Calculations were conducted using the Tier 2 method from the 2006 IPCC Guidelines for National Greenhouse Gas Inventories (IPCC, 2006), considering CO₂ emissions generated solely from limestone calcination. The calculation formula is as follows: 3Eprocess,i=Plime,i×EFlime,i where, Eprocess,i represents the industrial process CO₂ emissions from the lime industry in country i; Plime,i denotes the annual lime production of country i; EF_lime,i is the CO₂ emission factor for lime production in country i.

Carbon emission factors (CEFs) were calculated following the Tier 2 approach for lime production in the 2006 IPCC Guidelines for National Greenhouse Gas Inventories (IPCC, 2006). Under this approach, process CO₂ emissions are derived from the stoichiometric relationship between CO₂ and carbonate-derived CaO or CaO⋅MgO in lime products. In this study, sector-specific CaO contents were compiled for lime used in major end-use sectors, including metallurgy, construction, and the chemical industry. Because lime quality and CaO content differ among end-use sectors, these sectoral categories were used as practical proxies for product composition. Sector-specific emission factors were first derived by multiplying the CaO or CaO⋅MgO content of lime used in each sector by the corresponding IPCC stoichiometric ratio. Country-specific average CEFs were then calculated as weighted averages of sector-specific emission factors according to the lime-use shares of each sector. This approach is consistent with the IPCC Tier 2 principle of deriving emission factors from lime composition, while allowing national differences in lime-use structure and product quality to be reflected. Detailed CaO contents, sectoral lime-use shares, assumptions, and literature sources are provided in Supplement Table SI-3 Data 1.

The system boundary was established using material flow analysis (MFA; Fig. 1), based on the lime-carbonation framework of Liu et al. (2018). It includes ten lime-based materials classified by lifecycle stage. Lime kiln dust (LKD) is treated as a direct by-product of lime production. The remaining nine materials are grouped into three downstream sectors: metallurgy, including steel slag (SS), blast furnace slag (BFS), and red mud (RM); chemicals, including precipitated calcium carbonate (PCC), carbide slag (CS), carbonation sugar (SUG), and paper mill lime mud (LM); and construction, including lime-stabilized soil (LSS) and lime mortar (MOR). Most material flows follow Liu et al. (2018), while BFS is newly included to improve the accounting boundary.

To avoid double counting with existing cement-carbonation datasets, the system boundary for metallurgical slags (SS and BFS) is defined by the origin of CaO rather than by the subsequent use of the slag. Only CaO derived from lime fluxes and represented in the lime production activity data is attributed to the lime carbonation sink. CaO originating from iron ore, gangue minerals, limestone, dolomite, or other non-lime inputs is excluded. Although some SS and BFS are later used in cement or clinker production, existing cement-carbonation inventories do not account for the carbonation of lime-derived CaO in metallurgical slags, particularly BFS. Therefore, including this lime-derived CaO does not overlap with existing cement-carbonation estimates.

Based on the published 1930–2020 lime carbon uptake dataset established by Bing et al. (2023), we recalibrated China's lime production data for 1930–1995, expanded the lime-related basic activity data to nine additional countries, including the United Kingdom, France, Germany, Italy, Japan, Australia, Brazil, Russia, and Canada, and updated the dataset to 2024.

For the lime-related basic activity data, USGS statistics were used as the primary data backbone where available, followed by national statistical yearbooks, industry association reports, regression-based estimates, conversion-coefficient estimates, and linear interpolation for short data gaps. Where multiple sources overlapped, we systematically compared statistical units, product definitions, accounting boundaries, and year-to-year changes to identify missing observations, source inconsistencies, and implausible data changes. We acknowledge that combining activity data from different sources increases the complexity of uncertainty, especially because statistical boundaries, reporting practices, and data quality may differ among sources and periods.

