Doubling Of CO2 Concentration Research Articles

Climate effects of global land cover change

When changing from grass and croplands to forest, there are two competing effects of land cover change on climate: an albedo effect which leads to warming and an evapotranspiration effect which tends to produce cooling. It is not clear which effect would dominate. We have performed simulations of global land cover change using the NCAR CAM3 atmospheric general circulation model coupled to a slab ocean model. We find that global replacement of current vegetation by trees would lead to a global mean warming of 1.3°C, nearly 60% of the warming produced under a doubled CO2 concentration, while replacement by grasslands would result in a cooling of 0.4°C. It has been previously shown that boreal forestation can lead to warming; our simulations indicate that mid‐latitude forestation also could lead to warming. These results suggest that more research is necessary before forest carbon storage should be deployed as a mitigation strategy for global warming.

Prolonged Growth of Young Spruce (Picea koraiensis Nakai) Plants at Double Atmospheric CO2 Concentration Stimulates the Preferential Growth of Thick Roots

Two-year-old young spruce (Picea koraiensis Nakai) plants were grown in a climatic chamber during three summer months at double atmospheric CO2 concentration, sufficient content of soil inorganic nitrogen, and diurnal variation of temperature and illuminance, which simulate natural growth conditions. The control plants were grown in another climatic chamber under the same conditions, but at atmospheric CO2 concentration (350 ppm). CO2 exchange was measured with a Li-Cor 6400 infra-red gas analyzer in attached leaves placed in a climatic chamber in the morning under growth conditions and saturating light 1200 µE/(m2 s) in June, July, and August. In addition, dry weights of needles, leafless shoot parts of plant, fraction of thick (more than 0.5 mm in diameter) and thin (less than 0.5 mm in diameter) roots were recorded. The data were used to plot CO2 exchange rates as a function of carbon dioxide concentration and to calculate the increment of shoot and root phytomass. The maximum gas exchange rates in the treated and control plants similarly depended on CO2 concentration. The slope of the CO2 dependence curve, which corresponded to the kinetic characteristic Vm /KM of photosynthetic carboxylation, increased monotonically during the experiment. To the end of observation period, the proportion of thick roots in plant phytomass significantly increased in the plants grown at double atmospheric CO2 concentration, as compared to the control plants. Thus, the increase in the rate of photosynthetic gas exchange in plants grown for three months at double atmospheric CO2 concentration was only due to the increase in CO2, the substrate of Rubisco carboxylation activity. We found no differences in the CO2 characteristic for Rubisco between the treated and control plants. The ratio of needle to thin roots in the treated and control plants was similar and did not change during the experiment. The excess of photoassimilates in the treated, as compared to the control plants, was preferentially used for thick root growth. This result shows that photosynthesis in young spruce forests can deposit excess atmospheric CO2 in the soil horizon in the form of thick root phytomass.

Effect of doubled CO2 on morphology: Inhibition of stomata development in growing birch (Betula platyphylla Suk.) leaves

Two-year old birch (Betula platyphylla Suk.) seedlings were grown in climatic chambers for 7 weeks under various conditions: (1) ambient CO2 concentration (350 ppm) and an ordinary nitrogen content in soil (2 mM NH4NO3); (2) ambient CO2 concentration and a high nitrogen rate (16 mM NH4NO3); (3) doubled CO2 concentration (700 ppm) and ordinary nitrogen content, and (4) doubled CO2 concentration and a high nitrogen rate. Doubled CO2 concentration in combination with the high nitrogen rate activated mostly seedling growth, e.g., stem thickening and leaf initiation. In this treatment, the maximum rate of apparent photosynthesis (A max) was twice as high as in control seedlings. At doubled CO2 concentration and ordinary nitrogen content, we observed the phenomenon of stomata absence from the upper leaf surface and doubling their number on the lower surface, whereas, at doubled CO2 concentration and a high nitrogen rate, stomata partition was essentially similar as in control leaves. The conclusion is that, when the balance between CO2 concentration and nitrogen rate is shifted, doubled CO2 concentration exerts a morphotropic effect on differentiation of young epidermal tissue.

