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Electrochemical CO2 reduction is a promising method for converting atmospheric CO2 into valuable low‐carbon chemicals. In this study, a crystalline cadmium sulfide/amorphous cadmium hydroxide composite was successfully deposited on the carbon paper substrate surface by in‐situ chemical bath deposition (named as c‐CdS/a‐Cd(OH)2/CP electrodes) for the efficient electrochemical CO2 reduction to produce CO. The c‐CdS/a‐Cd(OH)2/CP electrode exhibited high CO Faradaic efficiencies (>90 %) under a wide potential window of 1.0 V, with the highest value reaching ~100 % at the applied potential ranging from −2.16 V to −2.46 V vs. ferrocene/ferrocenium (Fc/Fc+), superior to the crystalline counterpart c‐CdS/CP and c‐CdS/c‐Cd(OH)2@CP electrodes. Meanwhile, the CO partial current density reached up to 154.7 mA cm−2 at −2.76 V vs. Fc/Fc+ on the c‐CdS/a‐Cd(OH)2/CP electrode. The excellent performance of this electrode was mainly ascribed to its special three‐dimensional structure and the introduction of a‐Cd(OH)2. These structures could provide more active sites, accelerate the charge transfer, and enhance adsorption of *COOH intermediates, thereby improving the CO selectivity. Moreover, the electrolytes consisting of 1‐butyl‐3‐methylimidazolium tetrafluoroborate and acetonitrile also enhanced the reaction kinetics of electrochemical CO2 reduction to CO. [ABSTRACT FROM AUTHOR]

The article focuses on plastic is ubiquitous in people's lives, when plastic-containing items have fulfilled their missions, only a small amount is recycled into new products, which are often of lower quality, compared with the original material. Topics include the waste into high-value chemicals requires substantial energy, the researchers have combined a ruthenium-carbon catalyst, and the lower-energy reaction conditions to convert plastics used in bottles and other packaging into fuels.

The downwelling longwave radiation at the surface (DLR) is a key component of the Earth's surface energy budget. We present a novel set of equations that explicitly account for both clouds and the CO2 $\mathrm{C}{\mathrm{O}}_{\mathrm{2}}$ effect to calculate the all‐sky DLR. This paper first extends the clear‐sky DLR model of Shakespeare and Roderick (2021, https://doi.org/10.1002/qj.4176) to include temperature inversions and clouds. We parameterize relevant cloud properties through theoretical and empirical considerations to formulate an all‐sky model. Our model is more accurate than existing methods (reduces Root Mean Squared Error by 2.1–8.7 W/m2 $\mathrm{W}/{\mathrm{m}}^{\mathrm{2}}$ and 1.2–10.1 W/m2 $\mathrm{W}/{\mathrm{m}}^{\mathrm{2}}$ compared to ERA5 reanalysis and in‐situ data respectively), and provides a strong physical basis for the estimation of the downwelling longwave from near‐surface information. We highlight the important role of CO2 $\mathrm{C}{\mathrm{O}}_{\mathrm{2}}$ dependence by showing our model largely captures the change in atmospheric emissivity purely due to CO2 $\mathrm{C}{\mathrm{O}}_{\mathrm{2}}$ (i.e., the instantaneous radiative forcing) in CMIP6 models. Plain Language Summary: The downwelling longwave radiation (DLR) at the surface is a key component of the energy balance at the Earth's surface. Understanding how the DLR will change under future climate conditions is vital. For the first time, we explicitly write a set of equations to calculate the DLR that sufficiently account for the impact of CO2 $\mathrm{C}{\mathrm{O}}_{\mathrm{2}}$ and clouds simultaneously. Our model is more accurate than existing methods, and provides a much stronger physical basis for the estimation of the downwelling longwave from near‐surface information. In this paper, we extend an existing method for estimating the DLR under clear‐sky conditions (i.e., no clouds) to operate under all sky conditions. This method can be used to inform models where the DLR is needed, but only basic observations are available. Key Points: Downwelling longwave radiation (DLR) is a poorly estimated element of the surface energy budget by existing analytical modelsExplicitly accounting for temperature inversions and cloud emissivities improves the accuracy of DLR estimationConsidering the radiative forcing from increasing CO2 $\mathrm{C}{\mathrm{O}}_{\mathrm{2}}$ is necessary to produce unbiased future estimates of DLR [ABSTRACT FROM AUTHOR]

Ocean warming and associated deoxygenation caused by anthropogenic global warming are impacting marine ecosystems. This article contextualizes and provides perspectives on key insights from a recently published study by Fröb et al. in Earth's Future (2024). The authors employ historical and high‐emission scenario simulations through a state‐of‐the‐art Earth system model to detect abrupt and persistent changes in the viability of marine habitats by leveraging an ecophysiological framework that quantifies how temperature and oxygen jointly limit the distribution of life in the ocean for a number of ecophysiotypes. A changepoint analysis is used to objectively detect shifts in decadal to multi‐decadal mean states in potential marine habitats. They observe a decrease in the ocean volume capable of providing viable habitats for those ecophysiotypes with positive sensitivity to hypoxia. About half of these decreases occur abruptly, thus highlighting potential risks on the capacity of marine organisms to cope with a changing environment. Plain Language Summary: The unabated emission of atmospheric carbon dioxide from human activities threatens all ecosystems on Earth. In the ocean, marine organisms are encountering a warmer, less‐oxygenated and acidified environment. While many of these changes occur gradually, allowing (in some cases) marine organisms time for adaptation, some alterations may happen abruptly, jeopardizing their ability to cope. This paper comments on the recently published study of Fröb et al., which explores the occurrence of such abrupt changes in the ability of marine ecosystems to provide viable habitats, drawing upon the well‐established concept of the "metabolic index." This index assesses whether the resting metabolic requirements of organisms are met by the availability of oxygen at a given temperature. By employing historical (1850–2014) and a high‐emission scenario (2015–2100) as simulated by an Earth system model, the authors uncover that global warming has already begun to drive abrupt alterations in ocean habitability. These findings provide further evidence that ocean biodiversity is poised to undergo major changes during this century. Key Points: The ocean's capacity to provide viable habitats is being compromised by the combined threat of ocean warming and associated deoxygenationFor marine organisms to survive, changes in environmental conditions should be slower than their ability to adaptGlobal warming is leading to more frequent and severe abrupt changes in ocean habitability [ABSTRACT FROM AUTHOR]

This review paper explores the diverse applications of polylactide or polylactic acid (PLA) and its contributions to environmental sustainability. It delves into the synthesis, properties, and numerous applications of PLA, accompanied by illustrative examples demonstrating its ability to reduce carbon emissions. The environmentally friendly characteristics of PLA, coupled with its versatility, make it a vital player in the ongoing efforts to combat climate change. PLA generally requires lower extrusion temperatures than other 3D printing materials, such as ABS (Acrylonitrile Butadiene Styrene). Lower extrusion temperatures lead to reduced energy consumption during the printing process thus the reduction in carbon dioxide emissions during production. Plants, such as corn and sugarcane, play a crucial role in absorbing carbon dioxide from the atmosphere during their growth cycle. When these plants are utilized to produce PLA, the captured CO2 remains sequestered within the plastic material. This contributes to offsetting CO2 emissions from other sources. In conclusion, the usage of PLA has demonstrated positive contributions to the reduction of carbon dioxide emissions through its renewable sourcing, lower extrusion temperatures, lower dependence on fossil fuels, reduced greenhouse gas emissions during production, biodegradability, and participation in a closed carbon cycle. [ABSTRACT FROM AUTHOR]

In this paper, we examine differences in cloud adjustments (often called rapid adjustments) that occur as a direct result of abruptly increasing the solar constant by 4% or abruptly quadrupling of atmospheric CO2. In doing so, we devise a novel method for calculating the cloud adjustments for the abrupt solar forcing simulations that uses differences between coupled model simulations with abrupt solar and CO2 forcing, in combination with uncoupled, atmosphere‐only, abrupt CO2 forced experiments that have prescribed sea‐surface temperature. Our main findings are that (a) there are substantial differences in the responses of stratocumulus and cumulus clouds to solar and CO2 forcing, which follow the differences in the direct radiative effect that solar and CO2 forcing have at cloud top, and (b) there are differences in the adjustment of the average optical depth of high clouds to solar and CO2 forcing that we speculate are driven by the differences in the vertical profile of radiative heating and differences in the pattern of sea‐surface temperature change (for a fixed global mean temperature). These cloud adjustments contribute significantly to the total net cloud radiative effect, even after 150 years of simulation. Plain Language Summary: In climate change, clouds change due to a variety of mechanisms including surface temperature, dynamical circulations, and radiative forcing. In this paper, we examine the latter: how clouds respond to radiative forcing. We study this topic using climate model simulations where the brightness of the sun is abruptly increased by 4% and compare those with simulations where CO2 concentration is abruptly quadrupled. In doing so we find that, there are differences in the cloud response to changes in solar and CO2 forcing which include the occurrence of thick and thin high cloud, as well as the amount and height of low and mid‐level clouds. Key Points: Increasing CO2 causes a reduction and lowering of mid‐level and low‐level clouds which does not occur from solar forcingThere is large reduction in optically thin high clouds from solar forcing, especially as compared with CO2Even after 150 years adjustments make a significant contribution to the total net cloud radiative effect [ABSTRACT FROM AUTHOR]

There are many uncertainties in future climate, including how the Earth may react to different types of radiative forcing, such as CO2, aerosols, and even geoengineered changes in the amount of sunlight absorbed by Earth's surface. Here, we analyze model simulations where the climate system is subjected to an abrupt change of the solar constant by ±4%, and where the atmospheric CO2 concentration is abruptly changed to quadruple and half its preindustrial value. Using these experiments, we examine how clouds respond to changes in solar forcing, compared to CO2, and feedback on global surface temperature. The total cloud response can be decomposed into those responses driven by changes in global surface temperature, called the temperature mediated cloud feedbacks, and responses driven directly by the forcing that are independent of the global surface temperature. In this paper, we study the temperature mediated cloud changes to answer two primary questions: (a) How do temperature mediated cloud feedbacks differ in response to abrupt changes in CO2 and solar forcing? And (b) Are there symmetrical (equal and opposite) temperature mediated cloud feedbacks during global warming and global cooling? We find that temperature mediated cloud feedbacks are similar in response to increasing solar and increasing CO2 forcing, and we provide a short review of recent literature regarding the physical mechanisms responsible for these feedbacks. We also find that cloud responses to warming and cooling are not symmetric, due largely to non‐linearity introduced by phase changes in mid‐to‐high latitude low clouds and sea ice loss/formation. Plain Language Summary: As the global mean temperature changes, there are changes in cloud amount, location, and thickness, which can all impact the radiative balance of the Earth. Cloud changes driven directly by global temperature change are called temperature mediated cloud feedbacks. In this paper, we study the temperature mediated cloud feedbacks that occur in model simulations where the amount of sunlight incident upon the Earth is increased or decreased abruptly, and then held constant for 150 years. We compare the cloud changes in these experiments with experiments where the CO2 concentration is similarly increased or decreased abruptly and held constant for 150 years. In doing so we find that the temperature mediated cloud feedbacks following abrupt changes in solar radiation are characteristically similar to those occurring following CO2 increase. There are however substantial differences in the temperature mediated cloud feedbacks that occur while the climate is warming versus cooling. Key Points: The temperature mediated cloud changes and feedbacks incurred by changes in solar and CO2 forcing are similarOptical depth changes at high latitudes produce substantial differences in cloud feedbacks in cooling and warming experimentsLikewise, tropical circulations respond differently in models to cooling and warming, with a stronger change in the Walker circulation in warming experiments [ABSTRACT FROM AUTHOR]