We identified 17 groups of factors affecting the estimation of process CO₂ emissions from lime production and carbonation uptake by lime-based materials, comprising 1868 input parameters with specified statistical distributions (Supplement Table SI-3, Data 1–17). Given the substantial uncertainty in these parameters, we applied the Monte Carlo method recommended by the 2006 IPCC Guidelines for National Greenhouse Gas Inventories. The statistical distributions of these variables were incorporated into the accounting model, and 10 000 Monte Carlo iterations were performed. Final estimates are reported as the median of the simulated distributions. The 2.5th and 97.5th percentiles define the lower and upper bounds, respectively, of the 95 % confidence interval (CI).

Uncertainty introduced by historical activity-data reconstruction and source harmonization was explicitly included in the Monte Carlo framework. Source-specific uncertainty ranges were assigned according to data reliability, record completeness, and reconstruction method. Directly reported statistics were assigned narrower ranges than reconstructed data. For regression-derived estimates, uncertainty was characterized using model fitting errors, calibration diagnostics, and goodness-of-fit information reported in Supplement Table SI-2 Data1. For conversion-derived and interpolated estimates, uncertainty ranges were assigned based on the corresponding activity-data and conversion-parameter uncertainties in Supplement Table SI-3. Rather than introducing an additional standalone “source-integration” parameter that would be difficult to constrain independently, we incorporated discrepancies among overlapping datasets, uncertainty associated with limestone-to-lime conversion, differences in statistical boundaries, and regression-based reconstruction uncertainty into the uncertainty ranges assigned to historical activity data. This treatment differentiates complete statistical records from reconstructed, converted, and interpolated values, and allows uncertainty levels to vary among countries and time periods according to source quality.

During each Monte Carlo iteration, these activity-data uncertainty terms were jointly sampled with emission factors, CaO contents, material-use shares, carbonation ratios, and other model parameters, and then propagated through the process-emission and carbonation-uptake accounting models to generate distributions of annual and cumulative emissions, uptake, and net emissions.

No explicit cross-country or cross-parameter correlation matrix was imposed in the baseline Monte Carlo implementation; therefore, sampled variables were treated as independent within their assigned distributions, except for deterministic accounting relationships applied after sampling. We acknowledge that positive correlations may exist among some parameters, for example among countries using similar statistical sources or among material parameters governed by common industrial technologies. Accordingly, the reported 95 % UIs should be interpreted as conditional on this independence assumption and may be narrower than intervals obtained under a fully correlated error structure. This limitation is now explicitly stated, and the reported aggregate uncertainty is not interpreted as evidence that subdivision alone improves data quality.

Compared with our previous research, this study incorporates refinements in four key aspects. (1) Regional refinement to enhance the dataset's representativeness. We separated the United Kingdom, France, Germany, Italy, Russia, Japan, Brazil, Australia, and Canada from the rest-of-the-world (ROW) category used in previous studies. This allowed us to establish, for the first time, a lime carbonation sink dataset covering 11 countries, which collectively accounted for an average of 78.9 % of global lime production (see Supplement Table SI-2, Data 1). (2) More detailed, country-specific parameterization. The parameters were updated for lime CO₂ uptake in the newly added countries. The parameters include the proportion of lime usage across various sectors, the CaO content of different lime materials, and the production and utilization rates of lime materials. These improve the accuracy of the accounting compared to the CO₂ uptake parameters used for the ROW region in our previous work (see Supplement Table SI-3, Data 1–15). (3) Inclusion of BFS in the accounting system. BFS was incorporated to address the previous omission of its carbonation contribution from metallurgical slags (see Supplement Table SI-2, Data 3). (4) Data-constrained temporal and regional parameterization of SS and BFS. Complete annual and country-specific data were unavailable for the SS and BFS generation coefficients and for the fractions directed to road-base applications or open-air stockpiles. We therefore used four non-overlapping accounting periods: 1930–1949, 1950–1972, 1973–1999, and 2000–2024. These periods represent broad stages in iron- and steelmaking technology and serve only as common accounting windows; they do not imply synchronous technological transitions across countries. Crude steel and pig-iron production were obtained from statistical data and were not determined by these assumptions. Country-specific slag generation coefficients and pathway-allocation fractions were used where available. Otherwise, separate values were assigned to developed and developing regions based on differences in industrialization, technology-adoption timing, and slag-management practices. The parameter values, assumptions, and supporting references are provided in Supplement Table SI-3, Data 8–9.

