Atmospheric Carbon Dioxide Concentration Research Articles

Optimization of environmental variable functions of GPP quantitative model based on SCE-UA and minimum loss screening method

Environmental variable functions are of key importance for gross primary productivity (GPP) modeling. This study proposes a method about the optimization of environmental variable function to obtain a more robust and accurate GPP quantitative model. The key idea is to explore the impact of environmental factors on the accuracy of the GPP quantitative model from the following three aspects: the first is using tensor as the alternative environmental factor equation to construct the basis-function set of photosynthetically active radiation (PAR), atmospheric temperature and atmospheric carbon dioxide concentration for the given environmental conditions, and soil moisture functions of new environmental conditions. The second is building 144 candidate model based on a tensor product. The third is finding the best model from the candidates according to the Shuffled Complex Evolution (SCE-UA) algorithm and the Minimum Loss Screening Method. Through the above experiments, we have the following conclusions: First, this paper obtains two new best models from 144 candidate models, and their accuracy is higher than that of the initial model, indicating that this paper proposes a more robust and accurate GPP quantitative model. Then, the model proposed in this paper has common characteristics, that is, PAR and atmospheric temperature can be replaced by more appropriate quantitative functions, named Sigmoid-like function and Q10 equation, and the carbon dioxide equation can use half-saturated equation or Sigmoid function. Finally, the method in this paper can provide new ideas for simulating the fluxes of other ecosystems, including soil carbon decomposition and plant respiration.

Modeling cycles and interdependence in irregularly sampled geophysical time series

AbstractWe show how an autoregressive Gaussian process model incorporating a time scale coefficient can be used to represent irregularly sampled geophysical time series. Selection of this coefficient, together with the order of autoregression, provides flexibility of the model appropriate to the structure of the data. This leads to a valuable improvement in the identification of the periodicities within and dependence between such series, which arise frequently and are often acquired at some cost in time and effort. We carefully explain the modeling procedure and demonstrate its efficacy for identifying periodic behavior in the context of an application to dust flux measurements from lake sediments in a region of subtropical eastern Australia. The model is further applied to the measurements of atmospheric carbon dioxide concentrations and temperature obtained from Antarctic ice cores. The model identifies periods in the glacial‐interglacial cycles of these series that are associated with astronomical forcing, determines that they are causally related, and, by application to current measurements, confirms the prediction of climate warming.

Hydrological feedbacks on peatland CH4 emission under warming and elevated CO2: A modeling study

Peatland carbon cycling is critical for the land–atmosphere exchange of greenhouse gases, particularly under changing environments. Warming and elevated atmospheric carbon dioxide (eCO2) concentrations directly enhance peatland methane (CH4) emission, and indirectly affect CH4 processes by altering hydrological conditions. An ecosystem model ELM-SPRUCE, the land model of the E3SM model, was used to understand the hydrological feedback mechanisms on CH4 emission in a temperate peatland under a warming gradient and eCO2 treatments. We found that the water table level was a critical regulator of hydrological feedbacks that affect peatland CH4 dynamics; the simulated water table levels dropped as warming intensified but slightly increased under eCO2. Evaporation and vegetation transpiration determined the water table level in peatland ecosystems. Although warming significantly stimulated CH4 emission, the hydrological feedbacks leading to a reduced water table mitigated the stimulating effects of warming on CH4 emission. The hydrological feedback for eCO2 effects was weak. The comparison between modeled results with data from a field experiment and a global synthesis of observations supports the model simulation of hydrological feedbacks in projecting CH4 flux under warming and eCO2. The ELM-SPRUCE model showed relatively small parameter-induced uncertainties on hydrological variables and their impacts on CH4 fluxes. A sensitivity analysis confirmed a strong hydrological feedback in the first three years and the feedback diminished after four years of warming. Hydrology-moderated warming impacts on CH4 cycling suggest that the indirect effect of warming on hydrological feedbacks is fundamental for accurately projecting peatland CH4 flux under climate warming.