This paper aims to update our understanding of the carbon cycle in the Himalayas, the most intense collisional orogeny globally, by providing new insight into its impact on Cenozoic climate cooling through the use of isotopic variations in both organic and inorganic carbon and an isotopic mass balance model. Our results from 20 selected hot springs show that the relative contributions of dissolved carbon from the mantle, metamorphic decarbonization, aqueous dissolution, and soil organic matter are approximately 2%, 82%, 6%, and 10%, respectively. Approximately 87% ± 5% of CO2 generated in the deep crust precipitates as calcite, while approximately 5.5% ± 1% of this carbon is converted to biomass through microbial chemosynthesis at depths less than 2 km. Our random forests approach yielded a metamorphic carbon flux from the entire Himalayan orogenic belt of approximately 2.7 ∼ 4.5 × 1012 mol/yr. The minor CO2 released into the atmosphere (2.5 ∼ 4.2 × 1011 mol/yr) is comparable to the carbon consumption driven by Himalayan weathering. This paper provides new insights into deep carbon cycling, notably that approximately 93% of deeply sourced carbon is trapped in the shallow crust, rendering orogenic processes carbon neutral and possibly acting as one of the major triggers of long‐term climate cooling in the Cenozoic. Plain Language Summary: Large‐scale deep metamorphic decarbonization and CO2 release into the atmosphere during continental collision orogenesis worldwide have had significant impacts on Cenozoic global climate change. However, the carbon sources and sinks and the mechanisms underlying their impacts on climate change are not fully understood. This paper reports the chemistry of aqueous solutions, carbon isotopic compositions of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC), and helium and carbon isotopic compositions of free gases from hot springs in southern Tibet. The carbon isotope fractionation model between gas and aqueous solutions revealed that the carbon released from depth underwent six different stages. Based on the random forests machine learning algorithm, we estimated the metamorphic carbon flux across the Himalayan orogenic belt. Furthermore, only a small fraction (7%) of deep carbon is eventually released into the atmosphere, and this volume is the same magnitude as the amount of carbon absorbed by silicate weathering on the Tibetan Plateau. This paper emphasizes that the carbon sequestration process in the upper crust may have resulted in nearly carbon‐neutral geological bodies in the Himalayan orogenic belt, thus playing a critical role in Cenozoic climate cooling. Key Points: Approximately 87% of deeply sourced carbon precipitates as calcite, while approximately 5.5% is sequestered as biomass in the shallow crustThe carbon flux across the Himalayan orogenic belt was estimated by the random forests approachCrustal thickening has attenuated long‐term deep carbon emissions from the Himalayas [ABSTRACT FROM AUTHOR]

We present a cost model for implementing a deployment scale effort for conducting ocean iron fertilization (OIF) for marine‐based carbon dioxide removal (CDR). The model incorporates basic oceanographic parameters critical for estimating the effective export of newly fixed CO2 into biomass that is stimulated by Fe addition to an Fe‐limited region of the Southern Ocean. Estimated costs can vary by nearly 100‐fold between best‐case and worst‐case scenarios, with best‐case values of $7/net tonne C captured versus worst‐case $1,500/net tonne C captured, without accounting for verification costs. Primary oceanographic factors that influence cost are the net primary productivity increases achieved via OIF, the amount of C exported into the deep ocean, and the amount of CO2 ventilated back to the atmosphere. The model compares ship‐based versus aerial delivery of Fe to the ocean, and estimates aerial delivery can be 30%–40% more cost effective; however, the specific requirements for aerial delivery require additional research and development. The model also estimates costs associated with verification and environmental monitoring of OIF. These costs increase $/net tonne C captured by 3–4‐fold. Best, intermediate, and worst cases for aerial delivery and ship delivery are $21, $83, $2,033, and $24, $94, $4,691, respectively, inclusive of verification costs. The primary goal of this model is to demonstrate the variability in cost of OIF as a CDR method, and to better understand where additional research is needed to determine the major factors that may make OIF a tractable, nature‐based CDR method. Plain Language Summary: This paper presents a basic cost model for undertaking ocean iron fertilization (OIF) as a means of removing carbon dioxide from the atmosphere. It presents a simple application scenario that compares two different modes for delivering iron to the ocean, plane‐based and ship‐based, and estimates costs associated with verification of carbon export into the deep ocean, as well as assessing the environmental changes that may occur as result. Key findings are that, in terms of USD/tonnes carbon exported, OIF can be at the lower cost end (

The quantity of carbon dioxide in the atmosphere rises yearly because human activities emit more of it than the earth's natural processes can absorb. The overall carbon dioxide emissions continue to rise due to development demands. In a panel setting, this paper investigates the link dynamics between gross national spending, energy consumption, information and communications technology, and CO2 emissions in advanced nations from 2000 to 2020. We employ quantitative sequential approaches, such as DOLS, unit root test, and cointegration techniques, to ensure the coherence and feasibility of the study. Both versions of the estimators show statistically significant effects of gross national expenditure, energy consumption, and Information & Communications Technology on CO2 emissions. The findings of this paper show that there is a long‐run relationship between independent and dependent variables. The study also shows that rising exports of ICT services, energy consumption, and population need environmental protection and highlight the necessity for environmental regulations that can minimize emissions throughout the country's expansion. Even in advanced nations, climate vulnerability is not automatically reduced by development status but is instead reduced by the right sort of growth. [ABSTRACT FROM AUTHOR]

The long‐term absorption by the oceans of atmospheric carbon dioxide is leading to the slow decline of ocean pH, a process termed ocean acidification (OA). The Arctic is a challenging region to gather enough data to examine the changes in carbonate chemistry over sufficient scales. However, algorithms that calculate carbonate chemistry parameters from more frequently measured parameters, such as temperature and salinity, can be used to fill in data gaps. Here, these published algorithms were evaluated against in situ measurements using different data input types (data from satellites or in situ re‐analysis climatologies) across the Arctic Ocean. With the lowest uncertainties in the Atlantic influenced Seas (AiS), where re‐analysis inputs achieved total alkalinity estimates with Root Mean Squared Deviation (RMSD) of 21 μmol kg−1 and a bias of 2 μmol kg−1 (n = 162) and dissolved inorganic carbon RMSD of 24 μmol kg−1 and bias of −14 μmol kg−1 (n = 262). AiS results using satellite observation inputs show similar bias but larger RMSD, although due to the shorter time span of available satellite observations, more contemporary in situ data would provide further assessment and improvement. Synoptic‐scale observations of surface water carbonate conditions in the Arctic are now possible to monitor OA, but targeted in situ data collection is needed to enable the full exploitation of satellite observation‐based approaches. Plain Language Summary: The long‐term absorption by the oceans of atmospheric carbon dioxide is leading to the slow decline of ocean pH, a process termed ocean acidification (OA). Sea surface salinity and temperature measurements from satellites or in situ re‐analysis products can be used as input to empirical algorithms to calculate OA parameters. This paper provides a first analysis of published Arctic Ocean empirical algorithms to estimate surface water OA parameters using observation‐based data sets. Results show promise in the Atlantic influenced Seas using both in situ re‐analysis and satellite products, but satellite salinity is relatively recent, and a paucity of in situ data in the satellite salinity era precludes a robust assessment. To fully exploit satellite‐based approaches, efforts need to focus on collecting in situ data while these satellites are overhead and operating in orbit. Key Points: Observation‐based data sets enable synoptic spatio‐temporal assessments of Arctic Ocean carbonate system parametersRe‐analysis and satellite products predict total alkalinity with accuracies of ∼21 μmol kg−1Targeted in situ data collection is needed to fully exploit satellite observations in the Arctic to enable carbonate system monitoring [ABSTRACT FROM AUTHOR]

Estimation of climate sensitivity is fundamental to assessing how global climate will warm as atmospheric CO2 ${\mathrm{C}\mathrm{O}}_{2}$ concentration increases. Geological archives of environmental change provide insights into Earth's past climate, but the incomplete nature of paleoclimate reconstructions and their inherent uncertainties make estimation of climate sensitivity challenging. Thus, quantifying climate sensitivity and assessing how it changed through geological time requires statistical frameworks that can handle data uncertainties in a principled fashion. Here we demonstrate some of the hurdles to estimating climate sensitivity, with a focus on current statistical techniques that may underestimate both climate sensitivity and its associated uncertainty. To solve these issues, we present a Bayesian error‐in‐variables regression model, which can yield estimates of climate sensitivity without bias. The regression model is flexible and can account for data point uncertainties with a known parametric form. The utility of this approach is demonstrated by estimating specific climate sensitivity with uncertainty for the Eocene. Plain Language Summary: As atmospheric CO2 ${\mathrm{C}\mathrm{O}}_{2}$ increases due to human activities, the Earth will warm. But how much warming can be expected? Climate sensitivity describes how much global average surface temperature will warm with a given increase in atmospheric CO2 ${\mathrm{C}\mathrm{O}}_{2}$. While this is a simple definition, estimating climate sensitivity is difficult because Earth's climate system is complex with a number of poorly understood interacting parts. One approach to estimating climate sensitivity is to quantify how Earth's climate changed as a result of variations in atmospheric CO2 ${\mathrm{C}\mathrm{O}}_{2}$ through geological time. This information is invaluable, but it is patchy and has large uncertainties that make estimating climate sensitivity challenging. In particular, existing statistical techniques may underestimate climate sensitivity and, thus, underestimate future warming. In this paper we present an alternative approach to determining climate sensitivity that overcomes the underestimation problem and demonstrate its performance using geological data from the Eocene epoch. Key Points: We demonstrate that regression‐based estimates of specific climate sensitivity may be biased toward zero because of data uncertaintiesA Bayesian error‐in‐variables approach is developed that accounts for data uncertainties in regression‐based climate sensitivity estimatesEocene specific climate sensitivity is estimated to demonstrate the utility of Bayesian error‐in‐variables regression [ABSTRACT FROM AUTHOR]