Figure 3 presents global process CO₂ emissions from lime production. Between 1930 and 2024, annual process emissions from the global lime industry increased substantially, from 18.5 Mt CO₂ yr⁻¹ (95 % CI: 18.0–18.9 Mt CO₂ yr⁻¹) in 1930 to 299.2 Mt CO₂ yr⁻¹ (95 % CI: 288.4–310.2 Mt CO₂ yr⁻¹) in 2024. Cumulative emissions over this period reached 11.3 Gt CO₂ (95 % CI: 10.7–11.9 Gt CO₂; Fig. 3a). This increase was driven by continued global urbanization and industrialization and the resulting demand for lime in construction, metallurgy, the chemical industry, and environmental applications (Wu et al., 2024). Global lime production increased by approximately 394.6 Mt, from 25.4 Mt in 1930 to 420.0 Mt in 2024, equivalent to a 16.5-fold increase (United States Geological Survey, 2026a; Supplement Table SI-2, Data 1).

Global lime process emissions broadly followed the trend in lime production because lime production is the principal activity variable in the emission-accounting model. However, emissions increased more slowly than production because the production-weighted emission factor decreased over time. In the model, this emission factor varies with the allocation of lime among downstream sectors and the corresponding CaO contents of lime products. Therefore, the divergence between the growth rates of production and process emissions reflects changes in the modeled composition and sectoral use of lime rather than improvements in production technology.

Construction was the largest cumulative source of lime-related process emissions during 1930–2024 (Fig. 3b). Annual construction-sector emissions increased from 3.6 Mt CO₂ yr⁻¹ (95 % CI: 2.4–5.2 Mt CO₂ yr⁻¹) in 1930 to 130.9 Mt CO₂ yr⁻¹ (95 % CI: 97.7–164.2 Mt CO₂ yr⁻¹) in 2024. Cumulative construction-sector emissions reached 3.9 Gt CO₂ (95 % CI: 2.9–4.9 Gt CO₂), accounting for 34.5 % of total cumulative process emissions. Metallurgy was the second-largest contributor, with annual emissions increasing from 6.6 Mt CO₂ yr⁻¹ (95 % CI: 5.5–7.7 Mt CO₂ yr⁻¹) in 1930 to 96.2 Mt CO₂ yr⁻¹ (95 % CI: 65.3–129.5 Mt CO₂ yr⁻¹) in 2024. Cumulative metallurgical emissions reached 3.8 Gt CO₂ (95 % CI: 2.9–4.7 Gt CO₂), representing 33.5 % of the global total. Chemical-sector emissions increased from 3.6 Mt CO₂ yr⁻¹ (95 % CI: 2.6–4.7 Mt CO₂ yr⁻¹) in 1930 to 45.4 Mt CO₂ yr⁻¹ (95 % CI: 34.2–58.0 Mt CO₂ yr⁻¹) in 2024. Cumulative emissions from this sector reached 2.0 Gt CO₂ (95 % CI: 1.5–2.4 Gt CO₂), accounting for 17.2 % of total cumulative emissions. Cumulative emissions from other sectors amounted to 1.7 Gt CO₂ (95 % CI: 1.3–2.7 Gt CO₂), representing the remaining 14.7 %.

Process-emission trajectories differed substantially among countries between 1930 and 2024. Developed countries peaked at different times, ranging from 1964 in Germany and the 1970s–1980s in France, Japan, and the United Kingdom to 1999–2011 in Canada, the United States, Italy, and Australia, after which emissions generally declined. In the United States, emissions rebounded during the early 21st century, peaked in 2006, and subsequently decreased. In contrast, China and Brazil exhibited pronounced long-term growth, while Russia experienced a sharp decline following the dissolution of the Soviet Union and a partial rebound after 2000.

