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The 2030 emissions gap between current policies and pledges 1.5 C and 2 C as assessed in this study and by den Elzen (2022) is compared against levels of current policies, conditional NDCs, and unconditional NDCs as reported in den Elzen (2022). Median estimates of all values are used to compute the respective emission gaps.
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Taking stock of global progress towards achieving the Paris Agreement requires consistently measuring aggregate national actions and pledges against modelled mitigation pathways¹. However, national greenhouse gas inventories (NGHGIs) and scientific assessments of anthropogenic emissions follow different accounting conventions for land-based carbon...
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... What these results indicate is that we need to continue to deepen our understanding and more finely resolve our estimates and associated uncertainties of the components of the GCB, in particular the highly uncertain land terms (direct and indirect anthropogenic fluxes). A more refined understanding of these two fluxes is essential for improving model predictions of the future land sink, which is in turn critical to estimate the remaining carbon budget as well as Nationally Determined Contribution to meet internationally agreed upon global temperature targets (Gidden et al., 2023). A more refined understanding and ability to model anthropogenic disturbance regimes in anthromes will lead to a greater ability to diagnose sources and sinks in the GCB and predict the carbon cycle under future scenarios. ...
Societal Impact Statement
The global carbon budget provides annual updates to society on the main cause of climate change—CO2 emissions—and quantifies carbon‐uptake ecosystem services provisioned by the biosphere. We show that more consistent assumptions in the estimates of land‐atmosphere carbon exchange results in a global carbon budget that is imbalanced (gains do not equal losses). This imbalance implies that key processes causing land carbon fluxes, especially processes associated with human land management and recovery following abandonment in anthropogenic biomes (anthromes), have been misquantified. This impacts policy for land carbon management across scales and calls for better understanding of carbon cycling in anthromes.
Summary
Inconsistencies in the calculation of the two anthropogenic land flux terms of the global carbon cycle are investigated. The two terms—the direct anthropogenic flux (caused by direct human disturbance in anthromes, currently a carbon source to the atmosphere) and the indirect anthropogenic flux (caused indirectly by human activities that lead to global change and affecting all biomes, currently an atmospheric carbon sink)—are typically calculated independently, resulting in inconsistent underlying assumptions.
We harmonize the estimation of the two anthropogenic land flux terms by incorporating previous estimates of these inconsistencies. We recalculate the global carbon budget (GCB) and apply change‐point analysis to the cumulative budget imbalance.
Cumulative over 1850–2018 (1959–2018), harmonization results in a 13% lesser (4% greater) land use source from anthromes and a 20% (23%) lesser land sink. This recalculation yields a greater non‐closure of the GCB, indicating a missing carbon sink averaging 0.65 Pg C year⁻¹ since the early 20th century. The imbalance likely results from a combination of method discontinuity and structural errors in the assessment of the direct anthropogenic land use flux, greater ocean carbon uptake, structural errors in land models, and in how these land terms are quantified for the budget.
We caution against overconfidence in considering the GCB a solved problem and recommend further study of methodological discontinuities in budget terms. We strongly recommend studies that quantify the direct and indirect anthropogenic land fluxes simultaneously to ensure consistency, with a deeper understanding of human disturbance and legacy effects in anthromes.
... To consider these issues, we have implemented OSCAR-China, a refined 0.5°× 0.5°gridded version of the reduced-complexity model OSCAR, specifically tailored for China (Methods). Of the three bookkeeping models used in the GCB annual exercise, OSCAR distinguishes itself by incorporating biogeochemical processes that enable simulating all aspects of the land carbon cycle under environmental and land-use changes 11,12 and bridge the gap in definitions 13 . OSCAR-China inherits this feature and incorporates spatially explicit, observationbased historical land-use change data 9 . ...
... Furthermore, by adding the indirect effects in managed forest (−0.07 ± 0.03 Gt C yr −1 ) to the direct ones, the offset percentage increases to 43 ± 4%. However, we must insist that this inclusion of the indirect effects in the definition of carbon neutrality is incompatible with the notion of remaining carbon budgets, and precautions must be taken when doing so 13 . ...
