Ppmv CO2 Research Articles

ELEVATED CARBON DIOXIDE DIFFERENTIALLY ALTERS THE PHOTOPHYSIOLOGY OF THALASSIOSIRA PSEUDONANA (BACILLARIOPHYCEAE) AND EMILIANIA HUXLEYI (HAPTOPHYTA)(1).

Increasing anthropogenic carbon dioxide is causing changes to ocean chemistry, which will continue in a predictable manner. Dissolution of additional atmospheric carbon dioxide leads to increased concentrations of dissolved carbon dioxide and bicarbonate and decreased pH in ocean water. The concomitant effects on phytoplankton ecophysiology, leading potentially to changes in community structure, are now a focus of concern. Therefore, we grew the coccolithophore Emiliania huxleyi (Lohmann) W. W. Hay et H. Mohler and the diatom strains Thalassiosira pseudonana (Hust.) Hasle et Heimdal CCMP 1014 and T. pseudonana CCMP 1335 under low light in turbidostat photobioreactors bubbled with air containing 390 ppmv or 750 ppmv CO2 . Increased pCO2 led to increased growth rates in all three strains. In addition, protein levels of RUBISCO increased in the coastal strains of both species, showing a larger capacity for CO2 assimilation at 750 ppmv CO2 . With increased pCO2 , both T. pseudonana strains displayed an increased susceptibility to PSII photoinactivation and, to compensate, an augmented capacity for PSII repair. Consequently, the cost of maintaining PSII function for the diatoms increased at increased pCO2 . In E. huxleyi, PSII photoinactivation and the counter-acting repair, while both intrinsically larger than in T. pseudonana, did not change between the current and high-pCO2 treatments. The content of the photosynthetic electron transport intermediary cytochrome b6/f complex increased significantly in the diatoms under elevated pCO2 , suggesting changes in electron transport function.

The Initiation of Modern “Soft Snowball” and “Hard Snowball” Climates in CCSM3. Part I: The Influences of Solar Luminosity, CO2 Concentration, and the Sea Ice/Snow Albedo Parameterization

Abstract The “Snowball Earth” hypothesis, proposed to explain the Neoproterozoic glacial episodes in the period 750–580 million years ago, suggested that the earth was globally covered by ice/snow during these events. This study addresses the problem of the forcings required for the earth to enter such a state of complete glaciation using the Community Climate System Model, version 3 (CCSM3). All of the simulations performed to address this issue employ the geography and topography of the present-day earth and are employed to explore the combination of factors consisting of total solar luminosity, CO2 concentration, and sea ice/snow albedo parameterization that would be required for such an event to occur. The analyses demonstrate that the critical conditions beyond which runaway ice–albedo feedback will lead to global freezing include 1) a 10%–10.5% reduction in solar radiation with preindustrial greenhouse gas concentrations; 2) a 6% reduction in solar radiation with 17.5 ppmv CO2; or 3) 6% less solar radiation and 286 ppmv CO2 if sea ice albedo is equal to or greater than 0.60 with a snow albedo of 0.78, or if sea ice albedo is 0.58 with a snow albedo equal to or greater than 0.80. These bifurcation points are very sensitive to the sea ice and snow albedo parameterizations. Moreover, “soft Snowball” solutions are found in which tropical open water oceans stably coexist with year-round snow-covered low-latitude continents, implying that tropical continental ice sheets would actually be present. The authors conclude that a “soft Snowball” is entirely plausible, in which the global sea ice fraction may reach as high as 76% and sea ice margins may extend to 10°S(N) latitudes.

