BACKGROUND: Wood carbon fractions (CFs)-the proportion of dry woody biomass comprised of elemental carbon (C)-are a key component of forest C estimation protocols and studies. Traditionally, a wood CF of 50% has been assumed in forest C estimation protocols, but recent studies have specifically quantified differences in wood CFs across several different forest biomes and taxonomic divisions, negating the need for generic wood CF assumptions. The Intergovernmental Panel on Climate Change (IPCC), in its 2006 \"Guidelines for National Greenhouse Gas Inventories\", published its own multitiered system of protocols for estimating forest C stocks, which included wood CFs that (1) were based on the best available literature (at the time) and (2) represented a significant improvement over the generic 50% wood CF assumption. However, a considerable number of new studies on wood CFs have been published since 2006, providing more accurate, robust, and spatially- and taxonomically- specific wood CFs for use in forest C estimation.
METHODS: We argue that the IPCC\'s recommended wood CFs and those in many other forest C estimation models and protocols (1) differ substantially from, and are less robust than, wood CFs derived from recently published data-rich studies; and (2) may lead to nontrivial errors in forest C estimates, particularly for countries that rely heavily on Tier 1 forest C methods and protocols (e.g., countries of the Global South with large expanses of tropical forests). Based on previous studies on this topic, we propose an alternative set of refined wood CFs for use in multiscale forest C estimation, and propose a novel decision-making framework for integrating species- and location-specific wood CFs into forest C estimation models.
CONCLUSIONS: The refined wood CFs that we present in this commentary may be used by the IPCC to update its recommended wood CFs for use in forest C estimation. Additionally, we propose a novel decision-making framework for integrating data-driven wood CFs into a wider suite of multitiered forest C estimation protocols, models, and studies.

Grassland is one of the largest terrestrial biomes, providing critical ecosystem services such as food production, biodiversity conservation, and climate change mitigation. Global climate change and land-use intensification have been causing grassland degradation and desertification worldwide. As one of the primary medium for ecosystem energy flow and biogeochemical cycling, grassland carbon (C) cycling is the most fundamental process for maintaining ecosystem services. In this review, we first summarize recent advances in our understanding of the mechanisms underpinning spatial and temporal patterns of the grassland C cycle, discuss the importance of grasslands in regulating inter- and intra-annual variations in global C fluxes, and explore the previously unappreciated complexity in abiotic processes controlling the grassland C balance, including soil inorganic C accumulation, photochemical and thermal degradation, and wind erosion. We also discuss how climate and land-use changes could alter the grassland C balance by modifying the water budget, nutrient cycling and additional plant and soil processes. Further, we examine why and how increasing aridity and improper land use may induce significant losses in grassland C stocks. Finally, we identify several priorities for future grassland C research, including improving understanding of abiotic processes in the grassland C cycle, strengthening monitoring of grassland C dynamics by integrating ground inventory, flux monitoring, and modern remote sensing techniques, and selecting appropriate plant species combinations with suitable traits and strong resistance to climate fluctuations, which would help design sustainable grassland restoration strategies in a changing climate.

Companies are increasingly relying on emission reductions attributable to their adoption of renewable electricity to achieve net-zero emission targets. However, there is a risk of double counting of emission reductions threatening the credibility of corporate climate actions due to defective accounting rules of GHG emissions related to electricity consumption and the overlap between different market-based instruments, including carbon credit markets, renewable power purchase agreements, and renewable energy certificates. Using data of 63 major Chinese companies in seven sectors, we quantitatively assess the risks of double counting related to corporate sourcing of renewables and their consequent influences on the alignment of corporate emission trajectories with the 1.5 °C goal of the Paris Agreement. Results show that 7.1% of the electricity consumed by sample companies in 2021 was from renewable energy procurement and deployment, with which they reported 8.27 Mt of CO2e emission reductions compared to the scenario with no renewable electricity consumption. However, emission reductions that could be double counted are predicted to be 0.9-1.3 times as many as emission reductions that companies will report during 2021-2030. After adjustment of the reported emissions that might be underestimated due to double counting, the overall emission trajectories of sample companies are no longer aligned with the 1.5 °C goal. Our findings suggest that it is urgently needed to improve the corporate carbon accounting rules and increase the transparency of corporate carbon disclosures.

