CO2 Concentration Scenarios Research Articles

Environmental potentials from wood cascading: A future-oriented consequential yet dynamic approach considering market and time-dependent biogenic carbon effects for selected scenarios under German conditions

As sustainable forestry limits the roundwood supply, wood cascading emerges as a promising concept to meet the growing demand resulting from Germany's transition to a bioeconomy. To assess the environmental impacts of wood cascading resulting from shifting the incineration of recovered wood and the associated substitution of future energy mixes and materials, a consequential life cycle assessment (CLCA) of a wood cascading system providing glued-laminated timber (GLT), particleboard, heat, and electricity is conducted. The assessment of environmental consequences requires a holistic approach, including future-oriented German energy and market scenarios. Furthermore, to analyze the impact of biogenic carbon dynamics, this CLCA was coupled with a dynamic life cycle assessment (DLCA) considering forest growth scenarios and temporal aspects. The results indicate a strong influence of market shifts related to material substitution, followed by energy substitution on the environmental impacts of wood cascading. In fact, the results endorse the implementation of the concept of high-quality wood cascading for substituting non-wood products in Germany, as a transformational path towards a bioeconomy and the achievement of net greenhouse gas neutrality. Compared to the effects of the material and energy substitution scenarios, the forest growth scenarios, which focus on tree species composition influenced by future temperature change and CO2 concentration scenarios, only show a minor influence on global warming impacts. As the findings from applying DLCA contrast with the static approach, it emphasizes the importance of a time-differentiated analysis of biogenic carbon in the evaluation of wood cascading.

Responses of tree growth and intrinsic water-use efficiency of Robinia pseudoacacia to climate factors

We investigated tree growth in Robinia pseudoacacia plantations at Ansai in Shaanxi Province and at Ji-xian in Shanxi Province by comparing the tree-ring width, basal area increase (BAI), δ13C value, intrinsic water-use efficiency (iWUE), and stomatal regulation. We quantified the responses of tree growth and iWUE to climatic factors at each site. The tree-ring width at Ansai and Jixian decreased with stand age, whereas the BAI at Ansai increased, and that at Jixian decreased after the BAI peaked. The δ13C value and iWUE of trees at Jixian were higher than those at Ansai. The iWUE of trees at both sites was similar to the constant intercellular CO2 concentration/atmospheric CO2 concentration (Ci/Ca) scenario, indicating that the Ci of trees was elevated with increasing Ca, while the stomata remained open. The BAI at Ansai was significantly positively correlated with highest temperature in May, relative humidity in June, precipitation in August, relative humidity in September, and standardized precipitation evapotranspiration index (SPEI) in September and October of current year, but negatively correlated with temperature in June. The BAI at Jixian was significantly positively correlated with SPEI in June and July, and lowest temperature in October of current year. The iWUE of trees at Ansai was significantly positively correlated with relative humidity and precipitation in June of the current year, but negatively correlated with minimum temperature in May, relative humidity in June, and temperature and maximum temperature in July of current year. A significant positive correlation between iWUE of trees at Jixian and lowest temperature in June of current year was detected. At the annual scale, the BAI of trees at Ansai was positively correlated with precipitation and SPEI, but no significant relationship was observed for trees at Jixian. However, the iWUE of trees at both sites was significantly affected by precipitation. Path analysis showed that SPEI and minimum temperature had a direct effect on BAI and iWUE of trees at Ansai, whereas precipitation and average temperature indirectly affected BAI and iWUE through SPEI. The highest temperature had a direct effect on tree growth at Jixian, whereas precipitation, minimum temperature, and average temperature had direct effects on iWUE. These results suggested that SPEI was the main climatic factor that affected the growth of R. pseudoacacia, while Ci was an important physiological factor. Our results could provide reference for the protection and management of R. pseudoacacia plantations under climate change.

