Atmospheric Carbon Dioxide Emissions Research Articles

Techno-economic assessment of large-scale sedimentary basin stored–CO2 geothermal power generation

One approach to reducing atmospheric carbon dioxide (CO2) emissions is to adopt carbon capture utilization and storage (CCUS) strategies. This is particularly crucial for countries to achieve their net-zero goal. In this study, we investigate the techno-economic viability of a proposed CCUS process that utilizes geologically stored CO2, associated with hydrogen (H2) production from fossil fuels, as a working fluid to extract geothermal energy from deep, large-scale, sedimentary storage formations. The process ensures permanent geological storage of all injected CO2 while generating adaptable geothermal power through supercritical CO2 turbine expansion, thus, bolstering revenue and reducing the final cost of blue hydrogen production. We simulate subsurface-wellbore fluid flow and heat transport for a representative 4-way closed anticlinal Arabian reservoir and optimize system power output, including a comprehensive and integrated economic analysis. We find that CO2 captured from an equivalent blue H2 production of ∼4.1 Mt./year can be injected at an annual rate of 0.92–1 million metric tons (Mt) per well, resulting in a cumulative sequestration of ∼1.15 gigatons (Gt) of CO2 over 11.5 years. To mitigate the risks of reaching the formation parting pressure at the crest of the anticline and ensuring sufficient CO2 saturation at the production wells, phased drilling schedules and pressure-controlled injection and production are essential. With horizontal production wells, our simulations generate an average geothermal net electricity of 164 MW. The base-case economic analysis reveals a Levelized Cost of Electricity (LCOE) of 77 $/MWh and a Net Present Value (NPV) of 480 million USD over 50 years. In contrast, vertical production wells double LCOE, and the project remains unprofitable throughout its life (negative NPV). Our economic sensitivity analysis further emphasizes how the capacity factor, electricity selling price, and drilling costs govern LCOE and NPV. On the other hand, discount rates and Opex fraction are influential yet uncertain parameters affecting the system's techno-economic outlook. Therefore, our study provides valuable insights into the benefits of geothermal energy production from over 1 Gt of stored CO2 and the associated economic landscape.

Carbon-based materials for low concentration CO2 capture and electrocatalytic reduction

The gradual increase in carbon dioxide (CO2) concentration in the atmosphere has been recognized as a significant problem for humankind. CO2 flue gas is one of the most apparent contributing sources of emissions. CO2 capture and conversion are environmental-friendly and efficient ways to reduce atmospheric carbon dioxide emissions from flue gases. Considering the traditional expensive gas purification process of low-concentration CO2, the low-cost capturing and electrocatalytic CO2 reduction (ECR) at low concentration by newly-developed carbon-based materials provide an attractive approach to convert low-concentration CO2 in flue gas into high-value fuels and chemicals. Developing and integrating carbon-based capturing and catalytic materials with an understanding of the mechanism has a promising future and will promote this technology toward practical application. This review describes recent progress in the design, preparation, and structural characterization of existing carbon-based materials for the capture and catalysis of low-concentration CO2. The crucial factors of capturing and catalysis performance of all the carbon-based materials are also summarized. Furthermore, the review identifies existing research problems and challenges, and outlines future research directions. We also discuss the prospects for the industrialization of low-concentration CO2 capture and ECR. The remaining technological challenges and future directions for enhancing and applying of carbon-based materials for CO2 capture and electrocatalytic reduction are highlighted.

Ethylene Electrosynthesis via Selective CO2 Reduction: Fundamental Considerations, Strategies, and Challenges

