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The ocean's organic carbon export is a key control on atmospheric pCO2 and stimulating this export could potentially mitigate climate change. We use a data‐constrained model to calculate the sensitivity of atmospheric pCO2 to local changes in export using an adjoint approach. A perpetual enhancement of the biological pump's export by 0.1 PgC/yr could achieve a roughly 1% reduction in pCO2 at average sensitivity. The sensitivity varies roughly 5‐fold across different ocean regions and is proportional to the difference between the mean sequestration time τseq of regenerated carbon and the response time τpre of performed carbon, which is the reduction in the preformed carbon inventory per unit increase in local export production. Air‐sea CO2 disequilibrium modulates the geographic pattern of τpre, causing particularly high sensitivities (2–3 times the global mean) in the Antarctic Divergence region of the Southern Ocean. Plain Language Summary: Atmospheric CO2 levels could be reduced by stimulating plankton in the ocean to produce more organic carbon that then sinks to depth (is exported) at a higher rate. The resulting carbon deficit in surface waters drives atmospheric carbon into the ocean. The efficacy of this process depends on how long the exported carbon stays isolated from the surface and how quickly the surface deficit can be filled. Here we investigate how sensitive atmospheric CO2 levels are to a given enhancement in carbon export and where such enhancements would be most effective. We show that the sensitivity is determined by the difference between the time for which exported carbon stays sequestered at depth and the time with which the rest of the carbon in the ocean responds to the additional export rate. High sequestration times are found where the organic carbon is exported into old deep waters, while fast response times are found where it is easy for gas exchange to inject carbon into the ocean and where the additionally exported carbon is less likely to resurface and escape into the atmosphere. These factors result in the Southern Ocean and the tropics having greatest sensitivity. Key Points: pCO2 sensitivity to carbon export perturbations is governed by sequestration time, preformed response time, and atmospheric turnover timeHigh sensitivity occurs in the tropics and Southern Ocean where sequestration time is long and preformed response time is shortThe preformed response time is modulated by air‐sea CO2 disequilibrium and shortest in the Atlantic and Southern Ocean [ABSTRACT FROM AUTHOR]

[Display omitted] The Indo-Pacific warm pool (IPWP) is crucial for regional and global climates. However, the development of the IPWP and its effect on the regional climate during the Cenozoic remain unclear. Here, using a compilation of sea surface temperature (SST) records (mainly since the middle Miocene) and multimodel paleoclimate simulations, our results indicated that the extent, intensity and warmest temperature position of the IPWP changed markedly during the Cenozoic. Specifically, its extent decreased, its intensity weakened, and its warmest temperature position shifted from the Indian to western Pacific Ocean over time. The atmospheric CO 2 dominated its extent and intensity, while paleogeography, by restricting the distribution of the Indian Ocean and the width of the tropical seaways, controlled the shift in its warmest temperature position. In particular, the eastward shift to the western Pacific Ocean from the middle to late Miocene inferred from compiled SST records likely resulted from the constriction of tropical seaways. Furthermore, by changing the atmospheric thermal structure and atmospheric circulation, the reduced extent and intensity of the IPWP decreased the annual precipitation in the western Indian Ocean, eastern Asia and Australia, while the shift in the warmest temperature position from the Indian to western Pacific Ocean promoted aridification in Australia. Qualitative model-data agreements are obtained for both the IPWP SST and regional climate. From the perspective of past warm climates with high concentrations of atmospheric CO 2 , the expansion and strengthening of the IPWP will occur in a warmer future and favor excessive precipitation in eastern Asia and Australia. [ABSTRACT FROM AUTHOR]

The atmospheric carbon dioxide (CO2) concentration has been increasing rapidly since the Industrial Revolution, which has led to unequivocal global warming and crucial environmental change. It is extremely important to investigate the interactions among atmospheric CO2, the physical climate system, and the carbon cycle of the underlying surface for a better understanding of the Earth system. Earth system models are widely used to investigate these interactions via coupled carbon-climate simulations. The Chinese Academy of Sciences Earth System Model version 2 (CAS-ESM2.0) has successfully fixed a two-way coupling of atmospheric CO2 with the climate and carbon cycle on land and in the ocean. Using CAS-ESM2.0, we conducted a coupled carbon-climate simulation by following the CMIP6 proposal of a historical emissions-driven experiment. This paper examines the modeled CO2 by comparison with observed CO2 at the sites of Mauna Loa and Barrow, and the Greenhouse Gases Observing Satellite (GOSAT) CO2 product. The results showed that CAS-ESM2.0 agrees very well with observations in reproducing the increasing trend of annual CO2 during the period 1850–2014, and in capturing the seasonal cycle of CO2 at the two baseline sites, as well as over northern high latitudes. These agreements illustrate a good ability of CAS-ESM2.0 in simulating carbon-climate interactions, even though uncertainties remain in the processes involved. This paper reports an important stage of the development of CAS-ESM with the coupling of carbon and climate, which will provide significant scientific support for climate research and China's goal of carbon neutrality. [ABSTRACT FROM AUTHOR]

Abstract High-resolution regional model simulation of CO2 may be more beneficial to reduce the uncertainty in estimation of CO2 source and sink via inverse modeling. However, the study of atmospheric CO2 transport with regional models is rare over India. Here, weather research and forecasting chemistry model adjusted for CO2 (WRF-CO2) is used for simulating vertical profile of CO2 and its assessment is performed over Delhi, India (27.4–28.6° N and 77–96° E) by comparing aircraft observations (CONTRAIL) and a global model (ACTM) data. During August and September, the positive vertical gradient (~ 13.4 ppm) within ~ 2.5 km height is observed due to strong CO2 uptake by newly growing vegetation. A similar pattern (~ 4 ppm) is noticed in February due to photosynthesis by newly growing winter crops. The WRF-CO2 does not show such steep increasing slope (capture up to 5%) during August and September but same for February is estimated ~ 1.7 ppm. Generally, CO2 is quite well mixed between ~ 2.5 and ~ 8 km height above ground which is well simulated by the WRF-CO2 model. During stubble burning period of 2010, the highest gradient within 2.5 km height above ground was recorded in October (− 9.3 ppm), followed by November (− 7.6 ppm). The WRF-CO2 and ACTM models partially capture these gradients (October − 3.3 and − 2.7 ppm and November − 3.8 and − 4.3 ppm respectively). A study of the seasonal variability of CO2 indicates seasonal amplitudes decrease with increasing height (amplitude is ~ 21 ppm at the near ground and ~ 6 ppm at 6–8 km altitude bin). Correlation coefficients (CC) between the WRF-CO2 model and observation are noted to be greater than 0.59 for all the altitude bins. In contrast to simulated fossil CO2, the biospheric CO2 is in phase with observed seasonality, having about 80% at the lowest level and gradually declines with height due to mixing processes, reaching around 60% at the highest level. The model simulation reveals that meteorology plays a significant role of the horizontal and vertical gradient of CO2 over the region.

We explore the ability of the atmospheric CO2 record since 1900 to constrain the source of CO2 from land use and land cover change (hereafter "land use"), taking account of uncertainties in other terms in the global carbon budget. We find that the atmospheric constraint favors land use CO2 flux estimates with lower decadal variability and can identify potentially erroneous features, such as emission peaks around 1960 and after 2000, in some published estimates. Furthermore, we resolve an offset in the global carbon budget that is most plausibly attributed to the land use flux. This correction shifts the mean land use flux since 1900 across 20 published estimates down by 0.35 PgC year-1 to 1.04 ± 0.57 PgC year-1 , which is within the range but at the low end of these estimates. We show that the atmospheric CO2 record can provide insights into the time history of the land use flux that may reduce uncertainty in this term and improve current understanding and projections of the global carbon cycle.