Past and future trends of diurnal temperature range and their correlation with vegetation assessed by MODIS and CMIP6

Temperature anomalies and changes in the diurnal temperature range (DTR) are expected to pose physiological challenges to biota; hence, both spatial and temporal variations in DTR provide important insights into temperature-induced stress in humans, animals, and vegetation. Furthermore, vegetation could dampen temperature variability. Here, we use the Moderate Resolution Imaging Spectroradiometer (MODIS) remote sensing data of Land Surface Temperature (LST) to evaluate the global variation in DTR and its rate of change in spatial and temporal scales for the two decades spanning from 2001 to 2020. We show that North America, Africa, and Antarctica, as well as the global mean, experienced statistically significant DTR rates of change over the last 20 years in either summer, winter, or the annual mean. The rates were all negative, indicating the day-night temperature differences are decreasing in those regions because night temperatures are increasing at a faster rate than day temperatures. MODIS data of the Normalized Difference Vegetation Index (NDVI) revealed a strongly negative correlation with DTR, with a spatial correlation coefficient of −0.61. This correlation demonstrates a prominent dampening effect of vegetation on diurnal temperature oscillations. For future DTR projections, we used 19 models in the Coupled Model Intercomparison Project 6 (CMIP6) to predict global DTR trends from 2021 to 2050 with low and high CO2 concentration scenarios. The high CO2 emission scenario projects significant decreases in DTR in circumpolar regions, central Africa, and India compared to the low CO2 scenario. This difference in the two scenarios underscores the substantial influence of increased global temperatures and elevated CO2 concentration on DTR and, consequently, on the ecosystems in certain regions.

Rectifying low-frequency variability in future climate sea surface temperature simulations: are corrections for extreme change scenarios realistic?

Most procedures for redressing systematic bias in climate modeling are calibrated using current climate observations, and perform well. However, their performance in the future climate remains uncertain as no observations exist to compare against. In this context, we use the current and future climate outputs of an ultra-high resolution of Community Earth System Model (UHR-CESM) as the representative truth and bias correct monthly sea surface temperature (SST) simulations of eight Coupled Model Intercomparison Project 6 models over the Niño 3.4 region. A time-frequency bias correction approach is used to correct for bias in distributional, trend, and spectral attributes present in the models. This results in a near perfect power spectrum of the bias corrected current climate model simulations. Considering all correction procedures remain unchanged into the future, the overall representation of the corrected SST simulations shows improvement with consistency across models for the doubled CO2 scenario, but higher variability and lower consistency in the quadrupled CO2 concentration scenario.

Assessment of Climate Change Impact on Water Productivity and Yield of Wheat Cultivated Using Developed Seasonal Schedule Irrigation in the Nineveh Province

The agricultural lands that depend on supplementary irrigation methods for winter wheat cultivating in wide areas of the Nineveh province are most vulnerable to climate change concerns. Due to frequent rainfall shortages and the temperature increase recently noticed and predicted by the climate scenarios. Hence important to assess the climate effect on the crop response in terms of water consumption during the periods (2021-2040) and (2041-2060) by using high-resolution data extracted from 6 global climate data GCMs under SSP5-8.5 fossil fuel emission scenarios in changing and fixed CO2 concentration. And validate the Aqua-Crop model to estimate the yield and water productivity. And gives the RRSME of 7.1- 4.1 for the calibration and verification, respectively, d and R2 equal 1, indicating good model performance. From findings, the predicted response to the temperature increase and variability in rainfall between increase and decrease represents an increase in irrigation water productivity to 28% in 2060 related to the reference period in the developed schedule under changing CO2 scenario and a reduction by 13% in the near term related to the mid-term under the fixed CO2 concentration scenario. And the simulation of yield production increased by 30 % under the scenario of changing CO2 concentration. While a slight increase of 13 % under the fixed CO2 concentration scenario. These findings help realize the future uncertain resilience of agriculture in Iraq to create efficient adaptation measures to benefit from climate change opportunities.

Assessing climate change projections in the Volta Basin using the CORDEX-Africa climate simulations and statistical bias-correction