The Initiation of Modern “Soft Snowball” and “Hard Snowball” Climates in CCSM3. Part II: Climate Dynamic Feedbacks

Abstract This study investigates the climate dynamic feedbacks during a transition from the present climate to the extremely cold climate of a “Snowball Earth” using the Community Climate System Model, version 3 (CCSM3). With the land–sea distribution fixed to modern, it is found that by reducing solar luminosity and/or carbon dioxide concentration: 1) the amount of atmospheric water vapor and its attendant greenhouse effect decrease with the logarithm of sea ice cover, thereby promoting the expansion of sea ice; 2) over the sea ice, the cloud radiative feedback is positive, thus enhancing sea ice advance; over the ocean, the cloud radiative feedback is first negative and then becomes positive as sea ice enters the tropics; and 3) the strength of the atmospheric Hadley cell and the wind-driven ocean circulation increases significantly in the Southern Hemisphere, inhibiting the expansion of sea ice into the tropics. Meanwhile, the North Atlantic Deep Water cell disappears and the Antarctic Bottom Water cell strengthens and expands to occupy almost the entire Atlantic basin. In the experiment with 6% less solar radiation and 70 ppmv CO2 compared to the control experiment with 100% solar radiation and 355 ppmv CO2 near the ice edge (28°S latitude), the changes of solar radiation, CO2 forcing, water vapor greenhouse effect, longwave cloud forcing at the top of the model, and atmospheric and oceanic energy transport are −22.4, −6.2, −54.4, +6.2, and +16.3 W m−2, respectively. Therefore, the major controlling factors in producing global ice cover are ice albedo feedback (Yang et al., Part I) and water vapor feedback.

Glacial CO<sub>2</sub> cycle as a succession of key physical and biogeochemical processes

Abstract. During glacial-interglacial cycles, atmospheric CO2 concentration varied by about 100 ppmv in amplitude. While testing mechanisms that have led to the low glacial CO2 level could be done in equilibrium model experiments, an ultimate goal is to explain CO2 changes in transient simulations through the complete glacial-interglacial cycle. The computationally efficient Earth System model of intermediate complexity CLIMBER-2 is used to simulate global biogeochemistry over the last glacial cycle (126 kyr). The physical core of the model (atmosphere, ocean, land and ice sheets) is driven by orbital changes and reconstructed radiative forcing from greenhouses gases, ice, and aeolian dust. The carbon cycle model is able to reproduce the main features of the CO2 changes: a 50 ppmv CO2 drop during glacial inception, a minimum concentration at the last glacial maximum 80 ppmv lower than the Holocene value, and an abrupt 60 ppmv CO2 rise during the deglaciation. The model deep ocean δ13C also resembles reconstructions from deep-sea cores. The main drivers of atmospheric CO2 evolve in time: changes in sea surface temperatures and in the volume of bottom water of southern origin control atmospheric CO2 during the glacial inception and deglaciation; changes in carbonate chemistry and marine biology are dominant during the first and second parts of the glacial cycle, respectively. These feedback mechanisms could also significantly impact the ultimate climate response to the anthropogenic perturbation.

Carbon Black Polymer Sensor Array for Incipient Grain Spoilage Monitoring

Sensor arrays are currently used for classifying liquors, perfumes, and the quality of food products by mimicking the mammalian olfactory system. The use of this technology for the monitoring of stored grains and identifying the source of spoilage is a new application, which has the potential for broad economic impact. Carbon black polymer sensor array was fabricated and optimized for monitoring of incipient grain spoilage in a simulated stored grain bin. Various aspects of sensor array (flow rate, relative humidity, temperature, presence of background gas) were evaluated at stored grain conditions. Sensor response at low concentration (2% of vapour pressure) of 1-octanol, 1,4-benzoquinone, acetone was checked in presence of water vapour and 400 ppmv CO2 as background. Slightly variable sensor responses were observed compared to in absence of background gases. The responses were decreased by 6–15% on an average for poly(vinyl acetate), poly(bisphenol-A-carbonate) and poly(vinyl butaryl) sensor while exposed in presence of 50% water vapour. Polymers with high sensitive to background gases (H2O and CO2), such as PVP and P4VP were excluded from the array in this study. Co-polymers with styrene showed low sensitivity drop compared to non-styrene copolymers based on 9 months observation. Therefore, styrene copolymer sensors were best suited to build a stable sensor for the sensor array. Selected polymers for the sensor array retained their sensing properties despite being stored under a wide range of temperatures (−20 to 25°C). The sensor array could recognize pure wheat as well as was able to determine the presence of red flour beetle on it.