... First, the efficacy of expanding forest areas for enhancing direct carbon sequestration is limited in time: once the available area suitable for forestation is fully utilized, the carbon sink will inexorably diminish (Fig. 2). Second, the effectiveness of indirect carbon removal will likely weaken over time as global mitigation efforts progress, due to its dependence on atmospheric CO 2 levels, as well as deleterious climate impacts and increasing nutrients limitations 4,13,38,39 . Therefore, the carbon removal potential of the LULUCF sector is inherently limited but non-negligible. ...
China’s commitment to carbon neutrality by 2060 relies on the Land Use, Land-Use Change, and Forestry (LULUCF) sector, with forestation targets designed to enhance carbon removal. However, the exact sequestration potential of these initiatives remains uncertain due to differing accounting conventions between national inventories and scientific assessments. Here, we reconcile both estimates and reassess LULUCF carbon fluxes up to 2100, using a spatially explicit bookkeeping model, state-of-the-art historical data, and national forestation targets. We simulate a carbon sink of −0.24 ± 0.03 Gt C yr⁻¹ over 1994–2018 from past forestation efforts, aligned well with the national inventory. Should the official forestation targets be followed and extended, this could reach −0.35 ± 0.04 Gt C yr⁻¹ in 2060, offsetting 43 ± 4% of anticipated residual fossil CO2 emissions. Our findings confirm the key role of LULUCF in carbon sequestration, but its potential will decline if forestation efforts cease, highlighting the necessity for emission reductions in other sectors to achieve carbon neutrality.
... In the Global Carbon Budget (Friedlingstein et al., 2022b), for example, best estimates of land use emissions are derived from bookkeeping models (Hansis et al., 2015;Houghton and Nassikas, 2017;Quilcaille et al., 2023), which use empirical growth curves to estimate the transient carbon stock response to land use changes. Meanwhile, national inventories use different accounting conventions to those used in IAMS, ESMs and bookkeeping models -including not just transitions in land use but also land sinks in some regions whose usage remains static but are designated as managed (Gidden et al., 2023;Grassi et al., 2021). The 2028 global stocktake will be the next major global assessment of progress towards Paris Agreement goals. ...
... Beyond this, many high-ambition scenarios contain significant requirements for explicit representation of carbon dioxide removal (Fuss et al., 2014;Anderson and Peters, 2016) whose plausibility can potentially be assessed when represented in an Earth system model . Increasing understanding of how to map between national accounting systems and ESM/IAM output (Gidden et al., 2023;Grassi et al., 2021) can be strengthened with hybrid emissions-driven simulations (combined with well-chosen counterfactual experiments in LUMIP), where ensembles can provide ranges of modeled direct and indirect anthropogenic fluxes from land use change. ...
Previous phases of the Coupled Model Intercomparison Project (CMIP) have primarily focused on simulations driven by atmospheric concentrations of greenhouse gases (GHGs), for both idealized model experiments and climate projections of different emissions scenarios. We argue that although this approach was practical to allow parallel development of Earth system model simulations and detailed socioeconomic futures, carbon cycle uncertainty as represented by diverse, process-resolving Earth system models (ESMs) is not manifested in the scenario outcomes, thus omitting a dominant source of uncertainty in meeting the Paris Agreement. Mitigation policy is defined in terms of human activity (including emissions), with strategies varying in their timing of net-zero emissions, the balance of mitigation effort between short-lived and long-lived climate forcers, their reliance on land use strategy, and the extent and timing of carbon removals. To explore the response to these drivers, ESMs need to explicitly represent complete cycles of major GHGs, including natural processes and anthropogenic influences. Carbon removal and sequestration strategies, which rely on proposed human management of natural systems, are currently calculated in integrated assessment models (IAMs) during scenario development with only the net carbon emissions passed to the ESM. However, proper accounting of the coupled system impacts of and feedback on such interventions requires explicit process representation in ESMs to build self-consistent physical representations of their potential effectiveness and risks under climate change. We propose that CMIP7 efforts prioritize simulations driven by CO2 emissions from fossil fuel use and projected deployment of carbon dioxide removal technologies, as well as land use and management, using the process resolution allowed by state-of-the-art ESMs to resolve carbon–climate feedbacks. Post-CMIP7 ambitions should aim to incorporate modeling of non-CO2 GHGs (in particular, sources and sinks of methane and nitrous oxide) and process-based representation of carbon removal options. These developments will allow three primary benefits: (1) resources to be allocated to policy-relevant climate projections and better real-time information related to the detectability and verification of emissions reductions and their relationship to expected near-term climate impacts, (2) scenario modeling of the range of possible future climate states including Earth system processes and feedbacks that are increasingly well-represented in ESMs, and (3) optimal utilization of the strengths of ESMs in the wider context of climate modeling infrastructure (which includes simple climate models, machine learning approaches and kilometer-scale climate models).