High-resolution regional model simulation of CO2 may be more beneficial to reduce the uncertainty in estimation of CO2 source and sink via inverse modeling. However, the study of atmospheric CO2 transport with regional models is rare over India. Here, weather research and forecasting chemistry model adjusted for CO2 (WRF-CO2) is used for simulating vertical profile of CO2 and its assessment is performed over Delhi, India (27.4–28.6° N and 77–96° E) by comparing aircraft observations (CONTRAIL) and a global model (ACTM) data. During August and September, the positive vertical gradient (~ 13.4 ppm) within ~ 2.5 km height is observed due to strong CO2 uptake by newly growing vegetation. A similar pattern (~ 4 ppm) is noticed in February due to photosynthesis by newly growing winter crops. The WRF-CO2 does not show such steep increasing slope (capture up to 5%) during August and September but same for February is estimated ~ 1.7 ppm. Generally, CO2 is quite well mixed between ~ 2.5 and ~ 8 km height above ground which is well simulated by the WRF-CO2 model. During stubble burning period of 2010, the highest gradient within 2.5 km height above ground was recorded in October (− 9.3 ppm), followed by November (− 7.6 ppm). The WRF-CO2 and ACTM models partially capture these gradients (October − 3.3 and − 2.7 ppm and November − 3.8 and − 4.3 ppm respectively). A study of the seasonal variability of CO2 indicates seasonal amplitudes decrease with increasing height (amplitude is ~ 21 ppm at the near ground and ~ 6 ppm at 6–8 km altitude bin). Correlation coefficients (CC) between the WRF-CO2 model and observation are noted to be greater than 0.59 for all the altitude bins. In contrast to simulated fossil CO2, the biospheric CO2 is in phase with observed seasonality, having about 80% at the lowest level and gradually declines with height due to mixing processes, reaching around 60% at the highest level. The model simulation reveals that meteorology plays a significant role of the horizontal and vertical gradient of CO2 over the region. [ABSTRACT FROM AUTHOR]

During the transition from the Last Glacial Maximum (LGM) to the Holocene, terrestrial carbon sequestration occurred primarily in boreal forests and forest soils largely on landscapes that had been covered by ice sheets. Major processes operating during this period included radiative warming from rising concentrations of atmospheric CO2 (degassing oceans and oxidation of permafrost); increased seasonal warming associated with axial precession; melting of alpine glaciers and ice sheets; exposure of new land surfaces; and sequestration of carbon in expanding terrestrial vegetation and soils. We examine mechanisms of warming that melted glacial ice; temporal and spatial availability of newly exposed landscapes; rates at which plant colonization and soil development occurred; estimates of terrestrial carbon sequestration; and how those processes interacted with one another. Data from the West Antarctic Ice Sheet Divide ice core show that from 18 to 11 cal ka bp the concentration of atmospheric CO2 rose by ≈80 ppmv (≈170 Gt C); published estimates of net terrestrial carbon sequestration (following photosynthesis) are considerably higher (450–1250 Gt C). Thus, accumulation of carbon in terrestrial vegetation and soils played an important role in modulating atmospheric CO2 and, indirectly, Earth's climate during Termination 1, and possibly during earlier Quaternary ice ages. [ABSTRACT FROM AUTHOR]

In the context of past and present climate change, the Southern Ocean (SO) has been identified as a crucial region modulating the concentration of atmospheric CO2. The sustained upwelling of carbon-rich deep waters and inefficient nutrient utilization at the surface of the SO leads to an outgassing of natural CO2, while anthropogenic CO2 is entrained to depth during the formation of Antarctic Bottom water (AABW), Antarctic intermediate water (AAIW) and sub-Antarctic mode water (SAMW). Changes to the SO circulation resulting from both dynamic and buoyancy forcing can alter the rate of upwelling as well as formation and subsequent transport of AABW, AAIW and SAMW, thus impacting the air-sea CO2 exchange in the SO. Models of all complexity robustly show that stronger southern hemispheric (SH) westerlies enhance SO upwelling, thus leading to stronger natural CO2 outgassing, with a sensitivity of 0.13 GtC/yr for a 10% increase in SH westerly windstress. While the impact of changes in the position of the SH westerly winds was previously unclear, recent simulations with high-resolution ocean/sea-ice/carbon cycle models show that a poleward shift of the SH westerlies also enhances natural CO2 outgassing with a sensitivity of 0.08GtC/yr for a 5° poleward shift. While enhanced AABW transport reduces deep ocean natural DIC concentration and increases surface natural DIC concentration, it acts on a multi-decadal timescale. Future work should better constrain both the natural and anthropogenic carbon cycle response to changes in AABW and the compound impacts of dynamic and buoyancy changes on the SO marine carbon cycle. [ABSTRACT FROM AUTHOR]

In this study, the trajectory mapping domain-filling technology, which can provide more reliable statistical estimates of long-lived gas concentrations in a broader geographical area based on limited station data, is used to map the CO2 concentration data of six ground observation stations to the entire Shanxi Province. The technology combines a dynamical model of the atmosphere with trace gas observations, combining forward and backward trajectories to greatly expand the information on long-lived CO2 gas concentrations over a trajectory path. The mapped results show good agreement with the observation results, which reveals the generalizability of the trajectory mapping domain-filling technology. The results show that the spatio-temporal distribution characteristics of CO2 concentration in the entire Shanxi region is significant: during the five years, the provincial average CO2 concentration exhibits an overall increasing trend. The CO2 concentration increases from the north to the south across the province. Influenced by the economic growth rate and COVID-19, there are differences in the annual variation characteristics of the CO2 concentration across the entire province, with the highest year-on-year growth in 2019 and a year-on-year decrease in 2020. The increasing rate of the CO2 concentration in the northern low-value areas is faster than that in the southern high-value areas. Overall, there is a decreasing trend in the CO2 concentration growth from the north to the south in the entire province. There are seasonal differences in the CO2 concentration distribution across the entire province. The CO2 concentration and amplitude are higher in autumn and winter than they are in spring and summer. This study can provide scientific support and methodological reference for the spatio-temporal distribution characteristics analysis of GHGs at the provincial–regional scale, as well as at the national and global scales. [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]

Abstract The ocean's organic carbon export is a key control on atmospheric pCO2 and stimulating this export could potentially mitigate climate change. We use a data‐constrained model to calculate the sensitivity of atmospheric pCO2 to local changes in export using an adjoint approach. A perpetual enhancement of the biological pump's export by 0.1 PgC/yr could achieve a roughly 1% reduction in pCO2 at average sensitivity. The sensitivity varies roughly 5‐fold across different ocean regions and is proportional to the difference between the mean sequestration time τseq of regenerated carbon and the response time τpre of performed carbon, which is the reduction in the preformed carbon inventory per unit increase in local export production. Air‐sea CO2 disequilibrium modulates the geographic pattern of τpre, causing particularly high sensitivities (2–3 times the global mean) in the Antarctic Divergence region of the Southern Ocean.

Abstract This study presents an analysis of the atmospheric footprint sensitivities and CO2 enhancements measured at three in situ stations in South Korea (Anmyeondo (AMY), Gosan (JGS), Ulleungdo (ULD)) using the KIM-STILT and WRF-STILT atmospheric transport models. Monthly aggregated footprints for each station were compared between the models for July and December 2020. The footprints revealed major source regions and the sensitivity of atmospheric mole fractions at the receptor to upstream surface fluxes. In July, both models showed similar major source regions for the AMY station, including Korea, the Yellow Sea, and Japan. However, a discrepancy was observed in the Eastern Pacific Ocean, with KIM-STILT showing larger sensitivity compared to WRF-STILT. In December, both models indicated strong sensitivity over Northeast and Eastern China, but KIM-STILT exhibited smaller sensitivities towards Northwestern China and Mongolia compared to WRF-STILT. At station ULD in July, both models exhibited comparable source regions, but a notable difference was found in Southeast China, where KIM-STILT showed stronger sensitivity. For the JGS station, both models agreed on major sources, but WRF-STILT demonstrated stronger sensitivity over North and Northeastern China. Regarding CO2 enhancements, both models generally underestimated the amplitude of CO2 enhancements, especially in July. However, in December, there was better agreement with observed data. The models were able to reproduce the phase of measured ΔCO2 reasonably well despite the underestimation of CO2 amplitudes. The contribution of biospheric CO2 to the observed enhancements, along with fossil-fuel emissions, was highlighted. In specific cases with significant CO2 enhancements, the models provided varying estimates of CO2ff values, particularly in the source regions of Eastern China. The differences in sensitivity estimations emphasize the need for further investigation to understand the underlying factors causing disparities. Overall, this study provides valuable insights into the potential advantages of each model in capturing dispersion patterns in specific regions, highlighting the importance of understanding these differences to improve the accuracy of atmospheric transport models. Further work is necessary to address the observed disparities and enhance our understanding of the transport models in the studied regions.

Abstract We provide a 1‐year dataset of atmospheric surface CO2, CH4 and H2O concentrations and δ13C‐CO2 values from an Australian savanna site. These semi‐arid ecosystems act as carbon sinks in wet years but the persistence of the sink in dry years is uncertain. The dataset can be used to constrain uncertainties in modelling of greenhouse gas budgets, improve algorithms for satellite measurements and characterize the role of vegetation and soil in modulating atmospheric CO2 concentrations. We found pronounced seasonal variations in daily mean CO2 concentrations with an increase (by 5–7 ppmv) after the first rainfall of the wet season in early December with peak concentrations maintained until late January. The CO2 increase reflected the initiation of rapid microbial respiration from soil and vegetation sources upon initial wetting. As the wet season progressed, daily CO2 concentrations were variable, but generally decreased back to dry season levels as CO2 assimilation by photosynthesis increased. Mean daily concentrations of CH4 increased in the wet season by up to 0.2 ppmv relative to dry season levels as the soil profile became waterlogged after heavy rainfall events. During the dry season there was regular cycling between maximum CO2/minimum δ13C‐CO2 at night and minimum CO2/maximum δ13C‐CO2 during the day. In the wet season diel patterns were less regular in response to variable cloud cover and rainfall. CO2 isotope data showed that in the wet season, surface CO2 was predominantly a two‐component mixture influenced by C3 plant assimilation (day) and soil/plant respiration (night), while regional background air from higher altitudes represented an additional CO2 source in the dry season. Higher wind speeds during the dry season increased vertical mixing compared to the wet season. In addition, night‐time advection of high‐altitude air during low temperature conditions also promoted mixing in the dry season.