Bioactive Trace Metals and Their Isotopes as Paleoproductivity Proxies: An Assessment Using GEOTRACES‐Era Data

AbstractPhytoplankton productivity and export sequester climatically significant quantities of atmospheric carbon dioxide as particulate organic carbon through a suite of processes termed the biological pump. Constraining how the biological pump operated in the past is important for understanding past atmospheric carbon dioxide concentrations and Earth's climate history. However, reconstructing the history of the biological pump requires proxies. Due to their intimate association with biological processes, several bioactive trace metals and their isotopes are potential proxies for past phytoplankton productivity, including iron, zinc, copper, cadmium, molybdenum, barium, nickel, chromium, and silver. Here, we review the oceanic distributions, driving processes, and depositional archives for these nine metals and their isotopes based on GEOTRACES‐era datasets. We offer an assessment of the overall maturity of each isotope system to serve as a proxy for diagnosing aspects of past ocean productivity and identify priorities for future research. This assessment reveals that cadmium, barium, nickel, and chromium isotopes offer the most promise as tracers of paleoproductivity, whereas iron, zinc, copper, and molybdenum do not. Too little is known about silver to make a confident determination. Intriguingly, the trace metals that are least sensitive to productivity may be used to track other aspects of ocean chemistry, such as nutrient sources, particle scavenging, organic complexation, and ocean redox state. These complementary sensitivities suggest new opportunities for combining perspectives from multiple proxies that will ultimately enable painting a more complete picture of marine paleoproductivity, biogeochemical cycles, and Earth's climate history.

Assessing the representation of the Australian carbon cycle in global vegetation models

Abstract. Australia plays an important role in the global terrestrial carbon cycle on inter-annual timescales. While the Australian continent is included in global assessments of the carbon cycle such as the global carbon budget, the performance of dynamic global vegetation models (DGVMs) over Australia has rarely been evaluated. We assessed simulations of net biome production (NBP) and the carbon stored in vegetation between 1901 to 2018 from 13 DGVMs (TRENDY v8 ensemble). We focused our analysis on Australia's short-term (inter-annual) and long-term (decadal to centennial) terrestrial carbon dynamics. The TRENDY models simulated differing magnitudes of NBP on inter-annual timescales, and these differences resulted in significant differences in long-term vegetation carbon accumulation (−4.7 to 9.5 Pg C). We compared the TRENDY ensemble to several satellite-derived datasets and showed that the spread in the models' simulated carbon storage resulted from varying changes in carbon residence time rather than differences in net carbon uptake. Differences in simulated long-term accumulated NBP between models were mostly due to model responses to land-use change. The DGVMs also simulated different sensitivities to atmospheric carbon dioxide (CO2) concentration, although notably, the models with nutrient cycles did not simulate the smallest NBP response to CO2. Our results suggest that a change in the climate forcing did not have a large impact on the carbon cycle on long timescales. However, the inter-annual variability in precipitation drives the year-to-year variability in NBP. We analysed the impact of key modes of climate variability, including the El Niño–Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD), on NBP. While the DGVMs agreed on sign of the response of NBP to El Niño and La Niña and to positive and negative IOD events, the magnitude of inter-annual variability in NBP differed strongly between models. In addition, we find that differences in the timing of simulated phenology and fire dynamics are associated with differences in simulated or prescribed vegetation cover and process representation. We further find model disagreement in simulated vegetation carbon, phenology, and apparent carbon residence time, indicating that the models have different types and coverage of vegetation across Australia (whether prescribed or emergent). Our study highlights the need to evaluate parameter assumptions and the key processes that drive vegetation dynamics, such as phenology, mortality, and fire, in an Australian context to reduce uncertainty across models.

Incorporating carbon dioxide into a stoichiometric producer-grazer model.

Climate change models predict increases in atmospheric carbon dioxide concentration. As ecosystems equilibrate with the atmosphere, stimulation of photosynthesis is expected to occur. However, growth limitation due to soil nutrients may potentially limit sequestration of carbon. Additionally, changes in producer nutritional quality may cause a decline in grazer populations. Here we extend the WKL model to allow for consideration of the impacts of elevated atmospheric carbon dioxide concentration on producer-grazer dynamics. We do so by explicitly tracking the free carbon in the medium and allowing the producer's growth rate to be limited by available carbon instead of light. This model is analyzed using primarily local bifurcation analysis. Overall, these analyses show that carbon sequestration due to increased atmospheric carbon dioxide can be limited by insufficient available phosphorus. Furthermore, increased atmospheric carbon dioxide will cause decreased stoichiometric quality of producers where available phosphorus is limiting.