China was the largest contributor to both global lime production and associated process emissions. Its annual emissions increased from 0.4 Mt CO₂ yr⁻¹ (95 % CI: 0.2–0.7 Mt CO₂ yr⁻¹) in 1930 to 226.7 Mt CO₂ yr⁻¹ (95 % CI: 216.1–237.6 Mt CO₂ yr⁻¹) in 2024, corresponding to a compound annual growth rate of 6.9 %. China's cumulative emissions reached 5.5 Gt CO₂ (95 % CI: 4.9–6.0 Gt CO₂), accounting for 48.3 % of the global total (Fig. 3b). The United States was the largest cumulative emitter among developed countries, with emissions of 953.9 Mt CO₂ (95 % CI: 910.5–997.4 Mt CO₂), representing 8.4 % of the global total. Russia and Germany contributed 611.1 and 605.4 Mt CO₂, respectively, each accounting for 5.4 % of global cumulative emissions. Japan (370.2 Mt CO₂), Brazil (258.2 Mt CO₂), Italy (220.9 Mt CO₂), and France (189.2 Mt CO₂) contributed 3.3 %, 2.3 %, 2.0 %, and 1.7 %, respectively. Contributions from the United Kingdom (129.4 Mt CO₂), Canada (115.2 Mt CO₂), and Australia (76.4 Mt CO₂) were smaller, accounting for 1.1 %, 1.0 %, and 0.7 %, respectively. Cumulative emissions from the rest of the world amounted to 2.3 Gt CO₂ (95 % CI: 2.2–2.4 Gt CO₂), representing 20.5 % of the global total (Fig. 3b).

The global lime carbonation sink increased from 4.1 Mt CO₂ yr⁻¹ (95 % CI: 3.5–4.8 Mt CO₂ yr⁻¹) in 1930 to 136.1 Mt CO₂ yr⁻¹ (95 % CI: 107.9–171.5 Mt CO₂ yr⁻¹) in 2024, corresponding to a compound annual growth rate of 3.8 %. The cumulative carbonation sink over 1930–2024 reached 4.8 Gt CO₂ (95 % CI: 3.9–5.8 Gt CO₂; Fig. 4a). Net emissions, calculated as process emissions minus carbonation uptake, increased from 14.3 Mt CO₂ yr⁻¹ in 1930 to 163.2 Mt CO₂ yr⁻¹ in 2024, resulting in cumulative net emissions of 6.5 Gt CO₂. Overall, lime-based materials reabsorbed approximately 42.2 % of cumulative process emissions (Fig. 4b), 3.4 percentage points higher than the 38.8 % estimate reported by Bing et al. (2023).

The 11 countries represented in this study contributed a cumulative carbonation sink of 3.7 Gt CO₂, accounting for 77.4 % of the global total. Refinement of the activity data for nine additional countries reduced the share assigned to the aggregated rest-of-world region from 34.4 % in Bing et al. (2023) to 22.6 % in the present study (Fig. 4a). The accounting boundary was further refined by incorporating BFS and applying period-specific parameters to SS and BFS to reflect changes in iron- and steel-production practices.

The increasing carbon-offset level partly reflects the time lag between lime-material production and subsequent carbonation (Niu et al., 2025). Materials such as MOR, LSS, SS, and BFS do not attain their ultimate carbonation extent immediately and can continue to absorb CO₂ in subsequent years. Consequently, the annual carbonation sink includes both uptake by materials produced in the current year and continued uptake by materials inherited from previous years. In 2024, the lime carbonation sink was equivalent to approximately 1.5 %–2.0 % of the global terrestrial carbon sink in 2023 (Friedlingstein et al., 2025). Quantifying this anthropogenic carbonation sink provides data relevant to IPCC assessments and improves the completeness of the Global Carbon Budget.

Among the lime-derived materials considered, SS exhibited the largest cumulative carbon uptake, reaching 1.3 Gt CO₂ and accounting for 27.1 % of the global cumulative carbonation sink (Fig. 4d). BFS and MOR followed, each contributing approximately 0.9 Gt CO₂ and accounting for 19.6 % and 19.1 %, respectively. LKD and LSS each contributed approximately 0.5 Gt CO₂, representing 9.8 % and 9.6 % of the global total, respectively. Together, these five materials contributed 4.1 Gt CO₂, accounting for 85.2 % of the cumulative carbonation sink. PCC, CS, and SUG contributed 0.3 Gt CO₂ (6.5 %), 0.2 Gt CO₂ (4.5 %), and 0.2 Gt CO₂ (3.8 %), respectively. Contributions from RM and LM were negligible, each accounting for less than 0.1 % of the global total.