Atmospheric CO2 variability on the glacial–interglacial (G–IG) timescale reflects a balance between oceanic and terrestrial processes involving carbon uptake and release. The Southern Ocean CO2 uptake is considered as an important modulator for the G–IG atmospheric CO2 variability, while the role of tropical ocean ventilation remains enigmatic. We present critical evidence for CO2 ventilation from the tropical Indian Ocean through the reconstruction of the Arabian Sea‐surface pCO2 for the past ∼136 ka utilizing boron isotope (δ11B) record of planktic foraminifera, Globigerinoides ruber. Our site in the Arabian Sea presently acts as a significant source of CO2. The reconstructed ΔpCO2 (ΔpCO2 = pCO2 Seawater − pCO2 Atmosphere) record shows an enhanced CO2 degassing up to ∼50 ppm during the major cooling events, such as the Last Glacial Maximum, Younger Dryas, and Heinrich‐Stadials. Our investigation based on multiproxy records of sea‐surface temperature, salinity, and productivity suggests that the northward invasion and shoaling of southern source CO2‐rich water, coupled with stronger upwelling, resulted in CO2 degassing during these cold intervals. This finding is in align with the tropical Atlantic which also demonstrated an enhanced CO2 degassing during the cold intervals; however, most of the upwelled CO2 was consumed as the water moved away from the upwelling sites. Therefore, our finding, when considered alongside tropical Atlantic records, suggests that tropical oceans played a minor role in reducing atmospheric CO2 levels during the cold intervals of the last glacial cycle, supporting the prevailing hypothesis. Key Points: Foraminifera δ11B‐based CO2 record of Arabian Sea surface for the past ∼136 kaEnhanced CO2 degassing during the cold climate events, that is, Heinrich‐Stadials, Younger Dryas, and Last Glacial MaximumThis degassing was caused by more export of southern‐sourced water and its upwelling [ABSTRACT FROM AUTHOR]

Comparing satellite retrieval with high-precision ground observations is an essential component for the validation of CO2 satellite products. The initial stage of assessing the bias in retrieval products from satellite and ground sources involves establishing a geographical connection between observations that are temporally and spatially proximate. The primary aim of this paper is to evaluate the influence of variations in neighborhood definitions and colocation methods on the assessment of satellite products and provide quantitative references. To achieve this, a series of experiments were conducted involving the Global Total Column Carbon Observation Network (TCCON) and the OCO-2 satellite. Various spatial-temporal neighborhoods and colocation methods were considered in these experiments. The results indicate that spatial neighborhoods exert a more substantial influence on bias compared to temporal neighborhoods. In the mid-latitudes of the Northern Hemisphere, there is an observed linear increase trend between the difference of OCO-2 and TCCON observations and the spatial neighborhood, with an average increase of 0.32 ppm as the neighborhood size changes from 1 ° to 10 ° . Regarding colocation methods, the simple spatiotemporal geographic constraints tend to overlook changes in the atmospheric state to a certain extent. The target geographic constraint method reduces the bias by 2% to 5% by increasing the proportion of OCO-2 observations targeting TCCON while the method of introducing T700 potential temperature reduces by 2% to 13% by screening the gradient of CO2 concentration change. Moreover, an evident correlation exists between the bias and their corresponding latitudes, with a 0.20 ppm increase in bias observed for every 10 ° increment in latitudes in the Northern Hemisphere. The bias of TCCON and OCO-2 shows a pronounced seasonal regularity, with the highest in summer. The study also discusses the selection of spatiotemporal matching with low satellite coverage, the bias distribution, and the attribution of bias to the natural wind field. [ABSTRACT FROM AUTHOR]

Accurate assessment of the size and distribution of carbon dioxide (CO2) sources and sinks is important for efforts to understand the carbon cycle and support policy decisions regarding climate mitigation actions. Satellite retrievals of the column-averaged dry-air mole fractions of CO2 (XCO2) have been widely used to infer spatial and temporal variations of carbon fluxes through atmospheric inversion techniques. In this study, we present a global spatially resolved terrestrial and ocean carbon flux dataset for 2015–2022. The dataset was generated by the Global ObservatioN-based system for monitoring Greenhouse GAses (GONGGA) atmospheric inversion system through the assimilation of Orbiting Carbon Observatory 2 (OCO-2) XCO2 retrievals. We describe the carbon budget, interannual variability, and seasonal cycle for the global scale and a set of TransCom regions. The 8-year mean net biosphere exchange and ocean carbon fluxes were −2.22 ± 0.75 PgC yr−1 and –2.32 ± 0.18 PgC yr−1, absorbing approximately 23 % and 24 % of contemporary fossil fuel CO2 emissions, respectively. The annual mean global atmospheric CO2 growth rate was 5.17 ± 0.68 PgC yr−1, which is consistent with the National Oceanic and Atmospheric Administration (NOAA) measurement (5.24 ± 0.59 PgC yr−1). Europe has the largest terrestrial sink among the 11 TransCom land regions, followed by Boreal Asia and Temperate Asia. The dataset was evaluated by comparing posterior CO2 simulations with the observations from Total Carbon Column Observing Network (TCCON) and Observation Package (ObsPack). Compared with CO2 simulations using the unoptimized fluxes, the bias and root mean square error of posterior CO2 simulations were largely reduced across the full range of locations, confirming that the GONGGA system improves the estimates of spatial and temporal variations in carbon fluxes by assimilating OCO-2 XCO2 data. This dataset will improve the broader understanding of global carbon cycle dynamics and their response to climate change. [ABSTRACT FROM AUTHOR]

We provide a 1‐year dataset of atmospheric surface CO2, CH4 and H2O concentrations and δ13C‐CO2 values from an Australian savanna site. These semi‐arid ecosystems act as carbon sinks in wet years but the persistence of the sink in dry years is uncertain. The dataset can be used to constrain uncertainties in modelling of greenhouse gas budgets, improve algorithms for satellite measurements and characterize the role of vegetation and soil in modulating atmospheric CO2 concentrations. We found pronounced seasonal variations in daily mean CO2 concentrations with an increase (by 5–7 ppmv) after the first rainfall of the wet season in early December with peak concentrations maintained until late January. The CO2 increase reflected the initiation of rapid microbial respiration from soil and vegetation sources upon initial wetting. As the wet season progressed, daily CO2 concentrations were variable, but generally decreased back to dry season levels as CO2 assimilation by photosynthesis increased. Mean daily concentrations of CH4 increased in the wet season by up to 0.2 ppmv relative to dry season levels as the soil profile became waterlogged after heavy rainfall events. During the dry season there was regular cycling between maximum CO2/minimum δ13C‐CO2 at night and minimum CO2/maximum δ13C‐CO2 during the day. In the wet season diel patterns were less regular in response to variable cloud cover and rainfall. CO2 isotope data showed that in the wet season, surface CO2 was predominantly a two‐component mixture influenced by C3 plant assimilation (day) and soil/plant respiration (night), while regional background air from higher altitudes represented an additional CO2 source in the dry season. Higher wind speeds during the dry season increased vertical mixing compared to the wet season. In addition, night‐time advection of high‐altitude air during low temperature conditions also promoted mixing in the dry season. [ABSTRACT FROM AUTHOR]

In the context of past and present climate change, the Southern Ocean (SO) has been identified as a crucial region modulating the concentration of atmospheric CO2. The sustained upwelling of carbon-rich deep waters and inefficient nutrient utilization at the surface of the SO leads to an outgassing of natural CO2, while anthropogenic CO2 is entrained to depth during the formation of Antarctic Bottom water (AABW), Antarctic intermediate water (AAIW) and sub-Antarctic mode water (SAMW). Changes to the SO circulation resulting from both dynamic and buoyancy forcing can alter the rate of upwelling as well as formation and subsequent transport of AABW, AAIW and SAMW, thus impacting the air-sea CO2 exchange in the SO. Models of all complexity robustly show that stronger southern hemispheric (SH) westerlies enhance SO upwelling, thus leading to stronger natural CO2 outgassing, with a sensitivity of 0.13 GtC/yr for a 10% increase in SH westerly windstress. While the impact of changes in the position of the SH westerly winds was previously unclear, recent simulations with high-resolution ocean/sea-ice/carbon cycle models show that a poleward shift of the SH westerlies also enhances natural CO2 outgassing with a sensitivity of 0.08GtC/yr for a 5° poleward shift. While enhanced AABW transport reduces deep ocean natural DIC concentration and increases surface natural DIC concentration, it acts on a multi-decadal timescale. Future work should better constrain both the natural and anthropogenic carbon cycle response to changes in AABW and the compound impacts of dynamic and buoyancy changes on the SO marine carbon cycle.