AbstractThe electrochemical carbon dioxide reduction reaction (CO2RR) is a promising approach for reducing atmospheric carbon dioxide (CO2) emissions, allowing harmful CO2 to be converted into more valuable carbon‐based products. On one hand, single carbon (C1) products have been obtained with high efficiency and show great promise for industrial CO2 capture. However, multi‐carbon (C2+) products possess high market value and have demonstrated significant promise as potential products for CO2RR. Due to CO2RR's multiple pathways with similar equilibrium potentials, the extended reaction mechanisms necessary to form C2+ products continue to reduce the overall selectivity of CO2‐to‐C2+ electroconversion. Meanwhile, CO2RR as a whole faces many challenges relating to system optimization, owing to an intolerance for low surface pH, systemic stability and utilization issues, and a competing side reaction in the form of the H2 evolution reaction (HER). Ethylene (C2H4) remains incredibly valuable within the chemical industry; however, the current established method for producing ethylene (steam cracking) contributes to the emission of CO2 into the atmosphere. Thus, strategies to significantly increase the efficiency of this technology are essential. This review will discuss the vital factors influencing CO2RR in forming C2H4 products and summarize the recent advancements in ethylene electrosynthesis.

Atmospheric Carbon Sequestration Using Microalgae

This article outlines biotechnological methods that can help reduce atmospheric and industrial carbon dioxide emissions through the use of microalgae. A general description of microalgae was provided, and the most promising species for microalgal biotechnology were identified. The metabolic process by which microalgae capture and degrade carbon dioxide was described. The microalgae-based biotechnological systems and devices available today were analyzed. The key factors that need to be considered for the effective and successful use of microalgae were highlighted. Different products obtained from microalgal biomass after atmospheric carbon dioxide sequestration were overviewed.

The Impacts of Globalization, Economic Growth, Population and Urbanization on Carbon Dioxide Emissions in Afghanistan

The atmospheric carbon dioxide emissions have increased since last few years in Afghanistan. This increasing trend in carbon emissions may cause global warming, climate change and environmental pollution. Consequently, these indicated threats may suffer human life and ecological conditions in near future. Therefore, this study examines the impacts of globalization, economic growth, population and urbanization on carbon emissions in Afghanistan using annual time series data for the period 1990 – 2020. The study used the Augmented Dickey Fuller and Phillips–Perron unit root tests, the Breusch – Godfrey serial correlation Lagrange multiplier (LM) test and the autoregressive distributed lag (ARDL) bounds test to examine the short and long-run relationship of globalization, economic growth, population and urbanization with carbon emissions. The empirical results show that globalization, economic growth and population have a significant positive short and long-run relationship with carbon emissions. While urbanization has a significant short-run negative and long-run positive relationship with carbon emissions. Based on results, it is highly recommended that government should design environment friendly policies related to globalization, economic growth, population and urbanization to reduce environmental pollution in Afghanistan.

Research progress on sources, harms and countermeasures of marine pollution

Human behavior is posing a serious threat to the ecological environment of the global ocean. This paper explores three important issues related to the marine environment: nuclear pollution, ocean acidification and marine microplastic pollution. First, the problem of nuclear pollution focuses on the potential threat to marine ecosystems and human health from nuclear sewage discharge from the nuclear power plant in Japan. Although the Japanese government has taken some response measures, the relevant risks and impacts still need attention to and addressed. It is suggested to strengthen supervision and management, promote technological innovation, and reasonably support the affected communities. Second, the ocean acidification problem is exacerbated by excessive atmospheric carbon dioxide emissions, which has a serious impact on marine life and ecosystems. The article advocates reducing global greenhouse gas emissions, promoting renewable energy development, and strengthening international cooperation and scientific research to protect marine ecosystems. Finally, in response to marine microplastic pollution, it calls for strengthening the development and use of plastic alternatives, improving waste management and treatment, and promoting innovation in microplastic detection and removal technologies. Addressing these issues requires the combined efforts of governments, researchers and the public, including enhanced monitoring, research and development of effective management policies.

Carbonic Anhydrase Robustness for Use in Nanoscale CO2 Capture Technologies.

