Rising CO2 Concentrations Research Articles

Effect of Internal Moisture and Outer Relative Humidity on Concrete Carbonation

With steadily rising CO2 concentrations in the ambient air and fast-changing concrete compositions with reduced clinker contents, the availability of reliable and accelerated concrete carbonation tests is of crucial importance to design durable structures. This paper focuses on the effects of moisture under accelerated conditions and the effects of different CO2 exposure conditions. Mortar prisms incorporating three different cement types were cured and stored at either 50% or 65% relative humidity (RH). Afterwards, the prisms were carbonated at different ambient humidities (50, 57 and 65%), different CO2 concentrations (0.04, 1 and 3 vol.%) and complemented by a series of tests at increased gas pressure (2 barg). High-resolution test methods were used to explain the underlying carbonation mechanisms. The results show that pre-conditioning for two weeks—as currently suggested by the European Standard—seems to be too short because the initial inner moisture content severely affects the carbonation rate. Relative humidity during carbonation of 57% led to higher carbonation rates compared to 50% and 65%. In addition, climate data needs to be periodically (preferably permanently) recorded in research experiments and in laboratory testing to ensure fair interpretation of experimental results.

A global-drive analysis of ecosystem respiration in the Arctic and Third Pole

Terrestrial ecosystem respiration is an important component of the global terrestrial carbon cycle. The special environment of low temperatures in the Arctic and Third Pole makes ecosystem respiration extremely sensitive to the response of climate change. Therefore, understanding the response of Arctic and Third Pole (Tibetan Plateau) ecosystem respiration to individual global environmental drivers is critical for predicting future climate change caused by global warming. However, current studies have not systematically reported on the relative contributions of rising CO2 concentrations, nitrogen deposition, land-use change, and climate change, which are global change factors with multi-year trends and interannual variability, to ecosystem respiration in the Arctic and Third Pole. Here, we used multiple multi-scenario models of vegetation dynamic process model from 1901 to 2010, and divided each environmental driver, each season into long-term trend and interannual variability components by using a novel variance decomposition method. Our results showed that (1) ecosystems autotrophic respiration and heterotrophic respiration in Arctic and Third Pole are relatively low, which remains within 110 g C m−2 in both the Arctic and the Tibetan Plateau; (2) ecosystem respiration tends to increase in all scenarios, and the increase rate has accelerated significantly since 1980. The interannual variability of climate change contributes the most to the variability of ecosystem respiration, up to 52 % and 63 % in the Arctic and Tibetan Plateau, respectively. Both the multi-year trend and interannual variability of increasing atmospheric CO2 concentration contribute to the increase in ecosystem respiration, with relative contributions of 28 % and 32 %, respectively. (3) In the Arctic and the Tibetan Plateau, which are sensitive to temperature and short-wave radiation, summer is the key seasonal component controlling ecosystem respiration, and the contribution of this season (including long-term trends and interannual variability) to annual ecosystem respiration in the Arctic and the Tibetan Plateau is 64 % and 45 %, respectively. Our study bridged the gap in understanding the response of cold ecosystems to global changes at high altitudes and high latitudes, which provides a methodological reference for future accurate prediction of global environmental drivers of cold ecosystem respiration.

Recent Application of Core-Shell Nanostructured Catalysts for CO2 Thermocatalytic Conversion Processes.