Carbon release during continental rifting is thought to regulate atmospheric CO2 levels. Supercontinent dispersal‐induced extensional tectonics is similar during the Late Ediacaran and Jurassic, while they exhibit different increases in atmospheric CO2 concentration. The underlying mechanism of distinct CO2 emissions remains to be understood. Here, we conduct petrological‐thermomechanical modeling to show that metamorphic decarbonation and melting of carbonates that are derived from subducted sediments are ubiquitous during continental extension. We find that the hotter lithosphere and deeper storage of these carbonates cause more significant amounts of rift‐related CO2 release through volcanoes and faults. They may cause ∼12%–77% larger decarbonation efficiency, providing an efficient driving mechanism for a ∼31% larger increase in atmospheric CO2 levels during the Late Ediacaran than throughout the Jurassic. The rapid eruption and deposition of recycled carbonatite volcanic ash may contribute to the production of Late Ediacaran marine carbonates with the largest negative δ13C (−12‰). Plain Language Summary: The Late Ediacaran and Jurassic periods witnessed rapid increases in atmospheric CO2 concentration and significant negative carbon isotope excursions in marine carbonates during the Earth's history, but the dynamics of their changes remain enigmatic. In this study, we present high‐resolution petrological‐thermomechanical models of how these processes occur. Our results indicate that the extensional tectonics drives trans‐crustal faulting and thereby results in remobilized subcontinental lithospheric carbonates of subducted sedimentary origin (SLCSS) to melt and migrate upward along these faults. The efficiency of CO2 release from these carbonates via metamorphic reaction decarbonation is promoted by the deeper storage and hotter lithosphere, which can reach up to ∼12%–77% larger. Recycled carbonatite volcanic ash may rapidly erupt and deposit in shallow marine habitats following the emission of CO2 enriched in 13C, resulting in the formation of large negative δ13C in Late Ediacaran and Jurassic. We suggest that metamorphic CO2 degassing of remobilized subcontinental lithospheric mantle carbonates of subducted sedimentary origin (SLMCS) combined with a hotter lithosphere may be responsible for a 31% greater increase in atmospheric CO2 and the largest negative δ13C of −12‰ in the Late Ediacaran. Key Points: Numerical modeling of decarbonation of subducted sedimentary carbonates during continental riftingThermal structure of the continental lithosphere and carbon storage depth control the efficiency of CO2 degassingDecarbonation of stored sedimentary carbonates during continental rifting accounts for CO2 concentrations and negative δ13C in Late Ediacaran [ABSTRACT FROM AUTHOR]

The paleosol record of the Early Cretaceous Wonthaggi and Eumeralla formations of Victoria reveals a suite of non-calcareous Histosols and Ultisols, as well as stump casts, indicative of humid temperate ecosystems. At some stratigraphic levels, frigid temperatures are indicated by clastic dykes (ice wedges), load casts of mud (periglacial convolutions), and coal-mantled stone rolls (aapamires). The largest tree stumps and thickest paleosols correspond to known Early Cretaceous greenhouse spikes, as revealed by stomatal index of fossil ginkgo leaves, by black shales of oceanic anoxic events, and both marine and non-marine carbon isotopic anomalies. Temperature and CO2 spikes coincide with appearance of broadleaf deciduous forests, including Ginkgo australis, with dinosaurs, monotremes, placentals, early birds and angiosperms. In contrast, permafrost paleosols represent fern-lycopsid tundra and coniferous taiga vegetation. Early Cretaceous CO2 greenhouse spikes allowed southward migration of tree lines and polar biomes several times during the Cretaceous, which was not continuously a hothouse period. The same greenhouse spikes are recorded by maximal marine transgressions in the Great Artesian Basin of Queensland, and the frigid intervals by dropped pebbles and glendonites in South Australia, New South Wales and Arctic regions. Victorian Cretaceous Wonthaggi and Eumeralla formations have Histosol and Ultisol paleosols. Hauterivian and Barremian ice wedges, convolutions and aapamires were frigid. Temperature and CO2 spikes were times of polar invasion by taiga and broadleaf trees. Greenhouse spikes are also recorded by maximal marine transgressions in Queensland. Dropped pebbles and glendonites in Central Australia also represent frigid intervals. [ABSTRACT FROM AUTHOR]

Photorespiration, or C2 photosynthesis, is generally considered a futile cycle that potentially decreases photosynthetic carbon fixation by more than 25%. Nonetheless, many essential processes, such as nitrogen assimilation, C1 metabolism, and sulfur assimilation, depend on photorespiration. Most studies of photosynthetic and photorespiratory reactions are conducted with magnesium as the sole metal cofactor despite many of the enzymes involved in these reactions readily associating with manganese. Indeed, when manganese is present, the energy efficiency of these reactions may improve. This review summarizes some commonly used methods to quantify photorespiration, outlines the influence of metal cofactors on photorespiratory enzymes, and discusses why photorespiration may not be as wasteful as previously believed.

Abstract We developed a near-real-time estimation method for temporal changes in fossil fuel CO2 (FFCO2) emissions from China for 3 months [January, February, March (JFM)] based on atmospheric CO2 and CH4 observations on Hateruma Island (HAT, 24.06° N, 123.81° E) and Yonaguni Island (YON, 24.47° N, 123.01° E), Japan. These two remote islands are in the downwind region of continental East Asia during winter because of the East Asian monsoon. Previous studies have revealed that monthly averages of synoptic-scale variability ratios of atmospheric CO2 and CH4 (ΔCO2/ΔCH4) observed at HAT and YON in JFM are sensitive to changes in continental emissions. From the analysis based on an atmospheric transport model with all components of CO2 and CH4 fluxes, we found that the ΔCO2/ΔCH4 ratio was linearly related to the FFCO2/CH4 emission ratio in China because calculating the variability ratio canceled out the transport influences. Using the simulated linear relationship, we converted the observed ΔCO2/ΔCH4 ratios into FFCO2/CH4 emission ratios in China. The change rates of the emission ratios for 2020–2022 were calculated relative to those for the preceding 9-year period (2011–2019), during which relatively stable ΔCO2/ΔCH4 ratios were observed. These changes in the emission ratios can be read as FFCO2 emission changes under the assumption of no interannual variations in CH4 emissions and biospheric CO2 fluxes for JFM. The resulting average changes in the FFCO2 emissions in January, February, and March 2020 were 17 ± 8%, − 36 ± 7%, and − 12 ± 8%, respectively, (− 10 ± 9% for JFM overall) relative to 2011–2019. These results were generally consistent with previous estimates. The emission changes for January, February, and March were 18 ± 8%, − 2 ± 10%, and 29 ± 12%, respectively, in 2021 (15 ± 10% for JFM overall) and 20 ± 9%, − 3 ± 10%, and − 10 ± 9%, respectively, in 2022 (2 ± 9% for JFM overall). These results suggest that the FFCO2 emissions from China rebounded to the normal level or set a new high record in early 2021 after a reduction during the COVID-19 lockdown. In addition, the estimated reduction in March 2022 might be attributed to the influence of a new wave of COVID-19 infections in Shanghai.

In this study, the trajectory mapping domain-filling technology, which can provide more reliable statistical estimates of long-lived gas concentrations in a broader geographical area based on limited station data, is used to map the CO2 concentration data of six ground observation stations to the entire Shanxi Province. The technology combines a dynamical model of the atmosphere with trace gas observations, combining forward and backward trajectories to greatly expand the information on long-lived CO2 gas concentrations over a trajectory path. The mapped results show good agreement with the observation results, which reveals the generalizability of the trajectory mapping domain-filling technology. The results show that the spatio-temporal distribution characteristics of CO2 concentration in the entire Shanxi region is significant: during the five years, the provincial average CO2 concentration exhibits an overall increasing trend. The CO2 concentration increases from the north to the south across the province. Influenced by the economic growth rate and COVID-19, there are differences in the annual variation characteristics of the CO2 concentration across the entire province, with the highest year-on-year growth in 2019 and a year-on-year decrease in 2020. The increasing rate of the CO2 concentration in the northern low-value areas is faster than that in the southern high-value areas. Overall, there is a decreasing trend in the CO2 concentration growth from the north to the south in the entire province. There are seasonal differences in the CO2 concentration distribution across the entire province. The CO2 concentration and amplitude are higher in autumn and winter than they are in spring and summer. This study can provide scientific support and methodological reference for the spatio-temporal distribution characteristics analysis of GHGs at the provincial–regional scale, as well as at the national and global scales.