Modeling the potential effects of climate change on water temperature downstream of a shallow reservoir, lower madison river, MT

A numerical stream temperature model that accounts for kinematic wave flow routing, and heat exchange fluxes between stream water and the atmosphere, and stream water and the stream bed is developed and calibrated to a data-set from the Lower Madison River, Montana, USA. Future climate scenarios were applied to the model through changes to the atmospheric input data based on air temperature and solar radiation output from four General Circulation Models (GCM) for the region under atmospheric CO2 concentration doubling. The purpose of this study was to quantify potential climate change impacts on water temperature for the Lower Madison River, and to assess possible impacts to aquatic ecosystems. Because water temperature is a critical component of fish habitat, this information could be of use in future planning operations of current reservoirs. We applied air temperature changes to diurnal temperatures, daytime temperatures only, and nighttime temperatures only, to assess the impacts of variable potential warming trends. The results suggest that, given the potential climatic changes, the aquatic ecosystem downstream of Ennis Lake will experience higher water temperatures, possibly leading to increased stress on fish populations.Daytime warming produced the largest increases in downstream water temperature.

Respective and interactive effects of doubled CO2 and O3 concentration on membrane lipid peroxidation and antioxidative ability of soybean

Effects of doubled CO2 and O3 concentration on Soybean were studied in open-top chambers (OTC). Under doubled CO2 concentration, grain yield and biomass increased, the SOD activity, vitamin C (Vc) and carotenoid (Car) content also increased; Superoxide (O2-*) generating rate decreased, relative conductivity and malondialdehyde (MDA) content significantly declined. But under doubled O3 concentration, the SOD activity, Vc and Car contents declined, resulting in imbalance of activated-oxygen production, enhanced O2-* generating rate and accelerated process of lipid peroxidation and increase in MDA content and ion leakage of leaves. The final result was decreased grain yield and plant biomass. Interactive effects of doubled CO2 and O3 concentrations on soybean were mostly counteractive. However, the beneficial effects of concentration-doubled CO2 more than compensate the negative effects imposed by doubled O3, and the latter in its turn partly counteracted the positive effects of the former.

The impact of climate change on hailstorms in southeastern Australia

Data from a number of locations around southeastern Australia were analysed to determine the influence of climate change on the frequency and intensity of hail events in this region. The relationship between Convective Available Potential Energy (CAPE), frequently used as a measure of atmospheric instability, and hailstorms was investigated using both NCEP/NCAR reanalysis data (a data set comprising a blend of observations and model simulations) and also direct sounding data obtained from the Australian National Climate Centre. Two locations were chosen in southeastern Australia, Mount Gambier and Melbourne, over the months August to October for the period 1980–2001. A statistically significant relationship between hail incidence and CAPE values was established for both NCEP/NCAR and sounding data at both study sites. A stronger relationship was found between hail incidence and the CAPE, which was calculated using NCEP/NCAR data, than that between hail and the CAPE from the actual sounding data. A similar analysis was also conducted at both sites using the totals–totals index (TT index), which is an alternative measure of atmospheric instability. The CSIRO Mk3 Climate System Model was used to simulate values of CAPE for Mount Gambier in an environment containing double the pre-industrial concentrations of equivalent CO2. The results showed a significant decrease in CAPE values in the future. From this, assuming the relationship between CAPE and hail remains unchanged under enhanced greenhouse conditions, it is possible that there will be a decrease in the frequency of hail in southeastern Australia if current rates of CO2 emission are sustained. The severity of future hail events was investigated using crop-loss data from insurance companies. Strongest correlations were found between the crop-loss ratio (value of crop lost to hail damage over the total insured value of crop) and the number of days in a crop season with a TT index greater than 55. Results from the CSIRO Mk3 Climate System Model revealed that there was no significant difference between the number of days with a TT index over 55 for the simulation using current CO2 levels and that based on doubled equivalent pre-industrial CO2 concentrations (roughly equivalent to 2050 in the chosen emissions scenario). This implies that, for southeastern Australia, crop losses due to hail damage would not significantly increase under enhanced greenhouse conditions. Copyright © 2005 Royal Meteorological Society.