This paper aims to study the changes in the Indian Ocean seawater pH in response to the changes in sea‐surface temperature, sea‐surface salinity, dissolved inorganic carbon (DIC), and total alkalinity (ALK) over the period 1980–2019 and its driving mechanisms using a high‐resolution regional model outputs. The analysis indicates that the rate of change of declining pH in the Arabian Sea (AS), the Bay of Bengal (BoB), and the Equatorial Indian Ocean (EIO) is −0.014 ± $\pm $ 0.002, −0.014 ± $\pm $ 0.001, and −0.015 ± $\pm $ 0.001 unit dec−1, respectively. Both in AS and BoB (EIO), the highest (lowest) decadal DIC trend is found during 2000–2009. The surface acidification rate has accelerated throughout the IO region during 2010–2019 compared to the previous decades. Further, our analysis indicates that El Ninõ and positive Indian Ocean Dipole events lead to an enhancement of the Indian Ocean acidification. The increasing anthropogenic CO2 uptake by the ocean dominantly controls 80% (94.5% and 85.7%) of the net pH trend (1980–2019) in AS (BoB and EIO), whereas ocean warming controls 14.4% (13.4% and 7.0%) of pH trends in AS (BoB and EIO). The changes in ALK contribute to enhancing the pH trend of AS by 5.0%. ALK dominates after DIC in the EIO and, similar to the AS, contributes to increasing the negative pH trend by 10.7%. In contrast, it has a buffering effect in the BoB, suppressing the pH trend by −5.4%. Plain Language Summary: The oceans play a significant role in regulating the amount of CO2 in the atmosphere. The increasing oceanic uptake of CO2 counterbalances the increase in atmospheric CO2. This uptake has a considerable impact on marine biogeochemistry, leading to pH and alkalinity imbalances in the water column, commonly referred to as ocean acidification. In an acidic ocean, excess CO2 reacts with seawater to form carbonic acid, which is highly unstable and undergoes further reduction by releasing hydrogen ions (H+) and acidifying the seawater (reduces the pH). Several studies have projected a decline of upper ocean pH by 0.3–0.4 by the end of the 21st century, which has the potential to reduce oceanic biological production considerably. The number of available observations to study Indian Ocean acidification is limited. There is a critical need to understand the status of Indian Ocean acidification and identify its key drivers. This article consolidates the current level of understanding about the Indian Ocean acidification based on the available field observations, reconstructed data sets, and model simulations. Key Points: The Indian Ocean pH is decreasing at an average rate of 0.015 dec−1 from 1980 to 2019The trend of dissolved inorganic carbon primarily drives an increasing ocean acidification trend in the Indian OceanEl Ninõ and positive Indian Ocean Dipole events lead to an enhancement of the Indian Ocean acidification [ABSTRACT FROM AUTHOR]

To stabilize the climate, we need to urgently decarbonize our society and remove excess CO2 from the atmosphere. Ambitions for the transformation are ultimately limited by bio‐physical constraints, which cannot be transgressed even if all economic and societal obstacles could be overcome. Even though it is essential to know what transformation pathways are still feasible, there is a lack of studies and models exploring bio‐physical frontiers for climate action. In this paper, we take a first step to explore the energy frontier by introducing the "3‐machines energy transition model." This simplified representation of the global energy system includes energy feedbacks and is constrained by the maximum renewable energy potential. Simulation experiments with the model show that with most ambitious actions global peak heating may exceed 1.5°C with a chance of 14%. Simultaneously, it is still energetically possible to return to 350 ppm this century, which is considered to be a safe level for atmospheric CO2 concentration. While these energy‐constrained transformation pathways show that the climate can still be stabilized with a fair chance, they also illustrate the urgency and far‐reaching change required in society. Plain Language Summary: The rapidly depleting carbon budget for limiting peak heating to 1.5°C makes it necessary to design more ambitious and faster transformation pathways. Additionally, Earth's atmospheric CO2 concentration is rising faster than ever and far above the range of the past 1 million years. Stabilizing the climate in the long run will therefore require to return to a safe CO2 concentration. On our finite planet, there are, however, bio‐physical limits for accelerating climate action—yet, these frontiers are not well studied. This paper contributes a first step to explore the energy frontier for a fast and complete transition to renewable energy as well as removing excess CO2 from the atmosphere, identifying promising strategies to investigate further with more detailed modeling frameworks. Key Points: Given the urgency of the climate crisis, actions that are ultimately limited by the availability of energy have to be most ambitiousLowest climate risks can be achieved by a limited and short‐term increase of fossil emissions to kick‐start the fastest possible transitionReturning to safe climate conditions is energetically possible this century by using solar overcapacity on the built environment [ABSTRACT FROM AUTHOR]

Orbital precession has been linked to glacial cycles and the atmospheric carbon dioxide (CO2) concentration, yet the direct impact of precession on the carbon cycle is not well understood. We analyze output from an Earth system model configured under different orbital parameters to isolate the impact of precession on air‐sea CO2 flux in the Southern Ocean—a component of the global carbon cycle that is thought to play a key role on past atmospheric CO2 variations. Here, we demonstrate that periods of high precession are coincident with anomalous CO2 outgassing from the Southern Ocean. Under high precession, we find a poleward shift in the southern westerly winds, enhanced Southern Ocean meridional overturning, and an increase in the surface ocean partial pressure of CO2 along the core of the Antarctic Circumpolar Current. These results suggest that orbital precession may have played an important role in driving changes in atmospheric CO2. Plain Language Summary: Over the past one million years, Earth has experienced several glacial and interglacial periods. As a glacial period is ending, carbon in the atmosphere can rise by up to 50%. The cause for this change is currently unknown, but most theories suggest that this carbon is released from the deep ocean into the atmosphere. The Southern Ocean surrounding Antarctica is the location of a lot of carbon outgassing from the deep ocean into the atmosphere, so it could be responsible for some of this change in atmospheric carbon. One of Earth's orbital cycles, precession, has been shown to change circulation in the Southern Ocean, that can affect how much carbon is carried from the deep ocean to the surface and released into the atmosphere. This paper uses simulations of a climate model to show that high precession corresponds to a 20% increase in the release of carbon from the Southern Ocean into the atmosphere. These findings suggest that precession could have affected changes in past atmospheric carbon concentrations. Key Points: Increased insolation during austral summer due to orbital precession shifts the southern westerlies polewardPoleward shifted westerlies enhance CO2 outgassing due to increased turbulent exchange and vertical transport of carbon‐rich watersEnhanced transport of carbon‐rich waters is driven by a deepening of the overturning circulation in response to poleward shifted winds [ABSTRACT FROM AUTHOR]

This contribution to the RECCAP2 (REgional Carbon Cycle Assessment and Processes) assessment analyzes the processes that determine the global ocean carbon sink, and its trends and variability over the period 1985–2018, using a combination of models and observation‐based products. The mean sea‐air CO2 flux from 1985 to 2018 is −1.6 ± 0.2 PgC yr−1 based on an ensemble of reconstructions of the history of sea surface pCO2 (pCO2 products). Models indicate that the dominant component of this flux is the net oceanic uptake of anthropogenic CO2, which is estimated at −2.1 ± 0.3 PgC yr−1 by an ensemble of ocean biogeochemical models, and −2.4 ± 0.1 PgC yr−1 by two ocean circulation inverse models. The ocean also degasses about 0.65 ± 0.3 PgC yr−1 of terrestrially derived CO2, but this process is not fully resolved by any of the models used here. From 2001 to 2018, the pCO2 products reconstruct a trend in the ocean carbon sink of −0.61 ± 0.12 PgC yr−1 decade−1, while biogeochemical models and inverse models diagnose an anthropogenic CO2‐driven trend of −0.34 ± 0.06 and −0.41 ± 0.03 PgC yr−1 decade−1, respectively. This implies a climate‐forced acceleration of the ocean carbon sink in recent decades, but there are still large uncertainties on the magnitude and cause of this trend. The interannual to decadal variability of the global carbon sink is mainly driven by climate variability, with the climate‐driven variability exceeding the CO2‐forced variability by 2–3 times. These results suggest that anthropogenic CO2 dominates the ocean CO2 sink, while climate‐driven variability is potentially large but highly uncertain and not consistently captured across different methods. Plain Language Summary: The second REgional Carbon Cycle Assessment and Processes effort, or RECCAP2, provides a comprehensive assessment of global and regional greenhouse gas budgets. This paper focuses on the ocean carbon sink, and investigates the processes that control its magnitude, trends and variability. Observation‐based techniques estimate that the net transfer of CO2 from the atmosphere to the ocean, averaged over 1985–2018, is 1.6 billion tonnes of carbon per year, and that oceanic CO2 uptake is increasing by 0.61 billion tonnes of carbon per year each decade. Models say that most of this CO2 entering the ocean, and its increase over time, is driven by anthropogenic CO2 emissions, which causes the ocean to take up 2.1–2.4 billion tonnes of carbon per year. There are some hints that climate change might be accelerating ocean carbon uptake, but the errors in our estimates are too large to know for sure right now. Our methods and observations will have to be improved in order to better detect the impact of climate change on the ocean carbon sink. Key Points: The RECCAP2 global ocean analysis provides an authoritative multi‐model and observation‐based assessment of global ocean CO2 uptakepCO2‐based products yield a mean sea‐air CO2 flux from 1985 to 2018 of −1.6 ± 0.2 PgC yr−1 with a trend of −0.61 PgC yr−1 decade−1 since 2001Ocean anthropogenic CO2 uptake averages −2.1–2.4 PgC yr−1 from 1985 to 2018, with a trend of −0.34–0.41 PgC yr−1 decade−1 since 2001 [ABSTRACT FROM AUTHOR]

The increasing utilization of fossil fuels and industrial activities has resulted in a surge of CO2 emissions, which have significantly impacted global climate change. Carbon capture and utilization technologies offer a promising solution to decrease atmospheric CO2 concentrations and convert CO2 into valuable products. This study focuses on the capture and storage of CO2 through the mineralization of magnesium‐containing materials. The analysis encompasses the mineralization process of solid and liquid minerals, the various mineralization processes of magnesium‐containing minerals categorized as direct and indirect mineralization, and the latest research advancements in magnesium‐containing minerals. Brine and seawater from salt lakes are considered the most appropriate materials for mineralization due to their abundance and the simplicity of the process compared to solid mineralization. This paper analyzes the impact of temperature, impurity ions, additives, and microorganisms on the process of magnesium carbonate synthesis crystallization. The use of magnesium‐containing materials for carbon dioxide sequestration can effectively reduce carbon emission. The review offers guidance on carbon dioxide mineralization and explores the potential applications of magnesium mineralization. [ABSTRACT FROM AUTHOR]