Sustainable Synthesis of Cyclic Carbonates from Terminal Epoxides by a Highly Efficient CaI2/1,3-Bis[tris(hydroxymethyl)-methylamino]-propane Catalyst.

The nonstopping increment of atmospheric carbon dioxide (CO2) concentration keeps harming the environment and human life. The traditional concept of carbon capture and storage (CCS) is no longer sufficient and has already been corrected to carbon capture, utilization, and storage (CCUS). CCUS involves significant CO2 utilization, such as cyclic carbonate formation, for its cost effectiveness, less toxicity, and abundant C1 synthon in organic synthesis. However, the high thermodynamic and kinetic stability of CO2 limits its applications. Herein, we report a mild, efficient, and practical catalyst based on abundant, nontoxic CaI2 in conjunction with biocompatible ligand 1,3-bis[tris(hydroxymethyl)-methylamino]-propane (BTP) for CO2 fixation under atmospheric pressure with terminal epoxides to give the cyclic carbonates. The Job plot detected the 1:1 Ca2+/BTP binding stoichiometry. Furthermore, formation of a single crystal of the 1:1 Ca2+/BTP complex was confirmed by single-crystal X-ray crystallography. The bis(cyclic carbonate) products exhibit potentials for components in the non-isocyanate polyurethanes (NIPUs) process. Notably, this protocol shows attractive recyclability and reusability.

Modelling the growth response to climate change and management of Tectona grandis L. f. using the 3-PGmix model

Teak ( Tectona grandis L. f.) is a native tree species of India. It is one of the most desirable timber species because of its strength, fine texture, and durability. Its growth is strongly dependent on the climatic conditions, but empirical data are often unavailable to support management decisions. The physiological principles for predicting growth incorporated in the 3-PGmix model make it a useful tool in modelling the growth responses and management in the changing climate. We assessed that under elevated atmospheric carbon dioxide (CO 2 ) concentration and no thinning, teak would store more carbon than currently. Uncertainty and lack of scientific understanding about the growth response to climate change and thinning regimes have created challenges in teak sustainability, both regionally and globally. This research examines climate change and management implications on teak growth in India using the 3-PGmix model. The 3-PGmix model was coupled with climate scenarios (Representative Concentration Pathway (RCP) 4.5 and 8.5) to forecast growth response up to the year 2100 with 1981–2010 as the baseline under thinning (G-quality, P-quality) regimes. Thinning under G-quality is performed at earlier stand age than P-quality, and then simulations under ‘no thinning’ based on stocking/ha at different thinning intensity. Under ‘no thinning’, predicted net primary productivity (NPP) for RCP4.5 and RCP8.5 became 5.77 t/ha/year and 5.28 t/ha/year in 2100. However, under increasing CO2, it became 7.39 t/ha/year and 8.22 t/ha/year respectively in 2100. In the future, increasing CO2 would be the dominating factor for an increase in teak growth; however, abnormal precipitation and warmer temperature could produce an unforeseen growth condition. The carbon stock and CO2 sequestration are predicted to be higher under no thinning, which signifies the CO2 fertilisation effect in teak. The set of parameters used in 3-PGmix offers an opportunity to predict teak responses to future climatic conditions and management treatments.

РЕАЛЬНОСТЬ УГЛЕРОДНОГО СЛЕДА В ГЛОБАЛЬНОМ ИЗМЕНЕНИИ КЛИМАТА

The article calls into question the theory of the global greenhouse effect escalation attributable to the increase in the concentration of CO2 in the atmosphere due to human activity, as well as the very ability of industry to influence the Earth’s climate. The author finds dubitable the very approach to understanding greenhouse gases and their impact on the climate reflected in the Paris Agreement. Analysis of authoritative opinions of the world’s leading climate scientists leads to the conclusion that the increase in global temperatures due to industrial production, given a doubling of carbon dioxide concentration in the atmosphere, would constitute about 0,02 degrees. This is lower than the margin of error in modern global temperature measurements.