Effect of increased pCO2 on phytoplankton–virus interactions

Atmospheric carbon dioxide (CO2) has increased since the pre-industrial period and is predicted to continue to increase throughout the twenty-first century. The ocean is a sink for atmospheric CO2 and increased CO2 concentration will change the carbonate equilibrium of seawater and result in lower carbonate ion concentration and lower pH. This may affect the entire marine biota but in particular calcifying organisms. In this study we investigated the effect of increased CO2 on the virus host interaction of Emiliania huxleyi as a calcifying organism and of Phaeocystis poucheti as a non- calcifying organism. Both algae were grown in laboratory controlled conditions under past (280 ppmv), present (350 ppmv) and future (700 ppmv) CO2 concentrations with and without added virus. Increased CO2 had a negative effect on the growth rate of P. pouchetii, but not of E. huxleyi. No impact was found on viral lysis of P. pouchetii while increased burst size and slightly delayed lysis was observed for E. huxleyi with increased CO2. We conclude that this short time study could not confirm earlier reports and our hypothesis of a negative effect of high CO2 on E. huxleyi growth and E. huxleyi virus production.

A solid molecular basket sorbent for CO2capture from gas streams with low CO2concentration under ambient conditions

In this paper, a solid molecular basket sorbent, 50 wt% PEI/SBA-15, was studied for CO(2) capture from gas streams with low CO(2) concentration under ambient conditions. The sorbent was able to effectively and selectively capture CO(2) from a gas stream containing 1% CO(2) at 75 °C, with a breakthrough and saturation capacity of 63.1 and 66.7 mg g(-1), respectively, and a selectivity of 14 for CO(2)/CO and 185 for CO(2)/Ar. The sorption performance of the sorbent was influenced greatly by the operating temperature. The CO(2)-TPD study showed that the sorbent could be regenerated under mild conditions (50-110 °C) and was stable in the cyclic operations for at least 20 cycles. Furthermore, the possibility for CO(2) capture from air using the PEI/SBA-15 sorbent was studied by FTIR and proved by TPD. A capacity of 22.5 mg g(-1) was attained at 75 °C via a TPD method using a simulated air with 400 ppmv CO(2) in N(2).

Probabilistic Estimates of Transient Climate Sensitivity Subject to Uncertainty in Forcing and Natural Variability

Abstract In this paper, the authors address the impact of uncertainty on estimates of transient climate sensitivity (TCS) of the globally averaged surface temperature, including both uncertainty in past forcing and internal variability in the climate record. This study provides a range of probabilistic estimates of the TCS that combine these two sources of uncertainty for various underlying assumptions about the nature of the uncertainty. The authors also provide estimates of how quickly the uncertainty in the TCS may be expected to diminish in the future as additional observations become available. These estimates are made using a nonlinear Kalman filter coupled to a stochastic, global energy balance model, using the filter and observations to constrain the model parameters. This study verifies that model and filter are able to emulate the evolution of a comprehensive, state-of-the-art atmosphere–ocean general circulation model and to accurately predict the TCS of the model, and then apply the methodology to observed temperature and forcing records of the twentieth century. For uncertainty assumptions best supported by global surface temperature data up to the present time, this paper finds a most likely present-day estimate of the transient climate sensitivity to be 1.6 K, with 90% confidence the response will fall between 1.3 and 2.6 K, and it is estimated that this interval may be 45% smaller by the year 2030. The authors calculate that emissions levels equivalent to forcing of less than 475 ppmv CO2 concentration are needed to ensure that the transient temperature response will not exceed 2 K with 95% confidence. This is an assessment for the short-to-medium term and not a recommendation for long-term stabilization forcing; the equilibrium temperature response to this level of CO2 may be much greater. The flat temperature trend of the last decade has a detectable but small influence on TCS. This study describes how the results vary if different uncertainty assumptions are made and shows they are robust to variations in the initial prior probability assumptions.