Continued dependence on crude oil and natural gas resources for fossil fuels has caused global atmospheric carbon dioxide (CO2) emissions to increase to record-setting proportions. There is an urgent need for efficient and inexpensive carbon sequestration systems to mitigate large-scale emissions of CO2 from industrial flue gas. Carbonic anhydrase (CA) has shown high potential for enhanced CO2 capture applications compared to conventional absorption-based methods currently utilized in various industrial settings. This study aims to understand structural aspects that contribute to the stability of CA enzymes critical for their applications in industrial processes, which require the ability to withstand conditions different from those in their native environments. Here, we evaluated the thermostability and enzyme activity of mesophilic and thermophilic CA variants at different temperature conditions and in the presence of atmospheric gas pollutants like nitrogen oxides and sulfur oxides. Based on our enzyme activity assays and molecular dynamics simulations, we see increased conformational stability and CA activity levels in thermostable CA variants incubated week-long at different temperature conditions. The thermostable CA variants also retained high levels of CA activity despite changes in solution pH due to increasing NO and SO2 concentrations. A loss of CA activity was observed only at high concentrations of NO/SO2 that possibly can be minimized with the appropriate buffered solutions.

Biochar Aged for Five Years Altered Carbon Fractions and Enzyme Activities of Sandy Soil

Biochar applied to soil has been considered as an effective tool for mitigation of atmospheric carbon dioxide emission and enhancement of carbon storage in soil, which may also enhance soil quality. However, the effect of biochar aged for 5 years on the different carbon fractions and enzyme activities as well as its changes, is not well understood in the cropland sandy soil of northern China. Therefore, a field trial was carried out in 2014 with biochar applied once at 0, 5.25, 10.50, 21.00 and 42.00 g·kg−1 (BC0, BC1, BC2, BC3, and BC4, respectively). We evaluated the influence of biochar addition to the changes in soil organic carbon (SOC), labile carbon pools (readily oxidized carbon, dissolved organic carbon, and microbial biomass carbon) and enzyme activities (invertase, urease, and catalase). Biochar significantly increased SOC (122.00%) and altered the content of labile carbon (increased ROC, DOC and MBC by 71.29%, 10.35%, and 900.00%, respectively). Soil urease and invertase activities increased by 55.81% and 46.76%, respectively, with an increase in biochar application rate, but catalase activity significantly decreased by 31.79%. The values of the geometric means of labile carbon (0.88) and enzyme activities (2.39) for the BC3 treatment were higher than others, which indicated that the biochar application rate of 21.00 g·kg−1 is suggested for the sandy soil. Our results suggest that the application of biochar in sandy soil for five years increased soil carbon sequestration, changed enzyme activities and ameliorated soil quality.

Ocean Acidification, Climate and Health Hazard

Ocean acidification is a growing threat to marine life, ecosystems, and human health. Rising atmospheric carbon dioxide (CO2) emissions from human activities, primarily the burning of fossil fuels, are the main drivers of ocean acidification. As atmospheric CO2 levels continue to rise, the ocean’s pH decreases, making it more acidic. This review examines the impacts of ocean acidification on climate and health hazards, focusing on the causes and consequences of acidification, as well as potential solutions. The review discusses how ocean acidification is affecting marine life, including shellfish, corals, and fish, and how this can lead to economic and ecological consequences. Additionally, it explores how ocean acidification is exacerbating climate change and contributing to the occurrence of extreme weather events. The review also examines the potential health hazards associated with ocean acidification, including the impact on human health through the consumption of contaminated seafood, and the impact on mental health due to the loss of natural resources. Furthermore, this review outlines potential solutions to address ocean acidification, such as reducing CO2 emissions, improving wastewater treatment, and implementing sustainable fishing practices. The review concludes that urgent action is needed to reduce greenhouse gas emissions and mitigate the impacts of ocean acidification. It highlights the need for interdisciplinary collaboration to address this issue and underscores the importance of developing sustainable solutions to preserve the health of our oceans and the well-being of human populations worldwide.

Progress in the application of Cu-based catalysts in the electroreduction of CO2 to produce Cxs products