China's annual lime carbonation sink increased markedly from 0.1 Mt CO₂ yr⁻¹ (95 % CI: 0.04–0.2 Mt CO₂ yr⁻¹) in 1930 to 92.0 Mt CO₂ yr⁻¹ (95 % CI: 65.8–125.6 Mt CO₂ yr⁻¹) in 2024. Its cumulative carbon uptake reached 1.9 Gt CO₂ (95 % CI: 1.5–2.5 Gt CO₂), accounting for 40.7 % of the global total (Fig. 4c). This dominant contribution was primarily associated with sustained lime demand from China's large-scale construction and iron and steel industries.

Among developed countries, the United States made the largest contribution. Its annual carbonation sink increased from 1.2 Mt CO₂ yr⁻¹ (95 % CI: 0.8–1.7 Mt CO₂ yr⁻¹) in 1930 to 5.9 Mt CO₂ yr⁻¹ (95 % CI: 4.4–7.7 Mt CO₂ yr⁻¹) in 2024. Its cumulative uptake reached 629.6 Mt CO₂ (95 % CI: 456.2–843.5 Mt CO₂), equivalent to 13.2 % of the global total.

Japan, Russia, Germany, Brazil, and Italy contributed cumulative carbonation sinks of 292.1, 271.7, 186.4, 113.6, and 67.4 Mt CO₂, respectively, corresponding to 6.1 %, 5.7 %, 3.9 %, 2.4 %, and 1.4 % of the global total (Fig. 4c). France and Canada contributed 58.3 Mt CO₂ (1.2 %) and 57.4 Mt CO₂ (1.2 %), respectively. By contrast, the contributions from the United Kingdom and Australia were each below 1 %, amounting to 40.5 Mt CO₂ (0.8 %) and 33.9 Mt CO₂ (0.7 %), respectively. The rest of the world collectively contributed 1.1 Gt CO₂, representing 22.6 % of the global cumulative lime carbonation sink.

Industry-based analysis indicates that carbon uptake by lime-based materials generally increased across the major industrial sectors between 1930 and 2024. However, substantial inter-sectoral differences were observed in the magnitude of the carbonation sink, dominant material types, and temporal trajectories (Fig. 5). The metallurgical sector was the largest contributor to the global lime carbonation sink, followed by construction and the chemical industry. LKD, which is generated directly during lime production, was accounted for separately rather than allocated to a downstream industrial sector.

Carbon uptake in the metallurgical sector increased from 1.4 Mt CO₂ yr⁻¹ in 1930 (95 % CI: 1.0–1.9 Mt CO₂ yr⁻¹) to 57.6 Mt CO₂ yr⁻¹ in 2024 (95 % CI: 47.9–68.9 Mt CO₂ yr⁻¹). The cumulative carbonation sink over the study period reached 2.2 Gt CO₂ (95 % CI: 1.9–2.6 Gt CO₂), accounting for 46.6 % of the global lime carbonation sink (Fig. 5). Lime-derived materials generated during metallurgical processes, particularly SS and BFS, provide a substantial material basis for mineral carbonation. With the sustained growth of global iron and steel production over the past century, the carbonation potential of metallurgical slags has increased considerably. By incorporating period-specific historical parameters, this study accounts for temporal and cross-country variations in the generation and utilization of metallurgical by-products, thereby improving the representation of the sector's historical carbonation sink. Previous studies have identified pronounced differences among countries in their management of steel slag and blast-furnace residues (Guo et al., 2018; Horii et al., 2015; O'Connor et al., 2021; United States Geological Survey, 2026b). Developed countries generally established mature resource-utilization systems earlier, whereas developing countries have gradually shifted from long-term stockpiling toward more comprehensive utilization. Technological development and policy intervention have therefore played important roles in shaping the long-term evolution of the metallurgical carbonation sink.