Massive, kilometer thick deposits of carbon dioxide (CO2) ice have been detected at the south polar cap of Mars by radar investigations. These deposits are divided into several units that are separated by thin water ice bounding layers. Recent studies investigated the accumulation history of CO2 ice and found that the deposits most likely formed during several episodes in the past, when Martian obliquity was much lower than now. Those studies, while able to predict total volumes of CO2 ice consistent with those observed, did not attempt to explain the anomalous three‐dimensional distribution (thickness or extent) of CO2 ice or the ice's offset from the topographic high of the polar cap. In this paper we use a combination of feature analysis and numerical modeling to demonstrate that the CO2 deposits flow as glaciers and that glacial flow distributes the ice into its current position. Further, this distribution allows the ice to survive during high obliquity excursions. Plain Language Summary: Carbon dioxide (CO2) ice is found in a stack of deposits at Mars' south pole. These deposits are situated in basins, where they reach more than 1 km thick. Previous work suggested that the CO2 ice should be deposited when the axial tilt of the planet was lower, making the poles colder than they are now; however, the thickness and distribution of this ice should be much thinner than observed if only atmospheric effects are working on the ice. Therefore, the CO2 ice deposit distribution cannot be explained by atmospheric deposition alone. In this paper, we use glacial modeling and feature analysis to demonstrate that glacial flow better explains the distribution of ice in its present state. In addition, we show that the slopes on the south polar cap act to focus glacial flow into the basins, where it can survive warm periods by sublimating only the uppermost sections when the tilt of the planet is larger than present day. Key Points: Carbon dioxide ice has been mapped and modeled at the south pole of MarsDeposition models cannot explain the volumetric distribution of CO2 ice, thickness, or distributionWe present geomorphic and modeling evidence that the CO2 deposits flow as glaciers into basins to reach their observed volumetric distribution [ABSTRACT FROM AUTHOR]

The cloud properties and governing processes in Southern Ocean marine boundary layer clouds have emerged as a central issue in understanding the Earth's climate sensitivity. While our understanding of Southern Ocean cloud feedbacks have evolved in the most recent climate model intercomparison, the background properties of simulated summertime clouds in the Southern Ocean are not consistent with measurements due to known biases in simulating cloud condensation nuclei concentrations. This paper presents several case studies collected during the Capricorn 2 and Marcus campaigns held aboard Australian research vessels in the Austral Summer of 2018. Combining the surface‐observed cases with MODIS data along forward and backward air mass trajectories, we demonstrate the evolution of cloud properties with time. These cases are consistent with multi‐year statistics showing that long trajectories of air masses over the Antarctic ice sheet are critical to creating high droplet number clouds in the high latitude summer Southern Ocean. We speculate that secondary aerosol production via the oxidation of biogenically derived aerosol precursor gasses over the high actinic flux region of the high latitude ice sheets is fundamental to maintaining relatively high droplet numbers in Southern Ocean clouds during Summer. Plain Language Summary: The amount of warming the Earth will experience because of increasing carbon dioxide levels in the atmosphere is sensitive to the properties of clouds that occur over the Southern Ocean. The atmosphere over the circumpolar Southern Ocean is poorly understood and presents significant challenges to climate models. Here we document the properties of the ubiquitous Southern Ocean low‐level clouds that exert a strong influence on the albedo of this region. We find that high cloud droplet number concentrations are associated with air masses that have taken paths over the high‐altitude ice sheets. The chemistry of the aerosol on which the cloud droplets form suggests that aerosols that have recently condensed from gasses emitted by phytoplankton in the highly productive waters near Antarctica are an important component of the cloud properties that must be correctly simulated in models. Key Points: High cloud droplet number concentrations are associated with air masses that have recently passed over continental AntarcticaCloud droplet number concentrations decrease with time as clouds evolve in over‐water trajectories due to scavenging by precipitationKatabatic flows bring high concentrations of cloud condensation nuclei to the marine boundary layer where they influence cloud properties [ABSTRACT FROM AUTHOR]

The rising amount of greenhouse gases has been contributing to global warming and, subsequently, climate change. Industries such as refineries and power plants emit a significant amount of CO2 into the atmosphere. It is imperative to curb anthropogenic CO2 emissions, and hence, in this effort, we explore the utilization of a refinery emission stream to produce value‐added chemicals. The chosen emission stream for the said purpose is a typical flue gas stream from refineries. Following the capture step, this CO2 stream has been leveraged for subsequent valorization processes. Two strategies have been proposed in this paper to valorize the captured carbon dioxide. The first strategy employs the tri‐reforming process with a refinery‐specific fuel gas stream as the co‐reactant. The resulting syngas from tri‐reforming has been converted to chemicals such as methanol (MET) and ethanol. Furthermore, to improve the amount of CO2 valorized, another approach with green hydrogen has been considered. The second strategy aims at direct hydrogenation of the captured CO2 stream to produce MET and ethanol. The proposed strategies analyze the feasibility of valorizing captured CO2 from flue gas to MET and ethanol in terms of gross margin per feed and percentage of CO2 valorization. The performance assessment and analysis of the proposed processes have been carried out using simulations in Aspen Plus® that exhibited up to 74% valorization of CO2 into valuable chemicals. [ABSTRACT FROM AUTHOR]

Few observational platforms are able to sustain direct measurements of all the key variables needed in the bulk calculation of air‐sea carbon dioxide (CO2) exchange, a capability newly established for some Uncrewed Surface Vehicles (USVs). Western boundary currents are particularly challenging observational regions due to strong variability and dangerous sea states but are also known hot spots for CO2 uptake, making air‐sea exchange quantification in this region both difficult and important. Here, we present new observations collected by Saildrone USVs in the Gulf Stream during the winters of 2019 and 2022. We compared Saildrone data across co‐located vehicles and against the Pioneer Array moorings to validate the data quality. We explored how CO2 flux estimates differ when all variables needed to calculate fluxes from the bulk formulas are simultaneously measured on the same platform, relative to the situation where in situ observations must be combined with publicly‐available data products. We systematically replaced variables in the bulk formula with those often used for local and regional flux estimates. The analysis revealed that when using the ERA‐5 reanalysis wind speed in place of in situ observations, the ocean uptake of CO2 is underestimated by 8%; this underestimate grows to 9% if the NOAA Marine Boundary Layer atmospheric CO2 product and ERA‐5 significant wave height are also used in place of in situ observations. Overall our findings point to the importance of collecting contemporaneous observations of wind speed and ocean pCO2 to reduce biases in estimates of regional CO2 flux, especially during high wind events. Plain Language Summary: The North Atlantic Ocean absorbs a large amount of carbon dioxide (CO2) from the atmosphere. The ocean CO2 uptake mainly occurs during the winter months in a region where a swift ocean current, called the Gulf Stream, carries warm waters from the tropics to northern latitudes. Understanding how much CO2 this ocean region absorbs is important for constraining global scale assessments of the sources and sinks of CO2. In this paper, we reflect on the methods that are typically used to calculate the exchange of CO2 between the ocean and atmosphere. Using new data collected by uncrewed surface vehicles, that resemble small sailboats, in the North Atlantic Ocean in the vicinity of the Gulf Stream, we find that the estimate of the exchange of CO2 is larger when directly measured wind speeds are used in the calculation in comparison to wind speeds from a widely used data product. This result signifies the importance of co‐located sensors on the same observing platform. Key Points: Compared to Saildrone wind speeds, the ERA‐5 reanalysis appears to underestimate the highest wind speed events (>10 m s−1)Co‐located ocean pCO2 and wind speed observations results in larger uptake of CO2 in this region by 9%Using a sea‐state dependent gas transfer velocity leads to a 28% greater ocean uptake of CO2 compared to using a wind‐only equation [ABSTRACT FROM AUTHOR]

With increasingly serious environmental problems caused by the greenhouse effect, it has also become essential to reduce the concentration of CO2 in the atmosphere. In this paper, CaCO3‐supported Fe‐based catalysts doped with Mn, Al, and K are prepared by a straightforward method and used for CO2 hydrogenation. The fresh and spent catalysts were characterized by SEM‐EDS, BET, TG, CO2‐TPD, XRD, and XPS. The experimental results show that the highest CO2 conversion rate of Fe10Mn2Al10Ca is 35.99 %, the maximum FTY value is 293.98 μmolCO2 ⋅ gFe-1 ${{\rm{g}}_{{\rm{Fe}}}^{ - 1} }$ ⋅ s−1, the maximum O/P value is 6.61, and the lowest CO selectivity is 32.21 %. At the same time, according to the characterization results, the doping of Mn and Al increased the Fe3O4/FeCx ratio. As the Fe3O4/FeCx ratio increases, the proportion of short‐chain hydrocarbons (CH4, C2–4) in the products increases, and the proportion of long‐chain hydrocarbons (C5+) decrease. Therefore, the co‐doping of Mn and Al promotes the conversion of CO and reduces its selectivity, and promotes the formation of light olefins. Finally, it is hoped that this study can provide a reference for further research on CaCO3‐supported Fe catalysts. [ABSTRACT FROM AUTHOR]

Condensation and sublimation of ices at the surface of the planet is a key part of both the Martian H2O and CO2 cycles, either from a seasonal or diurnal aspect. While most of the ice is located within the polar caps, surface frost is known to be formed during nighttime down to equatorial latitudes. Here, we use data from the Emirates Mars Infrared Spectrometer onboard the Emirates Mars Mission to monitor the diurnal and seasonal evolution of the ices at the surface of Mars over almost one Martian year. The unique local time coverage provided by the instrument allows us to observe the apparition of equatorial CO2 frost in the second half of the Martian night around the equinoxes, to its sublimation at sunrise. Plain Language Summary: The H2O and CO2 ices that form at the surface on Mars play an important role in the exchange between the atmosphere and the surface of the planet. While most of the ice is located within the two polar caps that grew and shrink seasonally, ice is also known to condensate as surface frost during the night and sublimate during the day. This nighttime surface frost deposition can be observed even at equatorial latitudes. In this paper we use data from the Emirates Mars Infrared Spectrometer onboard the Emirates Mars Mission to detect the H2O and CO2 ices at the surface of the planet at all local times over almost one Martian Year, which allows us to monitor both the seasonal and diurnal evolution of the distribution of ices at the surface of Mars. We observe that nighttime CO2 frost forms at equatorial latitudes in the second half of the night to disappear at sunrise around the Martian equinoxes. Key Points: We monitor the seasonal growth and retreat of both polar caps over MY 36We monitor the presence of CO2 ice on the surface of Mars over MY 36, through the season and through all times of dayCO2 ice appears at the surface at equatorial latitudes during the second half of the night around the equinoxes [ABSTRACT FROM AUTHOR]