Photosynthesis, transpiration, and primary productivity: Scaling up from leaves to canopies and regions using process models and remotely sensed data

Biophysical and physiological processes in plants and ecosystems occur over a wide range of spatial and temporal scales. Our knowledge (or models) of these processes is largely at small scales. It is, however, difficult to directly apply mechanistic process‐oriented models over large scales due to heterogeneities in the distributions of processes, and nonlinearities in the functional responses of processes to environmental variables. On the other hand, simple parametric/empirical models in which system complexity is lumped into a small number of parameters have been widely employed to describe processes at larger scales. The variation of these parameters in these simple parametric/empirical models depends on the underlying biophysical processes. In this work, we showed that detailed process models and simple parametric models for primary production and transpiration could be effectively combined to scale leaf photosynthesis and transpiration up to large spatial scales. The integrated process model, General Energy Mass Transfer Model (GEMTM), was used to identify major factors contributing to the variability of the parameters in the parametric models for regional transpiration and primary production and quantify their responses to these factors. Simulations with the GEMTM showed that net carbon assimilation was proportional to intercepted photosynthetically active radiation (IPAR), but the radiation use efficiency (RUE) changed with leaf N concentration, temperature, and atmospheric CO2 concentration; transpiration was linearly correlated with the product of net primary production (NPP) and atmospheric water vapor pressure deficit (VPD), and the slope varied with leaf N concentration. RUE increased with leaf N content asymptotically, and responded to temperature in an asymmetric bell shape pattern with a 22°C and 26°C optimal temperature under current ambient and doubled CO2 concentration, respectively. A simple parametric NPP model and a regional transpiration model (Tr model) were developed from the relationships and parameter values obtained using the GEMTM. The NPP model reasonably simulated the seasonal and interannual variations of accumulated NPP estimated from field data. Simulated regional distribution of NPP over the Central Grassland Region of the United States was consistent with estimates obtained using other models. NPP increased from 120 gC/m2/year in the northwest to 956 gC/m2/year in the southeast. Simulated regional transpiration had a similar spatial distribution pattern as NPP, ranging from about 16 cmH2O/year to 136 cmH2O/year. The transpiration model introduced in this study provides a mechanism to explicitly couple transpiration and NPP in large‐scale analyses, although more complete analysis and validation are required.

Present and future surface climate in the western USA as simulated by 15 global climate models

We analyze results of 15 global climate simulations contributed to the Coupled Model Intercomparison Project (CMIP). Focusing on the western USA, we consider both present climate simulations and predicted responses to increasing atmospheric CO2. The models vary in their ability to predict the present climate. In the western USA, a few models produce a seasonal cycle for spatially averaged temperature and/or precipitation in good agreement with observational data. Other models tend to over-predict precipitation in the winter or exaggerate the amplitude of the seasonal cycle of temperature. The models also differ in their ability to reproduce the spatial patterns of temperature and precipitation in the USA. Considering the monthly mean precipitation responses to doubled atmospheric CO2, averaged over the western USA, we find some models predict increases while others predict decreases. The predicted temperature response, on the other hand, is invariably positive over this region; however, for each month, the range of values given by the different models is large compared to the mean model response. We look for possible relationships between the models’ temperature and precipitation responses to doubled CO2 concentration and their ability to simulate some aspects of the present climate. We find that these relationships are weak, at best. The precipitation response over the western USA in DJF and the precipitation response over the mid- and tropical latitudes seem to be correlated with the RMS error in simulated present-day precipitation, also calculated over the mid- and tropical latitudes. However, considering only the responses of the models with the smallest RMS errors does not provide a different estimate of the precipitation response to a doubled CO2 concentration, because even among the most accurate models, the range of model responses is so large. For temperature, we find that models that have smaller RMS errors in present-climate temperature in the north eastern Pacific region predict a higher temperature response in the western USA than the models with larger errors. A similar relation exists between the temperature response over Europe in DJF and the RMS error calculated over the Northern Atlantic.

Changing Global Climate: Historical Carbon and Nitrogen Budgets and Projected Responses of Ohio?s Cropland Ecosystems