Climate change potential impacts are evaluated through the changes in the local and regional climate. However, Global and Regional Climate simulated outputs do not often capture these changes well, hampering their direct applicability. Impact studies using coarse resolution data require bias-correction of climate variables, a process that minimizes the discrepancy between observed and simulated climate variables. This study assessed climate projections in the Volta Basin using an ensemble of 4 Regional Climate Models under the Representative Concentration Pathways-RCPs 4.5 and 8.5 scenarios in the CORDEX-Africa datasets. These datasets were bias-corrected using the Climate Model data for hydrologic modeling tool (CMhyd) and 27-years of Climate Forecast System Reanalysis data. The performances of the ensemble bias-corrected precipitation ranged from 97-99%, 93-99%, 70-485mm, and -9-5% for R2, NSE, RMSE, and PBIAS respectively. TMAX bias-correction performances ranged from 65-99%, 27-99%, 0-4°C and -2-7% for R2, NSE, RMSE and PBIAS respectively. For TMIN, the performances ranged from 91–99%, 91–99%, 0-1°C and 0-1% for R2, NSE, RMSE and PBIAS respectively. The annual projected change in precipitation under RCP4.5 and 8.5 indicated a decrease in precipitation for the near (the 2020s), the mid-century (2050s), and the end far (2080s) with a relative increase from late November to January, a period currently part of dry season period in the Volta Basin. This suggests that the basin could expect a potential shift in the rainy season. The 12-month standard precipitation index suggests more frequent and longer drought periods in the future. Changes in annual mean monthly maximum temperature revealed an increase under all scenarios and throughout the century with an intensified increase by the end of the century under the higher CO2 concentration scenario (RCP 8.5). The study showed that under RCP 4.5 and 8.5 scenarios, the Volta Basin will experience frequent drought and extreme precipitation events, warmer days, and nights temperatures although RCP 4.5 showed a relatively lower magnitude of these extremes. It is therefore important to emphasize the need for strong adaptation to preserve water resources, limit negative impacts on energy and agricultural production, and other ecosystems services in the Volta Basin.

Explicit silicate cycling in the Kiel Marine Biogeochemistry Model version 3 (KMBM3) embedded in the UVic ESCM version 2.9

Abstract. We describe and test a new model of biological marine silicate cycling, implemented in the Kiel Marine Biogeochemical Model version 3 (KMBM3), embedded in the University of Victoria Earth System Climate Model (UVic ESCM) version 2.9. This new model adds diatoms, which are a key component of the biological carbon pump, to an existing ecosystem model. This new model combines previously published parameterizations of a diatom functional type, opal production and export with a novel, temperature-dependent dissolution scheme. Modelled steady-state biogeochemical rates, carbon and nutrient distributions are similar to those found in previous model versions. The new model performs well against independent ocean biogeochemical indicators and captures the large-scale features of the marine silica cycle to a degree comparable to similar Earth system models. Furthermore, it is computationally efficient, allowing both fully coupled, long-timescale transient simulations and “offline” transport matrix spinups. We assess the fully coupled model against modern ocean observations, the historical record starting from 1960 and a business-as-usual atmospheric CO2 forcing to the year 2300. The model simulates a global decline in net primary production (NPP) of 1.4 % having occurred since the 1960s, with the strongest declines in the tropics, northern midlatitudes and Southern Ocean. The simulated global decline in NPP reverses after the year 2100 (forced by the extended RCP8.5 CO2 concentration scenario), and NPP returns to 98 % of the pre-industrial rate by 2300. This recovery is dominated by increasing primary production in the Southern Ocean, mostly by calcifying phytoplankton. Large increases in calcifying phytoplankton in the Southern Ocean offset a decline in the low latitudes, producing a global net calcite export in 2300 that varies only slightly from pre-industrial rates. Diatom distribution moves southward in our simulations, following the receding Antarctic ice front, but diatoms are outcompeted by calcifiers across most of their pre-industrial Southern Ocean habitat. Global opal export production thus drops to 75 % of its pre-industrial value by 2300. Model nutrients such as phosphate, silicate and nitrate build up along the Southern Ocean particle export pathway, but dissolved iron (for which ocean sources are held constant) increases in the upper ocean. This different behaviour of iron is attributed to a reduction of low-latitude NPP (and consequently, a reduction in both uptake and export and particle, including calcite scavenging), an increase in seawater temperatures (raising the solubility of particulate iron) and stratification that “traps” the iron near the surface. These results are meant to serve as a baseline for sensitivity assessments to be undertaken with this model in the future.

Simulated Variation Characteristics of Oceanic CO2 Uptake, Surface Temperature, and Acidification in Zhejiang Province, China