Abstract Carbon release during continental rifting is thought to regulate atmospheric CO2 levels. Supercontinent dispersal‐induced extensional tectonics is similar during the Late Ediacaran and Jurassic, while they exhibit different increases in atmospheric CO2 concentration. The underlying mechanism of distinct CO2 emissions remains to be understood. Here, we conduct petrological‐thermomechanical modeling to show that metamorphic decarbonation and melting of carbonates that are derived from subducted sediments are ubiquitous during continental extension. We find that the hotter lithosphere and deeper storage of these carbonates cause more significant amounts of rift‐related CO2 release through volcanoes and faults. They may cause ∼12%–77% larger decarbonation efficiency, providing an efficient driving mechanism for a ∼31% larger increase in atmospheric CO2 levels during the Late Ediacaran than throughout the Jurassic. The rapid eruption and deposition of recycled carbonatite volcanic ash may contribute to the production of Late Ediacaran marine carbonates with the largest negative δ13C (−12‰).

Diurnal variation of atmospheric CO2 and its driving factors are studied using high‐precision in situ mixing ratio measurements and stable carbon isotopic CO2 (δ13C‐CO2) for the first time over Shadnagar, a suburban site in India, from November 2018 to October 2019. The annual mean mixing ratios of atmospheric CO2 and δ13C‐CO2 are observed to be 414.76 ± 4.26 ppm and −11.19 ‰ ± 1.63 ‰. Maximum diurnal variability of atmospheric CO2 was observed in summer monsoon (17.30 ± 9.29 ppm), and the minimum was noticed in winter (7.19 ± 0.11 ppm), indicating strong seasonality in diurnal variability of amplitude. To characterize the atmospheric CO2 sources, the Miller‐Tans model was implemented separately using the CO2 and its δ13C‐CO2 isotopic data during day and night. However, a strong source signature of δ13C‐CO2 was observed during the night‐time of summer monsoon with a slope of −37.42‰ ± 0.73‰, obtained using a reduced major axis regression. The identified source indicates possible emissions from fossil fuel combustion. Further, a Lagrangian back trajectory analysis was performed to study the influence of transport on the observed CO2 mixing ratios. The model trajectory confirms the influence of the Indian summer monsoon on the variations of atmospheric CO2 mixing ratios. Our study shows that fossil fuel emissions are one of the major contributors of CO2 in the study location (about ∼2 to 4 ppm) with biogenic fluxes adding a clear seasonality ranging from −8 to 4 ppm. Plain Language Summary: At a suburban site in India, the present study looked at the diurnal variation of seasonal atmospheric CO2 and its stable isotopes, 13C‐CO2. We used the Miller‐Tans model on seasonal data to capture the driving processes of atmospheric CO2 during day and night hours. A high source/sink signature of 13C was identified during the night of the summer monsoon. The presence of C3 ecosystem respiration and combustion is attributed as the source. Our research provided clear evidence that, in addition to short‐ and long‐range anthropogenic impacts, changes in the isotopic composition of atmospheric CO2 during photosynthesis and biogenic respiration are related to changes in atmospheric CO2 concentration. Key Points: The study focused on the diurnal variability of atmospheric CO2 mixing ratio and δ13C‐CO2 on a seasonal basisDetermination of δ13C signature of atmospheric CO2 sources using Miller‐Tans modelInvestigated the influence of transport on seasonal variability of atmospheric CO2 using the Lagrangian transport model and inventory fluxes [ABSTRACT FROM AUTHOR]

Abstract Background Atmospheric CO2 may double by the year 2100, thereby altering plant growth, photosynthesis, leaf nutrient contents and water relations. Specifically, atmospheric CO2 is currently 50% higher than pre-industrial levels and is projected to rise as high as 936 μmol mol−1 under worst-case scenario in 2100. The objective of the study was to investigate the effects of elevated CO2 on woody plant growth, production, photosynthetic characteristics, leaf N and water relations. Methods A meta-analysis of 611 observations from 100 peer-reviewed articles published from 1985 to 2021 was conducted. We selected articles in which elevated CO2 and ambient CO2 range from 600–1000 and 300–400 μmol mol−1, respectively. Elevated CO2 was categorized into 700 μmol mol−1 concentrations. Results Total biomass increased similarly across the three elevated CO2 concentrations, with leguminous trees (LTs) investing more biomass to shoot, whereas non-leguminous trees (NLTs) invested to root production. Leaf area index, shoot height, and light-saturated photosynthesis (A max) were unresponsive at 700 μmol mol−1. However, shoot biomass and A max acclimatized as the duration of woody plants exposure to elevated CO2 increased. Maximum rate of photosynthetic Rubisco carboxylation (V cmax) and apparent maximum rate of photosynthetic electron transport (J max) were downregulated. Elevated CO2 reduced stomatal conductance (g s) by 32% on average and increased water use efficiency by 34, 43 and 63% for 700 μmol mol−1, respectively. Leaf N content decreased two times more in NLTs than LTs growing at elevated CO2 than ambient CO2. Conclusions Our results suggest that woody plants will benefit from elevated CO2 through increased photosynthetic rate, productivity and improved water status, but the responses will vary by woody plant traits and length of exposure to elevated CO2.

We developed a near-real-time estimation method for temporal changes in fossil fuel CO2 (FFCO2) emissions from China for 3 months [January, February, March (JFM)] based on atmospheric CO2 and CH4 observations on Hateruma Island (HAT, 24.06° N, 123.81° E) and Yonaguni Island (YON, 24.47° N, 123.01° E), Japan. These two remote islands are in the downwind region of continental East Asia during winter because of the East Asian monsoon. Previous studies have revealed that monthly averages of synoptic-scale variability ratios of atmospheric CO2 and CH4 (ΔCO2/ΔCH4) observed at HAT and YON in JFM are sensitive to changes in continental emissions. From the analysis based on an atmospheric transport model with all components of CO2 and CH4 fluxes, we found that the ΔCO2/ΔCH4 ratio was linearly related to the FFCO2/CH4 emission ratio in China because calculating the variability ratio canceled out the transport influences. Using the simulated linear relationship, we converted the observed ΔCO2/ΔCH4 ratios into FFCO2/CH4 emission ratios in China. The change rates of the emission ratios for 2020–2022 were calculated relative to those for the preceding 9-year period (2011–2019), during which relatively stable ΔCO2/ΔCH4 ratios were observed. These changes in the emission ratios can be read as FFCO2 emission changes under the assumption of no interannual variations in CH4 emissions and biospheric CO2 fluxes for JFM. The resulting average changes in the FFCO2 emissions in January, February, and March 2020 were 17 ± 8%, − 36 ± 7%, and − 12 ± 8%, respectively, (− 10 ± 9% for JFM overall) relative to 2011–2019. These results were generally consistent with previous estimates. The emission changes for January, February, and March were 18 ± 8%, − 2 ± 10%, and 29 ± 12%, respectively, in 2021 (15 ± 10% for JFM overall) and 20 ± 9%, − 3 ± 10%, and − 10 ± 9%, respectively, in 2022 (2 ± 9% for JFM overall). These results suggest that the FFCO2 emissions from China rebounded to the normal level or set a new high record in early 2021 after a reduction during the COVID-19 lockdown. In addition, the estimated reduction in March 2022 might be attributed to the influence of a new wave of COVID-19 infections in Shanghai. [ABSTRACT FROM AUTHOR]

The study explores the usefulness of infra-red CO2 gas analyzer in capturing diurnal and seasonal variations in atmospheric CO2 over three ecosystems, viz., mixed forest plantation (HFS), deciduous Sal forest (BFS), and sugarcane–wheat cropland (SFS). Half-hourly datasets of CO2 and meteorological parameters collected in the respective study sites were analyzed to depict the diurnal, seasonal, and annual variation in atmospheric CO2. The influence of meteorological variables on atmospheric CO2 concentration was depicted through biplot technique based on principal component analysis. Minimum and maximum CO2 values observed in late-afternoon and pre-dawn period, respectively. Among all the sites under study, SFS exhibited the highest range [438.55 ppm (pre-dawn maximum) – 345.99 ppm (late-afternoon minimum)] of CO2 concentration. Minimum CO2 concentration was observed in monsoon and post-monsoon seasons for HFS/BFS and SFS, respectively. Also, maximum "morning down-drop" was observed in monsoon and post-monsoon season in HFS/BFS and SFS, respectively which can be ascribed to rapid consumption of CO2 concentration due to higher biomass. Highest CO2 concentration was observed in SFS owing to the more anthropogenic emission in terms of biomass burning data obtained through long-term Fire Energetics and Emission Research version 1.0. The peak in normalized difference vegetation Index derived from MODIS satellite across three sites coincides with months of the lowest atmospheric CO2 due to strong photosynthetic activity. [ABSTRACT FROM AUTHOR]