... Global climate change poses a significant threat to human survival and advancement (Gidden et al 2023, Sharma et al 2023 and has become a major environmental issue of worldwide significance (Iyer et al 2022, Lincoln et al 2022. According to the United Nations Intergovernmental Panel on Climate Change (IPCC), Earth's average temperature has increased approximately 1.1°C since the post-Industrial Revolution (Beck and Oomen 2021), with excessive carbon dioxide emissions considered as the main bases for this global warming. ...
With the inevitability of global climate change, it has become increasingly important to understand the relationship between Agro-industrial Development (AID) and Agricultural Carbon Emissions (ACE) to promote the development of low carbon production in agriculture. Using a panel of datasets, as based on the ‘element-structure-function’ framework of 30 Chinese provinces over the period from 2011–2021, the entropy weight method was used to calculate the level of AID in each province. With this approach, it was possible to assess correlations and mechanisms between AID and ACE. Here, with use of fixed-effect, regulatory and threshold models, we determined some of the critical factors contributing to the effects of AID and ACE. Our findings revealed: (1) AID displays an inverse U-shape relationship with ACE, as verified through endogeneity and robustness assessment, (2) A review of the mechanisms suggests that the crossing of the turning point of the inverted u-curve can be accelerated by the moderating effect of agricultural finance. and (3) As based on the threshold effect analysis, a two-tier effect of the digital economy, rural human capital and farmers’ net income on AID, with facilitating effects on carbon emission reductions was obtained after the threshold crossing. The significance of this effect increases as a function of the post-threshold interval. Taken together, these findings demonstrate the long-standing interplay between AID and ACE. Thus, additional insights and empirical evidence that can inform the ongoing development of sustainable agricultural practices can be realized.
... These significant uncertainties in estimating forest carbon stock and sink could severely undermine their role in climate mitigation. Therefore, reducing uncertainties in global forest carbon flux estimates is critical to meeting climate targets for carbon storage and emission reductions [4]. ...
China’s forests act as a large carbon sink and play a vital role in achieving the carbon neutrality goal by the 2060s. To achieve this goal, the magnitude and spatial patterns of forest carbon sinks must be accurately quantified. In this study, we aim to provide the longest estimate of forest biomass carbon storage and sinks in China at a 1 km spatial resolution from 1990 to 2021 by merging long-term observations from optical and microwave remote sensing datasets with a field-validated benchmark map. We explored the spatial characteristics of aboveground biomass (AGB) and belowground biomass (BGB) carbon in China’s forests, as well as variations in AGB carbon sinks. The average AGB and BGB carbon storage from 1990 to 2021 in China’s forests were 8.42 ± 0.96 Pg C and 1.9 ± 0.21 Pg C, respectively. The average annual AGB carbon sink during this period was approximately 0.083 ± 0.023 Pg C yr⁻¹. Forests in the southwest region contributed 31.15% of the forest AGB carbon sink in China and contributed 41.01% of the forest AGB carbon storage. Our study presents an effective tool for assessing changes in forest biomass carbon by leveraging comprehensive multi-source remote sensing data and highlights the importance of obtaining large-scale, high-quality, consistent, and accessible plot survey data to validate the earth observation of biomass.