Worldwide impacts of atmospheric vapor pressure deficit on the interannual variability of terrestrial carbon sinks.

Interannual variability of the terrestrial ecosystem carbon sink is substantially regulated by various environmental variables and highly dominates the interannual variation of atmospheric carbon dioxide (CO2) concentrations. Thus, it is necessary to determine dominating factors affecting the interannual variability of the carbon sink to improve our capability of predicting future terrestrial carbon sinks. Using global datasets derived from machine-learning methods and process-based ecosystem models, this study reveals that the interannual variability of the atmospheric vapor pressure deficit (VPD) was significantly negatively correlated with net ecosystem production (NEP) and substantially impacted the interannual variability of the atmospheric CO2 growth rate (CGR). Further analyses found widespread constraints of VPD interannual variability on terrestrial gross primary production (GPP), causing VPD to impact NEP and CGR. Partial correlation analysis confirms the persistent and widespread impacts of VPD on terrestrial carbon sinks compared to other environmental variables. Current Earth system models underestimate the interannual variability in VPD and its impacts on GPP and NEP. Our results highlight the importance of VPD for terrestrial carbon sinks in assessing ecosystems’ responses to future climate conditions.

Climate change projections of terrestrial primary productivity over the Hindu Kush Himalayan forests

Abstract. Increasing atmospheric carbon dioxide concentration [CO2] caused by anthropogenic activities has triggered a requirement to predict the future impact of [CO2] on forests. The Hindu Kush Himalayan (HKH) region comprises a vast territory including forests, grasslands, farmlands and wetland ecosystems. In this study, the impacts of climate change and land-use change on forest carbon fluxes and vegetation productivity are assessed for HKH using the Lund–Potsdam–Jena General Ecosystem Simulator (LPJ-GUESS). LPJ-GUESS simulations were driven by an ensemble of three climate models participating in the CMIP5 (Coupled Model Intercomparison Project phase 5) database. The modelled estimates of vegetation carbon (VegC) and terrestrial primary productivity were compared with observation-based estimates. Furthermore, we also explored the net biome productivity (NBP) and its components over HKH for the period 1851–2100 under the future climate scenarios RCP2.6 and RCP8.5. A reduced modelled NBP (reduced C sink) is observed from 1986–2015 primarily due to land-use change. However, an increase in NBP is predicted under RCP2.6 and RCP8.5. The findings of the study have important implications for the management of the HKH region, in addition to informing strategic decision making and land-use planning, and clarifying policy concerns.

SIMULATING OF FUTURE CLIMATE CONDITIONS ON THE EFFECT OF IRRIGATION ON SUGARCANE YIELD IN SOUTHERN BRAZIL

The objective of this study was to evaluate the technical and economic feasibility of installing central pivot irrigation systems in current days (Scenario A) and in two future scenarios, one with a 10% increase in rainfall (Scenario B1) and the other with 10% reduction in rainfall (Scenario B2). For both future scenarios, an increase of 2ºC in the global temperature and the concentration of atmospheric carbon dioxide (CO2) increasing to 528 ppm (parts per million) were considered. For the study, the recommendation for an area of clayey soil and with the sugarcane cycle was evaluated on three different planting dates: May 15, August 15 and November 15. The DSSAT/CANEGRO model was used, and under the current conditions, the simulations indicated greater yield for planting in May, both for rainfed and irrigated. For scenario B1, there was an increase in yield of 22% for rainfed and 33% for irrigated. In addition, irrigation provided yield gains in the two future scenarios of 13% and 14% for B1 and B2, respectively. Based on the results obtained, central pivot irrigation proved economically viable in the simulated climatic conditions. Therefore, the increase in sugarcane production provided by irrigation in agronomic management was sufficient to make investment in the region in question feasible. It is suggested to repeat the study in other regions, since the existing synergy between the factors that define agricultural yield can change the decision making about the implantation of irrigation systems in the production environment.