As the evidence of global climate change continues to mount, its consequences for cropland productivity assume particular significance. Against the backdrop of past agricultural practices, simulation models offer a glimpse into the future, showing the effect of temperature changes on crop production. In this study, we first quantified the carbon (C) and nitrogen (N) budgets of Ohio’s cropland ecosystems using inventory yield data of corn for grain, oat, and all wheat for the period 1866–1996 and soybean for the period 1924–96. Then we explored the responses of Ohio’s continuous soybean croplands to changes in temperature, carbon dioxide (CO2) concentration, initial soil organic C and N (SOC-N) pools, soil texture, and management practices by developing a simple cropland ecosystem model (CEM) and performing a long-term sensitivity analysis. Finally, CEM simulations were evaluated against independent observations of SOC values (0–19 cm) averaged over 470 northwest Ohio sites between 1954 and 1987 under conventional tillage and rotations of corn–soybean–winter wheat by using the historical yield data (r 2 = 0.8). The C contents per hectare of crop harvests increased by 178% for oats, 300% for corn for grain, and 652% for all wheat between 1866 and 1996 and by 305% for soybean between 1924 and 1996. Ohio croplands acted as C–N sources, releasing average net ecosystem emissions (NEE), including the removal of harvested C–N, of 4,598 kg CO2 ha−1 and 141 kg N ha−1 in 1886 and 205 kg CO2 ha−1 (except for the corn-for-grain cropland) and 39 kg N ha−1 in 1996. The continuous corn croplands continued to become a C sink, sequestering 255 kg C ha−1 in 1996. Results of the sensitivity analysis for Ohio’s continuous soybean croplands revealed that the SOC pool increased by 6.9% and decreased by 7.5% in response to a doubled CO2 concentration and a temperature increase of 2.8°C over 100 years, respectively. The sequestration potential of the SOC pool increased by 6.5% at a rate of 24.6 kg C ha−1 y−1 for the same period with finer soil texture (loam to silty clay loam). The shift from conventional to conservation residue practice led to an 11% increase in the steady-state SOC storage at a rate of 42 kg C ha−1 y−1 for 100 years.

The Response of Ultrastructure and Function of Chloroplasts from Cycads to Doubled CO2Concentration

I. Abstract This study examines the effects of doubled CO2 concentration on the ultrastructure and function of chloroplasts from cycads and, for control from two other herbaceous angiosperms. Under a doubled CO2 concentration condition, the chloroplast ultrastructure of the two cycads (Cycas multipinnata with a shade-type chloroplast and C. panzhihuaensis with a sun-type chloroplast) changed little: The conformation of the thylakoid membrane system kept well, and almost no starch grains accumulated. In contrast, under the same conditions the chloroplast ultrastructure of soybean and foxtail millet changed considerably, with starch grains accumulating in their chloroplasts and some of thylakoids (especially stroma thylakoid) membranes being destroyed to some degree by the more numerous and larger starch grains that accumulated in the chloroplasts. Interestingly, the changes in the ultrastructure of the chloroplasts from the two cycads was correlated with the 77K fluorescence emission spectra of their chlor...

Effects of sunspot cycle length and CO2 on air temperature along Qinghai-Xizang railway and air temperature’s trend prediction

There are well coherences between annual averaged air temperatures at every meteorological station along the Qinghai-Xizang railway, and its 10-year moving average correlation coefficient is 0.92. Thus, the regional averaged annual mean temperature series along the Qinghai-Xizang railway (Trw) from 1935 to 2000 are constructed. The investigation is suggested that: Trw had significant responses to the 5-year lagged sunspot cycle length (SCL) and 15-year lagged concentration of atmospheric carbon dioxide (CO2), and the correlation coefficients between them are -0.76 (SCL) and 0.88 (CO2), respectively. The future SCL is predicted by the model of average generated function constructed with its main cycles of 76a, 93a, 108a, 205a and 275a. The result shows that the SCL would be becoming longer in the first half of the 21st century, and then it could be becoming shorter in the second half of the 21st century. Based on the natural change of SCL and the effect of double CO2 concentration, inrw in the 21st century is forecasted. It could warm up about 0.50°C in the first half of the 21st century compared with the last decade of last century. The mean maximum air temperature could be likely about 0.20°C in July and from 0.40°C to 1.10°C in January. The annual air temperature difference would likely reduce 0.3–1.00°C. The probability of above predictions ranges from 0.64 to 0.73.