Carbon-intensive industries must deem carbon capture, utilization, and storage initiatives to mitigate rising CO2 concentration by 2050. A 45% national reduction in CO2 emissions has been projected by government to realize net zero carbon in 2030. CO2 utilization is the prominent solution to curb not only CO2 but other greenhouse gases, such as methane, on a large scale. For decades, thermocatalytic CO2 conversions into clean fuels and specialty chemicals through catalytic CO2 hydrogenation and CO2 reforming using green hydrogen and pure methane sources have been under scrutiny. However, these processes are still immature for industrial applications because of their thermodynamic and kinetic limitations caused by rapid catalyst deactivation due to fouling, sintering, and poisoning under harsh conditions. Therefore, a key research focus on thermocatalytic CO2 conversion is to develop high-performance and selective catalysts even at low temperatures while suppressing side reactions. Conventional catalysts suffer from a lack of precise structural control, which is detrimental toward selectivity, activity, and stability. Core-shell is a recently emerged nanomaterial that offers confinement effect to preserve multiple functionalities from sintering in CO2 conversions. Substantial progress has been achieved to implement core-shell in direct or indirect thermocatalytic CO2 reactions, such as methanation, methanol synthesis, Fischer-Tropsch synthesis, and dry reforming methane. However, cost-effective and simple synthesis methods and feasible mechanisms on core-shell catalysts remain to be developed. This review provides insights into recent works on core-shell catalysts for thermocatalytic CO2 conversion into syngas and fuels.

Assessment of Projected Climate Change Impact on Green Gram Productivity through DSSAT Model under South Gujarat Environmental Condition

An investigation on climate change impact on green gram was conducted at Agronomy farm, NAU, Navsari, Gujarat during the rabi seasons of 2021-22. The calibrated and validated DSSAT CROPGRO simulation model was used to determine the productivity of green grams under various climate change scenarios. In this experiment, the effects of CO2 concentration, solar radiation and maximum and minimum temperatures on green gram productivity were examined individually and in combination. According to the sensitivity of the DSSAT CROPGRO model, under the conditions of projected climate change, the best case scenario for its favourable impact on green gram yield was a rise in CO2 concentration (600 ppm), along with solar radiation up to a certain level (1 unit), which may nullified the adverse effect of increases in temperature on green gram productivity.

Investigation of Hydrodynamic Parameters in an Airlift Photobioreactor on CO2 Biofixation by Spirulina sp.

The rise of CO2 concentration on Earth is a major environmental problem that causes global warming. To solve this issue, carbon capture and sequestration technologies are becoming more and more popular. Among them, cyanobacteria can efficiently sequestrate CO2, which is an eco-friendly and cost-effective way of reducing carbon dioxide, and algal biomass can be harvested as valuable products. In this study, the hydrodynamic parameters of an airlift photobioreactor such as gas holdup, mean bubble diameter and liquid circulation velocity were measured to investigate CO2 biofixation by Spirulina sp. The total gas holdup was found to increase linearly with the increase in the gas velocity from 0.185 to 1.936 cm/s. The mean bubble velocities in distilled water only and in the cyanobacterial culture on the first and sixth days of cultivation were 109.97, 87.98, and 65.89 cm/s, respectively. It was found that shear stress at gas velocities greater than 0.857 cm/s led to cyanobacterial death. After 7 days of batch culture, the maximum dry cell weight reached 1.62 g/L at the gas velocity of 0.524 cm/s, whereas the highest carbon dioxide removal efficiency by Spirulina sp. was 55.48% at a gas velocity of 0.185 cm/s, demonstrating that hydrodynamic parameters applied in this study were suitable to grow Spirulina sp. in the airlift photobioreactor and remove CO2.

Climate warming outweighs vegetation greening in intensifying flash droughts over China

The increasing occurrence of flash droughts with rapid onsets poses a great threat to food security and ecosystem productivity. While temporal trends in flash droughts have been extensively studied, the contributions of climate warming, vegetation greening, and the physiological effect of rising CO2 to trends in flash drought characteristics remain unclear. Here we show there are significant increasing trends in flash drought frequency, duration, and intensity for most of China during 1961–2016. Warmer temperatures and vegetation greening increase evapotranspiration and decrease soil moisture, and explain 89% and 54% of the increasing frequency of flash drought respectively. Rising CO2 concentrations reduce stomatal conductance, which acts to decelerate the increasing drought frequency trend by 18%, whereas the physiological effects of rising CO2 on flash drought duration and intensity are smaller. Warming also outweighs vegetation greening for the increasing trends of flash drought duration and intensity over most of China, except North China. Our study highlights the role of climate warming in increasing the risk of flash droughts.