UNASSIGNED: Data on the carbon footprint of external beam radiotherapy (EBRT) are scarce. Reliable and exhaustive data, including a detailed carbon inventory, are needed to determine effective mitigation strategies.
UNASSIGNED: This study proposes a methodology for calculating the carbon footprint of EBRT and applies it to a single center. Mitigation strategies are derived from the carbon inventory, and their potential reductions are quantified whenever possible.
UNASSIGNED: The average emission per treatment and fraction delivered was 489 kg CO₂eq and 27 kg CO₂eq, respectively. Patient transportation (43 %) and the construction and maintenance of linear accelerators (LINACs) and scanners (17 %) represented the most significant components. Electricity, the only energy source used, accounted for only 2 % of emissions.Derived mitigation strategies include a data deletion policy (reducing emissions in 30 years by 12.5 %), geographical appropriateness (-12.2 %), transportation mode appropriateness (-9.3 %), hypofractionation (-5.9 %), decrease in manufacturers\' carbon footprint (-5.2 %), and an increase in machine durability (-3.5 %).
UNASSIGNED: Our findings indicate that a significant reduction in the carbon footprint of a radiotherapy unit can be achieved without compromising the quality of care.This study provides a methodology and a starting point for comparison and proposes and quantifies mitigation strategies, paving the way for others to follow.

Determining wood carbon (C) fractions (CFs)-or the concentration of elemental C in wood on a per unit mass basis-in harvested wood products (HWP) is vital for accurately accounting embodied C in the built environment. Most estimates of embodied C assume that all wood-based building material is comprised of 50 % C on a per mass basis: an erroneous assumption that emerges from the literature on tree- and forest-scale C estimation, which has been shown to lead to substantial errors in C accounting. Here, we use published wood CF data from live trees, alongside laboratory analyses of sawn lumber, to quantify generalizable wood CFs for HWPs. Wood CFs in lumber average 51.7 %, deviating significantly from a 50 % default wood CF, as well as from CFs in live wood globally (which average 47.6 % across all species, and 47.1 % in tree species not typically employed in construction). Additionally, the volatile CF in lumber-i.e., the quantity of C lost upon heating of wood samples, but often overlooked in C accounting-is lower than the volatile CF in live wood, but significantly >0 % suggesting that industrial lumber drying processes remove some, but not all, of volatile C-based compounds. Our results demonstrate that empirically-supported wood CFs for construction material can correct meaningful systematic biases when estimating C storage in the built environment.

BACKGROUND: As interest in the voluntary soil carbon market surges, carbon registries have been developing new soil carbon measurement, reporting, and verification (MRV) protocols. These protocols are inconsistent in their approaches to measuring soil organic carbon (SOC). Two areas of concern include the type of SOC stock accounting method (fixed-depth (FD) vs. equivalent soil mass (ESM)) and sampling depth requirement. Despite evidence that fixed-depth measurements can result in error because of changes in soil bulk density and that sampling to 30 cm neglects a significant portion of the soil profile\'s SOC stock, most MRV protocols do not specify which sampling method to use and only require sampling to 30 cm. Using data from UC Davis\'s Century Experiment (\"Century\") and UW Madison\'s Wisconsin Integrated Cropping Systems Trial (WICST), we quantify differences in SOC stock changes estimated by FD and ESM over 20 years, investigate how sampling at-depth (> 30 cm) affects SOC stock change estimates, and estimate how crediting outcomes taking an empirical sampling-only crediting approach differ when stocks are calculated using ESM or FD at different depths.
RESULTS: We find that FD and ESM estimates of stock change can differ by over 100 percent and that, as expected, much of this difference is associated with changes in bulk density in surface soils (e.g., r = 0.90 for Century maize treatments). This led to substantial differences in crediting outcomes between ESM and FD-based stocks, although many treatments did not receive credits due to declines in SOC stocks over time. While increased variability of soils at depth makes it challenging to accurately quantify stocks across the profile, sampling to 60 cm can capture changes in bulk density, potential SOC redistribution, and a larger proportion of the overall SOC stock.
CONCLUSIONS: ESM accounting and sampling to 60 cm (using multiple depth increments) should be considered best practice when quantifying change in SOC stocks in annual, row crop agroecosystems. For carbon markets, the cost of achieving an accurate estimate of SOC stocks that reflect management impacts on soils at-depth should be reflected in the price of carbon credits.