Interannual Variability of Summer Net Ecosystem CO2 Exchange in High Arctic Tundra

AbstractArctic terrestrial ecosystems may be contributing to increasing atmospheric carbon dioxide (CO2) concentrations under amplified climate change at high‐latitudes. This research investigates how summer net ecosystem CO2 exchange (NEE) and its component fluxes, gross primary production (GPP), and ecosystem respiration (Reco) varied over five years (2008, 2009, 2010, 2012, and 2014) at the Cape Bounty Arctic Watershed Observatory (74.92°N, 109.58°W). The eddy covariance technique was used to measure NEE and a combined light and temperature response model was used to partition NEE into GPP and Reco. Total summer NEE varied from −19.8 to 7.9 g C m−2. Despite two summers with net CO2 uptake, this tundra was likely a source of CO2 on an annual basis. In most years, growing degree days with a base 0°C (GDD0) had more predictive power than other environmental variables in random forest analyses of daily NEE. Interannual variability in total summer NEE over the five study years was also attributed to greater variability in GPP than Reco (coefficient of variation: 62% and 27%, respectively). However, total summer GDD0 significantly correlated with total summer Reco but not NEE nor GPP. Instead, summer total NEE and GPP significantly correlated with satellite‐derived normalized difference vegetation index (NDVI), which may have exhibited carry‐over effects from one year to the next to limit the impact of current year GDD0 on total summer NEE at this tundra site.

Elevated CO2 and warming affect pollen development in a tropical legume forage species

Global climate change is expected to have impacts on the physiological, phenological, and morphological traits of plants. However, the vulnerability of tropical plant reproductive processes in response to climate change events has been poorly studied. Here, we assess if warming and elevated CO2 compromise the pollen characteristics of Stylosanthes capitata Vogel, a tropical legume forage species. This work was conducted in a Trop-T-FACE (combined Free-Air Temperature Controlled Enhancement and Free-Air Carbon Dioxide Enrichment) facility, where we exposed the plants to four treatments: C (Control-ambient atmospheric carbon dioxide concentration [CO2] and ambient temperature); eCO2 (increase in [CO2] to 600 ppm and ambient temperature); eT (canopy temperature increase by 2°C and ambient [CO2]); and eCO2+eT, a combination of both treatments. We analyzed pollen morphology of samples taken from the different treatments through light microscopy (LM) and scanning electron microscopy (SEM). In addition, pollen viability was analyzed through colorimetry. Based on the histological LM analysis, the tapetum cells of pollen sacs showed early degeneration under eT (72%) added to hypertrophy under eCO2 (67%) and eCO2+eT (90%) treatments. SEM images showed compaction of pollen exine and less distinguishable pollen apertures in the treated plots (eCO2, eT, and eCO2+eT), possibly, by the early death of the tapetum cells. These morphological abnormalities may hinder the viability of pollen grains, as observed especially in the eCO2+eT treatment (%V=64%) that was the lowest in comparison with the Control (71%) and the other treatments (eCO2 = 69%, eT = 67%). These results indicate that during the reproductive cycle of S. capitata pollen sacs and pollen grains are vulnerable to warming, elevated CO2, and their combined effects.

Review: How will climate change impact the ‘many little hammers’ of ecological weed management?

AbstractIncreasing atmospheric carbon dioxide concentrations [CO2] and climate change are impacting farming worldwide. Ecological weed management (EWM) principles, including use of diverse tactics already employed by many farmers, may assist in adapting to and mitigating climate change. We systematically reviewed the literature on EWM and climate change and here summarise practical considerations related to changing efficacy and utility of non‐chemical EWM practices. Localised changes in precipitation will affect tillage and cultivation. We expect that mulching, transplanting and some weed seedbank management strategies, which add resiliency to a weed management programme, may show increased utility in a future with more extreme and variable weather. Innovations in autonomous robotic weeding technologies and cultivation tool design show promise in helping to overcome challenges related to low and variable cultivation efficacy and traditionally slow working rates. EWM practices that help farmers achieve multiple objectives and provide benefits beyond climate change adaptation, such as financial gains, may be most advantageous, the development of which could be facilitated by interdisciplinary research and outreach efforts. Overall, we conclude that in an increasingly variable climate, farmers will have to employ a greater diversity of weed management tactics in order to spread risk and enable climate resilience through farming systems diversification.

