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Improved forest management (IFM) has the potential to remove and store large quantities of carbon from the atmosphere. Around the world, 293 IFM offset projects have produced 11% of offset credits by voluntary offset registries to date, channeling substantial climate mitigation funds into forest management projects. This paper summarizes the state of the scientific literature for key carbon offset quality criteria—additionality, baselines, leakage, durability, and forest carbon accounting—and discusses how well currently used IFM protocols align with this literature. Our analysis identifies important areas where the protocols deviate from scientific understanding related to baselines, leakage, risk of reversal, and the accounting of carbon in forests and harvested wood products, risking significant over-estimation of carbon offset credits. We recommend specific improvements to the protocols that would likely result in more accurate estimates of program impact, and identify areas in need of more research. Most importantly, more conservative baselines can substantially reduce, but not resolve, over-crediting risk from multiple factors.

In tropical South America there has been substantial progress in atmospheric monitoring capacity, but the region still has a limited number of continental atmospheric stations relative to its large area, hindering net carbon flux estimates using atmospheric inversions. In this study, we use dry-air CO.sub.2 mole fractions measured at the Amazon Tall Tower Observatory (ATTO) and airborne vertical CO.sub.2 profiles in an atmospheric inversion system to estimate net carbon exchange in tropical South America from 2010 to 2018. Given previous knowledge of a bias due to undried samples in the airborne vertical profiles, we calculate the effect of this systematic uncertainty in our inverse estimates and propose a water-vapor correction to the airborne CO.sub.2 profiles. We focus our analysis on the biogeographic Amazon and its neighboring \"Cerrado and Caatinga\" biomes. Including the water-vapor correction changes the posterior ensemble median from -0.33 to -0.04 PgC yr.sup.-1 with a posterior uncertainty of 0.33 PgC yr.sup.-1 for the Amazon and for the Cerrado and Caatinga from 0.31 to 0.50 PgC yr.sup.-1, with an uncertainty of 0.24 PgC yr.sup.-1 . Our estimates of carbon exchange include the contributions from both net vegetation exchange and release from fires. Assuming that the correction brings the observational data closer to the truth implies that the Amazon is a weaker sink of carbon and that the Cerrado and Caatinga is a larger source. We do not find a strong spatial shift of fluxes within the biogeographic Amazon due to the correction, nor do we find a strong impact on the interannual variations. Finally, to further reduce the uncertainty in regional carbon balance estimates in tropical South America, we call for an expansion of the atmospheric monitoring network on the continent, mainly in the Amazon-Andes foothills.

Scanning wind lidars provide a large potential to measure wind conditions remotely at distances of multiple kilometres. With increased measurement range, their pointing accuracy, especially on the elevation axis, becomes increasingly important. Current wind lidars use scanners to steer their beam, introducing static angle offsets due to manufacturing processes. Existing methods for the determination of these offsets exist, which require additional instrumentation or might not be applicable offshore. We suggest the Sea Surface Calibration (SSC) as one solution for offshore applications to determine and correct for the inherent static elevation offsets of scanning lidars. The method adapts and improves the previously introduced Sea Surface Levelling (SSL) which determines the lidar tilt by measuring the range to the planar sea surface at different azimuth angles. To improve SSC we propose two physics-based methods for a more accurate determination of the lidar-sea surface range. We validate our methods using a specific measurement setup at a harbour dock. Our results indicate that the new methods provide accurate measures of the lidar-sea surface range, correcting for errors of existing SSL methods. With the enhanced methods, we apply the SSC to accurately determine the static elevation offset, the height over the sea surface, and the external misalignment of the device.

Reducing emissions from deforestation and forest degradation (REDD+) has gained international attention over the past decade, as manifested in both United Nations policy discussions and hundreds of voluntary projects launched to earn carbon-offset credits. There are ongoing discussions about whether and how projects should be integrated into national climate change mitigation efforts under the Paris Agreement. One consideration is whether these projects have generated additional impacts over and above national policies and other measures. To help inform these discussions, we compare the crediting baselines established ex-ante by voluntary REDD+ projects in the Brazilian Amazon to counterfactuals constructed ex-post based on the quasi-experimental synthetic control method. We find that the crediting baselines assume consistently higher deforestation than counterfactual forest loss in synthetic control sites. This gap is partially due to decreased deforestation in the Brazilian Amazon during the early implementation phase of the REDD+ projects considered here. This suggests that forest carbon finance must strike a balance between controlling conservation investment risk and ensuring the environmental integrity of carbon emission offsets. Relatedly, our results point to the need to better align project- and national-level carbon accounting.