This study presents an analysis of the atmospheric footprint sensitivities and CO2 enhancements measured at three in situ stations in South Korea (Anmyeondo (AMY), Gosan (JGS), Ulleungdo (ULD)) using the KIM-STILT and WRF-STILT atmospheric transport models. Monthly aggregated footprints for each station were compared between the models for July and December 2020. The footprints revealed major source regions and the sensitivity of atmospheric mole fractions at the receptor to upstream surface fluxes. In July, both models showed similar major source regions for the AMY station, including Korea, the Yellow Sea, and Japan. However, a discrepancy was observed in the Eastern Pacific Ocean, with KIM-STILT showing larger sensitivity compared to WRF-STILT. In December, both models indicated strong sensitivity over Northeast and Eastern China, but KIM-STILT exhibited smaller sensitivities towards Northwestern China and Mongolia compared to WRF-STILT. At station ULD in July, both models exhibited comparable source regions, but a notable difference was found in Southeast China, where KIM-STILT showed stronger sensitivity. For the JGS station, both models agreed on major sources, but WRF-STILT demonstrated stronger sensitivity over North and Northeastern China. Regarding CO2 enhancements, both models generally underestimated the amplitude of CO2 enhancements, especially in July. However, in December, there was better agreement with observed data. The models were able to reproduce the phase of measured ΔCO2 reasonably well despite the underestimation of CO2 amplitudes. The contribution of biospheric CO2 to the observed enhancements, along with fossil-fuel emissions, was highlighted. In specific cases with significant CO2 enhancements, the models provided varying estimates of CO2ff values, particularly in the source regions of Eastern China. The differences in sensitivity estimations emphasize the need for further investigation to understand the underlying factors causing disparities. Overall, this study provides valuable insights into the potential advantages of each model in capturing dispersion patterns in specific regions, highlighting the importance of understanding these differences to improve the accuracy of atmospheric transport models. Further work is necessary to address the observed disparities and enhance our understanding of the transport models in the studied regions. [ABSTRACT FROM AUTHOR]

The temporal variation of greenhouse gas concentrations in China during the COVID-19 lockdown in China is analyzed in this work using high resolution measurements of near surface △CO 2 , △CH 4 and △CO concentrations above the background conditions at Lin'an station (LAN), a regional background station in the Yangtze River Delta region. During the pre-lockdown observational period (IOP-1), both △CO 2 and △CH 4 exhibited a significant increasing trend relative to the 2011-2019 climatological mean. The reduction of △CO 2 , △CH 4 and △CO during the lockdown observational period (IOP-2) (which also coincided with the Chinese New Year Holiday) reached up to 15.0 ppm, 14.2 ppb and 146.8 ppb, respectively, and a reduction of △CO 2 /△CO probably due to a dramatic reduction from industrial emissions. △CO 2 , △CH 4 and △CO were observed to keep declining during the post-lockdown easing phase (IOP-3), which is the synthetic result of lower than normal CO 2 emissions from rural regions around LAN coupled with strong uptake of the terrestrial ecosystem. Interestingly, the trend reversed to gradual increase for all species during the later easing phase (IOP-4), with △CO 2 /△CO constantly increasing from IOP-2 to IOP-3 and finally IOP-4, consistent with recovery in industrial emissions associated with the staged resumption of economic activity. On average, △CO 2 declined sharply throughout the days during IOP-2 but increased gradually throughout the days during IOP-4. The findings showcase the significant role of emission reduction in accounting for the dramatic changes in measured atmospheric △CO 2 and △CH 4 associated with the COVID-19 lockdown and recovery. [Display omitted] [ABSTRACT FROM AUTHOR]

By using cavity ring-down spectroscopy (CRDS) technology, the present study measured the CO2 mole fraction (1 × 10-6, ppm) for the period 2014--2016 in the Guangzhou Panyu Atmospheric Composition Site (GPACS), a suburban site in the Pearl River Delta (PRD) region of China, and the correlations of CO2 concentration with surface wind were also investigated. Results show that: (1) Atmospheric CO2 has obvious geographical inhomogeneity in the PRD region, and the annual average value of background concentration in GPACS is 22.5 ppm higher than the value in the global background area. (2) The CO2 concentration is the highest in spring, moderate in winter and autumn, and the lowest in summer, with the annual average value being 426.64 ± 15.76 ppm. The diurnal CO2 shows two peaks: one peak at 05:00--07:00 and the other at 21:00--22:00 Local Standard Time, and the minimum value appears at 13: 00--15: 00. Together, these patterns indicate that the CO2 is affected by the combined effects of anthropogenic and biogenic processes. (3) The diurnal CO2 anomaly and wind speed show a significant negative correlation (p<0.01) during spring and summer, but they show a significant positive correlation (p< 0.01) during autumn and winter. In spring and summer, winds from the directions of S-WSW and NNE-N result in lower CO2 concentrations. By contrast, in autumn and winter, winds from the directions of SSE-S and N substantially lower the CO2. Winds from the directions of NW and NE-ENE significantly increase the CO2 concentration throughout the year, and furthermore, winds from the directions of NW-NNW, and NNE-ENE contribute 0.42 ppm and 0.32 ppm to the corresponding CO2 concentration, which indicates that the CO2 may have a potential source in these sectors. [ABSTRACT FROM AUTHOR]

Terrestrial ecosystems provide crucial ecosystem services to human beings, and their functions are largely dependent on soil moisture availability. Although many studies have evaluated the effects of vegetation and climate changes on soil moisture at the ecosystem scale, changes in ecosystem water limitation remain poorly understood. This study evaluated the spatiotemporal changes of ecosystem water limitation in the Yellow River Basin (YRB)—the second largest river basin of China—during 1982–2016 and identified the major drivers by establishing ecosystem limitation index (ELI) using soil moisture, transpiration, net radiation, and air temperature. The results show a significant and widespread spatiotemporal increase in the water limitation of ecosystems in YRB during the 35‐year study period. Temporally, areas with positive ELI (water‐limited regime) exhibited a significant upward trend (p < 0.01). Spatially, above 75.0% of the total areas showed an upward trend in ELI. Almost all ecosystems showed significant upward trends in water limitation over this period. Further analysis using two different but comparable methods, partial correlation and Lindeman‐Merenda‐Gold, show that vegetation change was the major driver of changes in water limitation, with contributions of more than 35.0%. Air temperature and atmospheric CO2 changes contributed comparably to changes in positive ELI, followed by precipitation changes. These findings improve the understanding of the spatiotemporal pattern and underlying mechanisms of ecosystem water limitation in the greening and warming YRB. Plain Language Summary: Functions of terrestrial ecosystems are largely dependent on soil moisture availability. Plenty of past studies have been conducted to investigate the vegetation and climate effects on soil moisture. However, the ecosystem water limitation and its spatiotemporal changes are rarely explored. We used a correlation difference as the ecosystem limitation index (ELI) to investigate the ecosystem water limitation over the Yellow River Basin (YRB)—the second largest river basin of China during 1982–2016. We found a significant and widespread increase in the water limitation of all ecosystems in YRB during the 35‐year study period. In total, above 75.0% of the total areas showed an upward trend in ELI (increasing water limitation). We used two different methods to attribute ELI and found that vegetation change was the major driver of changes in water limitation, with contributions of above 35.0%. Air temperature and atmospheric CO2 changes contributed comparably to ELI, followed by precipitation changes. The findings highlight the key role of vegetation in ecosystem water limitations in the greening and warming YRB. Key Points: Widespread increasing ecosystem water limitation was found in Yellow River Basin during 1982–2016All ecosystem types showed significant increasing water limitation regimesVegetation was found to be the major driver of the increased ecosystem water limitation [ABSTRACT FROM AUTHOR]

Based on inferences from proxy records the Miocene (23.03–5.33 Ma) was a time of amplified polar warmth compared to today. However, it remains a challenge to simulate a warm Miocene climate and pronounced polar warmth at reconstructed Miocene CO2 concentrations. Using a state‐of‐the‐art Earth‐System‐Model, we implement a high‐resolution paleobathymetry and simulate Miocene climate at different atmospheric CO2 concentrations. We estimate global mean surface warming of +3.1°C relative to the preindustrial at a CO2 level of 450 ppm. An increase of atmospheric CO2 from 280 to 450 ppm provides an individual warming of ∼1.4°C, which is as strong as all other Miocene forcing contributions combined. Substantial changes in surface albedo are vital to explain Miocene surface warming. Simulated surface temperatures fit well with proxy reconstructions at low‐ to mid‐latitudes. The high latitude cooling bias becomes less pronounced for higher atmospheric CO2 concentrations. At such CO2 levels simulated Miocene climate shows a reduced polar amplification, linked to a breakdown of seasonality in the Arctic Ocean. A pronounced warming in boreal fall is detected for a CO2 increase from 280 to 450 ppm, in comparison to weaker warming for CO2 changes from 450 to 720 ppm. Moreover, a pronounced warming in winter is detected for a CO2 increase from 450 to 720 ppm, in contrast to a moderate summer temperature increase, which is accompanied by a strong sea‐ice concentration decline that promotes cloud formation in summer via enhanced moisture availability. As a consequence planetary albedo increases and dampens the temperature response to CO2 forcing at a warmer Miocene background climate. Key Points: At a CO2 level of 450 ppm, a Miocene simulation shows a global mean surface warming of +3.1°C relative to the preindustrial stateAtmospheric CO2 increase from 280 to 450 ppm causes a warming of ∼1.4°C, which is as strong as all other forcing factors combinedAt higher atmospheric CO2 levels, the Miocene climate shows a reduced polar amplification linked to a breakdown of seasonality in the Arctic [ABSTRACT FROM AUTHOR]