Monoterpene and herbivore-induced emissions from cabbage plants grown at elevated atmospheric CO2 concentration

Abstract The warming of the lower atmosphere due to elevating CO2 concentration may increase volatile organic compound (VOC) emissions from plants. Also, direct effects of elevated CO2 on plant secondary metabolism are expected to lead to increased VOC emissions due to allocation of excess carbon on secondary metabolites, of which many are volatile. We investigated how growing at doubled ambient CO2 concentration affects emissions from cabbage plants (Brassica oleracea subsp. capitata) damaged by either the leaf-chewing larvae of crucifer specialist diamondback moth (Plutella xylostella L.) or generalist Egyptian cotton leafworm (Spodoptera littoralis (Boisduval)). The emission from cabbage cv. Lennox grown in both CO2 concentrations, consisted mainly of monoterpenes (sabinene, limonene, α-thujene, 1,8-cineole, β-pinene, myrcene, α-pinene and γ-terpinene). (Z)-3-Hexenyl acetate, sesquiterpene (E,E)-α-farnesene and homoterpene (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT) were emitted mainly from herbivore-damaged plants. Plants grown at 720 μmol mol −1 of CO2 had significantly lower total monoterpene emissions per shoot dry weight than plants grown at 360 μmol mol −1 of CO2, while damage by both herbivores significantly increased the total monoterpene emissions compared to intact plants. (Z)-3-Hexenyl acetate, (E,E)-α-farnesene and DMNT emissions per shoot dry weight were not affected by the growth at elevated CO2. The emission of DMNT was significantly enhanced from plants damaged by the specialist P. xylostella compared to the plants damaged by the generalist S. littoralis. The relative proportions of total monoterpenes and total herbivore-induced compounds of total VOCs did not change due to the growth at elevated CO2, while insect damage increased significantly the proportion of induced compounds. The results suggest that VOC emissions that are induced by the leaf-chewing herbivores will not be influenced by elevated CO2 concentration.

Assessment of climate change on the Canadian prairies from downscaled GCM data

Climate data were taken from the Canadian Centre for Climate Modelling and Analysis (CCCma) Second Generation Global Circulation Model (GCMII) and the more recently developed Canadian Coupled Global Circulation Model with aerosol (CGCM1‐A). The GCM output difference for a current and doubling CO2 concentration was used to modify a 30‐year historic time series. Regional climate change data under a doubling of CO2 were produced by downscaling to a grid of 50 by 50 km across Alberta, Saskatchewan and Manitoba. Two scenarios were produced containing GCM‐generated temperatures and precipitation. Results show that, across all three provinces, maximum air temperature is predicted to have a mean increase of 4.0° to 5.7°C (GCMII) and 2.5° to 3.3°C (CGCM1‐A) above climate normal values. Minimum air temperature is expected to have a mean increase of 5.0° to 5.6°C (GCMII) and 3.0° to 3.3°C (CGCM1‐A). Precipitation is predicted to have a mean increase of 29 to 36% (GCMII) and 3 to 7% (CGCM1‐A). Both the GCMII and CGCM1‐A indicate that central Alberta will benefit the most during the summer and winter from increased precipitation, the eastern Prairies, however, will see little change (winter) in precipitation with smaller increases (30 mm under GCMII) or a decrease (30 mm under CGCM1‐A). Overall, the CGCM1‐A results are more consistent than GCMII with historic large‐scale spatial patterns.

Light‐acquisition and use of individuals as influenced by elevated CO2 in even‐aged monospecific stands of Chenopodium album

Summary We studied the effect of CO2 elevation on photosynthesis and growth of individuals in even‐aged monospecific stands of an annual, Chenopodium album, established at ambient and doubled CO2 concentrations in open‐top chambers. The whole‐plant photosynthesis of every individual in the stand was calculated from (1) the distribution of light and leaf nitrogen and (2) the relationships between photosynthetic parameters and leaf nitrogen content per area. Elevated CO2 increased light‐saturated rates of photosynthesis by 10–15% and the initial slope of the light‐response curve by 11%, but had no effect on the convexity of the light‐response curve and dark respiration. The relative rate of photosynthesis (RPR, the rate of photosynthesis per unit above‐ground mass) was analysed as the product of light capture (Φmass, the photon flux captured per unit above‐ground mass) and light‐use efficiency (LUE, plant photosynthesis per unit photon capture). At an early stage of stand development (33 days after germination), RPR was nearly constant and no difference was found between ambient and elevated CO2. However, CO2 elevation influenced the components of RPR such that the reduction in Φmass at elevated CO2 offsets the effect of the higher LUE. Later (47 days), RPR was positively correlated with plant mass at both CO2 concentrations. When compared at an equal plant mass, RPR was lower at elevated CO2, which was caused by a reduction in Φmass despite some compensation by higher LUE. We conclude that elevated CO2 increases size inequality of a stand through enhanced photosynthesis and growth of dominants, which reduce the light availability for subordinates and consequently increase size inequality in the stand.