The combustion behaviour of forced-draught industrial burners when fired within the EASEE-gas range of Wobbe Index

In Europe, a common business practice for the cross-border exchange of natural gases has been formulated by EASEE-gas. The proposed range of Wobbe Index for this purpose is 48.96–56.92 MJ/Nm 3 (25 °C/0 °C, 1013.25 hPa). However, it is unclear whether the entire range of end-use equipment can accept the suggested range and still function as desired. Research is currently underway tot assess whether this range of gases can be accepted by domestic appliances. To our knowledge, there has been little systematic investigation of the acceptable range of gas quality for large-scale, forced-draught industrial burners. Although natural gas is predominantly methane with lesser amounts of higher hydrocarbons and inerts, the variation in gas composition can have significant effects on burner performance. The vast majority of forced-draught industrial burners features a flow of air independent of the gas composition, therefore the air factor is (inversely) proportional to the Wobbe Index of the gas. In this paper we present the results of experiments on a number of generic large-scale industrial burners for boilers and industrial processes in which the Wobbe Index is varied across the EASEE-gas range. The combustion effects focused mainly on flame stability (burner overheating/blow-off and vibrations) and the pollutant emissions, such as CO, NO x and unburned hydrocarbons over the desired range of turndown ratio. The experimental results showed that, for the burners studied the measured oxygen concentration was the predominant factor governing burner behaviour; between 0.5 and 7% O 2, all burners showed a stable flame while emitting less than 400 ppmv (dry, air free) CO. Outside this O 2 range, the low-NO x boiler burners, being the most sensitive, showed decreasing flame stability and increasing CO production. One burner even exhibited blow-off, causing the safety system to shut down burner operation, an undesirable event in practice. In the burners studied, the NO x emission can increase significantly with increasing Wobbe Index. Even a relatively small increase can cause the burner to exceed the locally enforced NO x limit. The visible flame length increased with increasing Wobbe Index, due to the concomitant decrease in air factor and increase in thermal input. This can lead to a higher thermal load on furnaces, which may be unacceptable in some cases. The experimental results indicate that to widen the acceptable range some form of active control is necessary for the burners for boilers. The merits of using a feed-back control system, using oxygen measurement in the flue gas, compared to a feed-forward control using the Wobbe Index of the fuel gas are discussed. In particular, aspects regarding safety in the event of sensor malfunction are seen to be important when choosing a system. In this case, the Wobbe method seems technically preferable.

Impacts of land cover and climate data selection on understanding terrestrial carbon dynamics and the CO<sub>2</sub> airborne fraction

Abstract. Terrestrial and oceanic carbon cycle processes remove ~55 % of global carbon emissions, with the remaining 45 %, known as the "airborne fraction", accumulating in the atmosphere. The long-term dynamics of the component fluxes contributing to the airborne fraction are challenging to interpret, but important for informing fossil-fuel emission targets and for monitoring the trends of biospheric carbon fluxes. Climate and land-cover forcing data for terrestrial ecosystem models are a largely unexplored source of uncertainty in terms of their contribution to understanding airborne fraction dynamics. Here we present results using a single dynamic global vegetation model forced by an ensemble experiment of climate (CRU, ERA-Interim, NCEP-DOE II), and diagnostic land-cover datasets (GLC2000, GlobCover, MODIS). For the averaging period 1996–2005, forcing uncertainties resulted in a large range of simulated global carbon fluxes, up to 13 % for net primary production (52.4 to 60.2 Pg C a−1) and 19 % for soil respiration (44.2 to 54.8 Pg C a−1). The sensitivity of contemporary global terrestrial carbon fluxes to climate strongly depends on forcing data (1.2–5.9 Pg C K−1 or 0.5 to 2.7 ppmv CO2 K−1), but weakening carbon sinks in sub-tropical regions and strengthening carbon sinks in northern latitudes are found to be robust. The climate and land-cover combination that best correlate to the inferred carbon sink, and with the lowest residuals, is from observational data (CRU) rather than reanalysis climate data and with land-cover categories that have more stringent criteria for forest cover (MODIS). Since 1998, an increasing positive trend in residual error from bottom-up accounting of global sinks and sources (from 0.03 (1989–2005) to 0.23 Pg C a−1 (1998–2005)) suggests that either modeled drought sensitivity of carbon fluxes is too high, or that carbon emissions from net land-cover change is too large.