Most companies include carbon offsets in their net-zero strategy. However, many offset projects are poor quality and fail to reduce emissions as claimed. Here we focus on the twenty companies retiring the most offsets from the voluntary carbon market over 2020–2023. We examine if their offsets could be considered high quality and likely to benefit the climate. We curate an original company-level dataset to examine quality and climate benefits across four dimensions: (1) use of offsets from low/high-risk project types; (2) age of projects and credits; (3) price of credits; and (4) country of implementation. We find that companies have predominantly sourced low-quality, cheap offsets: 87% carry a high risk of not providing real and additional emissions reductions, with most offsets originating from forest conservation and renewable energy projects. Further, most offsets do not meet industry standards regarding age and country of implementation. These findings provide further evidence that the voluntary carbon market is not supporting effective climate mitigation. Particularly, we show that its persisting quality issues are exacerbated by the demand for low-quality offsets by individual companies. Trencher and colleagues investigate the twenty companies making the largest purchases of offsets from the voluntary carbon market from 2020 to 2023. They find that 87% of the purchased offsets carry a high risk of not providing real and additional emissions reductions. Further, most offsets do not meet industry standards regarding age and country of implementation. The findings reinforce concerns that the voluntary carbon market is failing to support effective climate mitigation.

Biodiversity and nature‐based carbon offsets are central to strategies addressing biodiversity loss and climate change. Their credibility depends on permanence—the expectation that biodiversity gains or sequestered carbon persist at least as long as the impacts they compensate for, or in perpetuity. Yet ecosystems are dynamic and increasingly exposed to disturbance, making perpetual outcomes difficult to guarantee. Despite this, many offset programs rely on fixed durations and static assumptions ill‐suited to managing long‐term risks, creating a structural misalignment between ecological permanence and the safeguards intended to secure it. To assess this misalignment, we reviewed three decades of literature to identify risks to long‐term durability and strategies for managing them. We developed a typology spanning three domains. Non‐physical risks, such as weak governance and limited data transparency, were most frequently reported, often co‐occurred, and enabled other failures. Physical risks such as fire, storms, or flooding cause material damage and are intensifying with climate change. Methodological risks, including oversimplified metrics and flawed design, expose structural weaknesses in offset systems. Our typology provides a framework for assessing permanence risks and strengthening offset governance. Credible, enduring offsets are achievable, provided robust risk management and adaptive governance are aligned with ecological realities.

Biodiversity offsets have become a widely accepted means of attempting to compensate for biodiversity loss from development, and are applied in planning and decision-making processes at many levels. Yet their use is contentious, and numerous problems with both the concept and the practice have been identified in the literature. Our starting point is the understanding that offsets are a kind of biodiversity compensation measure through which the goal of no net loss (or net gain) of biodiversity can be at least theoretically achieved. Based on a typology of compensation measures distinguishing between habitat protection, improvement (including restoration, habitat creation and improved management practices) and other compensation, we review the literature to develop a framework of conditions that must be met if habitat protection and improvement initiatives can be truly considered offsets and not merely a lesser form of compensation. It is important that such conceptual clarity is reflected in offset policy and guidance, if offsets are to be appropriately applied and to have any chance of fully compensating for biodiversity loss. Our framework can be used to support the review and ongoing development of biodiversity offset policy and guidance, with the aim of improving clarity, rigour and therefore the chances that good biodiversity outcomes can be achieved.

We present a recalibration of the photometric systems in the Pantheon+ sample of Type Ia supernovae (SNe Ia) including those in the SH0ES distance-ladder measurement of H 0. We utilize the large and uniform sky coverage of the public Pan-STARRS stellar photometry catalog to cross calibrate against tertiary standards released by individual SN Ia surveys. The most significant updates over the “SuperCal” cross calibration used for the previous Pantheon and SH0ES analyses are: (1) expansion of the number of photometric systems (now 25) and filters (now 105), (2) solving for all filter offsets in all systems simultaneously to produce a calibration uncertainty covariance matrix for cosmological-model constraints, and (3) accounting for the change in the fundamental flux calibration of the Hubble Space Telescope CALSPEC standards from previous versions on the order of 1.5% over a Δλ of 4000 Å. We retrain the SALT2 model and find that our new model coupled with the new calibration of the light curves themselves causes a net distance modulus change (d μ/dz) of 0.04 mag over the redshift range 0 < z < 1. We introduce a new formalism to determine the systematic impact on cosmological inference by propagating the covariance in the fitted calibration offsets through retraining simultaneously with light-curve fitting and find a total calibration uncertainty impact of σ w = 0.013; roughly half the size of the sample statistical uncertainty. Similarly, we find the systematic SN calibration contribution to the SH0ES H 0 uncertainty is less than 0.2 km s−1 Mpc−1, suggesting that SN Ia calibration cannot resolve the current level of the “Hubble Tension.”

The GLASS-JWST Early Release Science (hereafter GLASS-JWST-ERS) Program will obtain and make publicly available the deepest extragalactic data of the ERS campaign. It is primarily designed to address two key science questions, namely, “what sources ionized the universe and when?” and “how do baryons cycle through galaxies?”, while also enabling a broad variety of first look scientific investigations. In primary mode, it will obtain NIRISS and NIRSpec spectroscopy of galaxies lensed by the foreground Hubble Frontier Field cluster, Abell 2744. In parallel, it will use NIRCam to observe two fields that are offset from the cluster center, where lensing magnification is negligible, and which can thus be effectively considered blank fields. In order to prepare the community for access to this unprecedented data, we describe the scientific rationale, the survey design (including target selection and observational setups), and present pre-commissioning estimates of the expected sensitivity. In addition, we describe the planned public releases of high-level data products, for use by the wider astronomical community.