An optimal approach to overlapping bands with correlated k distribution method and its application to radiative calculations

It is found that the possibly achieved higher accuracy cannot be obtained for all overlapping bands if only one scheme is used to treat them in atmospheric absorption calculations. The commonly used multiplication transmittance scheme is not acceptable when correlation existing in the practical absorption spectra becomes strong. Therefore an optimized scheme to obtain k distribution parameters for overlapping bands is developed in this paper based on the completely uncorrelated, perfectly correlated, and partly correlated schemes. Two partial correlation formulae are given in the paper. Calculations of radiative flux and atmospheric heating (or cooling) rate are validated in detail using a line‐by‐line model described in the paper for six model atmospheres. The optimized scheme developed here has an accuracy in longwave clear skies of 0.07 K d−1 in the entire troposphere and 0.35 K d−1 above the tropopause; the accuracy of upward, downward, and net fluxes is 0.76 W m−2 at all altitudes. In shortwave region, the absolute errors of the heating rate are less than 0.05 K d−1 in the troposphere and less than 0.25 K d−1 above the tropopause; net flux errors are less than 0.9 W m−2 at all altitudes. For an ensemble of 42 diverse atmospheres, the new scheme guarantees an average maximum error of longwave heating rate of 0.068 K d−1 in troposphere, 0.22 K d−1 above tropopause, and an accuracy of 1.1 W m−2 of radiative net flux for all the levels. For a case of doubled CO2 concentration, radiative forcing calculations have an accuracy of 0.04 W m−2.

Effect of water addition and nitrogen fertilization on the fluxes of CH<sub>4</sub>, CO<sub>2</sub>, NO<sub>x</sub>, and N<sub>2</sub>O following five years of elevated CO<sub>2</sub> in the Colorado Shortgrass Steppe

Abstract. An open-top-chamber (OTC) CO2 enrichment (~720 mmol mol-1) study was conducted in the Colorado shortgrass steppe from April 1997 through October 2001. Aboveground plant biomass increased under elevated CO2 and soil moisture content was typically higher than under ambient CO2 conditions. Fluxes of CH4, CO2, NOx and N2O, measured weekly year round were not significantly altered by CO2 enrichment over the 55 month period of observation. During early summer of 2002, following the removal of the open-top-chambers from the CO2 enrichment sites in October 2001, we conducted a short term study to determine if soil microbial processes were altered in soils that had been exposed to double ambient CO2 concentrations during the growing season for the past five years. Microplots were established within each experimental site and 10 mm of water or 10 mm of water containing the equivalent of 10 g m-2 of ammonium nitrate-N was applied to the soil surface. Fluxes of CO2, CH4, NOx and N2O fluxes within control (unchambered), ambient CO2 and elevated CO2 OTC soils were measured at one to three day intervals for the next month. With water addition alone, CO2 and NO emission did not differ between ambient and elevated CO2 soils, while CH4 uptake rates were higher and N2O fluxes lower in elevated CO2 soils. Adding water and mineral N resulted in increased CO2 emissions, increased CH4 uptake and decreased NO emissions in elevated CO2 soils. The N addition study confirmed previous observations that soil respiration is enhanced under elevated CO2 and N immobilization is increased, thereby decreasing NO emission.

Ocean Heat Uptake in Transient Climate Change: Mechanisms and Uncertainty due to Subgrid-Scale Eddy Mixing

Abstract The ocean heat uptake (OHU) is studied using the Massachusetts Institute of Technology (MIT) ocean general circulation model (OGCM) with idealized ocean geometry. The OGCM is coupled with a statistical–dynamic atmospheric model. The simulation of OHU in the coupled model is consistent with other coupled ocean–atmosphere GCMs in a transient climate change when CO2 concentration increases by 1% yr–1. The global average surface air temperature increases by 1.7°C at the time of CO2 concentration doubling (year 70). The ocean temperature increases by about 1.0°C near the surface, 0.1°C at 1000 m in the Pacific, and 0.3°C in the Atlantic. The maximum overturning circulation (MOTC) in the Atlantic at 1350 m decreases by about 4.5 Sv (1 Sv ≡ 106 m3 s–1). The center of MOTC drifts upward about 300 m, and therefore a large OTC anomaly (14 Sv) is found at 2700 m. The MOTC recovers gradually, but the OTC anomaly at 2700 m does not seem to recover after CO2 concentration is kept constant during 400-yr simulat...

