This week’s publication highlights cover a range of topics related to forestation, ocean alkalinity enhancement, enhanced rock weathering and direct air capture.
Climate effects of a future net forestation scenario in CMIP6 models
Abstract
Forestation may reduce temperatures by lowering atmospheric CO2. However, biogeophysical changes from forestation may weaken this cooling. We use twelve Coupled Model Intercomparison Project (CMIP6) models to quantify the biogeochemical (carbon cycle) and biogeophysical (non-carbon cycle) effects of net forestation, as quantified as the difference between the end of two future scenarios: ssp370-ssp126Lu and ssp370. Biogeochemical effects have an inferred global multi-model mean cooling (−0.08 ± 0.02 K). Changes in fires have no significant effect on land carbon storage globally. In contrast with studies indicating biogeophysical impacts counteract biogeochemical impacts by up to 50%, we find that biogeophysical effects lead to insignificant global mean cooling (−0.002 ± 0.041 K). Tropical land shows cooling (−0.058 ± 0.058 K) with eight of twelve models indicating cooling, consistent with prior studies. Using the Surface Energy Balance Decomposition, we find cooling is primarily from increased evapotranspiration and decreased downwelling solar radiation related to clouds and aerosols.
Gomez, J. et al. (2025) Climate effects of a future net forestation scenario in CMIP6 models 297 (8) Climate and Atmospheric Science.
Read the full paper here: Climate effects of a future net forestation scenario in CMIP6 models I Climate and Atmospheric Science.
The Economics of Carbon Dioxide Removal
Abstract
Carbon dioxide removal (CDR) is an emerging topic in climate policy. We review the nascent economic literature on the governance of CDR and discuss policy design and institutions. We first assess the role of CDR in climate policy portfolios that include abatement and adaptation. Cost-saving technological progress could make CDR a game changer in climate policy: CDR creates new sectoral, intertemporal, and international flexibilities, which reduce overall costs and allow a return to a temperature target after temporary overshooting. Moreover, CDR can reduce the problem of international cooperation due to substantially lower supply-side leakage via fossil fuel markets. A key challenge lies in its governance and incentive structure, which are complicated by the nonpermanence of carbon storage and default risks of the firms committed to future CDR. For CDR governance, we survey approaches that incentivize removals by price instruments or include CDR in (modified) emissions trading schemes.
Edenhofer, O. et al. (2025) The Economics of Carbon Dioxide Removal 17 Annual Review of Resource Economics.
Read the full paper here: The Economics of Carbon Dioxide Removal I Annual Review of Resource Economics.
Novel field trial for ocean alkalinity enhancement using electrochemically derived aqueous alkalinity
Abstract
Ocean alkalinity enhancement is a proposed method of marine carbon dioxide removal that enhances the ocean’s uptake of atmospheric carbon dioxide (CO2) and converts it to dissolved bicarbonate for long-term ocean storage. This method of marine carbon dioxide removal has been gaining attention for its potential to durably (10,000+ years) store large amounts of CO2 (Gt + where 1 Gt = 1 × 109 tons), while potentially ameliorating acidification in the vicinity of the alkalinity release. This study focuses on a novel release of electrochemically derived aqueous alkalinity into Sequim Bay, WA, through a previously established wastewater treatment plant (WWTP). This research was made possible through the collaboration of industry, academic, and federal partners, which enabled the establishment of an Ebb Carbon electrochemical mCDR system at the Pacific Northwest National Laboratory in Sequim, WA, for ocean alkalinity enhancement field trials. During these field trials, pH was measured across the WWTP system from the initial alkalinity dosing, throughout the WWTP, and at the outfall. We use the NBS scale for pH throughout this study as it is the scale used in discharge permit limits specified for WWTP and NPDES regulation and compliance monitoring. The background pHNBS of Sequim Bay seawater was between 7.5 and 7.7 for the November and February field tests. The mixing tank’s pHNBS was raised to the maximum value permitted for the WWTP (9.0) and maintained across the system (±0.2) during the outfall releases. At the outfall, the elevated pH and alkalinity was quickly diluted, such that the region with a measurable signal was limited to within ∼2.5 m of the discharge pipe. We were able to successfully monitor an increase in pHNBS across all four pulses of alkalinity-enhanced seawater discharge during the February 2025 field trial, with peak pHNBS values of 8.3 or 8.1, as recorded by outfall-adjacent YSI Exo 2 sonde and SAMI-pH sensors, respectively. The alkalinity-enhanced seawater did not measurably alter the surrounding waters’ temperature, salinity, turbidity, or oxygen. This study provides proof-of-concept for a conservative small-scale release of electrochemically generated alkalinity-enhanced seawater from a coastal outfall.