Influence of plant ecophysiology on ozone dry deposition: comparing between multiplicative and photosynthesis-based dry deposition schemes and their responses to rising CO<sub>2</sub> level

Abstract. Dry deposition is a key process for surface ozone (O3) removal. Stomatal uptake is a major component of O3 dry deposition, which is parameterized differently in current land surface models and chemical transport models. We developed and used a standalone terrestrial biosphere model, driven by a unified set of prescribed meteorology, to evaluate two widely used dry deposition modeling frameworks, Wesely (1989) and Zhang et al. (2003), with different configurations of stomatal resistance: (1) the default multiplicative method in the Wesely scheme (W89) and Zhang et al. (2003) scheme (Z03), (2) the traditional photosynthesis-based Farquhar–Ball–Berry (FBB) stomatal algorithm, and (3) the Medlyn stomatal algorithm (MED) based on optimization theory. We found that using the FBB stomatal approach that captures ecophysiological responses to environmental factors, especially to water stress, can generally improve the simulated dry deposition velocities compared with multiplicative schemes. The MED stomatal approach produces higher stomatal conductance than FBB and is likely to overestimate dry deposition velocities for major vegetation types, but its performance is greatly improved when spatially varying slope parameters based on annual mean precipitation are used. Large discrepancies were also found in stomatal responses to rising CO2 levels from 390 to 550 ppm: the multiplicative stomatal method with an empirical CO2 response function produces reduction (−35 %) in global stomatal conductance on average much larger than that with the photosynthesis-based stomatal method (−14 %–19 %). Our results show the potential biases in O3 sink caused by errors in model structure especially in the Wesely dry deposition scheme and the importance of using photosynthesis-based representation of stomatal resistance in dry deposition schemes under a changing climate and rising CO2 concentration.

Elevated CO2 effect on the response of stomatal control and water use efficiency in amaranth and maize plants to progressive drought stress

Rising CO2 concentration ([CO2]) in the atmosphere may modulate the response of crop plants to drought stress. This study aimed to investigate the response of leaf gas exchange and plant growth of two C4 species representing both dicot (amaranth) and monocot (maize) to progressive drought under two different [CO2] (ambient (a[CO2], 400 ppm) and elevated (e[CO2], 800 ppm)). The soil water status in the pots was expressed as the fraction of transpirable soil water (FTSW). The results showed that as compared to a[CO2], e[CO2] significantly increased net photosynthetic rate (An) at non-stress condition (An max) for both species, while the increase was more pronounced in maize than in amaranth. Stomatal conductance (gs) at non-stress condition was significantly lower at e[CO2] in both species. The FTSW threshold, at which An starts to decrease, was higher in maize grown at e[CO2] than at a[CO2], whereas it was not affected in amaranth. In both species, gs decreased at higher FTSW threshold when grown at e[CO2] than at a[CO2]. e[CO2] decreased stomatal density (SD) in amaranth but increased it in maize; drought increased SD in amaranth but not in maize. Intrinsic water use efficiency (WUEi) was significantly enhanced by e[CO2] and drought stress at FTSW ranged from 0.0 to 0.6, particularly in maize. e[CO2] increased leaf area of well-watered plants in maize and decreased specific leaf area in amaranth. In amaranth, water consumption of well-watered plants was increased and plant WUE was decreased at e[CO2]. The varied responses of leaf gas exchange and WUE to soil water deficits and e[CO2] among the two C4 species imply their different mechanisms in stomatal control over carbon gain versus water loss in dicot and monocot plants, which is essentially important for selecting crop species and developing strategies to optimize crop WUE in a future drier and CO2-enriched climate. The more physiological and biochemical response from soil, stomatal to plant scale related to various environments would be considered in further investigation.

Light-Mediated Reduction in Photosynthesis in Closed Greenhouses Can Be Compensated for by CO2 Enrichment in Tomato Production.