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The detailed study of diatom laminations conducted by means of backscattered electron imaging serves as tool to unravel details of past ocean dynamics. In this paper we apply this method to the analysis of the diatomites of Cerro Los Quesos, Upper Miocene Pisco Fm, Peru. Numerous studies have been conducted on the Pisco Fm; however, a focus on its paleoceanographic significance is still lacking. In this work, we provide information on the oceanographic setting in the area at the time of diatomites deposition. The high abundance of deep‐living Coscinodiscus laminae, proceeded by either a mixed lamina or a terrigenous one, let us hypothesize a deep position of the thermocline during the deposition of the Pisco diatomites; together with the scarcity of Chaetoceros Hyalochaete spp. resting spores, this evidence confutes the belief that equals high biogenic silica content in marine sediments with enhanced upwelling. Conversely, the depositional setting of the Pisco Fm diatomites is more similar to what is known as "permanent El Niño" (or "El Padre") state, meaning a constant weakened upwelling (or upwelling of nutrients‐poor waters). Climate modeling warns that an increase in atmospheric CO2 may lead to this mean state in the near future. Thanks to this study we also obtained refined information on the diatomites sedimentations rates. The comparison of the Pisco diatomites sedimentation rates with those of Quaternary diatomites gave strength to the hypothesis that the formation of the vertebrate Lagerstätte may have been enhanced, among others, by the so‐called "impact‐burial" mechanism. Plain Language Summary: Some sedimentary rocks are formed by the remains of small organisms. This is the case of diatoms, microscopic algae with a siliceous exoskeleton. As we know the ecological conditions of the modern oceans in which different diatom species live, when we found them in sedimentary rocks, we can infer the ecological conditions of the oceans millions of years ago. Here, we present the species that we found in some Peruvian rocks, the so‐called Pisco Formation, which dates back to 7/6 Million of years ago. Different species are preserved in these rocks in the same order in which they bloomed, so that we can identify small "laminae" (horizontal strips in the rock with thicknesses smaller than 1 mm) for each blooming season. The species that we recognize are those that today bloom during "El‐Niño," a climatic warm condition that causes loss of large fishery stocks, inundations and droughts. This small finding helps us hypothesize how climate may evolve if the Earth's temperatures keep on rising. Also, the Pisco formation is famous because of their huge content of fossil whales and dolphins, thus the study of this rock helps us understand how these large mammals got preserved trough millions of years. Key Points: Laminae of the Upper Miocene diatomaceous Pisco Formation reveal that the fall dump mechanism regulated marine export productionThe predominance of fall dump over upwelling implies a drop of the temperature gradient between the Western and Eastern PacificEvidences highlight a need of caution when using biogenic silica as a proxy for paleo upwelling [ABSTRACT FROM AUTHOR]

The capture of CO2 from air via direct air capture (DAC) is a promising way to reduce the carbon dioxide concentration in the atmosphere. The carbonation of calcium‐based adsorbents using ambient conditions is particularly interesting for DAC due to its high theoretical CO2 uptake capacity and its low cost. In this paper, a new preparation method of synthetic calcium oxide‐based pellets for a DAC process was investigated. Their CO2 capture performance was studied experimentally in a fixed‐bed column and characterization was performed via Brunauer‐Emmett‐Teller (BET) analysis, mercury porosimetry, X‐ray diffraction, and scanning electron microscopy. Higher heating rates during the precursor calcination process and higher relative humidities during the carbonation process were found to lead to higher CO2 capture efficiencies. All prepared pellets showed good mechanical stability. [ABSTRACT FROM AUTHOR]

Vertical motions across the ocean are central to processes, like CO2 fixation, heat removal or pollutant transport, which are essential to the Earth's climate. This work explores 3D conveyor routes associated with the Atlantic Meridional Overturning Circulation (AMOC). Our findings show the geometry of mixing structures in the upper and deep ocean layers by means of Lagrangian Coherent Structures. This tool identifies among others, zones linked to vertical transport and characterizes vertical transport time scales. We focus the study in two regions. The first one is the Flemish Cap region, a zone of interaction between the major AMOC components, where our analysis identifies a domain of deep waters that ascend very rapidly to the ocean surface. The second one is the Irminger Sea, where our analysis confirms the existence of a downwelling zone, and reveals a previously unreported upwelling connection between very deep waters and the ocean surface. Plain Language Summary: The Atlantic Meridional Overturning Circulation (AMOC) is a complex oceanic convective system involved in the tridimensional distribution of heat, carbon or nutrients. The horizontal transport across the AMOC is well studied, however, there are not many studies exploring mixing and transport processes across the vertical water column, that is, from the surface to the deep ocean and viceversa. To fully understand this 3D system, this paper follows a methodology that links apparently unrelated elements such as mixing and geometry. This approach is very promising to better characterize transport across the vertical column of major ocean currents and determining their impact on the global climate system. Key Points: Lagrangian Coherent Structures reveal the complex mixing geometry of 3D circulating watersSupported by this tool we are able to highlight upwelling and downwelling routes across the Atlantic Meridional Overturning CirculationThis approach seems promising to determine the role of vertical mixing on major ocean currents in the Earth's climate system [ABSTRACT FROM AUTHOR]

Enigmatic is a word that often comes up in discussions about Proterozoic molar tooth carbonate structures (MTS). But when unusual features such as these are common in rocks of a particular age, there is almost always an important message waiting to be discovered. In this case, the observed temporal patterns for MTS likely track first‐order trends in evolving compositions in the oceans during Earth's middle history when CO2 in the atmosphere and carbonate saturation in the ocean were high but declining and oxygen (O2) in the ocean‐atmosphere system was on the rise. A new paper by Tang et al. (2023, https://doi.org/10.1029/2022JG007077) gives us a new way to think about MTS origins, and nested within their model are wide ranging implicit and explicit linkages to Earth surface evolution as life was becoming more complex in a slow march toward the world we know today. Key Points: Temporal patterns for molar tooth carbonate structures (MTS) likely track first‐order trends in evolving compositions in the oceans and atmosphereEarth's middle chapters, because of prevailing redox and ocean compositions, were an ideal window for MTS formationMTS represent the transition from high to lower atmospheric carbon dioxide and low to higher biospheric oxygen [ABSTRACT FROM AUTHOR]

Past studies have demonstrated that synoptically active weather systems play an important role in the spatial and temporal variations of atmospheric carbon dioxide (CO2) within and above the planetary boundary layer. For the first time, we investigate the spatial variability of column‐averaged dry‐air mole fractions of CO2 ${\mathrm{C}\mathrm{O}}_{2}$ (i.e.,XCO2 $\mathrm{i}.\mathrm{e}.,{\mathrm{X}\mathrm{C}\mathrm{O}}_{2}$) due to the impact of synoptic scale transport using retrievals from the Orbiting Carbon Observatory‐2 (OCO‐2) for 66 summer cold front passage cases over the conterminous U.S. and Mexico from 2015 to 2019. XCO2 ${\mathrm{X}\mathrm{C}\mathrm{O}}_{2}$ differences across cold fronts in summer were found to be in good agreement with observations obtained from the Atmospheric Carbon and Transport (ACT‐America) field campaign, though with a reduced magnitude due the flat averaging kernel representing fairly uniform vertical sensitivity in the troposphere as opposed to in situ CO2 ${\mathrm{C}\mathrm{O}}_{2}$ measurements. OCO‐2 observed XCO2 ${\mathrm{X}\mathrm{C}\mathrm{O}}_{2}$ frontal differences are statistically distinct from north‐south XCO2 ${\mathrm{X}\mathrm{C}\mathrm{O}}_{2}$ climatological spatial variations on similar spatial‐scales on synoptically benign days, implying that the frontal passages contribute to enhanced XCO2 ${\mathrm{X}\mathrm{C}\mathrm{O}}_{2}$ spatial contrasts. An exploratory analysis finds no evidence of a linkage between the temperature differences and XCO2 ${\mathrm{X}\mathrm{C}\mathrm{O}}_{2}$ differences, but a more thorough exploration is left as future work. Plain Language Summary: Atmospheric CO2 ${\mathrm{C}\mathrm{O}}_{2}$ is one of the main contributors to climate change among the various long‐lived greenhouse gases. The spatial distributions of atmospheric CO2 ${\mathrm{C}\mathrm{O}}_{2}$ may change abruptly on short time scales (e.g., hours or less) and gradually on long time scales (e.g., years or longer). Due to weather, there are several mechanisms for atmospheric CO2 ${\mathrm{C}\mathrm{O}}_{2}$ spatial redistribution, for example, the advection of upwind sources and/or sinks. In this paper, we explore the spatial CO2 ${\mathrm{C}\mathrm{O}}_{2}$ differences related to summer cold fronts. We collect 66 summer cold fronts as seen from NASA's Orbiting Carbon Observatory‐2 over the CONUS and north Mexico between 2015 and 2019. The results suggest that the column‐averaged CO2 ${\mathrm{C}\mathrm{O}}_{2}$ (XCO2 ${\mathrm{X}\mathrm{C}\mathrm{O}}_{2}$) differences across these 66 summer cold fronts are statistically distinct from the climatological XCO2 ${\mathrm{X}\mathrm{C}\mathrm{O}}_{2}$ north‐south gradients. The summer cold‐front‐relative contrasts between warm and cold sectors can provide a reference for models in simulating the horizontal advection, source, and/or sink changes in the synoptic weather. Key Points: XCO2 ${\mathrm{X}\mathrm{C}\mathrm{O}}_{2}$ retrievals from Orbiting Carbon Observatory‐2 (OCO‐2) exhibit enhanced contrasts across cold fronts in the conterminous US during 2015–2019 summers, with larger XCO2 ${\mathrm{X}\mathrm{C}\mathrm{O}}_{2}$ values in the warm sectors than the cold sectorsAnalyses reveal that OCO‐2 observed transient XCO2 ${\mathrm{X}\mathrm{C}\mathrm{O}}_{2}$ frontal contrasts that were greater than climatological XCO2 ${\mathrm{X}\mathrm{C}\mathrm{O}}_{2}$ spatial differences on days without cold fronts in the CONUS in summers during the period 2015‐2019 [ABSTRACT FROM AUTHOR]