Since preindustrial times, atmospheric CO2 content increased continuously, leading to global warming through the greenhouse effect. Oceanic carbon sequestration mitigates global warming; on the other hand, oceanic CO2 uptake would reduce seawater pH, which is termed ocean acidification. We perform Earth system model simulations to assess oceanic CO2 uptake, surface temperature, and acidification for Zhejiang offshore, one of the most vulnerable areas to marine disasters. In the last 40 years, atmospheric CO2 concentration increased by 71 ppm, and sea surface temperature (SST) in Zhejiang offshore increased at a rate of 0.16°C/10a. Cumulative oceanic CO2 uptake in Zhejiang offshore is 0.3 Pg C, resulting in an increase of 20% in sea surface hydrogen ion concentration, and the acidification rate becomes faster in the last decade. During 2020–2040, under four RCP scenarios, SST in Zhejiang offshore increases by 0.3–0.5°C, whereas cumulative ocean carbon sequestration is 0.150–0.165 Pg C. Relative to RCP2.6, the decrease of surface pH in Zhejiang offshore is doubled under RCP8.5. Furthermore, simulated results show that the relationship between CO2 scenario and oceanic carbon cycle is nonlinear, which hints that deeper reduction of anthropogenic CO2 emission may be needed if we aim to mitigate ocean acidification in Zhejiang offshore under a higher CO2 concentration scenario. Our study quantifies the variation characteristics of oceanic climate and carbon cycle fields in Zhejiang offshore, and provides new insight into the responses of oceanic carbon cycle and the climate system to oceanic carbon sequestration.

Historical and future global burned area with changing climate and human demography

Summary Wildfires influence terrestrial carbon cycling and represent a safety risk, and yet a process-based understanding of their frequency and spatial distributions remains elusive. We combine satellite-based observations with an enhanced dynamic global vegetation model to make regionally resolved global assessments of burned area (BA) responses to changing climate, derived from 34 Earth system models and human demographics for 1860–2100. Limited by climate and socioeconomics, recent BA has decreased, especially in central South America and mesic African savannas. However, future simulations predict increasing BA due to changing climate, rapid population density growth, and urbanization. BA increases are especially notable at high latitudes, due to accelerated warming, and over the tropics and subtropics, due to drying and human ignitions. Conversely, rapid urbanization also limits BA via enhanced fire suppression in the immediate vicinity of settlements, offsetting the potential for dramatic future increases, depending on warming extent. Our analysis provides further insight into regional and global BA trends, highlighting the importance of including human demographic change in models for wildfire under changing climate.

Hysteresis of the Earth system under positive and negative CO2 emissions

Carbon dioxide removal (CDR) from the atmosphere is part of all emission scenarios of the IPCC that limit global warming to below 1.5 °C. Here, we investigate hysteresis characteristics in 4× pre-industrial atmospheric CO2 concentration scenarios with exponentially increasing and decreasing CO2 using the Bern3D-LPX Earth system model of intermediate complexity. The equilibrium climate sensitivity (ECS) and the rate of CDR are systematically varied. Hysteresis is quantified as the difference in a variable between the up and down pathway at identical cumulative carbon emissions. Typically, hysteresis increases non-linearly with increasing ECS, while its dependency on the CDR rate varies across variables. Large hysteresis is found for global surface air temperature (SAT), upper ocean heat content, ocean deoxygenation, and acidification. We find distinct spatial patterns of hysteresis: SAT exhibits strong polar amplification, hysteresis in O2 is both positive and negative depending on the interplay between changes in remineralization of organic matter and ventilation. Due to hysteresis, sustained negative emissions are required to return to and keep a CO2 and warming target, particularly for high climate sensitivities and the large overshoot scenario considered here. Our results suggest, that not emitting carbon in the first place is preferable over carbon dioxide removal, even if technologies would exist to efficiently remove CO2 from the atmosphere and store it away safely.

Characterizing past and future trend and frequency of extreme rainfall in urban catchments: a case study

Abstract Urban communities in developing countries are one of the most vulnerable areas to extreme rainfall events. The availability of local information on extreme rainfall is therefore critical for proper planning and management of urban flooding impacts. This study examined the past and future characteristics of extreme rainfall in the urban catchments of Dar es Salaam, Tanzania. Investigation of trends and frequency of annual, seasonal and extreme rainfall was conducted, with the period 1967–2017 taken as the past scenario and 2018–2050 as the future scenario; using data from four key ground-based weather stations and RCM data respectively. Mann–Kendall trend analysis and Sen's slope estimator were used in studying changes in rainfall variability. Frequencies of extreme rainfall events were modeled using the Generalized Pareto model. Overall, the results of trend analysis provided evidence of a significant increase in annual and seasonal maximum rainfall and intensification of extreme rainfall in the future under the RCP4.5 CO2 concentration scenario. It was determined that extreme rainfall will become more frequent in the future, and their intensities were observed to increase approximately between 20 and 25% relative to the past. The findings of this study may help to develop adaptation strategies for urban flood control in Dar es Salaam.

