, as simulated by BIOME4 in an inverse process, was compatible with pollen data while DEMETER successfully simulated carbon storage values with corresponding outputs of BIOME4. The carbon model was validated with present-day observations of vegetation biomes and soil carbon, and the inversion scheme was tested against 1491 surface pollen spectra sample sites procured in Africa and Eurasia. Results show that this method can successfully simulate biomes and related climates at most selected pollen sites, providing a coefficient of determination ( R) of 0.83–0.97 between the observed and reconstructed climates, while also showing a consensus with an R-value of 0.90–0.96 between the simulated biome average terrestrial carbon variables and the available observations. The results demonstrate the reliability and feasibility of the climate reconstruction method and its potential efficiency in reconstructing past terrestrial carbon storage. [ABSTRACT FROM AUTHOR]

The equilibrium carbon storage capacity of the terrestrial biosphere has been investigated by running the Lund–Potsdam–Jena Dynamic Global Vegetation Model to equilibrium for a range of CO2 concentrations and idealized climate states. Local climate is defined by the combination of an observation-based climatology and perturbation patterns derived from a 4 × CO2 warming simulations, which are linearly scaled to global mean temperature deviations, Δ Tglob. Global carbon storage remains close to its optimum for Δ Tglob in the range of ±3°C in simulations with constant atmospheric CO2. The magnitude of the carbon loss to the atmosphere per unit change in global average surface temperature shows a pronounced nonlinear threshold behavior. About twice as much carbon is lost per degree warming for Δ Tglob above 3°C than for present climate. Tropical, temperate, and boreal trees spread poleward with global warming. Vegetation dynamics govern the distribution of soil carbon storage and turnover in the climate space. For cold climate conditions, the global average decomposition rate of litter and soil decreases with warming, despite local increases in turnover rates. This result is not compatible with the assumption, commonly made in global box models, that soil turnover increases exponentially with global average surface temperature, over a wide temperature range. [ABSTRACT FROM AUTHOR]

The equilibrium carbon storage capacity of the terrestrial biosphere has been investigated by running the Lund–Potsdam–Jena Dynamic Global Vegetation Model to equilibrium for a range of CO2 concentrations and idealized climate states. Local climate is defined by the combination of an observation-based climatology and perturbation patterns derived from a 4 × CO2 warming simulations, which are linearly scaled to global mean temperature deviations, Δ Tglob. Global carbon storage remains close to its optimum for Δ Tglob in the range of ±3°C in simulations with constant atmospheric CO2. The magnitude of the carbon loss to the atmosphere per unit change in global average surface temperature shows a pronounced nonlinear threshold behavior. About twice as much carbon is lost per degree warming for Δ Tglob above 3°C than for present climate. Tropical, temperate, and boreal trees spread poleward with global warming. Vegetation dynamics govern the distribution of soil carbon storage and turnover in the climate space. For cold climate conditions, the global average decomposition rate of litter and soil decreases with warming, despite local increases in turnover rates. This result is not compatible with the assumption, commonly made in global box models, that soil turnover increases exponentially with global average surface temperature, over a wide temperature range. [ABSTRACT FROM AUTHOR]