Concepts of semi-closed greenhouses can be used to save energy, whereas their technical equipment often causes a decrease in the light received by the plants. Nevertheless, higher yields are achieved, which are presumably triggered by a higher CO2 concentration in the greenhouse and associated higher photosynthesis because of the technical cooling and the longer period of closed ventilation. Therefore, we examined the effects of photosynthetic photon flux density (PPFD) and CO2 concentration on plant photosynthesis and transpiration in tomato using a multiple cuvette gas exchange system. In a growth chamber experiment, we demonstrated that a light-mediated reduction in photosynthesis can be compensated or even overcompensated for by rising CO2 concentration. Increasing the CO2 concentration from 400 to 1000 µmol mol−1 within the PPFD range from 303 to 653 µmol m−2 s−1 resulted in an increase in net photosynthesis of 51%, a decrease in transpiration of 5 to 8%, and an increase in photosynthetic water use efficiency of 60%. Estimations showed that light reductions of 10% can be compensated for via increasing the CO2 concentration by about 100 µmol mol−1 and overcompensated for by about 40% if CO2 concentration is kept at 1000 instead of 400 µmol mol−1.

Simulating tree growth response to climate change in structurally diverse oak and beech forests

This study aimed to simulate oak and beech forest growth under various scenarios of climate change and to evaluate how the forest response depends on site properties and particularly on stand characteristics using the individual process-based model HETEROFOR. First, this model was evaluated on a wide range of site conditions. We used data from 36 long-term forest monitoring plots to initialize, calibrate, and evaluate HETEROFOR. This evaluation showed that HETEROFOR predicts individual tree radial growth and height increment reasonably well under different growing conditions when evaluated on independent sites.In our simulations under constant CO2 concentration ([CO2]cst) for the 2071-2100 period, climate change induced a moderate net primary production (NPP) gain in continental and mountainous zones and no change in the oceanic zone. The NPP changes were negatively affected by air temperature during the vegetation period and by the annual rainfall decrease. To a lower extent, they were influenced by soil extractable water reserve and stand characteristics. These NPP changes were positively affected by longer vegetation periods and negatively by drought for beech and larger autotrophic respiration costs for oak. For both species, the NPP gain was much larger with rising CO2 concentration ([CO2]var) mainly due to the CO2 fertilisation effect. Even if the species composition and structure had a limited influence on the forest response to climate change, they explained a large part of the NPP variability (44% and 34% for [CO2]cst and [CO2]var, respectively) compared to the climate change scenario (5% and 29%) and the inter-annual climate variability (20% and 16%). This gives the forester the possibility to act on the productivity of broadleaved forests and prepare them for possible adverse effects of climate change by reinforcing their resilience.

Comparative Study of CO2 Capture by Adsorption in Sustainable Date Pits-Derived Porous Activated Carbon and Molecular Sieve.

The rising CO2 concentration has prompted the quest of innovative tools to reduce its effect on the environment. A comparative adsorption study using sustainable low-cost date pits-derived activated carbon and molecular sieve has been carried out for CO2 separation. The adsorb ents were characterized for surface area and morphological properties. The outcomes of flow rate, temperature and initial adsorbate concentration on adsorption performance were examined. The process effectiveness was investigated by breakthrough time, adsorbate loading, efficiency, utilized bed height, mass transfer zone and utilization factor. The immensely steep adsorption response curves demonstrate acceptable utilization of adsorbent capability under breakthrough condition. The adsorbate loading 73.08 mg/g is achieved with an 0.938 column efficiency for developed porous activated carbon at 298 K. The reduced 1.20 cm length of mass transfer zone with enhanced capacity utilization factor equal 0.97 at 298 K with Cin = 5% signifies better adsorption performance for date pits-derived adsorbent. The findings recommend that produced activated carbon is greatly promising to adsorb CO2 in fixed bed column under continuous mode.