Since the industrial revolution, human dependence on fossil fuels has resulted in increasingly severe atmospheric carbon dioxide (CO2) emissions. Electrocatalytic CO2 RR has attracted much attention because of its many advantages, such as mild reaction conditions, controllable reaction rate, low cost and scalable electrolyzer.[7] More importantly, electrocatalytic CO2 RR can control the selective generation of target products by rationally adjusting the reaction potential, electrolyte and catalyst species. However, the CO2 molecular structure is stable, and obtaining the key CO2 -based anionic intermediate CO2– from activated CO2 molecules requires overcoming a huge energy barrier. Copper (Cu) catalysts are the only monometallic catalysts to date that can form two-carbon (C2) products, which establishes their special position in the field. However, the poor selectivity of Cu for a particular product has led to a wide distribution of reduction products, covering the range from carbon monoxide (CO), a reduction product at 2e-, to ethanol (C H25 OH), a reduction product at 12e-. Meanwhile, Cu catalysts are generally less stable, which can seriously affect their commercialization. Currently, in order to obtain highly selective C2+ products (mainly ethylene and ethanol), [16]this article reviews the various methods developed by different scholars in China and abroad to modify Cu catalysts. Finally, this article suggests ways to improve the performance of Cu-based catalysts to enhance the Faraday efficiency of the C2 product from the electroreduction of C02 and gives an outlook on the future direction of Cu-based catalysts.[19]

Benefits of Blue Carbon Stocks in a Coastal Jazan Ecosystem Undergoing Land Use Change

Coastal ecosystems are characterized by high content of soil carbon storage; however, they experience severe land conversions in the past decades. The current study aims to examine how different land use/land cover (LU/LC) impact carbon stock in coastal ecosystem along Jazan coast, Saudi Arabia. In this study, impacts of LU/LC on carbon stocks in the coastal zone of Jazan, Saudi Arabia in 2009, 2013, and 2021 were assessed. Also, the LU/LC dynamics were evaluated using data provided by the land use dynamic model. The carbon stocks were modelled based on LU/LC using the InVEST program. Our study results showed that the decrease in mangroves from 2013 to 2021 reflects the high atmospheric emissions of carbon dioxide (CO2). Also, the increase in built-up areas might negatively impact total carbon stock. The estimated carbon stocks for the coastal zone of Jazan biome were 7279027.42 Mg C in 2009 (1Mg = 106 g). It decreased to 2827817.84 Mg C in 2013, with a total loss of − 4450675.40 Mg C, and an average of annual loss of − 1,112,669 Mg C in the study period with net value of − 461240790.53 US$. On the other hand, the total estimated carbon stock was increased from 2013 to 2021 with a 3772968.31 Mg C in 2021 (a total gain 944840.87 Mg C). Based on the current findings, we recommend that land-use-policy makers and environmental government agencies should implement conservation policies to reduce land use change at Jazan coastal ecosystems.

Comparing the Effects of N and P Deficiency on Physiology and Growth for Fast- and Slow-Growing Provenances of Fraxinus mandshurica

With the continuous increase in atmospheric carbon dioxide emissions, nitrogen (N) and phosphorus (P) as mineral elements increasingly restrict plant growth. To explore the effect of deficiency of P and N on growth and physiology, Fraxinus mandshurica (hereafter “F. mandshurica”) Rupr. annual seedlings of Wuchang (WC) provenance with fast growth and Dailing (DL) provenance with slow growth were treated with complete nutrition or starvation of N (N-), P (P-) or both elements (NP-). Although P- and N- increased the use efficiency of P (PUE) and N (NUE), respectively, they reduced the leaf area, chlorophyll content and activities of N assimilation enzymes (NR, GS, GOGAT), which decreased the dry weight and P or N amount. The free amino acid content and activities of Phosphoenolpyruvate carboxylase (PEPC) and acid phosphatase enzymes were reduced by N-. The transcript levels of NRT2.1, NRT2.4, NRT2.5, NRT2.7, AVT1, AAP3, NIA2, PHT1-3, PHT1-4 and PHT2-1 in roots were increased, but those of NRT2.1, NRT2.4, NRT2.5, PHT1-3, PHT1-4, PHT2-1 and AAP3 in leaves were reduced by P-. WC was significantly greater than DL under P- in dry weight, C amount, N amount, leaf area, PUE, NUE, which related to greater chlorophyll content, PEPC enzyme activity, N assimilation enzyme activities, and transcript levels of N and P transporter genes in roots and foliage, indicating a greater ability of WC to absorb, transport and utilize N and P under P-. WC was also greater than DL under N- in terms of the above indicators except the transcript levels of N and P assimilation genes, but most of the indicators did not reach a significant level, indicating that WC might be more tolerant to N- than DL, which requires further verification. In summary, WC was identified as a P-efficient provenance, as the growth rate was greater for the genetic type with high than low tolerance to P-.