Atmospheric inversions provide estimates of carbon dioxide (CO2) fluxes between the surface and atmosphere based on atmospheric CO2 concentration observations. The number of CO2 observations is projected to increase severalfold in the next decades from expanding in situ networks and next‐generation CO2‐observing satellites, providing both an opportunity and a challenge for inversions. This study introduces the TRACE Regional Atmosphere–Carbon Ensemble (TRACE) system, which employ an ensemble‐based simultaneous state and parameter estimation (ESSPE) approach to enable the assimilation of large volumes of observations for constraining CO2 flux parameters. TRACE uses an online full‐physics mesoscale atmospheric model and assimilates observations serially in a coupled atmosphere–carbon ensemble Kalman filter. The data assimilation system was tested in a series of observing system simulation experiments using in situ observations for a regional domain over North America in summer. Under ideal conditions with known prior flux parameter error covariances, TRACE reduced the error in domain‐integrated monthly CO2 fluxes by about 97% relative to the prior flux errors. In a more realistic scenario with unknown prior flux error statistics, the corresponding relative error reductions ranged from 80.6% to 88.5% depending on the specification of prior flux parameter error correlations. For regionally integrated fluxes on a spatial scale of 106 km2, the sum of absolute errors was reduced by 34.5%–50.9% relative to the prior flux errors. Moreover, TRACE produced posterior uncertainty estimates that were consistent with the true errors. These initial experiments show that the ESSPE approach in TRACE provides a promising method for advancing CO2 inversion techniques. Plain Language Summary: To gain a better understanding of the main drivers behind atmospheric carbon dioxide (CO2) variations and trends, it is essential to accurately quantify CO2 exchanges—also known as fluxes—between the atmosphere and other components of the Earth system. It is generally not possible to directly measure surface CO2 fluxes at regional scales; however, fluxes can be inferred from a network of atmospheric CO2 concentration observations combined with atmospheric modeling and inversion methods, which seek to find the most likely fluxes given prior knowledge and observational evidence. This paper presents a new regional inversion framework called TRACE Regional Atmosphere–Carbon Ensemble (TRACE) for deriving CO2 fluxes at high resolution in space and time. One of the major innovations in TRACE is the ensemble‐based dual state and parameter estimation approach, which makes it computationally feasible to ingest large volumes of observations into the system. A series of experiments were carried out in a domain over North America to test the new framework in a controlled setting. In the experiments, we used synthetic tower observations of atmospheric CO2 concentrations to constrain parameters controlling terrestrial biogenic and oceanic CO2 fluxes. The results show that TRACE is capable of accurately estimating both the magnitude and spatial pattern of regional CO2 fluxes. Key Points: An ensemble‐based simultaneous state and parameter estimation approach is introduced for regional CO2 flux inversionsThe new dual‐state TRACE Regional Atmosphere–Carbon Ensemble (TRACE) framework provides a flexible platform for conducting coupled atmosphere–carbon data assimilationControlled experiments show that TRACE is effective at constraining regional CO2 fluxes using in situ CO2 concentration observations [ABSTRACT FROM AUTHOR]

The article offers information on the views of author on various works of limnologists published in different journals regarding atmospheric carbon. Topics discussed include papers of scholar Michel Meybeck "Riverine transport of atmospheric carbon: sources, global typology, and budget" published in periodical Water Air and Soil Pollution; works on plumbing by scholar Grace Wilkinson; and scholarly works of George Kling.

CO2 emission is an important environmental issue leading to global climate change, notably an increase in global temperatures; therefore, it is so imperative to reduce CO2 emissions to the atmosphere. Absorption columns using amine‐based solutions are a promising approach for CO2 removal from industrial gas streams. Many modeling and simulation research have been performed on CO2 absorption columns in which computational fluid dynamics (CFD) strategy is very appropriate and well‐known. As CFD modeling and simulation is a fast‐developing method, the most recent review papers do not include the core research in this field of study. In this study, numerical simulations of CO2 absorption columns using CFD strategy have been carried out applying various types of amine‐based solutions. Furthermore, the effect of various types of packing mesh generation on the absorption columns' efficiency was studied. Investigation of synergetic influence such as application of various nanoparticles in different amine‐based solutionsand activators, double diameter packed bed absorption columns with different packings, rotating packed columns with double diameter are proposed for future studies. [ABSTRACT FROM AUTHOR]

The El Niño‐Southern Oscillation (ENSO) in the equatorial Pacific is the dominant mode of global air‐sea carbon dioxide (CO2) flux interannual variability (IAV). Air‐sea CO2 fluxes are driven by the difference between atmospheric and surface ocean pCO2, with variability of the latter driving flux variability. Previous studies found that models in Coupled Model Intercomparison Project Phase 5 (CMIP5) failed to reproduce the observed ENSO‐related pattern of CO2 fluxes and had weak pCO2 IAV, which were explained by both weak upwelling IAV and weak mean vertical dissolved inorganic carbon (DIC) gradients. We assess whether the latest generation of CMIP6 models can reproduce equatorial Pacific pCO2 IAV by validating models against observations‐based data products. We decompose pCO2 IAV into thermally and non‐thermally driven anomalies to examine the balance between these competing anomalies, which explain the total pCO2 IAV. The majority of CMIP6 models underestimate pCO2 IAV, while they overestimate sea surface temperature IAV. Insufficient compensation of non‐thermal pCO2 to thermal pCO2 IAV in models results in weak total pCO2 IAV. We compare the relative strengths of the vertical transport of temperature and DIC and evaluate their contributions to thermal and non‐thermal pCO2 anomalies. Model‐to‐observations‐based product comparisons reveal that modeled mean vertical DIC gradients are biased weak relative to their mean vertical temperature gradients, but upwelling acting on these gradients is insufficient to explain the relative magnitudes of thermal and non‐thermal pCO2 anomalies. Plain Language Summary: To date, the global ocean has been responsible for absorbing over a third of carbon dioxide (CO2) emissions, slowing down the growth of atmospheric CO2 levels which drives global warming. Of interest is the equatorial Pacific Ocean, which is the largest oceanic source of CO2 to the atmosphere with large fluctuations that are apparent in the record of global atmospheric CO2. To study the ocean's ability to absorb future CO2 emissions, we need models of the Earth system that can accurately capture fluctuations in the equatorial Pacific. In this paper, we assess surface ocean CO2 fluctuations in the equatorial Pacific in the latest generation of models and we examine their deviations from observations. Compared to observations, models underestimate surface ocean CO2 fluctuations as a result of excessive cancellation between competing drivers of CO2 change. We find that the vertical gradient of carbon in models is too weak, which through ocean circulation, would contribute to weak surface CO2 fluctuations. However, this does not fully account for underestimations in surface CO2 fluctuations. Other processes have a significant role in excessively canceling surface CO2 concentrations and requires further research. Key Points: The majority of models underestimate pCO2 IAV, while they overestimate sea surface temperature IAVThe ratio of non‐thermal‐to‐thermal pCO2 IAV is systematically underestimated in models, which results in weak total pCO2 IAVVertical dissolved inorganic carbon gradients are biased weak more than temperature gradients, but this alone doesn't explain the relative sizes of pCO2 components [ABSTRACT FROM AUTHOR]

The mid Miocene represents an important target for paleoclimatic study because the atmospheric CO2 concentration ranged from near modern values to ∼800 ppm, while a large, dynamic Antarctic ice sheet was likely to have been present throughout much of this interval. In this special issue, Modestou et al. (2020) (doi.org/10.1029/2020PA003927) reconstruct deep ocean warmth based on the clumped isotopic composition of benthic foraminifera, a technique that allows the ice volume and thermal components of the benthic oxygen isotope stack to be separated. These data reveal a very warm deep ocean while simultaneously suggesting that continental ice volume may, at times, have been greater than today. Here, I review these results in the context of recent developments in geochemical proxies and ice sheet modeling, and explore how the presence of a large Miocene ice sheet could be reconciled with CO2 at least as high as present. More broadly, I argue that many of the 'paradoxes' that pepper the paleoclimate literature result as much from our imperfect understanding of the proxies, as from our understanding of the climate system. Robust proxies with a well‐understood mechanistic basis, as employed by Modestou et al. (2020), as well as advances in model‐data comparability usher in a new era of palaeoclimate research; an exciting future of untangling Earth's myriad past climate states awaits. Plain Language Summary: Reconstructing climate variation in Earth's geologic past informs us of the broad features of warm climates, which is relevant to preparing for climate change over the coming centuries. Moreover, these data can be compared to state‐of‐the‐art climate models, which provides a test of the degree to which our models can reproduce warm climate states. A paper recently published in this journal applies a new method in order to reconstruct the temperature of the deep ocean in the middle Miocene (between 17 and 12 million years ago), when the atmospheric CO2 concentration was naturally similar to or higher than it is today. Coupled with decades of previous study, these exciting results depict an unfamiliar world characterized by a warm deep ocean, and yet a large ice sheet was present on Antarctica. Both models and data agree that the Antarctic ice sheet in the Miocene was highly responsive to changes in the atmospheric CO2 concentration, a clear cause of concern in the context of ongoing anthropogenic climate change. Key Points: The importance of a paper by Modestou et al. (2020) is explained, which reports middle Miocene benthic foraminifera clumped isotope dataWays in which a large Antarctic ice sheet can be reconciled with a warm deep ocean and moderately high CO2 are exploredMore broadly, I argue that recent advances in proxy methodology are resulting in ever increasing confidence in paleoclimate reconstructions [ABSTRACT FROM AUTHOR]

This paper deals with the analysis of the relationship between CO2 emissions and temperatures. For this purpose, global CO2 emissions and four measures of global temperatures (land, land and ocean, northern and southern temperatures) are used. We used techniques based on fractional integration and cointegration. The results indicate first that the orders of integration differ in the two variables. Thus, while emissions are I(1) or I(d) with d higher than 1, temperatures display orders of integration strictly smaller than 1 and thus invalidating the hypothesis of cointegration between the two variables. Due to this, another approach is conducted where we suppose that the emissions are weakly exogenous in relation to the temperatures. The results using this approach show a significantly positive relationship between the two variables with a long memory pattern. [ABSTRACT FROM AUTHOR]

Ag‐based nanocrystals have emerged as an important candidate for CO2 reduction reaction (CO2RR) owing to the increasing amount of CO2 in the atmosphere, which has shown a propensity to alleviate environmental problems and produce high value‐added chemicals. This paper reviews the surface and interface engineering of Ag‐based catalysts towards CO2RR, which involve in the morphology control, composition manipulation, and support effects. Various synthesis approaches are presented to discuss their influence on the size, crystal structure and morphology of Ag‐based catalysts, including pure Ag NPs, Ag‐based alloys, Ag/metal oxides composites as well as Ag/carbon materials. Next, the development of Ag‐based surface and interface engineering that is essential to accelerate the formation of CO and its further conversion to C1 or even multicarbon products is systematically discussed. Finally, we give a short conclusion, and perspectives on the rational design of Ag‐based catalysts based on surface and interface engineering will be discussed. [ABSTRACT FROM AUTHOR]

Protonic ceramic fuel cells (PCFCs) using BaZr0.8−xCexY0.2O3−δ (BZCY) as electrolyte materials have attracted widespread attention because of their high performance at reduced temperature. However, there are few systematic studies on both the performance and stability of BZCY materials. In this paper, we report our work on the electrochemical performance and chemical stability of BaZr0.8−xCexY0.2O3−δ (x = 0, 0.1, 0.3, 0.5, and 0.7) series. The results show that electronic hole conductivity decreases with increasing Ce4+ content, especially at high temperature. In addition, H2 atmosphere reduces the conductive activation energy of BZCY. On the contrary, air atmosphere causes serious electronic leakage. These effects are also reflected in the operation of PCFCs, that is, the higher the Ce4+ content, the higher the open‐circuit voltage and output power density. However, low Ce4+ content may stabilize the materials in CO2 atmosphere. At 700°C, an anode‐supported PCFC based on BaZr0.1Ce0.7Y0.2O3−δ electrolyte, using humid H2 fuel, gives a peak power density of 1.0 W cm−2. At 600°C, BaZr0.8Y0.2O3−δ and BaZr0.7Ce0.1Y0.2O3−δ show a good stability in CO2‐containing atmosphere. [ABSTRACT FROM AUTHOR]