Sensitivity of Potato Yield and Biomass to Climate Change Effects in Gisozi, Burundi, and Washington, USA, and Assessment of LINTUL4 Model Behavior

Understanding climate change effects on crop production and evaluate the effectiveness of adaptation strategies in both developed and developing countries is of key importance. Crop simulation models can provide useful insight on the effects of increasing temperatures and rising CO2 concentrations [CO2] as well as rainfall variations. In this study, the LINTUL4 model was used to study the sensitivity effect of five temperature (T) levels (-3, 0, 3, 6, and 9oC above/below minimum/maximum temperatures), three precipitation (W) changes (30% decrease, baseline and 30% increase), and CO2 levels (baseline(360), 450, 540, 630 and 720ppm) on nutrient limited yield (Yn), water limited yield (Yw), water and nutrient limited yield (Ynw) and potential yield (Yp) of potato crop in high-input Washington, USA and low-input Gisozi, Burundi. The maximum weight of the tuber yield and aboveground biomass for Yp and Yw in Gisozi, and Yn and Yp in Washington was observed at combinations of lower temperature and elevated [CO2]. For Gisozi, maximum tuber yield for Yn and Ynw was observed at [CO2] of less than 720ppm. The results suggest that nutrient supply will continue to be the major limiting factor for potato production under elevated [CO2] in Gisozi, and water availability will limit Yw and Ynw rain-fed production in Washington. Generally, the LINTUL4 model performs well with few data input, but fails to predict the differential effect of high temperature on assimilate partitioning to aboveground and belowground biomass.

Different responses of ammonia-oxidizing archaea and bacteria in paddy soils to elevated CO2 concentration

The elevated atmospheric CO2 concentration is well known to have an important effect on soil nutrient cycling. Ammonia oxidation, mediated by ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB), is the rate-limiting step in soil nitrification, which controls the availability of two key soil nutrients (ammonium and nitrate) for crops. Until now, how the AOA and AOB communities in paddy soils respond to elevated CO2 remains largely unknown. Here, we examined the communities of AOA and AOB and nitrification potential at both surface (0–5 cm) and subsurface (5–10 cm) soil layers of paddy fields under three different CO2 treatments, including CK (ambient CO2 concentration), LT (CK + 160 ppm of CO2) and HT (CK + 200 ppm of CO2). The elevated CO2 was found to have a greater impact on the community structure of AOB than that of AOA in surface soils as revealed by high-throughput sequencing of their amoA genes. However, no obvious variation of AOA or AOB communities was observed in subsurface soils among different CO2 treatments. The abundance of AOA and AOB, and nitrification potential were significantly increased in surface soils under elevated CO2. The variation of AOB abundance correlated well with the variation of nitrification potential. The soil water content and dissolved organic carbon content had important impacts on the dynamic of AOB communities and nitrification potential. Overall, our results showed different responses of AOA and AOB communities to elevated CO2 in paddy ecosystems, and AOB were more sensitive to the rising CO2 concentration.

Catalytic gasification of coal in a decoupled dual loop gasification system over alkali-feldspar

The catalytic gasification of Yuyang coal for the production of hydrogen-rich syngas has been performed in a novel decoupled dual loop gasification system using alkali-feldspar as an in-situ catalytic bed material. This experimental setup is comprised of a fluidized bed gasifier (FBG), a moving bed reformer (MBR), a riser combustor (RC) and a particle grading cyclone (PGC). By the PGC, two loops, i.e. a gasification loop with quartz sand as circulating bed material between the FBG and the RC and a reforming loop with alkali-feldspar as circulating bed material between the MBR and the RC, are formed. The effects of process parameters such as reformer temperature (700–850 °C), steam/coal ratio (S/C) (0.6–1.5) and air equivalence ratio (ER) (0.15–0.30) on the composition of product gas, lower heating value (LHV), tar content, yield of product gas, the carbon and water conversions and the cold gas efficiency were investigated. At the reformer temperature of 850 °C, the lowest tar content 5.8 g/Nm3 and the maximum yield of product gas 1.0 Nm3/kg daf were obtained. The addition of steam increased the H2 yield. The maximum hydrogen concentration of 65.1 vol% in product gas was attained at the S/C ratio of 1.5. Oxygen as a part of gasification agent led to the rise of CO2 concentration from 24.3 to 46.3 vol% and the reduction of H2 concentration from 54.4 to 33.0 vol% with the increase of ER from 0.15 to 0.30.