... The same applies to the Global Stocktake, which relies on an accurate assessment of the success of climate mitigation through LULUCF by halting deforestation or by implementing re/afforestation projects. As future environmental conditions are expected to diverge further from the present-day state, E LUC estimates are projected to grow further apart in future decades 9 , yet decisively depending on the future evolution of CO 2 concentrations and climate change 41 . ...
... While our study argues that these latter sinks should be attributed to natural terms, including them under anthropogenic activities may be advantageous from a political viewpoint: counting the additional, natural sinks as activities in the LULUCF sector and thus allowing for CO 2 credits may incentivize carbon dioxide removal, such as through re/afforestation. However, the future evolution of these additional sinks-as the natural land sink in generalis highly dependent on the socioeconomic pathway and mitigation efforts humanity will follow 4,41 . Land sinks may even turn to large-scale sources under future weather extremes 32,49 or when atmospheric CO 2 concentrations eventually decline. ...
Accurate estimates of CO2 emissions from anthropogenic land-use change (ELUC) and of the natural terrestrial CO2 sink (SLAND) are crucial to precisely know how much CO2 can still be emitted to meet the goals of the Paris Agreement. In current carbon budgets, ELUC and SLAND stem from two model families that differ in how CO2 fluxes are attributed to environmental and land-use changes, making their estimates conceptually inconsistent. Here we provide consistent estimates of ELUC and SLAND by integrating environmental effects on land carbon into a spatially explicit bookkeeping model. We find that state-of-the-art process-based models overestimate SLAND by 23% (min: 8%, max: 33%) in 2012–2021, as they include hypothetical sinks that in reality are lost through historical ecosystem degradation. Additionally, ELUC increases by 14% (8%, 23%) in 2012–2021 when considering environmental effects. Altogether, we find a weaker net land sink, which makes reaching carbon neutrality even more ambitious. These results highlight that a consistent estimation of terrestrial carbon fluxes is essential to assess the progress of net-zero emission commitments and the remaining carbon budget.
... For instance, notable disparities exist in estimating anthropogenic land-use carbon fluxes between the model-based Global Carbon Budget (GCB) and the inventories submitted by countries to the United Nations Framework Convention on Climate Change (UNFCCC). The former includes only direct anthropogenic effects, while the inventories reported by countries generally include indirect removals on that land, such as the fertilization effect caused by increasing atmospheric CO 2 concentrations , Gidden et al., 2023. Similarly, the anthropogenic ocean carbon sink operates independently of human management, primarily in response to increased atmospheric CO 2 . ...
... This understanding assists parties in formulating mitigation targets consistent with the temperature goals of the Paris Agreement. Similar concerns have been raised for terrestrial ecosystems, highlighting the need for improved monitoring of natural and anthropogenic carbon fluxes [Gidden et al., 2023, Nabuurs et al., 2023. ...
The national climate action plans to cut greenhouse gas emissions, referred to as Nationally Determined Contributions (NDCs), currently include anthropogenic land-based carbon fluxes but typically exclude open ocean carbon sinks within Exclusive Economic Zones (EEZs). Here, we utilise a high-resolution global ocean biogeochemical model alongside available observations to illustrate why including EEZ carbon sinks in NDCs would be both conceptually and practically highly problematic.
To demonstrate this, we focus on the case of the French EEZ, where we simulate an anthropogenic carbon sink of 0.21 GtCO2·yr–1 over the past decade, representing nearly 50% of France’s territorial greenhouse gas emissions over the same period. However, it should be noted that this anthropogenic carbon uptake results from the physical and biogeochemical properties of water masses, rather than from human management practices. Additionally, the EEZ oceanic carbon sink is already considered in estimates of remaining carbon budgets to meet the goals of the Paris Agreement. Therefore, integrating these fluxes into NDCs would lead to inconsistency between national objectives and global climate goals.
We argue that to identify the additionality of management measures aimed at enhancing the anthropogenic carbon sink in EEZ waters, robust assessments of the baseline carbon sink and how it would have evolved without intervention will be needed. As we show, this is complicated by the spatially and temporally dynamic nature of ocean carbon fluxes. More fundamentally, there is no colocalization between air–sea fluxes and the subsequent sequestration of carbon in the ocean due to circulation and mixing. Consequently, the measurement, reporting, and verification requirements for national stocktakes would be highly challenging. Moreover, as fluxes predominantly occur in the high latitude oceans and sequestration in the subtropics, the national allocation of credits would involve contentious issues of equity and justice.