An increase in the seasonal cycle amplitude (SCA) of atmospheric CO2 since the 1960s has been observed in the Northern Hemisphere (NH). However, the underlying dominant drivers are still debated. The peak season CO2 uptake by vegetation is critical in shaping the CO2 seasonality. Using satellite‐upscaled gross primary production (GPP) from FLUXCOM and near‐infrared reflectance of vegetation (NIRV), we demonstrate that peak GPP has increased across the NH over the last two decades. We relate this productivity increase to changes in the CO2 SCA using an atmospheric transport model. The increased photosynthesis has strongly contributed to CO2 SCA trends, but with substantial latitudinal and longitudinal variations. Despite a general increase in the CO2 SCA, there are distinct regional differences. These differences are mainly controlled by regional biosphere carbon fluxes, with the remainder explained by non‐biome factors, including large‐scale atmospheric transport, changes in fossil fuel combustion, biomass burning and oceanic fluxes. Using the global flask and in situ CO2 measurement sites, we find that SCA trends at high latitude are mainly driven by increasingly productive natural ecosystems, whereas mid latitude sites around the Midwest United States are mainly impacted by intensified agriculture and atmospheric transport. Averaging across the 15 long‐term surface sites, forests contribute 26% (7%) to the SCA trends, while crops contribute 17% (24%) and the combined shrubland, grassland and wetland regions contribute 23% (37%) for simulations driven by FLUXCOM (NIRv) ecosystem fluxes. Our findings demonstrate that satellite inferred trends of ecosystem fluxes can capture the observed CO2 SCA trend. Plain Language Summary: An increase in the seasonal cycle amplitude (SCA) of atmospheric carbon dioxide (CO2) since the 1960s has been observed in the Northern Hemisphere (NH). However, dominant drivers of the amplified CO2 seasonality are still debated. In this study, we employ satellite‐based remote sensing observations to track spatial and temporal changes in global gross primary production (GPP) of different vegetation types. Then, we use a state‐of‐art atmospheric transport model to examine whether our bottom‐up estimates of ecosystem fluxes can capture the magnitude of CO2 SCA trends at multiple surface sites. Further, we explore dominant drivers of the observed CO2 SCA trends across different locations of sites. To our best knowledge, this paper makes the first effort to link long‐term satellite remote sensing observations with ground atmospheric CO2 measurements across the NH to explore how terrestrial carbon fluxes shape and change spatiotemporal pattern of atmospheric CO2. Key Points: Peak growing season gross primary production has increased across the northern extratropics over the last two decades based on satellite observationsThe remote sensing‐based global terrestrial carbon fluxes well capture the observed CO2 seasonal cycle amplitude trends at surface sitesMajor factors driving the observed increase in the atmospheric CO2 seasonal amplitude trends vary across the location of sites [ABSTRACT FROM AUTHOR]

Agriculture is one of the primary contributors to Pakistan's economy. However, over the last few decades, the atmospheric carbon dioxide emission has been amplified to a great extent in Pakistan. This amplification may cause climate change, global warming, and environmental mitigation in Pakistan. This paper empirically investigates the impact of CO2 emissions on the agricultural export trade of Pakistan over the period 1975–2017. Evidence suggests that climate change could be a primary cause for the decline in Pakistan's agriculture export trade; no studies have been carried out for this specific issue, particularly over time. In this paper, the empirical analysis suggests the negative coefficient of agriculture export trade with CO2 emissions subsequently decreases agriculture export trade, which leads to direct impact on Pakistan's economy. Both theoretical and empirical outcomes suggest that the adaptation of clean and green energies and technologies are the key to reduce pollution in Pakistan. Overall, the effects of carbon dioxide emissions on agriculture export trade are stronger in the long‐run dynamics, thus making the finding heterogeneous. Possible initiatives should be taken by the government of Pakistan to improve the agriculture sector and it should also introduce new policies to reduce the emissions of carbon dioxide. [ABSTRACT FROM AUTHOR]

This article describes the development of a new technology based on the application of liquid metal and aims to produce hydrogen by decarbonization (pyrolysis process) of both natural and artificially synthesized hydrocarbons. When biogas with a sufficiently high carbon dioxide content is used as a feedstock, or by the targeted addition of CO2 to methane, a mixture of hydrogen and carbon monoxide (synthesis gas) can be produced. Furthermore, the paper describes another very interesting application of the technology to create negative emissions. In this scenario, the processes direct air capture, methanation, electrolysis and methane pyrolysis are combined to synthesize solid carbon from atmospheric CO2. The broad range of process options investigated indicates that, when the technology is scaled up to industrial scale, the result will be a process that is flexible in both the use of reactants and the resulting products. [ABSTRACT FROM AUTHOR]

The marine biological carbon pump (BCP) stores carbon in the ocean interior, isolating it from exchange with the atmosphere and thereby coregulating atmospheric carbon dioxide (CO2). As the BCP commonly is equated with the flux of organic material to the ocean interior, termed "export flux," a change in export flux is perceived to directly impact atmospheric CO2, and thus climate. Here, we recap how this perception contrasts with current understanding of the BCP, emphasizing the lack of a direct relationship between global export flux and atmospheric CO2. We argue for the use of the storage of carbon of biological origin in the ocean interior as a diagnostic that directly relates to atmospheric CO2, as a way forward to quantify the changes in the BCP in a changing climate. The diagnostic is conveniently applicable to both climate model data and increasingly available observational data. It can explain a seemingly paradoxical response under anthropogenic climate change: Despite a decrease in export flux, the BCP intensifies due to a longer reemergence time of biogenically stored carbon back to the ocean surface and thereby provides a negative feedback to increasing atmospheric CO2. This feedback is notably small compared with anthropogenic CO2 emissions and other carbon‐climate feedbacks. In this Opinion paper, we advocate for a comprehensive view of the BCP's impact on atmospheric CO2, providing a prerequisite for assessing the effectiveness of marine CO2 removal approaches that target marine biology. [ABSTRACT FROM AUTHOR]

Soil organic carbon (SOC) sequestration is a key function of natural and semi-natural ecosystems. Restoring this property in terrestrial ecosystems has become central to the EU's climate change mitigation and adaptation strategies. However, SOC sequestration is a widely misunderstood concept. The different methodological approaches used to investigate and compare SOC stock under sustainable agricultural practices play a key role in reinforcing misconceptions about this complex process. This commentary paper aimed not only to provide a clear definition of SOC sequestration, but also to interpret the results that can be obtained for SOC stock change estimation using the SOC stock difference and the paired comparison methods, as well as to identify the soil carbon-related processes that achieve climate mitigation. SOC sequestration can be defined as the progressive increase in a site's SOC stock compared with pre-intervention via a net depletion and transfer of atmospheric CO2 into the soil, where it is retained as soil organic matter (SOM), by plants, plant residues, or other organic solids such as the material derived from the organic fraction of farming solid waste, which can be used as a fertilizer (e.g., manure, compost, biochar, and digestate), and that is produced or derived from that land unit. To date, the most appropriate way to determine whether a land unit's soil is a sink or rather a source of atmospheric CO2 is to implement the SOC stock difference method, provided the non-occurrence of carbon exchange between ecosystems. [ABSTRACT FROM AUTHOR]

Expectations about the future removal of carbon dioxide from the atmosphere have mobilized projects which seek to demonstrate carbon removal methods, at various stages of development. Public perceptions play a critical role in demonstrations and funders widely require demonstration projects to identify and consult affected groups and communities. This review examines the extant research on perceptions of carbon removal, analyzing how studies have conceptualized the public and the role perceptions play in field trials and experiments of carbon removal methods. The paper develops a novel analytical framework distinguishing between "procedural" and "performative" approaches to demonstrations. Attending to performativity, we suggest, makes clear why demonstration projects often surface conflicting expectations about future technology development. We apply the analytical framework to the academic literature on perceptions of carbon removal using a systematic search and interpretive review. We find that much perceptions research on carbon removal adopts elements from linear models of innovation, foregrounding the problem of social acceptance and distancing the public from experimental presentations and displays. We situate these findings in a discussion of the roles that expectations about carbon removal play in demonstrations and the positioning of perceptions research as a tool for managing "opposition" from external audiences. Moving beyond instrumental approaches to public perception, the review makes the case for closer engagement in perceptions research with conflicting expectations that emerge around projects demonstrating the "promise" of carbon removal. This article is categorized under:The Social Status of Climate Change Knowledge > Knowledge and PracticePerceptions, Behavior, and Communication of Climate Change > Perceptions of Climate ChangeClimate, History, Society, Culture > Technological Aspects and Ideas [ABSTRACT FROM AUTHOR]

We present ΔO2/Ar‐based estimates of mixed layer net community production (NCP) from three summer cruises in the North American Arctic and Subarctic oceans. Coupling shipboard underway and discrete observations with output from an ocean circulation model, we correct the NCP estimates for vertical mixing fluxes impacting the surface O2 budget. Large positive mixing fluxes, exceeding 100 mmol O2 m−2 d−1, were derived in regions of strong wind‐driven mixing, such as the Labrador Sea (LS), and in the physically‐dynamic Canadian Arctic Archipelago. In contrast, flux corrections were small (<10 mmol O2 m−2 d−1, on average) in the density‐stratified Baffin Bay, where mixing was low, and parts of the well‐mixed Hudson Strait (HS), where vertical O2 gradients were weak. The distribution of corrected NCP was highly heterogenous across the study region, reflecting varying contributions of nutrient supply, freshwater input and sea ice dynamics. Elevated NCP was apparent in the LS, HS, and nearshore regions influenced by glacial meltwater and recent ice retreat. Low NCP and localized net heterotrophy occurred in Baffin Bay, and near strong freshwater and organic matter sources in Hudson Bay and the Queen Maud Gulf. A multiple linear regression model developed using available oceanographic data explained ∼58% of the observed NCP variability. Our work demonstrates the spatially explicit influence of vertical mixing on ΔO2/Ar‐based NCP calculations across varied hydrographic conditions, and presents a novel approach to account for this process. This study contributes new knowledge of biological productivity distributions in under‐sampled, rapidly changing, high‐latitude waters. Plain Language Summary: Net community production (NCP; i.e., net organic matter production) constrains the ocean's ability to support marine ecosystems and remove carbon dioxide from the atmosphere. A common approach to estimating NCP involves measurements of upper ocean oxygen (O2) concentrations. However, while vertical mixing may be a significant component of the surface water O2 budget in some regions, applications of this approach typically do not quantify the magnitude of this flux, which can lead to potentially inaccurate NCP estimates. In this paper, we introduce a method combining ship‐based measurements and the output from an ocean circulation model to refine NCP calculations for vertical mixing effects in North American Arctic and Subarctic oceans. The data set reveals high NCP in the Labrador Sea (Inuktitut: Lâbradorip Imappinga), North Atlantic, Hudson Strait (Ikirasarjuaq) and northern Canadian Arctic Archipelago (CAA), and low values in Baffin Bay (Saknirutiak Imanga) and southern CAA. Riverine freshwater input to Hudson Bay (Tasiujarjuar) and the Queen Maud Gulf (Ugjulik) can reduce local NCP, while glacial meltwater may stimulate NCP elsewhere. Overall, this work provides a new NCP data set in an under‐sampled region. Similar studies will be necessary to document changes in biological productivity in response to changing environmental conditions in polar waters. Key Points: Ship‐based observations and numerical model output were used to correct net community production (NCP) estimates for vertical mixing biasesCorrected NCP was correlated with nutrient supply and sea ice dynamics, as reflected in a multiple linear regressionFreshwater from glaciers and rivers may stimulate productivity or drive local respiration through nutrient and organic carbon inputs [ABSTRACT FROM AUTHOR]