Does a Large Ear Type Wheat Variety Benefit More From Elevated CO2 Than That From Small Multiple Ear-Type in the Quantum Efficiency of PSII Photochemistry?

Recently, several reports have suggested that the growth and grain yield of wheat are significantly influenced by high atmospheric carbon dioxide concentration (CO2) because of it photosynthesis enhancing effects. Moreover, it has been proposed that plants with large carbon sink size will benefit more from CO2 enrichment than those with small carbon sink size. However, this hypothesis is yet to be test in winter wheat plant. Therefore, the aim of this study was to examine the effect of elevated CO2 (eCO2) conditions on the quantum efficiency of photosystem II (PSII) photochemistry in large ear-type (cv. Shanhan 8675; greater ear C sink strength) and small multiple ear-type (cv. Early premium; greater vegetative C source strength) winter wheat varieties. The experiment was conducted in a free air CO2 enrichment (FACE) facility, and three de-excitation pathways of the primary reaction of PSII of flag leaf at the anthesis stage were evaluated under two CO2 concentrations (ambient [CO2], ∼415 μmol⋅mol–1, elevated [CO2], ∼550 μmol⋅mol–1) using a non-destructive technique of modulated chlorophyll fluorescence. Additionally, the grain yield of the two varieties was determined at maturity. Although elevated CO2 increased the quantum efficiency of PSII photochemistry (ΦPSII) of Shanhan 8675 (SH8675) flag leaves at the anthesis stage, the grain number per ear and 1,000-kernel weight were not significantly affected. In contrast, the ΦPSII of early premium (ZYM) flag leaves was significantly lower than that of SH8675 flag leaves at the anthesis stage, which was caused by an increase in the regulatory non-photochemical energy dissipation quantum (ΦNPQ) of PSII, suggesting that light energy absorbed by PSII in ZYM flag leaf was largely dissipated as thermal energy. The findings of our study showed that although SH8675 flag leaves exhibited higher C sink strength and quantum efficiency of PSII photochemistry at the anthesis stage, these factors alone do not ensure improved grain yield under eCO2 conditions.

Constraining fluid-rock interactions during eogenetic karst and their impacts on carbonate reservoirs: Insights from reactive transport modeling

Eogenetic karst has been regarded as a dominant origin of hydrocarbon reservoirs, whereas quantifying the fluid-rock interactions and their impacts on porosity evolution during the palaeokarst process remain persistent challenges that limit the accuracy of reservoir quality prediction. This study investigates the dissolution of carbonate rocks with potential controlling factors by reactive transport modeling that couples fluid flow, mineral reactions and porosity changes in a one-dimensional vadose meteoric water-rock system. Simulation results of base case scenario and sensitivity analyses show that the duration of subaerial exposure and recharge capacity of rainwater significantly determine the karst-affected depth and porosity increment. The amount of calcite dissolution is also affected by a downward decrease in calcite solubility (temperature-dependent) and the enrichment of Ca2+ and HCO3− in the lower part. The atmospheric carbon dioxide concentration has a minor impact on the vertical extent of karst, while it facilitates the dissolution rate under high pCO2 conditions. The influence of atmospheric pCO2 variation over geological time on the porosity increment was reconstructed under hydrogeological conditions of the base case scenario (exposure time = 130 ka; rainfall = 628 mm/a). The differences in the dissolution rates and extent of karst between limestone and dolostone can be interpreted as the results of different rate-determining reaction mechanisms, i.e., thermodynamically controlled calcite and kinetically controlled dolomite.