Neither elevated nor reduced CO 2 affects the photophysiological performance of the marine Antarctic diatom Chaetoceros brevis

Enhanced or reduced pCO 2 (partial pressure of CO 2) may affect the photosynthetic performance of marine microalgae since changes in pCO 2 can influence the activity of carbon concentrating mechanisms, modulate cellular RuBisCO levels or alter carbon uptake efficiency. In the present study we compared the photophysiology of the Antarctic diatom Chaetoceros brevis at two pCO 2 extremes: 750 ppmv (2× ambient) and 190 ppmv (0.5× ambient) CO 2. Cultures were acclimated to four irradiance regimes: two regimes simulating deep or shallow vertical mixing, and two regimes mimicking limiting and saturating stable water column conditions. Then, growth rate, pigmentation, RuBisCO large subunit expression, RuBisCO activity, photosynthesis vs irradiance curves, effective quantum yield of PSII (F v/F m), and POC were measured. The four irradiance regimes induced a suite of photophysiological responses, ranging from low light acclimation to efficient photoprotection. Growth was reduced under the low constant and the deep mixing regime, compared to the shallow mixing and the stable saturating regime. Low stable irradiance resulted in higher light harvesting pigment concentrations, lower RuBisCO activity and a lower light saturation point (E k) compared to the other irradiance regimes. Highest RuBisCO activity as well as P max levels was measured in the shallow mixing regime, which received the highest total daily light dose. Photoprotection by xanthophyll cycling was observed under all irradiance regimes except the low stable irradiance regime, and xanthophyll cycle pool sizes were higher under the dynamic irradiance regimes. For the fluctuating irradiance regimes, F v/F m was hardly affected by previous excess irradiance exposure, suggesting minimal PSII damage. No significant differences between the two pCO 2 levels were found, with respect to growth, pigment content and composition, photosynthesis, photoprotection and RuBisCO activity, for all four irradiance regimes. Thus, within the range tested, pCO 2 does not significantly affect the photophysiological performance of C. brevis.

Long-term implications of alternative light-duty vehicle technologies for global greenhouse gas emissions and primary energy demands

This study assesses global light-duty vehicle (LDV) transport in the upcoming century, and the implications of vehicle technology advancement and fuel-switching on greenhouse gas emissions and primary energy demands. Five different vehicle technology scenarios are analyzed with and without a CO 2 emissions mitigation policy using the GCAM integrated assessment model: a reference internal combustion engine vehicle scenario, an advanced internal combustion engine vehicle scenario, and three alternative fuel vehicle scenarios in which all LDVs are switched to natural gas, electricity, or hydrogen by 2050. The emissions mitigation policy is a global CO 2 emissions price pathway that achieves 450 ppmv CO 2 at the end of the century with reference vehicle technologies. The scenarios demonstrate considerable emissions mitigation potential from LDV technology; with and without emissions pricing, global CO 2 concentrations in 2095 are reduced about 10 ppmv by advanced ICEV technologies and natural gas vehicles, and 25 ppmv by electric or hydrogen vehicles. All technological advances in vehicles are important for reducing the oil demands of LDV transport and their corresponding CO 2 emissions. Among advanced and alternative vehicle technologies, electricity- and hydrogen-powered vehicles are especially valuable for reducing whole-system emissions and total primary energy.