Microalgal Hydrogen Production in Relation to Other Biomass-Based Technologies—A Review

Hydrogen is an environmentally friendly biofuel which, if widely used, could reduce atmospheric carbon dioxide emissions. The main barrier to the widespread use of hydrogen for power generation is the lack of technologically feasible and—more importantly—cost-effective methods of production and storage. So far, hydrogen has been produced using thermochemical methods (such as gasification, pyrolysis or water electrolysis) and biological methods (most of which involve anaerobic digestion and photofermentation), with conventional fuels, waste or dedicated crop biomass used as a feedstock. Microalgae possess very high photosynthetic efficiency, can rapidly build biomass, and possess other beneficial properties, which is why they are considered to be one of the strongest contenders among biohydrogen production technologies. This review gives an account of present knowledge on microalgal hydrogen production and compares it with the other available biofuel production technologies.

Forest carbon stocks under three canopy densities in Sitapahar natural forest reserve in Chittagong Hill Tracts of Bangladesh

Tropical forests play a significant role in sequestrating and storing atmospheric carbon di-oxide (CO2) emissions. However, estimation of forest carbon (C) stocks in relation to changes in forest structure and disturbances are less studied. We estimated forest C stocks in live trees, saplings, lianas, deadwood, forest floor, and soil in Sitapahar natural forest reserve of Bangladesh based on field measurements and laboratory assessments. We categorized the 99 temporary sample plots into three canopy densities: closed, moderately closed, and open. According to the results, the forest C stocks were dominated by the soil C pool and forest C stocks in the closed canopy (91 Mg ha−1) differed significantly from that in the open canopy (50 Mg ha−1). Forest C stocks were also affected by basal area (BA) and deadwood C stocks. In the open canopy, the second highest contributor to forest C stock was deadwood, whereas it was above and below-ground live biomass in the closed and moderately closed canopies. In the open canopy, forest disturbances significantly decreased height and BA, and C stocks in live biomass were significantly lower compared to the other two canopy densities. In the open canopy, decreased tree density resulted in the lowest C stock in litterfall and humus, and they were up to 95% lower compared to the other two canopy densities. C stocks in humus were higher than those in litterfall in the closed and moderately closed canopies, which was opposite to that in the open canopy. The soil C stock decreased with soil depth and the highest C stocks across all depths were in the closed canopy, followed by the moderately closed and open canopy. This study also provided a stand-level estimation of C stocks that contribute to determining which tree species sequester more carbon, such as Swintonia floribunda, Lannea coromandelica, Anacardiaceae and Moraceae.

Design and thermodynamic analysis of a novel methanol, hydrogen, and power trigeneration system based on renewable energy and flue gas carbon dioxide

In this paper, a new trigeneration system is proposed to decrease atmospheric carbon dioxide emission and produce methanol, hydrogen, and power. The system is composed of an organic Rankine cycle, a direct methanol fuel cell, a carbon capture unit, a proton exchange membrane electrolyzer, and a methanol synthesis unit. A flue gas stream with a defined composition, solar energy, and the atmospheric air are the system's inlets. In the design step, special attention is paid to heat and mass integration between different components so that its waste can be lowered as much as possible. Then, mass balance law, energy conservation principle, exergy relations, and auxiliary equations are applied for each subsystem to investigate the system's thermodynamic performance. Also, the effect of changing operating parameters on the performance of each subsystem is studied. The obtained results show that the proposed system has the energy and exergy efficiencies of 66.84% and 55.10%, respectively. Furthermore, 94% of the total exergy destruction rate belongs to the water electrolyzer, while the contribution of the organic Rankine cycle is negligible. The performance of the methanol synthesis reactor depends strongly on its inlet temperature. Maximum equilibrium methanol concentration and carbon dioxide conversion are achieved at the inlet temperature of 210 °C. The parametric studies reveal that there is an optimum fuel cell current density in which its produced power density is maximized.