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The 6th Assessment Report from the Intergovernmental Panel on Climate Change lacked sufficient land-sector scenario information to estimate total carbon dioxide removal deployment. Here, using a dataset of land-based carbon dioxide removal based on the scenarios assessed by the Intergovernmental Panel on Climate Change, we show that removals via afforestation and reforestation play a critical near-term role in mitigation, accounting for around 10% (median) of the net greenhouse gas emission reductions between 2020 and 2030 in scenarios that limit warming to 1.5 °C with limited overshoot. Novel carbon dioxide removal technologies such as direct air carbon capture and storage scale to multi-gigatonne levels by 2050 and beyond to balance residual emissions and draw down warming. We show that reducing fossil fuel and deforestation emissions (gross emissions) accounts for over 80% of net greenhouse gas reductions until global net zero carbon dioxide (CO2) independent of climate objective stringency. We explore the regional distributions of gross emissions and total carbon dioxide removal in cost-effective mitigation pathways and highlight the importance of incorporating fairness and broader sustainability considerations in future assessments of mitigation pathways with carbon dioxide removal.
... Here we analyse global net-zero CO 2 but many countries also include non-CO 2 emissions but also additional carbon ows from managed forests in their pledge to net-zero. In particualr, signi cant discrepancies between country level land sink accounting and accounting in IAMs currently exist due to inconsistencies in the de nition of anthropogenic ows from forests 33 . Finally, this analysis assumes a globally uniform carbon price, perfect foresight and full international cooperation to reach the speci ed net-zero targets. ...
Net-zero commitments have become the central focal point for countries to communicate long-term climate targets. However, to this point it is not clear to what extent conventional emissions reductions and carbon dioxide removal (CDR) will contribute to net-zero. An integrated market for emissions and removals with a uniform carbon price delivers the economically efficient contribution of CDR to net-zero, yet it might not fully internalise sustainability risks of CDR and hence could lead to its overuse. In this study, we explore the implications of separating targets for emission reductions and CDR for global net-zero emissions pathways with the Integrated Assessment Model REMIND. Even though it entails a deviation from the solution of the integrated market, we find that efficiency losses are moderate. Limiting CDR lowers the financial burden for public finance, limits reliance on geologic CO 2 storage and leads to lower cumulative emissions, yet this increase in ambition comes at higher total mitigation costs.
... A portion of inventory-based removal estimates therefore falls outside this report's definition of CDR, as the removals are not directly human caused and, crucially, depend on the future trajectory of global emissions and environmental change. 336 These indirect anthropogenic effects have been excluded from the proposed CDR levels for 2030 and 2050. To do so, the same conceptual approach as in Grassi et al., 2021, and the Global Carbon Budget has been followed, 417,418 as described in the Chapter 9 Technical Appendix. ...
The State of CDR reports are intended to regularly inform researchers, policymakers and practitioners on the state of progress, by systematically collecting and analysing the vast amount of data and developments in many parts of the world.
The second edition continues the assessment of CDR development, expanding geographical coverage and including new topics such as voluntary markets and monitoring, reporting and verification.
Starting with Edition 2, authors of the report have compiled data on a number of Key Indicators of the State of CDR. These indicators showcase the current state of play, direction of travel, and benchmarks for future CDR needs consistent with sustainably limiting temperature increase in line with the Paris Agreement. The data behind these indicators will be freely available via the newly developed State of CDR data portal.
The State of Carbon Dioxide Removal Edition 2 identified a subset of scenarios that can be considered “more sustainable”. Across this group of scenarios, the central range of CDR deployment is 7 to 9 GtCO₂ per year in 2050.
Around 2 GtCO₂ per year of CDR is taking place already. Almost all of this comes from conventional CDR methods. Novel CDR methods contribute 1.3 million tons (0.0013 Gt) of CO₂ removal per year. That is less than 0.1% of total CDR, but novel methods are growing more rapidly than conventional methods.