Nutritional quality of crops in a high CO2 world: an agenda for research and technology development

Essential nutrients, including carbohydrates, proteins, fats, vitamins, and minerals, are required for human health and development. Inadequate intake can negatively affect development and result in a wide range of adverse health outcomes. Rice, maize, and wheat provide over 60% of the world’s food energy intake. Atmospheric carbon dioxide (CO2), water, nitrogen, and soil micronutrients are the basis of this plant material. Since 1850–1900, CO2 concentrations have increased about 50%, with most of that increase since 1950. Higher CO2 concentrations increase photosynthesis, which then increases plant biomass, but also alters the nutritional quality of wheat, rice, and other C3 plants. We review the possible impacts of rising CO2 concentrations on human health, highlight uncertainties, and propose a research agenda to maintain the nutritional quality of C3 plants. We also synthesize options for addressing this critical challenge to nutritional safety and security. A complete research agenda requires addressing data and knowledge gaps surrounding plant biology and policy responses. Data on key nutrients are lacking, leading to a limited mechanistic understanding of the response of the plant ionome to elevated CO2 concentrations. Regular data are largely missing on nutritional status and food safety in low- and middle-income countries, limiting assessments of the magnitude of the risks. Research opportunities to fill gaps in data and understanding include herbaria studies, field-based natural and manipulative studies, leveraging natural plant variability, and innovations in seed quality. Improved models of cereal crop nutritional quality can project the magnitude and direction of possible future challenges; incorporating the effects of climate change into those models can further improve their robustness. Transdisciplinary research involving at least ecologists, plant physiologists, economists, and experts in human nutrition is essential for developing a systems-based understanding of the potential impacts of rising CO2 concentrations for human nutrition and the attendant consequences for achieving the sustainable development goal on food security.

Impacts of climate change on terrestrial hydrological components and crop water use in the Chesapeake Bay watershed

This study assessed the impacts of climate change on terrestrial hydrological components and Crop Water Use (CWU) over the Chesapeake Bay watershed using a combination of Global Climate Models (GCMs) and a land surface model. To better understand the impacts of climate change on the hydrological cycle, long-term simulations of multiple earth system models from the Coupled Model Intercomparison Project (CMIP Phase 5) are statistically downscaled and bias-corrected using Multivariate Adaptive Constructed Analogs (MACA) scheme for use as model forcing. Precipitation indices from the twenty MACA-based GCMs are used to identify six best performing models. A mesoscale approach is developed, where CWU is estimated by accounting for the impacts of changing climate conditions and rising CO2 levels. Daily grid-based crop coefficients are derived from evapotranspiration data. The findings indicate a significant annual increase in precipitation (10 %) and temperature (+4.5 K) for the RCP 8.5 scenario towards the end of the 21st century. A significant reduction (13 % and 17 % respectively) in CWU is estimated for corn and soybeans, resulting from increased total precipitation and rising CO2 levels suppressing evapotranspiration. Our results indicate that even in a warmer regime, crop water use decreased due to rising CO2 concentrations due to climate change.

Water use efficiency of chickpea agro-ecosystems will be boosted by positive effects of CO2 and using suitable genotype × environment × management under climate change conditions

The agricultural production faces the inevitable challenges under the climate change conditions which threaten the food security. Under these circumstances, the increase of productivity can be regarded to ensure the food security. The interaction of genetic management determines the performance of given crop and environmental factors, and these elements should be simultaneously considered to have a sustainable production. To enhance the productivity and eco-efficiency of chickpea agro-ecosystems in the west and northwest of Iran, we optimized the genotype (G) × environment (E) × management (M) interactions to access optimum grain yield and water use efficiency using SSM-legume model. Three genotypes, eight locations, and 3 irrigation regimes were considered G, E, and M factors, respectively. The projections of future climate were conducted due to a 5–multi‐model ensemble under two emission scenarios (RCP4.5 and RCP8.5) for 2040–2070 using a methodology introduced by Agricultural Model Intercomparison and Improvement Project (AgMIP). The results indicated that across two RCPs, the climate change increased chickpea grain yield (11%) due to the positive effects of rising CO2 concentration which slightly increased WUE (0.03%) based on an increase in the evapotranspiration (10.9%) and mean temperature (3.4%) and a decrease during the chickpea growing period (21.9%). However, these decreases and increases can be mitigated and boosted using an optimal G × E × M combination. ILC482 (mid-maturity genotype) × cold northwest environment × SI Pod-60 (supplementary irrigation of 60 mm at pod filling) was the best G × E × M interaction due to optimum WUE (6.98 kg ha-1 mm-1) and grain yield (1808.4 kg ha-1) for chickpea agro-ecosystems in upcoming period (2040–2070). In general, climate change and rising CO2 concentration open up the opportunities to produce more grain yield in chickpea agro-ecosystems. Moreover, this production can be sustainably generated regarding WUE by adopting a suitable G × E × M interaction.