Competitiveness, role, and impact of microalgal biodiesel in the global energy future

This paper examines the competitiveness, role, and impact of microalgal biodiesel in the 21st century using a global energy system model with a detailed technological representation. The major conclusions are the following. First, the competitiveness of microalgal biodiesel decreases as CO 2 stabilization constraints become more stringent. The share of microalgal biodiesel and renewable jet fuel produced from it in total global final energy consumption over the time horizon 2010–2100 is 5.1% in the case without CO 2 constraints compared with 3.9% and 0.7% in the case of CO 2 stabilization at 550 ppmv and 400 ppmv, respectively. This is because production and combustion of microalgal biodiesel release as much CO 2 as is captured from anthropogenic sources and assimilated by microalgae and because CO 2 prices raised by stringent CO 2 stabilization constraints make the economics of microalgal biodiesel unattractive. Second, the competitiveness of microalgal biodiesel is also greatly affected by microalgal production cost and microalgal lipid yield. Under a 400 ppmv CO 2 stabilization constraint, a 50% microalgal production cost decrease leads to increase in total global microalgal biodiesel production over the time horizon by a factor of 6.5, while a 50% microalgal lipid yield increase leads to increase in it by a factor of 4.5. Third, microalgal biodiesel plays an important role in satisfying the energy demand in the transport sector, thereby replacing petroleum products and Fischer–Tropsch synfuels. An increasing proportion of microalgal biodiesel is converted into renewable jet fuel over time to be used as a fuel for aircraft. Fourth, either without CO 2 constraints or under the 550 ppmv CO 2 stabilization constraint, the participation of microalgal biodiesel in the global energy market would have a large impact on the global energy supply and consumption structure. This is not only because of its substitution for other forms of final energy, but also because of the need to satisfy the demand for CO 2 for microalgal production.

Isoprene emissions from plants are mediated by atmospheric CO2 concentrations

The tropical African tree species Acacia nigrescens Oliv. was grown in environmentally controlled growth chambers at three CO2 concentrations representative of the Last Glacial Maximum (∼180 ppmv), the present day (∼380 ppmv), and likely mid-21st century (∼600 ppmv) CO2 concentrations. Isoprene (C5H8) emissions, per unit leaf area, were greater at lower-than-current CO2 levels and lower at higher-than-current CO2 levels relative to controls grown at 380 ppmv CO2. Changes in substrate availability and isoprene synthase (IspS) activity were identified as the mechanisms behind the observed leaf-level emission response. In contrast, canopy-scale emissions remained unaltered between the treatments as changes in leaf-level emissions were offset by changes in biomass and leaf area. Substrate concentration and IspS activity-CO2 responses were used in a biochemical model, coupled to existing isoprene emission algorithms, to model isoprene emissions from A. nigrescens grown for over 2 years at three different CO2 concentrations. The addition of the biochemical model allowed for the use of emission factors measured under present day CO2 concentrations across all three CO2 treatments. When isoprene emissions were measured from A. nigrescens in response to instantaneous changes in CO2 concentration, the biochemical model satisfactorily represented the observed response. Therefore, the effect of changes in atmospheric CO2 concentration on isoprene emission at any timescale can be modelled and predicted.