A review of geothermal energy status and potentials in Middle-East countries

Geothermal energy production and consumption is one of the world’s top priorities as it ensures sustainable developments via steady yield of renewable energy and helps to reduce atmospheric carbon dioxide (CO2) emissions and air pollution levels. The objective of this study is to critically assess geothermal energy prospects in terms of number of proven geothermal reservoirs, thermal energy capacities, and potential areas of utilization across thirteen Middle East countries (MECs). The findings from this study show that most oil-rich MECs have not adequately explored/exploited their geothermal resources as evidenced by lack of research and exploration activities. It was found that the current geothermal reservoirs/resources across all the MECs are mostly medium (100–150 °C) and low ( 150 °C) enthalpy geothermal fields. For low/depleted oil and gas reserves countries, full exploitation of geothermal energy is deemed as one of the options to meet their energy demands. In order to fully optimize the geothermal energy productions, it is imperative for these countries to employ advanced geothermal energy production technologies (GEPTs). MECs could learn the experiences of Europe and US to develop their own GEPTs including national and regional strategies and policy frameworks to help fully harness these valuable geothermal resources. These targets are possible through research, trainings, and international collaborations.

Influence of Gas Density on the Clay Wettability: Implication for CO2 Geo-Sequestration

Carbon dioxide capture and storage (CCS) is considered as the most promising technological method to decrease atmospheric Carbon dioxide (CO2) emissions. However, due to density difference between the injected CO2 and the formation brine, CO2 tends to move vertically upwards in the reservoir, which results in leakage risk. This vertical migration of CO2 can be prevented by four trapping mechanisms, i.e. structural/residual trapping, capillary trapping, solubility trapping, and mineral trapping. The capacities of structural and residual trapping are highly affected by rock wettability. Clay wettability is one of the crucial parameters in evaluation CO2 geo-sequestration. However, the literature data show that there are many uncertainties associated with clay experimental measurements. One of these uncertainties is the influence of the effect of gas density on the clay mineral wettability. Thus, here, we compared the wettability of a clay mineral (i.e. montmorillonite) with three different gas densities scenarios (i.e. low (Helium), moderate (Nitrogen) and high (CO2) gas densities). To do so, we measured the advancing and receding contact angle (i.e. wettability) of montmorillonite for CO2/water, nitrogen/water, and Helium/water systems at a constant (333 K) under four different pressures (5, 10, 15, and 20 MPa). The brine composition used was 4 wt% NaCl, 4 wt% CaCl2, 1 wt% MgCl2 and 1 wt% KCl, for all gas density scenarios. The results indicate that gas density has a significant effect on the clay mineral wettability and that both advancing and receding contact angles increase with an increase in gas density. The results show that the higher gas density gas has higher contact angle with montmorillonite, measured at the same temperature and pressure. For example, the advancing contact angle of montmorillonite at 333 K and 15 MPa was only 50 (water-wet) for the Helium/water system, while it was 101 (intermediate-wet) for the CO2/water system. Thus, we conclude that the gas density affects the clay wettability and that higher gas density leads to increase the CO2-wettability of the clay. This phenomenon reduces the estimated CO2 geo-sequestration capacity and containment security. This implication can be utilised to improve the wettability predictions, and thus, the assessments of reservoir CO2 geo-sequestration capacity.

Would firm generators facilitate or deter variable renewable energy in a carbon-free electricity system?

To reduce atmospheric carbon dioxide emissions and mitigate impacts of climate change, countries across the world have mandated quotas for renewable electricity. But a question has remained largely unexplored: would low-cost, firm, zero-carbon electricity generation technologies enhance—or would they displace—deployment of variable renewable electricity generation technologies, i.e., wind and solar photovoltaics, in a least-cost, fully reliable, and deeply decarbonized electricity system? To address this question, we modeled idealized electricity systems based on historical weather data and considered only technoeconomic factors. We did not apply a predetermined use model. We found that cost reductions in firm generation technologies (starting at current costs, ramping down to nearly zero) uniformly resulted in increased penetration of the firm technologies and decreased penetration of variable renewable electricity generation, in electricity systems where technology deployment is primarily driven by relative costs, and across a wide array of future technology cost assumptions. Similarly, reduced costs of variable renewable electricity (starting at current costs, ramping down to nearly zero) drove out firm generation technologies. Yet relative to deployment of “must-run” firm generation technologies, and when the studied firm technologies have high fixed costs relative to variable costs, the addition of flexibility to firm generation technologies had only limited impacts on the system cost, less than a 9% system cost reduction in our idealized model. These results reveal that policies and funding that support particular technologies for low- or zero-carbon electricity generation can inhibit the development of other low- or zero-carbon alternatives.