Effects of elevated CO2 and temperature on development and consumption rates of Octotoma championi and O. scabripennis feeding on Lantana camara

AbstractWe carried out a factorial experiment to explore the effect of doubled CO2 concentration and a 3 °C temperature increase on the development of a complete generation of the beetles Octotoma championi Baly and O. scabripennis Guérin‐Méneville (Coleoptera: Chrysomelidae). These species are biological control agents of Lantana camara L. (Verbenaceae), with a leaf‐mining larval phase and free‐living, leaf‐chewing adults.Plants grown at elevated CO2 had enhanced above‐ground biomass, thicker leaves, reduced nitrogen concentration, and increased C:N ratios. Under the high temperature treatment, plants grown at ambient CO2 suffered wilting and premature leaf loss, despite daily watering; this effect was ameliorated at elevated CO2. The wilting of plants in the ambient CO2/high temperature treatment reduced the emergence success of the beetles, particularly O. championi. Development time was accelerated by approximately 10–13 days at the higher temperature, but was not affected by CO2. Neither CO2 nor temperature affected adult beetle weight. Consumption rates of free‐living beetles were not affected by either CO2 or temperature. By contrast, in the short‐term trials using excised foliage, beetles given no choice between ambient and elevated CO2‐grown foliage, consumed more from ambient plants. When beetles were offered a choice between foliage grown at the two CO2 levels, O. championi did not display a significant preference but O. scabripennis consumed more ambient CO2‐grown foliage when feeding at the lower temperature.This study indicates that under future conditions of higher temperatures, amelioration of water stress in host plants growing in elevated CO2 may benefit some endophagous insects by reducing premature leaf loss. Under some circumstances, this benefit may outweigh the deleterious effects of lower leaf nitrogen. Our results also indicate that foliage consumption under elevated CO2 by mobile, adult insects on whole plants may not be significantly increased, as was previously indicated by short‐term experiments using excised foliage.

Effects of doubled atmospheric CO2 concentration on the photosynthesis and growth of Chlorella pyrenoidosa cultured at varied levels of light

Chlorella pyrenoidosa was cultured with 350 and 700 p.p.m.v. CO2 at varied levels of light to see the impacts of doubled atmospheric CO2 concentration on its growth and photosynthesis. The CO2 enrichment did not affect the growth rate (mu), but significantly increased the cell density when light was sufficiently supplied. The CO2 enrichment significantly depressed light-saturated photosynthesis and dark respiration in the cells grown under a high-light regime, but not those under a low-light regime. The light-saturating point for photosynthesis and photosynthetic efficiency was not affected by the CO2 enrichment under either the high-light or low-light conditions.

Vegetation sensitivity to global anthropogenic carbon dioxide emissions in a topographically complex region

Anthropogenic increases in atmospheric carbon dioxide (CO2) concentrations may affect vegetation distribution both directly through changes in photosynthesis and water‐use efficiency, and indirectly through CO2‐induced climate change. Using an equilibrium vegetation model (BIOME4) driven by a regional climate model (RegCM2.5), we tested the sensitivity of vegetation in the western United States, a topographically complex region, to the direct, indirect, and combined effects of doubled preindustrial atmospheric CO2 concentrations. Those sensitivities were quantified using the kappa statistic. Simulated vegetation in the western United States was sensitive to changes in atmospheric CO2 concentrations, with woody biome types replacing less woody types throughout the domain. The simulated vegetation was also sensitive to climatic effects, particularly at high elevations, due to both warming throughout the domain and decreased precipitation in key mountain regions such as the Sierra Nevada of California and the Cascade and Blue Mountains of Oregon. Significantly, when the direct effects of CO2 on vegetation were tested in combination with the indirect effects of CO2‐induced climate change, new vegetation patterns were created that were not seen in either of the individual cases. This result indicates that climatic and nonclimatic effects must be considered in tandem when assessing the potential impacts of elevated CO2 levels.