Combined effects of ocean acidification and solar UV radiation on photosynthesis, growth, pigmentation and calcification of the coralline alga Corallina sessilis (Rhodophyta)

AbstractPrevious studies have shown that increasing atmospheric CO2 concentrations affect calcification in some planktonic and macroalgal calcifiers due to the changed carbonate chemistry of seawater. However, little is known regarding how calcifying algae respond to solar UV radiation (UVR, UVA+UVB, 280–400 nm). UVR may act synergistically, antagonistically or independently with ocean acidification (high CO2/low pH of seawater) to affect their calcification processes. We cultured the articulated coralline alga Corallina sessilis Yendo at 380 ppmv (low) and 1000 ppmv (high) CO2 levels while exposing the alga to solar radiation treatments with or without UVR. The presence of UVR inhibited the growth, photosynthetic O2 evolution and calcification rates by13%, 6% and 3% in the low and by 47%, 20% and 8% in the high CO2 concentrations, respectively, reflecting a synergistic effect of CO2 enrichment with UVR. UVR induced significant decline of pH in the CO2‐enriched cultures. The contents of key photosynthetic pigments, chlorophyll a and phycobiliproteins decreased, while UV‐absorptivity increased under the high pCO2/low pH condition. Nevertheless, UV‐induced inhibition of photosynthesis increased when the ratio of particulate inorganic carbon/particulate organic carbon decreased under the influence of CO2‐acidified seawater, suggesting that the calcified layer played a UV‐protective role. Both UVA and UVB negatively impacted photosynthesis and calcification, but the inhibition caused by UVB was about 2.5–2.6 times that caused by UVA. The results imply that coralline algae suffer from more damage caused by UVB as they calcify less and less with progressing ocean acidification.

Individual and interacting effects of <i>p</i>CO<sub>2</sub> and temperature on <i>Emiliania huxleyi</i> calcification: study of the calcite production, the coccolith morphology and the coccosphere size

Abstract. The impact of ocean acidification and increased water temperature on marine ecosystems, in particular those involving calcifying organisms, has been gradually recognised. We examined the individual and combined effects of increased pCO2 (180 ppmV CO2, 380 ppmV CO2 and 750 ppmV CO2 corresponding to past, present and future CO2 conditions, respectively) and temperature (13 °C and 18 °C) during the exponential growth phase of the coccolithophore E. huxleyi using batch culture experiments. We showed that cellular production rate of Particulate Organic Carbon (POC) increased from the present to the future CO2 treatments at 13 °C. A significant effect of pCO2 and of temperature on calcification was found, manifesting itself in a lower cellular production rate of Particulate Inorganic Carbon (PIC) as well as a lower PIC:POC ratio at future CO2 levels and at 18 °C. Coccosphere-sized particles showed a size reduction with both increasing temperature and CO2 concentration. The influence of the different treatments on coccolith morphology was studied by categorizing SEM coccolith micrographs. The number of well-formed coccoliths decreased with increasing pCO2 while temperature did not have a significant impact on coccolith morphology. No interacting effects of pCO2 and temperature were observed on calcite production, coccolith morphology or on coccosphere size. Finally, our results suggest that ocean acidification might have a larger adverse impact on coccolithophorid calcification than surface water warming.

Holocene carbon cycle dynamics

We are investigating the late Holocene rise in CO2 by performing four experiments with the climate‐carbon‐cycle model CLIMBER2‐LPJ. Apart from the deep sea sediments, important carbon cycle processes considered are carbon uptake or release by the vegetation, carbon uptake by peatlands, and CO2 release due to shallow water sedimentation of CaCO3. Ice core data of atmospheric CO2 between 8 ka BP and preindustrial climate can only be reproduced if CO2 outgassing due to shallow water sedimentation of CaCO3 is considered. In this case the model displays an increase of nearly 20 ppmv CO2 between 8 ka BP and present day. Model configurations that do not contain this forcing show a slight decrease in atmospheric CO2. We can therefore explain the late Holocene rise in CO2 by invoking natural forcing factors only, and anthropogenic forcing is not required to understand preindustrial CO2 dynamics.