The ecological integrity of US national parks and other protected areas are under threat in the Anthropocene. For Yellowstone National Park (YNP), the impacts that global change has already had on the park's capacity to sustain its large migratory herds of wild ungulates is incompletely understood. Here we examine how two understudied components of global change, the historical increase in atmospheric CO2 and the spread of nonnative, invasive plant species, may have altered the capacity of YNP to provide forage for ungulates over the last 200‐plus years. We performed two experiments: (1) a growth chamber study that determined the growth rates of important invasive and native YNP grasses that are forages for ungulates under preindustrial (280 ppm) versus modern (410 ppm) CO2 levels and (2) a field study that compared the effect of defoliation (clipping) on the shoot growth of invasive and native mesic grassland plants under ambient CO2 conditions in 2019. The growth chamber experiment revealed that modern CO2 increased the growth rates of both invasive and native grasses, and invasive grasses grew faster regardless of CO2 conditions. The field results showed a continuum of positive to negative responses of shoot growth to defoliation, with a subgroup of invasive species responding most positively. Altogether the results indicated that the historical increase in CO2 and the spread of invasive species, some of which were planted to provide forage for ungulates in the early and mid‐1900s, have likely increased the capacity of forage production in YNP. However, rising CO2 has also resulted in regional warming and increased aridity in YNP, which will likely reduce grassland productivity. The challenge for global change biologists and park managers is to determine how competing components of global change have already affected and will increasingly affect forage dynamics and the sustainability of Yellowstone's iconic ungulate herds in the Anthropocene. [ABSTRACT FROM AUTHOR]

The relationship between the source and sink of atmospheric CO2 has always been a widely discussed issue in global climate change research. Recent studies revealed that the chemical weathering of carbonate rocks contributed to 1/3 (~0.5 Pg C/yr) of the missing carbon sinks (MCS) globally, and there are still 2/3 of MCS (~0.5 Pg C/yr) that need to be explored. As one of the main overburdened parts of the earth, loess is one of the important driving factors for atmospheric CO2 consumption. Here, we elaborated on the dissolution process and the carbon sink effect from carbonate and silicate minerals in loess. The relationship between carbonate dissolution and carbon source/sink is elucidated, and the mechanism of carbon sink formation from secondary carbonates in loess is clarified. Additionally, the commonly used methods for the identification of primary and secondary carbonates are summarized, and the methods for the study of loess carbon sinks and the influencing factors of loess carbon sinks are also revealed. Based on the research results and progress interpretations, the prospects of loess carbon sinks are discussed to provide a scientific basis for further research on loess carbon sinks. [ABSTRACT FROM AUTHOR]

Comparing satellite retrieval with high-precision ground observations is an essential component for the validation of CO2 satellite products. The initial stage of assessing the bias in retrieval products from satellite and ground sources involves establishing a geographical connection between observations that are temporally and spatially proximate. The primary aim of this paper is to evaluate the influence of variations in neighborhood definitions and colocation methods on the assessment of satellite products and provide quantitative references. To achieve this, a series of experiments were conducted involving the Global Total Column Carbon Observation Network (TCCON) and the OCO-2 satellite. Various spatial-temporal neighborhoods and colocation methods were considered in these experiments. The results indicate that spatial neighborhoods exert a more substantial influence on bias compared to temporal neighborhoods. In the mid-latitudes of the Northern Hemisphere, there is an observed linear increase trend between the difference of OCO-2 and TCCON observations and the spatial neighborhood, with an average increase of 0.32 ppm as the neighborhood size changes from 1° to 10°. Regarding colocation methods, the simple spatiotemporal geographic constraints tend to overlook changes in the atmospheric state to a certain extent. The target geographic constraint method reduces the bias by 2% to 5% by increasing the proportion of OCO-2 observations targeting TCCON while the method of introducing T700 potential temperature reduces by 2% to 13% by screening the gradient of CO2 concentration change. Moreover, an evident correlation exists between the bias and their corresponding latitudes, with a 0.20 ppm increase in bias observed for every 10° increment in latitudes in the Northern Hemisphere. The bias of TCCON and OCO-2 shows a pronounced seasonal regularity, with the highest in summer. The study also discusses the selection of spatiotemporal matching with low satellite coverage, the bias distribution, and the attribution of bias to the natural wind field.

This article is a Commentary on Cassan et al. (2023), 239: 992–1004. [ABSTRACT FROM AUTHOR]

Rising atmospheric CO2 concentration is a key driver of enhanced global greening, thought to account for up to 70% of increased global vegetation in recent decades. CO2 fertilization effects have further profound implications for ecosystems, food security and biosphere-atmosphere feedbacks. However, it is also possible that current trends will not continue, due to ecosystem level constraints and as plants acclimate to future CO2 concentrations. Future predictions of plant response to rising [CO2 ] are often validated using single-generation short-term FACE (Free Air CO2 Enrichment) experiments but whether this accurately represents vegetation response over decades is unclear. The role of transgenerational plasticity and adaptation in the multigenerational response has yet to be elucidated. Here, we propose that naturally occurring high CO2 springs provide a proxy to quantify the multigenerational and long-term impacts of rising [CO2 ] in herbaceous and woody species respectively, such that plasticity, transgenerational effects and genetic adaptation can be quantified together in these systems. In this first meta-analysis of responses to elevated [CO2 ] at natural CO2 springs, we show that the magnitude and direction of change in eight of nine functional plant traits are consistent between spring and FACE experiments. We found increased photosynthesis (49.8% in spring experiments, comparable to 32.1% in FACE experiments) and leaf starch (58.6% spring, 84.3% FACE), decreased stomatal conductance (gs , 27.2% spring, 21.1% FACE), leaf nitrogen content (6.3% spring, 13.3% FACE) and Specific Leaf Area (SLA, 9.7% spring, 6.0% FACE). These findings not only validate the use of these sites for studying multigenerational plant response to elevated [CO2 ], but additionally suggest that long-term positive photosynthetic response to rising [CO2 ] are likely to continue as predicted by single-generation exposure FACE experiments.

We explore the ability of the atmospheric CO2 record since 1900 to constrain the source of CO2 from land use and land cover change (hereafter "land use"), taking account of uncertainties in other terms in the global carbon budget. We find that the atmospheric constraint favors land use CO2 flux estimates with lower decadal variability and can identify potentially erroneous features, such as emission peaks around 1960 and after 2000, in some published estimates. Furthermore, we resolve an offset in the global carbon budget that is most plausibly attributed to the land use flux. This correction shifts the mean land use flux since 1900 across 20 published estimates down by 0.35 PgC year−1 to 1.04 ± 0.57 PgC year−1, which is within the range but at the low end of these estimates. We show that the atmospheric CO2 record can provide insights into the time history of the land use flux that may reduce uncertainty in this term and improve current understanding and projections of the global carbon cycle. [ABSTRACT FROM AUTHOR]

During the late Miocene, global cooling occurred alongside the establishment of near‐modern terrestrial and marine ecosystems. Significant (3°C–5°C) sea surface cooling from 7.5 to 5.5 Ma is recorded by proxies at midlatitudes to high latitudes, yet the magnitude of tropical cooling and the role of atmospheric carbon dioxide (pCO2) in driving this trend are debated. Here, we present a new orbital‐resolution sea surface temperature (SST) record spanning the late Miocene to earliest Pliocene (9–5 Ma) from the eastern equatorial Indian Ocean (International Ocean Discovery Program Site U1443) based on Mg/Ca ratios measured in tests of the planktic foraminifer Trilobatus trilobus. Our SST record reveals a 3.2°C decrease from 7.4 to 5.8 Ma, significantly increasing previous estimates of late Miocene tropical cooling. Analysis of orbital‐scale variability shows that before the onset of cooling, SST variations were dominated by precession‐band (19–23 kyr) variability, whereas tropical temperature became highly sensitive to obliquity (41 kyr) after 7.5 Ma, suggesting an increase in high‐latitude forcing. We compare a revised global SST database with new paleoclimate model simulations and show that a pCO2 decrease from 560 to 300 ppm, in the range suggested by pCO2 proxy records, could explain most of the late Miocene sea surface cooling observed at Site U1443. Using our new Site U1443 record as representative of tropical SST evolution, estimated meridional SST gradients suggest a much more modest increase over the late Miocene than previously suggested, in agreement with modeled meridional SST gradients. Plain Language Summary: The late Miocene is an interesting time period for paleoclimatologists because the Earth underwent important climatic and ecological changes that led to the establishment of our modern climate. An important cooling of global surface oceans was recorded by tracers used to reconstruct past temperature; however, the amplitude of this cooling in the tropics and the role of atmospheric carbon dioxide (CO2) in driving it are unclear. We present a new reconstruction of sea surface temperatures from the eastern equatorial Indian Ocean based on the temperature‐dependent ratio of magnesium to calcium measured in fossil shells of zooplankton (Foraminifera). Our results reveal a cooling (3.2°C) higher than previous estimates of tropical ocean cooling (1°C–2.5°C). To understand the role of atmospheric CO2 in driving this cooling, we simulated Miocene climate using a complex model and find that an atmospheric CO2 decrease from 560 to 300 ppm could explain most of the reconstructed surface ocean cooling. We also find that ocean surface temperature gradients between the tropics (using our new reconstruction) and the northern high latitudes shows a more modest increase over the late Miocene than suggested by previous studies, in agreement with new and existing climate model results. Key Points: New late Miocene orbital‐resolution Mg/Ca sea surface temperature record from the eastern equatorial Indian Ocean spanning 9–5 MaTropical cooling is >3°C; new model simulations suggest that a pCO2 decrease from 560 to 300 ppm could account for most of this coolingIncrease in meridional sea surface temperature gradients over the late Miocene more modest than previously suggested [ABSTRACT FROM AUTHOR]