Multi-Year Comparison of CO2 Concentration from NOAA Carbon Tracker Reanalysis Model with Data from GOSAT and OCO-2 over Asia

Accurate knowledge of the carbon budget on global and regional scales is critically important to design mitigation strategies aimed at stabilizing the atmospheric carbon dioxide (CO2) emissions. For a better understanding of CO2 variation trends over Asia, in this study, the column-averaged CO2 dry air mole fraction (XCO2) derived from the National Oceanic and Atmospheric Administration (NOAA) CarbonTracker (CT) was compared with that of Greenhouse Gases Observing Satellite (GOSAT) from September 2009 to August 2019 and with Orbiting Carbon Observatory 2 (OCO-2) from September 2014 until August 2019. Moreover, monthly averaged time-series and seasonal climatology comparisons were also performed separately over the five regions of Asia; i.e., Central Asia, East Asia, South Asia, Southeast Asia, and Western Asia. The results show that XCO2 from GOSAT is higher than the XCO2 simulated by CT by an amount of 0.61 ppm, whereas, OCO-2 XCO2 is lower than CT by 0.31 ppm on average, over Asia. The mean spatial correlations of 0.93 and 0.89 and average Root Mean Square Deviations (RMSDs) of 2.61 and 2.16 ppm were found between the CT and GOSAT, and CT and OCO-2, respectively, implying the existence of a good agreement between the CT and the other two satellites datasets. The spatial distribution of the datasets shows that the larger uncertainties exist over the southwest part of China. Over Asia, NOAA CT shows a good agreement with GOSAT and OCO-2 in terms of spatial distribution, monthly averaged time series, and seasonal climatology with small biases. These results suggest that CO2 can be used from either of the datasets to understand its role in the carbon budget, climate change, and air quality at regional to global scales.

The effects of constant and fluctuating elevated pCO2 levels on oxygen uptake rates of coral reef fishes

Ocean acidification, resulting from increasing atmospheric carbon dioxide (CO2) emissions, can affect the physiological performance of some fishes. Most studies investigating ocean acidification have used stable pCO2 treatments based on open ocean predictions. However, nearshore systems can experience substantial spatial and temporal variations in pCO2. Notably, coral reefs are known to experience diel fluctuations in pCO2, which are expected to increase on average and in magnitude in the future. Though we know these variations exist, relatively few studies have included fluctuating treatments when examining the effects of ocean acidification conditions on coral reef species. To address this, we exposed two species of damselfishes, Amblyglyphidodon curacao and Acanthochromis polyacanthus, to ambient pCO2, a stable elevated pCO2 treatment, and two fluctuating pCO2 treatments (increasing and decreasing) over an 8 h period. Oxygen uptake rates were measured both while fish were swimming and resting at low-speed. These 8 h periods were followed by an exhaustive swimming test (Ucrit) and blood draw examining swimming metrics and haematological parameters contributing to oxygen transport. When A. polyacanthus were exposed to stable pCO2 conditions (ambient or elevated), they required more energy during the 8 h trial regardless of swimming type than fish exposed to either of the fluctuating pCO2 treatments (increasing or decreasing). These results were reflected in the oxygen uptake rates during the Ucrit tests, where fish exposed to fluctuating pCO2 treatments had a higher factorial aerobic scope than fish exposed to stable pCO2 treatments. By contrast, A. curacao showed no effect of pCO2 treatment on swimming or oxygen uptake metrics. Our results show that responses to stable versus fluctuating pCO2 differ between species - what is stressful for one species many not be stressful for another. Such asymmetries may have population- and community-level impacts under higher more variable pCO2 conditions in the future.