Declining Oxygen Level as an Emerging Concern to Global Cities

Rising CO2 concentration and temperatures in urban areas are now well-known, but the potential of an emerging oxygen crisis in the world's large cities has so far attracted little attention from the science community. Here, we investigated the oxygen balance and its related risks in 391 global large cities (with a population of more than 1 million people) using the oxygen index (OI), which is the ratio of oxygen consumption to oxygen production. Our results show that the global urban areas, occupying only 3.8% of the global land surface, accounted for 39% (14.3 ± 1.5 Gt/yr) of the global terrestrial oxygen consumption during 2001-2015. We estimated that 75% of cities with a population more than 5 million had an OI of greater than 100. Also, cities with larger OI values were correlated with more frequent heatwaves and severe water withdrawals. In addition, cities with excessively large OI values would likely experience severe hypoxia in extremely calm weather. Thus, mitigation measures should be adopted to reduce the urban OI in order to build healthier and more sustainable cities.

Predicting the Future Distribution of Ara rubrogenys, an Endemic Endangered Bird Species of the Andes, Taking into Account Trophic Interactions

Species distribution models (SDMs) are commonly used with climate only to predict animal distribution changes. This approach however neglects the evolution of other components of the niche, like food resource availability. SDMs are also commonly used with plants. This also suffers limitations, notably an inability to capture the fertilizing effect of the rising CO2 concentration strengthening resilience to water stress. Alternatively, process-based dynamic vegetation models (DVMs) respond to CO2 concentration. To test the impact of the plant modelling method to model plant resources of animals, we studied the distribution of a Bolivian macaw, assuming that, under future climate, DVMs produce more conservative results than SDMs. We modelled the bird with an SDM driven by climate. For the plant, we used SDMs or a DVM. Under future climates, the macaw SDM showed increased probabilities of presence over the area of distribution and connected range extensions. For plants, SDMs did not forecast overall response. By contrast, the DVM produced increases of productivity, occupancy and diversity, also towards higher altitudes. The results offered positive perspectives for the macaw, more optimistic with the DVM than with the SDMs, than initially assumed. Nevertheless, major common threats remain, challenging the short-term survival of the macaw.

Effects of elevated CO2 on the C:N stoichiometry of plants, soils, and microorganisms in terrestrial ecosystems

The stoichiometry of carbon to nitrogen ratio (C:N) plays an important role in biogeochemical cycling in terrestrial ecosystems. As time goes by, the increase in atmospheric CO2 levels is expected; however, the impact of elevated atmospheric CO2 on the C:N stoichiometry of soils, plants, and microorganisms remains largely unclear. The results of the meta-analysis that included 174 studies with 1009 observations demonstrated that above- and below-ground C concentrations and C:N ratio increased under elevated CO2 regimes, whereas N concentrations decreased. Importantly, these responses were more pronounced with rising CO2 concentrations and longer experimental durations. Moreover, the responses of C, N, and C:N to elevated CO2 were similar across croplands, forests, and grasslands ecosystems with varying climates. Our results revealed that the C:N stoichiometry of soils, plants, and microorganisms responded consistently to the rising global CO2 levels, which indicated that terrestrial ecosystems might have the capacity to mitigate increased atmospheric CO2 concentrations by increasing C sequestration in plants, soils, and microorganisms in future.