Radiocarbon (Δ14C) was measured for four years (2019–2022) in Zagreb (Croatia) and in Cvetković village near Jastrebarsko (Zagreb County, Croatia) to see whether there are differences between the city site and the rural one because of the fossil fuel combustion. The δ13C CO2 was measured as grab samples once in a month in period December 2020–November 2022. The bomb-produced 14C has been globally distributed across the planet, but the combustion of fossil fuels that do not contain 14C causes a local effect of lowering Δ14C. Zagreb is considered to be a location with heavy fossil fuel combustion as compared to the Cvetković (rural site). Monthly 14C activity at Zagreb is constantly below the 14C activity at Cvetković. Mean 14C activity at Zagreb (Δ14C Zagreb = −18.4 ± 2.6 ‰) is lower than that in Cvetković (Δ14C Cve = −2.9 ± 2.1 ‰) due to fossil fuel combustion in the city of Zagreb. This is especially pronounced during winter when the mean value in Zagreb is Δ14C Zagreb = −26.0 ± 4.3 ‰ and in Cvetković Δ14C Cve = −5.9 ± 3.4 ‰. Natural gas consumption was used as the proxy for fossil fuel combustion, and it shows better correlation with Δ14C in Zagreb than in Cvetković. The Δ14C difference, Δ14C Cve ‒ Δ14C Zagreb , becomes statistically negligible when natural gas consumption is small. No difference is observed on δ13C CO2 ; in Zagreb mean δ13C CO2 is −11.0 ± 1.3 ‰, and in Cvetković −11.4 ± 1.4 ‰. Lower δ13C CO2 values are observed in winter (Zagreb −11.9 ± 1.1 ‰, −12.2 ± 1.5 ‰ Cvetković) than in summer (−10.1 ± 0.8 ‰ vs. −10.4 ± 1.0 ‰) at both locations. Together with higher Δ14C in Cvetković, it indicates that at the area of Cvetković biogenic samples of modern origin (biomass, wood) as energy source for heating is more pronounced. • Δ14C of atmospheric CO 2 in Zagreb was constantly lower than in village Cvetković. • Overall fossil fuel contribution in the city of Zagreb is 1.9 %, in winter 2.4 %. • Natural gas consumption better correlates with the Zagreb Δ14C data. • δ13C CO2 data are the same in Zagreb and in Cvetković; both show seasonal variation. • Origin of CO 2 in Cvetković is burning of contemporaneous organic matter (biomass). [ABSTRACT FROM AUTHOR]

Heatwaves, expected to become more frequent, pose a significant threat to plant biomass production. This experiment was designed to estimate heatwave influence on Brassica juncea phytoremediation when superimposed on different CO 2 levels. A 7-day heatwave was generated during the species flowering stage. Heatwaves decreased all B. juncea dry weights. The lowest species dry weight was recorded when the heatwave was accompanied by 250 ppm CO 2 , in which the biomass significantly decreased by 40.0% relative to that of no heatwave under the same atmospheric CO 2 conditions. Heatwave superposition with 250 ppm CO 2 reduced the Cd content in B. juncea aerial parts by 28.1% relative to that of identical environmental conditions without heatwave, whereas the opposite result was observed under 550 ppm CO 2 conditions. The heatwave caused oxidative damage to B. juncea under all CO 2 conditions, as manifested by increased malondialdehyde levels in the plant shoots. With heatwave superposition, antioxidant enzyme activity was enhanced by exposure to 400 and 550 ppm CO 2. Considering biomass yield generation and Cd uptake capacity, heatwave superposition decreased the B. juncea phytoremediation effects, and high atmospheric CO 2 conditions could alleviate detrimental effects to a certain extent. This study uniquely examines the combined effects of heatwaves and varying CO 2 levels on phytoremediation, providing microscopic insights into oxidative damage and enzyme activity, highlighting the potential for CO 2 enrichment to mitigate heatwave impacts, and offering comprehensive analysis for future agricultural practices and environmental management. [Display omitted] • Heatwaves caused the most pronounced B. juncea biomass decrease at 250 ppm CO 2. • Elevated CO 2 levels enhanced Cd phytoremediation effect, especially at 550 ppm CO 2. • Heatwaves and CO 2 interaction increased antioxidant activity but decreased Cd removal effect. [ABSTRACT FROM AUTHOR]

Observations of ice sheet stability in Antarctica in the past, during significantly warmer climatic periods than today, are hampered by a paucity of continental outcrops but they are essential if we are to test and more fully understand established concepts of ice sheet growth and decay and robustly predict Earth's future during rapid global warming. In this paper we use the unique terrestrial record preserved in the three most southerly volcanoes on Earth to reconstruct Antarctica's environmental landscape in the Transantarctic Mountains for three time slices (at 20.1, 19.31 and c. 17 Ma). We demonstrate that the East Antarctic Ice Sheet margin was highly dynamic and fluctuated greatly during the Early Miocene. The period included a much-reduced ice cover that left the southern Transantarctic Mountains virtually ice-free, although a few tidewater glaciers reached the shores of the Early Miocene Ross Sea (Sheridan Bluff; 20.1 Ma); and a substantially thicker, much more voluminous ice mass (represented by volcanism at Mount Early; 19.31 Ma). An intermediate stage of ice retreat is also indicated (at c. 17 Ma), when the East Antarctic Ice Sheet had again withdrawn to behind the Transantarctic Mountains. It is represented by a subglacial volcanic centre identified remotely by aerogeophysics and sampled only as glacial erratics. The associated ice cover at c. 17 Ma had a relatively low surface elevation but it was confluent with thin ice domes that covered the adjacent mountains. Although the ice margin probably did not extend down to the Ross Sea coast, several glaciers fed icebergs into the Ross Sea. The large ice sheet indicated by the Mount Early volcanic centre is the only known physical record of a significant glacial event that took place at 19.31 ± 0.32 Ma ('Mount Early glacial'). The records examined at the other two volcanic sites correspond to eruptions during periods of substantially reduced ice in Antarctica, of which that at 20.1 ± 0.4 Ma is the most remarkable ('Sheridan Bluff interglacial'). The causes of the extreme variations in ice sheet thickness and extent indicated are uncertain but they occurred during a period of rapidly fluctuating atmospheric CO 2 compositions. Although Milankovitch astronomical forcing probably also played a significant part, the results suggest that the East Antarctic Ice Sheet was highly susceptible to comparatively slight changes in CO 2 during the warm Early Miocene. • Transantarctic Mountains landscapes reconstructed using glaciovolcanic sequences for three time slices in the Early Miocene • Large, deep, unfrozen freshwater lake identified at 87°S and c. 2000 m elevation, not predicted by current modelling • Very large ice sheet recognized, more expanded than today, which overtopped the Transantarctic Mountains • Ross Sea margin of the East Antarctic Ice Sheet was highly dynamic between 20 and 17 Ma • Ice sheet margin was highly sensitive to comparatively small changes in CO 2 [ABSTRACT FROM AUTHOR]

Research findings concerning the main processes influencing water resources differ substantially, and so the topic remains controversial. Recent studies indicate that the changes in water yield, expressed through the n-parameter of Budyko framework, are associated with vegetation coverage changes. Here, we use runoff measurements and outputs from 13 dynamic global vegetation models, to investigate the underlying drivers of the n-parameter changes. Unlike previous studies, we instead find that climate change is the primary driver of adjustments on water resources. Changing climatic characteristics, particularly the intensity and seasonality of rainfall, modulates the runoff generation process. Indirect effects of climate change occur through altering vegetation properties, which in turn also impact river flow. We also find that in the arid and sparse vegetation regions, water yield is more sensitive to changes in n-parameter. Thus, the Budyko framework provides a reliable parameter-sparse representation of runoff changes, and reveals that terrestrial water cycle is changing substantially under climate change. This climate forcing requires on-going investigation to generate more refined and reliable projections of future water availability.