Feasible climate targets: The roles of economic growth, coalition development and expectations

The analysis presented here follows the design specified by the Energy Modeling Forum (EMF) Transition Scenarios study on achieving climate stabilization goals with delayed participation by developing countries. We use the MERGE model to evaluate the core EMF scenarios for both the international and the US-specific studies. Our results indicate that a radiative forcing target equivalent to 450 ppmv CO 2-e cannot be met even allowing for full participation and overshoot during the entire 21st century. With delayed participation of developing countries, a target of 550 ppmv CO 2-e is only attainable with pessimistic assumptions about economic growth, and even then only at very high cost. A target of 650 ppmv CO 2-e can be met with delayed participation for a more affordable cost. We highlight sensitivities to the core scenarios in two key dimensions: (i) the effect of the unfolding global financial crisis on the rate of economic growth and (ii) the willingness of initially non-participating countries to agree at the beginning of the next commitment period (i.e. 2012) to join the coalition at a pre-specified date in the future. We find that while the recession does not fundamentally change the crucial role of developing country involvement, advance agreement on their part to future targets could substantially reduce costs for all countries.

A strategy for introducing modern bioenergy into developing Asia to avoid dangerous climate change

This paper explores the cost-effective strategy for introducing modern bioenergy into developing Asia through the 21st century under a 400 ppmv CO 2 stabilization constraint using a global energy model that treats the bioenergy sector in detail. The major conclusions are the following. First, under the 400 ppmv CO 2 stabilization constraint, it is cost-effective to use modern bioenergy largely to generate heat and replace direct coal use in developing Asia in the first half of the century, because direct heat generation from modern biomass is efficient and expected to achieve large CO 2 reduction. As second-generation bioenergy conversion technologies (mainly gasification-based technologies) become mature in the second half of the century, it becomes cost-effective to introduce biomass-derived hydrogen, electricity, and Fischer–Tropsch synfuels and bioethanol produced using these technologies into developing Asia instead of modern biomass-derived heat. All biomass gasification-based conversion technologies are combined with CO 2 capture and storage from 2060, which enables negative CO 2 emissions and makes a substantial contribution to achieving the stringent climate stabilization target. Second, due to its small availability of biomass resources, large-scale import of biofuels and wood pellets is inevitable in developing Asia except southeastern Asia under the CO 2 constraint used here. It is shown that this contributes to diversifying liquid fuel import sources and improving energy security in developing Asia. Third, sensitivity analysis shows that these findings are robust to bioenergy-related cost parameters.

Leaf isoprene emission rate as a function of atmospheric CO2 concentration

AbstractThere is considerable interest in modeling isoprene emissions from terrestrial vegetation, because these emissions exert a principal control over the oxidative capacity of the troposphere. We used a unique field experiment that employs a continuous gradient in CO2 concentration from 240 to 520 ppmv to demonstrate that isoprene emissions in Eucalyptus globulus were enhanced at the lowest CO2 concentration, which was similar to the estimated CO2 concentrations during the last Glacial Maximum, compared with 380 ppmv, the current CO2 concentration. Leaves of Liquidambar styraciflua did not show an increase in isoprene emission at the lowest CO2 concentration. However, isoprene emission rates from both species were lower for trees grown at 520 ppmv CO2 compared with trees grown at 380 ppmv CO2. When grown in environmentally controlled chambers, trees of Populus deltoides and Populus tremuloides exhibited a 30–40% reduction in isoprene emission rate when grown at 800 ppmv CO2, compared with 400 ppmv CO2. P. tremuloides exhibited a 33% reduction when grown at 1200 ppmv CO2, compared with 600 ppmv CO2. We used current models of leaf isoprene emission to demonstrate that significant errors occur if the CO2 inhibition of isoprene is not taken into account. In order to alleviate these errors, we present a new model of isoprene emission that describes its response to changes in atmospheric CO2 concentration. The model logic is based on assumed competition between cytosolic and chloroplastic processes for pyruvate, one of the principal substrates of isoprene biosynthesis.