The construction sector constituted the second-largest global lime carbonation sink. Annual carbon uptake increased from 0.8 Mt CO₂ yr⁻¹ in 1930 (95 % CI: 0.5–1.2 Mt CO₂ yr⁻¹) to 48.4 Mt CO₂ yr⁻¹ in 2024 (95 % CI: 25.4–80.2 Mt CO₂ yr⁻¹). The cumulative carbonation sink reached 1.4 Gt CO₂ (95 % CI: 0.9–2.0 Gt CO₂), accounting for 28.8 % of the global total (Fig. 5). This contribution primarily resulted from the widespread use of MOR and LSS, together with their continued carbonation during service. Since the second half of the twentieth century, accelerating urbanization and infrastructure investment have substantially expanded the use of lime-based construction materials, driving a corresponding increase in carbon uptake (Manzoor and Yousuf, 2020).

The chemical industry made a smaller but relatively stable contribution. Its annual carbon uptake increased from 1.2 Mt CO₂ yr⁻¹ in 1930 (95 % CI: 0.9–1.7 Mt CO₂ yr⁻¹) to 17.5 Mt CO₂ yr⁻¹ in 2024 (95 % CI: 12.1–24.2 Mt CO₂ yr⁻¹). Cumulative uptake reached 0.7 Gt CO₂ (95 % CI: 0.5–0.9 Gt CO₂), accounting for 14.8 % of the global lime carbonation sink. Carbon uptake in this sector occurred mainly through industrial carbonation pathways involving CS, PCC, SUG, RM, and LM.

LKD generated directly during lime production contributed the remaining 0.5 Gt CO₂, equivalent to 9.8 % of the global cumulative carbonation sink. Because LKD is a production-stage by-product rather than a material associated with a specific downstream industry, it was reported separately from the metallurgical, construction, and chemical sectors.

From spatial perspective, industry-dominated patterns of lime carbon sequestration exhibit pronounced heterogeneity across countries and regions (Fig. 5). Developed countries (e.g., the United States, Japan, and major European nations), characterized by long histories of iron and steel production and well-established circular economy systems, have long been dominated by metallurgical-sector lime carbonation sink, with cumulative effects that are particularly evident on historical timescales (Spring and Cirella, 2022). In contrast, developing countries undergoing rapid industrialization and urbanization (e.g., China, Brazil, and parts of the rest-of-world regions) have experienced surging demand for lime-based materials in the construction sector, which has gradually become the primary regional source of lime-related carbon sequestration. In China, carbon uptake by lime materials in the construction sector accelerated markedly in the early twenty-first century, closely coinciding with the timing of rapid urbanization (Cai et al., 2020).

Overall, the differentiated global distribution of lime carbonation sink across industries and regions fundamentally reflects the combined influences of industrial structure, economic development pathways, resource utilization efficiency, and policy frameworks. Clarifying the relative contributions of different sectors and their underlying evolutionary mechanisms is of critical scientific importance for designing sector-specific carbon management strategies for enhancing the carbon sequestration potential of lime-based materials.

Both current-year and historical CO₂ uptake by global lime-based materials exhibited long-term increasing trends between 1930 and 2024, although interannual fluctuations occurred (Fig. 6a). “Current-year uptake” refers to CO₂ absorbed by materials produced in the corresponding year, whereas “historical uptake” represents continued CO₂ uptake in subsequent years by material cohorts produced in earlier years.

Mechanistically, the time-lag effect reflects the accumulation of legacy material stocks and the progressive carbonation of reactive Ca-bearing phases. Within the accounting framework, annual uptake comprises uptake attributed to materials produced in the current year and continued uptake by incompletely carbonated materials inherited from previous years. For PCC and SUG, carbonation is integral to the production process, and uptake is therefore assigned to the production year. LKD, LM, RM, and CS are represented using literature-derived, one-year, pile-average CaO conversion parameters; this treatment does not assume complete conversion of CaO. By contrast, LSS and MOR follow the slab model, whereas SS and BFS follow the spherical-particle model and continue to carbonate over multiple years (Sect. 2.3.1–2.3.2).