This paper synthesises insights and offers new quantitative analyses of data gathered during 40 years of stream research by Danish researchers and international associates. Lowland Danish streams mostly drain fertile cropland and contain high nutrient concentrations saturating maximum yield and growth rate of plants. Concentrations of carbon dioxide (CO2) are variable, although usually high, supporting a range of wetland and permanently submerged species.All terrestrial and most amphibious species are obligate CO2 users, while the majority of permanently submerged species can supplement their inorganic carbon demand with bicarbonate. In lake outlets, the average CO2 concentration was close to air saturation during summer, whereas sites with no lake influence were 9‐fold supersaturated. The 20% increase of atmospheric CO2 concentrations over the past 40 years has marginal influence on CO2 concentrations in the streams.In lake outlets with low CO2 concentrations, calculations on 33 stream species showed essentially no underwater photosynthesis by temporarily submerged terrestrial species, low rates by amphibious species, and high rates by permanently submerged bicarbonate users. Underwater photosynthetic rates increased at sites with high CO2 concentrations (no lake influence): they were lowest for terrestrial wetland species (mean 1.8 mg O2 g dry weight−1 hr−1), followed by homophyllous (3.0) and heterophyllous amphibious species (5.6), and highest among permanently submerged species (15.0). Terrestrial and amphibious species grew very slowly when CO2 levels were low, but rapidly in CO2 rich water, or when in contact with air above the water's surface. Decreasing CO2 concentrations from upstream to downstream caused lower photosynthesis rates of amphibious species, while photosynthesis by bicarbonate users was consistently high.The relative abundance of terrestrial and amphibious species decreased significantly as CO2 resources decline from upstream to downstream, while the abundance of permanently submerged species increased as streams progressed. However, plant abundance as a function of CO2 concentrations did not differ markedly among the plant groups.We conclude that photosynthesis and growth of species of different plant types under controlled experimental conditions resembling high in situ nutrient availability are closely related to inorganic carbon supplies, while their representation in plant assemblages is influenced by the spatially and temporally highly diverse ecological conditions from upstream to downstream in the mostly CO2‐rich lowland streams.Submerged terrestrial and amphibious species restricted to CO2 use for photosynthesis can partly escape the slow gas diffusion under water by growing in very CO2‐rich streams and having apical leaves in contact with air. Thus, strong restrictions on their growth and existence should be identified at sites where CO2 concentrations are consistently low and no air contact is possible, while co‐limitation by nutrients is likely to be marginal.Generally, rising atmospheric CO2 is irrelevant to photosynthesis of permanently submerged plants because of their ability to use bicarbonate and the high CO2 supersaturation in most stream sites. In contrast, photosynthesis and growth of amphibious and terrestrial plants under water are highly dependent on CO2 concentrations varying from close to air saturation in lake outlets to supersaturation in headwaters. [ABSTRACT FROM AUTHOR]

The atmospheric concentration of CO2 is steadily increasing and causing climate change. To achieve the Paris 1.5 or 2°C target, negative emission technologies must be deployed in addition to reducing carbon emissions. The ocean is a large carbon sink but the potential of marine primary producers to contribute to carbon neutrality remains unclear.Here we review the alterations to carbon capture and sequestration of marine primary producers (including traditional 'blue carbon' plants, microalgae and macroalgae) in the Anthropocene, and, for the first time, assess and compare the potential of various marine primary producers to carbon neutrality and climate change mitigation via biogeoengineering approaches.The contributions of marine primary producers to carbon sequestration have been decreasing in the Anthropocene due to the decrease in biomass driven by direct anthropogenic activities and climate change. The potential of blue carbon plants (mangroves, saltmarshes and seagrasses) is limited by the available areas for their revegetation. Microalgae appear to have a large potential due to their ubiquity but how to enhance their carbon sequestration efficiency is very complex and uncertain. On the other hand, macroalgae can play an essential role in mitigating climate change through extensive offshore cultivation due to higher carbon sequestration capacity and substantial available areas. This approach seems both technically and economically feasible due to the development of offshore aquaculture and a well‐established market for macroalgal products.Synthesis and applications. This paper provides new insights and suggests promising directions for utilizing marine primary producers to achieve the Paris temperature target. We propose that macroalgae cultivation can play an essential role in attaining carbon neutrality and climate change mitigation, although its ecological impacts need to be assessed further. [ABSTRACT FROM AUTHOR]

The work assesses the availability and localizations of different raw materials suitable for ocean alkalinity enhancement (OAE), like limestone, olivine, magnesite and brucite, since several billion tons of rocky materials are needed to achieve meaningful results for carbon sequestration through OAE. Resources of carbonates are immense and widespread around all continents. Availability of pure carbonates is still very large (outcrop area 4.1 million km2) and is not a constraint for the large‐scale development of OAE. Outcrops of pure carbonates within 10 km from the coastline and below bare ground or scrub/shrub, preferred for the logistics of exploitation, account for about 70,000 km2, and could provide about 5,000 Gt of limestone. These values increase by a factor of 3 and 8 within 50 and 100 km from the coastline, respectively. Potential resources of olivine, less easily identifiable from the geological data, are estimated in the order of a few hundred billion tons and could provide only a minor contribution to ocean‐based carbon removal strategies. A comparison with the current level of world extraction of mineral raw materials is also provided. The annual production of limestone, estimated to be more than 6.6 Gt from deposits scattered all around the world, is about 9% of the world production of mineral raw materials (around 44 Gt yr−1), and is of the same order of magnitude as coal (7.3 Gt yr−1). The annual productions of magnesite (29 Mt yr−1), olivine (8.4 Mt yr−1) and brucite (1.5 Mt yr−1) are two orders of magnitude lower. Plain Language Summary: The ongoing acidification of the oceans due to the increase of carbon dioxide (CO2) concentration in the atmosphere and the consequent increased uptake by the sea can be tackled by adding alkaline compounds under controlled conditions. Since this promotes a number of reactions in the carbonate system which ultimately results in a drawdown of atmospheric CO2, the enhancement of ocean alkalinity can also contribute to the global effort of limiting global warming, and it is widely studied in the literature among the CO2 removal technologies. A limiting factor can be the worldwide availability of alkaline materials to be used for such a scope. The paper shows that the global availability of pure carbonates is vast, although unevenly distributed, and it could largely satisfy the requirement for large‐scale development of ocean alkalinization. The required up‐scaling of limestone production compared to the current level is much lower than what would be needed for other raw materials that could be used, such as olivine, magnesite and brucite. Moreover, a large fraction of pure limestone resources that could be exploitable is located nearby the coastline, in areas without or with low vegetation cover, which favors the logistics related to the exploitation. Key Points: Pure carbonate potential resources are of several trillion tons and are not a constraint for the development of global‐scale ocean limingA large part of pure limestone resources is located nearby the coastline, in area with no to low vegetation cover, mainly in North Africa and IranThe global limestone yearly production is similar to that of coal, thus the needed upscale is far lower than for olivine, magnesite and brucite [ABSTRACT FROM AUTHOR]

This article explores the concept of the Anthropocene, a term used to describe the period in which human activities have significantly impacted the Earth's environment. It discusses the "Great Acceleration," which encompasses processes like climate change, urbanization, and species extinction. The recognition of the Anthropocene as a geological unit is a topic of ongoing debate, and geographers play a crucial role in understanding and defining this concept. The article also highlights the challenges in determining the beginning of the Anthropocene and the importance of using various datasets to study the Great Acceleration. Geographers are encouraged to contribute papers that offer conceptual frameworks and solutions for addressing the challenges of the Anthropocene, with the Covid-19 pandemic serving as a template for studying this phenomenon. [Extracted from the article]

We begin this month's issue with the first in a series of papers re‐examining one aspect associated with the sinking of the Titanic. In 'Titanic's mirage, part 1: The enigma of the Arctic High and a cold‐water tongue of the Labrador Current' on p. 119, Mila Zinkova presents an excellent review of the meteorology of visibility over cold waters and the areas where mixing occurs. At the beginning of 2019, radar used operationally for weather forecasting and hydrology passed a significant anniversary in the United Kingdom. On p. 128, the short paper 'Radar for hydrological forecasting in the UK 50 years on' describes the development and use of this essential tool. Chris Collier was involved in much of this development and his review reveals the importance of the project and its value. On p. 130, we publish the last of the papers marking the cold weather and snow of February and March 2018, the others the content of the Special Issue of March 2019. Bill Pike and his co‐authors kept records of the snow cover and other weather factors during the event in Berkshire, Suffolk and Kent. These are reproduced in 'Weather diaries during the easterlies of February and March 2018'. An important question that is often raised in this period of anthropogenic warming is the effect of carbon dioxide on temperature. 'Climate sensitivity: how much warming results from increases in atmospheric carbon dioxide (CO2)?', the latest in our Climate‐change shorts series, provides an answer to this rather complex question and one that we all need to understand. Many readers will know that tropical meteorology is frequently associated with thunderstorms, but these storms vary in their frequency by area and time of year, as revealed by Omvir Singh and Pankaj Bhardwaj in 'Spatial and temporal variations in the frequency of thunderstorm days over India' on p. 138. The replacement of instruments always presents a challenge – not least, thermometers, the readings from which form the longest climatic series in the world. Almost all instruments have had to be replaced as automation and electronic sensing have come to the fore. A standard form of electronic thermometer and its exposure, together able to reproduce well‐established temperature series, are discussed by Ian Strangeways in 'The replacement of mercury thermometers in Stevenson screens' on p. 145. A growing area of research in meteorology and climatology is the association of weather with disease. This is discussed on p. 148 by in 'The relationship between meteorological factors and the risk of bacillary dysentery in Hunan Province, China' by Xuewen Li and her co‐authors. As we understand how weather can affect diseases, we can put into place appropriate measures to combat them. Our final paper this month is 'Brewster's dark patch: a neglected optical phenomenon in the landscape' – an optical phenomenon little discussed in meteorological literature. G P Können puts this right in his eminent explanation of its formation on p. 154. [ABSTRACT FROM AUTHOR]