The proposal of the dual carbon goal and the blue economy in China has sparked a keen interest in carbon emissions reduction from sewage treatment. Carbon accounting in urban sewage plants serves as the foundation for carbon emission reduction in sewage treatment. This paper re-evaluated carbon accounting in the operational processes for urban sewage treatment plants to develop a novel carbon emission evaluation model for anaerobic-anoxic-oxic treatment plants. The results show that the carbon emissions generated by non-carbon dioxide gases far exceed the carbon emissions from carbon dioxide alone. Moreover, the recycling of sewage leads to carbon emissions reduction that offsets the carbon emissions generated during the operation of the sewage plant. Also, the carbon emissions generated by sewage treatment plants are lower than those generated by untreated sewage. The findings and insights provided in this paper provide valuable references for carbon accounting and the implementation of low-carbon practices in urban sewage treatment plants.

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Significant climate finance gaps exist for small islands in transitioning to net zero, as climate commitments far outweigh the government budget and international financing. To create alignment between resource allocation and climate commitments, a roadmap for strategic and cost-effective decarbonization is of supreme importance. This paper presents a geographic carbon accounting model which incorporates emissions from electricity, transportation, food systems, and human respiration, whilst accounting for the carbon uptake by the terrestrial biosphere in view of identifying high-intensity aggregated emissions estimated in the range of 200-215 ktCO2e in the coastal and inland urban regions of the remote island of Mauritius. An estimated 4641 ktCO2e, representing 79.4% of overall emissions, has been observed to originate from buildings, food, and waste systems. About 1150 ktCO2e, accounting for a share of 19.7%, is derived from transport systems. The study advocates for the enhanced participation of local authorities to better contribute to climate governance, whilst supporting legislative, financial, technological, and behavioural reforms. Despite the relatively low sequestration potential of forests replacing all non-habitable lands, which is estimated at 1002 ktCO2e and representing about 17.1% of annual net emissions, afforestation programmes are encouraged owing to multiple ecosystem services provided by trees.

Mainland Southeast Asian (MSEA) countries (Cambodia, Laos, Thailand, Myanmar, and Vietnam) are likely to become one of the next hotspots for emission reduction, since CO2 emissions in this area will have a two-thirds increase by 2040 due to rapid economy growth and associated energy consumption. As one of the most vulnerable areas to climate change, MSEA countries need to develop low-carbon roadmaps based on accurate emission data. This study provides emission inventories for MSEA countries for 2010-2019, based on the IPCC territorial emission accounting approach , including emissions from five types of fuels (i.e., coal, crude oil, oil products, natural gas, and biofuels & waste) used in 47 economic sectors. The results show that the emissions in MSEA countries are on the rise, with average annual growth rates ranging from 2.5% in Thailand to 19.3% in Laos. Biomass is one of the most important sources of carbon emissions, contributing between 11.8% and 76.7% of total carbon emissions, but its share has been declining in most countries, whereas the share of emissions from coal has risen sharply in Laos, Vietnam, and Cambodia. We further examine the drivers behind the changes in emissions using index decomposition analysis. Economic growth was the strongest driver of growth in emissions, while population growth has only had a small effect on emission growth. Energy intensity varies widely across nations, but only significantly reduced CO2 emission growth in Thailand. The secondary sector considerable contributed to an increase in CO2 emissions in Laos and Vietnam, while the tertiary sector only moderately contributed to emissions in Thailand. Our study provides a better understanding of the composition and underlying factors of emission growth in MSEA countries, this could shape their low-carbon development pathway. Our results could also inform other emerging economies, which may become emission hotspots in the next decades, to develop low-carbon roadmaps, thereby contributing to the achievement of global climate change targets.