Savoie, A. et al. (2025) Novel field trial for ocean alkalinity enhancement using electrochemically derived aqueous alkalinity. Frontiers.
Read the full paper here: Novel field trial for ocean alkalinity enhancement using electrochemically derived aqueous alkalinity I Frontiers.
Carbon dioxide removal during dissolution of granular basalt: A mass balance test of enhanced rock weathering at the hillslope scale
Abstract
Enhanced rock weathering (ERW) is proposed as a carbon dioxide removal (CDR) strategy that sequesters carbon through the carbonic acid-promoted dissolution of ground silicate rocks. Studies have explored the efficacy of ERW through geochemical models and bench-scale reactors, but field-scale experimentation is limited. A year-long, replicated study was conducted at the Landscape Evolution Observatory (LEO) at Biosphere 2 to quantify basaltic CDR at the hillslope scale. LEO comprises three mesoscale surfaces (each 330 m2) with 1 m depth of granular basalt. We subjected these structures to three 30 d irrigation events followed by progressively lengthened dry periods. Aqueous discharge was collected bihourly for major and trace chemistry, and subsurface interactions were observed at 15 min intervals through distributed sensors enabling continuous monitoring of PCO2, volumetric water content, and total hillslope mass. This approach enabled closing of the carbon and water mass balance of the system for the duration of the experiment. CDR was quantified through direct monitoring of bicarbonate (HCO3−) concentrations as validated through the charge balance of non-hydrolyzing cations and strong-acid anions. Concentration-discharge relations for HCO3− showed dilution trends with clockwise hysteresis, while a decrease in CO2 uptake occurred with increased hillslope water saturation (Shydro). The CDR rate, normalized to the specific surface area of the basalt, was -13.45 log10 moles C m−2 s−1, while other studies report CDR rates from -14 to -10 log10 moles m−2 s−1. We found that basalt CDR rates were impacted by depletions of PCO2 upon hydrologic infiltration, variable Shydro, and incongruent dissolution.
Cunningham, C. et al. (2025) Carbon dioxide removal during dissolution of granular basalt: A mass balance test of enhanced rock weathering at the hillslope scale 671 (119662) Earth and Planetary Science Letters.
Read the full paper here: Carbon dioxide removal during dissolution of granular basalt: A mass balance test of enhanced rock weathering at the hillslope scale I Earth and Planetary Science Letters.
Direct air capture of CO2: an industrial perspective
Abstract
Direct air capture (DAC) is a crucial carbon dioxide removal (CDR) technology for achieving net-zero emissions by balancing atmospheric CO₂ release with removal. It serves two key roles: (a) when integrated with Carbon Capture and Storage (DAC-CCS), it enables permanent CO₂ removal to offset emissions from hard-to-abate sources like aviation; and (b) when combined with Carbon Capture and Utilization (DAC-CCU), it provides non-fossil CO₂ for producing defossilized fuels and zero-carbon chemicals. To fulfill these roles, DAC systems must be scalable and economically viable. While academic studies often focus on assessing sorbent performance under a limited range of weather conditions and for limited periods, we advocate that industrial scale deployment demands DAC systems with additional key features such as low pressure drop, high reliability for long periods (years) in a wide range of weather conditions (temperature, relative humidity), resistance to fouling from particulates in air, and without loss of performance by reingestion of CO2 depleted air. These key features are more commonly addressed in patent literature by companies nearing commercialization rather than in academic publications. Moreover, DAC technologies must be capital-efficient, and use low-cost, recyclable sorbents.
Nisbet, T. et al. (2025) Direct air capture of CO2: an industrial perspective 50 (101190) Current Opinion in Chemical Engineering.
Read the full paper here: Direct air capture of CO2: an industrial perspective I Current Opinion in Chemical Engineering.