Failure Analysis of the Water Supply Network in the Aspect of Climate Changes on the Example of the Central and Eastern Europe Region

The consequences of climate changes are felt by society every day. A sudden increase or decrease in air temperature, increasingly frequent, extreme weather phenomena can cause enormous economic damage to countries and cities. The occurrence of random weather phenomena and their negative impact on technical infrastructure nowadays are the basic problem related to ensuring the safety of the functioning of each system. Climate changes and significant air temperature amplitudes have a direct impact on the functioning of the critical infrastructure of cities, which includes collective water supply systems (CWSS). The paper presents the impact of climate change on the failure of a water supply network. Correlation between failure rate and air temperature was determined. This was used to determine the number of failures for the near 2036–2050 and distant 2086–2100 future in terms of climate change (temperature increase). The results confirm the thesis known from the literature that the failure rate decreases as the temperature increases. For forecasted periods as a result of temperature rise due to climate change, the reduction of the number of water pipe failures is expected in the range of 1.22% to 2.35% for the 2036–2050 period and from 2.96% to 8.66% for the 2086–2100 period, depending on the development of Representative CO2 Concentration Scenarios (RCP). The decrease in the total number of failures will have an impact on the increase in the reliability and safety of water supply to consumers.

Increase of the transient climate response to cumulative carbon emissions with decreasing CO2 concentration scenarios

Near-constancy of the transient climate response to cumulative carbon emissions (TCRE) facilitates the development of future emission pathways compatible with temperature targets. However, most studies have explored TCRE under scenarios of temperature increase. We used an Earth system model (MIROC-ESM) to examine TCRE in scenarios with increasing and stable CO2 concentrations, as well as overshoot pathways in which global mean temperatures peak and decline. Results showed that TCRE is stable under scenarios of increasing or stable CO2 concentration at an atmospheric CO2 concentration (pCO2) double the pre-industrial level. However, in the case of overshoot pathways and a stable pCO2 scenario at a quadrupled pCO2 level, the TCRE increases by 10%–50%, with large increases over a short period just after pCO2 starts to decrease. During the period of pCO2 increase, annual ocean heat uptake (OHU) and ocean carbon storage (CO) (or cumulative ocean carbon uptake from the start of the experiment) exhibit similar changes, resulting in a stable TCRE. During the pCO2 decrease period, after a sudden TCRE increase when pCO2 starts to decrease, the OHU decreases and CO increases (relative to the pCO2 increase period) balance each other out, resulting in a stable TCRE. In overshoot pathways, the temperature distribution when the global mean temperature anomaly cools to 1.5 °C reveals small warming over land and large warming over the oceans relative to the 1% per annum pCO2 increasing scenario, particularly in some high-latitude areas of both hemispheres. The increase in TCRE with overshoot pathways decreases the carbon budget for the temperature anomaly targets in such scenarios. Our analysis showed a 16%–35% decrease in the remaining carbon budget for the 1.5 °C global warming target, in comparison with the reference scenario with a 1% per year pCO2 increase, for pathways peaking at the doubled pCO2 level followed by decline to the pre-industrial level.

On the dynamic instability of Arctic sea ice

The last few decades have seen a significant decline in Arctic sea ice, generating concerns about both its causes and its longer-term implications. In this paper, we introduce an empirical technique to examine the dynamics of Arctic sea ice extent. Using quantile autoregression, we find that the negative effect of atmospheric CO2 is stronger in the upper tail of the ice distribution. We also document that Arctic sea ice dynamics have become more unstable over the last three decades, especially during the summer. The rising summer instability occurs across quantiles, indicating that it is due to the joint effects of rising atmospheric CO2 and nonlinear feedbacks (and not due to outside shocks). While we do not find evidence of “critical slowing”, we see the increasing instability as a cause for concern. We also use the model to predict the evolution of Arctic sea ice extent under alternative CO2 concentration scenarios.