As carbonation proceeds, the formation of a CaCO₃-rich product layer can impede inward CO₂ transport, shifting the reaction from relatively rapid initial uptake toward a slower, diffusion-controlled stage (Xi et al., 2016; Niu et al., 2025). For metallurgical slags, carbonation is further controlled by particle size, reactive Ca-bearing mineral phases, humidity, temperature, and stockpiling or reuse conditions (Zhao et al., 2025). Each year introduces a new cohort of lime-based materials, while incompletely carbonated cohorts from previous years continue to absorb CO₂. Over most of the study period, additions to this historical reactive stock exceeded its depletion, explaining the sustained increase in historical uptake. This mechanism also explains why carbonation sinks can decline more slowly than process emissions in countries that have already reached their emission peaks.

Current-year uptake increased from 4.1 Mt CO₂ yr⁻¹ in 1930 to 72.6 Mt CO₂ yr⁻¹ in 2024, corresponding to a compound annual growth rate of 3.1 %. Cumulative current-year uptake reached 2.7 Gt CO₂, accounting for 56.2 % of the total cumulative uptake. Historical uptake increased from 0.7 Mt CO₂ yr⁻¹ in 1931 to 63.5 Mt CO₂ yr⁻¹ in 2024, with a compound annual growth rate of 5.0 %. Cumulative historical uptake reached 2.1 Gt CO₂, representing the remaining 43.8 % (Fig. 6a).

MOR was the largest contributor to current-year uptake, accumulating 703.7 Mt CO₂ and accounting for 26.2 % of cumulative current-year uptake, followed by LKD with 465.1 Mt CO₂ (17.3 %). In contrast, SS dominated historical uptake, accumulating 949.3 Mt CO₂ and accounting for 45.3 % of cumulative historical uptake, followed by BFS with 570.3 Mt CO₂ (27.2 %) (Supplement Table SI-1, Data 7–8). These results highlight the distinct temporal patterns of carbonation among lime-based materials (Fig. 6b). Historical uptake from SS and BFS exceeded their current-year uptake because these materials do not attain their material-specific maximum carbonation extent in the year they are generated, and substantial uptake therefore occurs gradually in subsequent years (Liu et al., 2018). Their natural carbonation rates are also influenced by environmental conditions, particularly temperature and humidity (Zhao et al., 2025). Future research could evaluate accelerated carbonation and CO₂ mineralization technologies within carbon capture, utilization, and storage frameworks to enhance controlled and verifiable CO₂ sequestration (Yang et al., 2024).

Based on lime process emissions and carbonation sink data, this study reveals significant regional heterogeneity in the global lime carbon balance: developed countries, represented by Europe, North America, Japan, and Australia, have generally achieved carbon peaking, whereas developing and transition economies show continued long-term growth or a post-2000 rebound in process emissions.

In developed countries, CO₂ emissions peaked between the 1960s and early 2010s. Germany (1964, 12.7 Mt CO₂), France (1974, 3.7 Mt CO₂), Japan (1973, 8.6 Mt CO₂), and the UK (1980, 2.9 Mt CO₂) peaked earlier, followed by Canada (1999, 1.9 Mt CO₂), the USA (2006, 15.6 Mt CO₂), Italy (2007, 4.4 Mt CO₂), and Australia (2011, 1.8 Mt CO₂). The carbon offset levels in their respective peak years were 21.6 % for Germany, 25.6 % for France, 57.0 % for Japan, 24.1 % for the UK, 50.6 % for Canada, 48.1 % for the USA, 30.0 % for Italy, and 33.2 % for Australia. Following the peak year, lime process emissions in these countries generally declined, with compound annual decline rates from the peak year to 2024 ranging from 0.8 % to 5.2 %. Carbonation sinks also tended to decrease with reductions in lime production, but the decline in carbon uptake was often less pronounced than that of process emissions because of the time-lag effect in the carbonation of certain lime-based materials. Consequently, carbon offset levels generally increased after the emission peak, helping to narrow net emissions from the lime production sector. This characteristic is closely related to mature secondary resource recycling systems and stringent climate policy constraints in developed countries (Dolphin et al., 2023), particularly the high recovery and comprehensive utilization of metallurgical by-products such as BFS and SS (Yi et al., 2012). In construction and civil engineering, substituting primary lime materials with these alkaline solid wastes can reduce process-related carbon emissions during production while maintaining carbonation sink potential through continuous mineral carbonation during their secondary-use phase (Pan et al., 2017).