G protein \u03b3 subunit qPE9-1 is involved in rice adaptation under elevated CO2 concentration by regulating leaf photosynthesis

G protein γ subunit qPE9-1 plays multiple roles in rice growth and development. However, the role of qPE9-1 in rice exposed to elevated carbon dioxide concentration (eCO2) is unknown. Here, we investigated its role in the regulation of rice growth under eCO2 conditions using qPE9-1 overexpression (OE) lines, RNAi lines and corresponding WT rice. Compared to atmospheric carbon dioxide concentration (aCO2), relative expression of qPE9-1 in rice leaf was approximately tenfold higher under eCO2. Under eCO2, the growth of WT and qPE9-1-overexpressing rice was significantly higher than under aCO2. Moreover, there was no significant effect of eCO2 on the growth of qPE9-1 RNAi lines. Furthermore, WT and qPE9-1-overexpressing rice showed higher net photosynthetic rate and carbohydrate content under eCO2 than under aCO2. Moreover, the relative expression of some photosynthesis related genes in WT, but not in RNAi3 line, showed significant difference under eCO2 in RNA-seq analysis. Compared to WT and RNAi lines, the rbcL gene expression and Rubisco content of rice leaves in qPE9-1-overexpressors were higher under eCO2. Overall, these results suggest that qPE9-1 is involved in rice adaptation under elevated CO2 concentration by regulating leaf photosynthesis via moderating rice photosynthetic light reaction and Rubisco content.

A nonautonomous mathematical model to assess the impact of algae on the abatement of atmospheric carbon dioxide

The world’s oceans have played an important role in sequestering atmospheric carbon dioxide through solubility and the action of algae. Fixation of atmospheric carbon dioxide by photoautotrophic algal cultures has the potential to diminish the release of carbon dioxide into the atmosphere, thereby helping to alleviate the trend toward global warming. This work investigates the role of algae in controlling the level of atmospheric carbon dioxide. Partial Rank Correlation Coefficients (PRCCs) technique is used to address how the concentration of atmospheric carbon dioxide is affected by changes in a specific parameter disregarding the uncertainty over the rest of the model parameters. Parameters related to algal growth are shown to significantly reduce the level of atmospheric CO2. Further, we explore the dynamics of nonautonomous system by incorporating the seasonal variations of some ecologically important model parameters. Our nonautonomous system exhibits globally attractive positive periodic solution, and also the appearance of double periodic solution is observed. Moreover, by letting the seasonally forced parameters as almost periodic functions of time, we show almost periodic behavior of the system. Our findings suggest that the policy makers should focus on continuous addition of nutrients in the ocean to accelerate the algal growth thereby reducing the level of carbon dioxide in the atmosphere.

Land carbon-concentration and carbon-climate feedbacks are significantly reduced by nitrogen and phosphorus limitation

We quantify the impact of nutrient (nitrogen and phosphorus) limitation on land carbon uptake and the sensitivity of this uptake to atmospheric carbon dioxide (CO2) concentrations (land carbon-concentration feedback) and surface air temperature (land-carbon climate feedback). We analyse simulations of the Australian Earth System Model (ACCESS-ESM1.5) with a prescribed 1% yr−1 CO2 increase in three different configurations: (1) without nutrient limitation, (2) with nitrogen limitation only and (3) with nitrogen and phosphorus limitation combined. Our results suggest a reduction in land carbon uptake and feedback strength of about 30% by including nitrogen limitation only. This reduction agrees well with the ensemble mean of models with and without nitrogen limitation from the sixth Coupled Model Intercomparison Project (CMIP6). By adding phosphorus limitation to our model, the response is even stronger with a further 50% reduction for the carbon-concentration feedback and a further 75% reduction for the carbon-climate feedback. We find that the feedback strength in all three nutrient configurations is mostly determined by vegetation productivity (i.e. Net Primary Production) with little contribution from soil heterotrophic respiration. Our simulations show that nutrient limitation has the largest impact in the northern mid latitudes (around 50∘), reducing land carbon uptake by about 50% when accounting for nitrogen and phosphorus limitation combined. The strong response of land carbon uptake and feedback strength to nutrients in our model simulations underlines the importance of including both nitrogen and phosphorus limitation in other Earth System Models in order to derive better estimates of future land carbon uptake and to assess the effectiveness of land-based carbon mitigation.