Sensitivity to solar activity of the Northern Hemisphere warming for the years 1980–2500

We used a thermodynamic climate model to compute the Northern Hemisphere temperature anomaly for the period 1980–2500. We obtained temperature anomalies for the ocean, the combined ocean-land area and the land. Two IPCC et al. (2007) CO2 concentration scenarios were considered, the high RCP8.5 and the low RCP4.5, we also included two estimates of the Total Solar Irradiance (TSI). We found that in the RCP8.5 scenario the effect of the TSI is to prevent the temperature for having a runaway behavior after the year 2240, that otherwise it would have due to the high CO2 emission; it is the TSI that makes the temperature anomalies to have an inflection and start decreasing. For the RCP4.5 scenario, without the solar effect, the temperature anomaly after 2075 presents an inflection and becomes constant after the year 2120, but the temperature anomaly has a clear decreasing trend when including the TSI. The TSI presents three future secular minima in the studied period. They introduce only perturbations on the general decreasing trend. The land presents the largest temperature anomalies as well as the most prominent changes, followed by the land-ocean and the ocean. We concluded that the TSI has a fundamental role in the temperature behavior over the long-term.

BGC-val: a model- and grid-independent Python toolkit to evaluate marine biogeochemical models

Abstract. The biogeochemical evaluation toolkit, BGC-val, is a model- and grid-independent Python toolkit that has been built to evaluate marine biogeochemical models using a simple interface. Here, we present the ideas that motivated the development of the BGC-val software framework, introduce the code structure, and show some applications of the toolkit using model results from the Fifth Climate Model Intercomparison Project (CMIP5). A brief outline of how to access and install the repository is presented in Appendix A, but the specific details on how to use the toolkit are kept in the code repository. The key ideas that directed the toolkit design were model and grid independence, front-loading analysis functions and regional masking, interruptibility, and ease of use. We present each of these goals, why they were important, and what we did to address them. We also present an outline of the code structure of the toolkit illustrated with example plots produced by the toolkit. After describing BGC-val, we use the toolkit to investigate the performance of the marine physical and biogeochemical quantities of the CMIP5 models and highlight some predictions about the future state of the marine ecosystem under a business-as-usual CO2 concentration scenario (RCP8.5).

Experience in a Climate Microworld: Influence of Surface and Structure Learning, Problem Difficulty, and Decision Aids in Reducing Stock-Flow Misconceptions.

Research shows that people’s wait-and-see preferences for actions against climate change are a result of several factors, including cognitive misconceptions. The use of simulation tools could help reduce these misconceptions concerning Earth’s climate. However, it is still unclear whether the learning in these tools is of the problem’s surface features (dimensions of emissions and absorptions and cover-story used) or of the problem’s structural features (how emissions and absorptions cause a change in CO2 concentration under different CO2 concentration scenarios). Also, little is known on how problem’s difficulty in these tools (the shape of CO2 concentration trajectory), as well as the use of these tools as a decision aid influences performance. The primary objective of this paper was to investigate how learning about Earth’s climate via simulation tools is influenced by problem’s surface and structural features, problem’s difficulty, and decision aids. In experiment 1, we tested the influence of problem’s surface and structural features in a simulation called Dynamic Climate Change Simulator (DCCS) on subsequent performance in a paper-and-pencil Climate Stabilization (CS) task (N = 100 across four between-subject conditions). In experiment 2, we tested the effects of problem’s difficulty in DCCS on subsequent performance in the CS task (N = 90 across three between-subject conditions). In experiment 3, we tested the influence of DCCS as a decision aid on subsequent performance in the CS task (N = 60 across two between-subject conditions). Results revealed a significant reduction in people’s misconceptions in the CS task after performing in DCCS compared to when performing in CS task in the absence of DCCS. The decrease in misconceptions in the CS task was similar for both problems’ surface and structural features, showing both structure and surface learning in DCCS. However, the proportion of misconceptions was similar across both simple and difficult problems, indicating the role of cognitive load to hamper learning. Finally, misconceptions were reduced when DCCS was used as a decision aid. Overall, these results highlight the role of simulation tools in alleviating climate misconceptions. We discuss the implication of using simulation tools for climate education and policymaking.