Conversely, developing and transition economies exhibit continued growth pressure or emission rebound. China's lime process emissions increased from 0.4 Mt CO₂ yr⁻¹ in 1930 to 226.7 Mt CO₂ yr⁻¹ in 2024 (CAGR: 6.9 %), with a post-2002 annual growth rate of 4.0 %, driven by urbanization and infrastructure demand. China's carbonation sink reached 92.0 Mt CO₂ yr⁻¹ in 2024, corresponding to an offset level of 40.6 %. Nevertheless, abatement pressure remains substantial because of the country's large absolute process emissions. Brazil's lime process emissions also increased over the long term, reaching 5.9 Mt CO₂ yr⁻¹ in 2024, with an offset level of 44.3 %, although emissions declined slightly from their 2013 peak of 6.1 Mt CO₂. Russia peaked during the Soviet era in 1988 at 12.2 Mt CO₂, but its emissions rebounded after 2000 (CAGR: 1.3 %), reaching 8.0 Mt CO₂ yr⁻¹ in 2024, with an offset level of 52.8 %. Lime process emission growth in these regions is mainly associated with infrastructure demand during industrialization and urbanization (Chen et al., 2022), while Russia's rebound is related to economic recovery and the restoration of industrial capacity after 2000.

In summary, regional differences in process emissions and carbonation sink trajectories reflect distinct development stages. Developed countries have achieved inflection points through industrial transformation, resource recycling, and policy intervention, whereas developing countries face the dual challenge of supporting economic growth while reducing process emissions. The divergence in carbon offset levels further reflects cross-country differences in the recycling efficiency and secondary utilization of lime-based materials.

The uncertainty analysis in this study was designed to reflect data-source reliability, reconstruction intensity, and country-level heterogeneity. Building on the accounting model established by Xi et al. (2016) and the framework of Bing et al. (2023), probability distributions were assigned to process-emission factors, CaO contents, material-use shares, carbonation ratios, activity data, and reconstruction parameters. In addition, source-specific uncertainty ranges were assigned to directly reported statistics, regression-derived estimates, conversion-derived estimates, and interpolated values. To show country-level differences in uncertainty, Fig. 6 presents the 95 % uncertainty intervals for process emissions, carbonation sink, and net emissions across 11 countries. The corresponding uncertainty parameters are provided in Supplement Table SI-3 Data1–15.

The results indicate that cumulative global lime process emissions from 1930 to 2024 were 11.3 Gt CO₂ (95 % CI: 10.7–11.9 Gt CO₂), while the cumulative lime carbonation sink was 4.8 Gt CO₂ (95 % CI: 3.9–5.8 Gt CO₂). The relative half-width of the 95 % confidence interval was 5.1 % for cumulative process emissions and 19.5 % for cumulative carbonation sink, indicating that carbonation uptake is substantially more uncertain than process emissions. This larger uncertainty mainly arises from variability in CaO contents, carbonation rates, material-use allocation, utilization rates, time-lag parameters, and the additional uncertainty introduced during historical data-source harmonization.

Country-level uncertainty results further show that uncertainty is not uniform across regions or variables (Fig. 7). In 2024, the relative half-width of the 95 % uncertainty intervals for process emissions across the 11 countries ranged from 4.5 % to 4.8 %, reflecting the dominant role of reported statistical data in recent emission estimates. In contrast, carbonation-sink uncertainty was larger, with relative half-widths ranging from 19.2 % in Russia to 36.2 % in the United Kingdom, because uptake estimates depend on material allocation, carbonation kinetics, and utilization assumptions. When emissions and uptake are similar in magnitude, net-emission uncertainty can be further amplified. These results indicate that the uncertainty framework used in this study captures important differences between original and reconstructed data, among countries, and between emission and uptake processes.