The optimal CO2 concentrations for the growth of three perennial grass species

BackgroundGrasslands are one of the most representative vegetation types accounting for about 20% of the global land area and thus the response of grasslands to climate change plays a pivotal role in terrestrial carbon balance. However, many current climate change models, based on earlier results of the doubling-CO2 experiments, may overestimate the CO2 fertilization effect, and as a result underestimate the potentially effects of future climate change on global grasslands when the atmospheric CO2 concentration goes beyond the optimal level. Here, we examined the optimal atmospheric CO2 concentration effect on CO2 fertilization and further on the growth of three perennial grasses in growth chambers with the CO2 concentration at 400, 600, 800, 1000, and 1200 ppm, respectively.ResultsAll three perennial grasses featured an apparent optimal CO2 concentration for growth. Initial increases in atmospheric CO2 concentration substantially enhanced the plant biomass of the three perennial grasses through the CO2 fertilization effect, but this CO2 fertilization effect was dramatically compromised with further rising atmospheric CO2 concentration beyond the optimum. The optimal CO2 concentration for the growth of tall fescue was lower than those of perennial ryegrass and Kentucky bluegrass, and thus the CO2 fertilization effect on tall fescue disappeared earlier than the other two species. By contrast, the weaker CO2 fertilization effect on the growth of perennial ryegrass and Kentucky bluegrass was sustained for a longer period due to their higher optimal CO2 concentrations than tall fescue. The limiting effects of excessively high CO2 concentrations may not only associate with changes in the biochemical and photochemical processes of photosynthesis, but also attribute to the declines in stomatal conductance and nitrogen availability.ConclusionsIn this study, we found apparent differences in the optimal CO2 concentrations for the growth of three grasses. These results suggest that the growth of different types of grasses may respond differently to future elevated CO2 concentrations through the CO2 fertilization effect, and thus potentially alter the community composition and structure of grasslands. Meanwhile, our results may also be helpful for improving current process-based ecological models to more accurately predict the structure and function of grassland ecosystems under future rising atmospheric CO2 concentration and climate change scenarios.

Climate and environmental changes driving idiosyncratic shifts in the distribution of tropical and temperate worm reefs

An increasing number of studies have forecast the potential responses of marine life to future climate change. This study predicts how the distributional range of temperate and tropical worm reefs (WRs) might respond to climate and environmental changes (CECs). Compared with current distributions, the tested hypotheses were: (i) under a low CO2concentration and active atmospheric carbon capturing scenario (RCP2.6), both tropical and temperate WRs will maintain their current distributions and face only slight multi-directional biogeographic changes along the century; and (ii) under a high CO2concentration scenario (RCP8.5) WRs will shift toward higher latitudes, with marked changes for tropical species and slight changes for temperate species, specifically at the end of the 21st century. The hypotheses were tested using species distribution modelling, and exploratory statistical analyses were performed to tune model settings. Under scenario RCP2.6, in the middle of the century, areas of suitable habitat are predicted to slightly increase for the temperate WRs and conversely contract for tropical WRs. At the end of the century, multi-directional shifts without range retraction were predicted for both species, but tropical WRs showed major changes in their distribution. Under scenario RCP8.5 and throughout the century, multi-directional shifts increased the areas of suitable habitat for temperate WRs, whereas tropical WRs experienced shifts toward high latitudes and significant retraction at low latitudes. Results indicate that biogeographic range shifts are idiosyncratic for temperate and tropical WRs depending on the CECs scenarios considered.

Potential Impact of Climate Change on Suspended Sediment Yield in NW Spain: A Case Study on the Corbeira Catchment

Soil losses and the subsequent sediment delivery constitute significant environmental threats. Climate change is likely to have an impact on the availability of water and therefore on sediment yield in catchments. In this context, quantifying the sediment response to an increased atmospheric CO2 concentration and climate change is of utmost importance to the proper management of rural catchments. However, quantitative assessment of climate change impact remains a complex task. In this study, the potential medium (2031–2060) and long-term (2069–2098) impacts of projected changes of temperature, rainfall and CO2 concentration on sediment yield in a small rural catchment located in NW Spain were evaluated using the Soil and Water Assessment Tool (SWAT) model. Climate change scenarios were created using future climate data projected by regional climate models from the ENSEMBLES project and two CO2 concentration scenarios (550 and 660 ppm). The results showed that climate change would have a noticeable impact on suspended sediment if the forecast temperature, rainfall and CO2 concentration changes included in this study were met. Overall, suspended sediment is expected to decrease (2031–2060: −11%, 2069–2098: −8%) compared to the baseline period (1981–2010), mainly due to decreased streamflow. However, an increase in sediment transport in winter is predicted, possibly associated with increased erosion in cultivated areas (11%–17%), suggesting that, at this time of the year, the effect of soil detachment prevails over sediment transport capacity. Consequently, management practices aimed at reducing soil erosion in cultivated areas should be carried out, because these are the main source of sediment in the study area.