Long-term Carbon Dioxide Research Articles

Comparative analysis of separation technologies for processing carbon dioxide rich natural gas in ultra-deepwater oil fields

Offshore oil production in ultra-deepwater, with associated natural gas showing high carbon dioxide content and high gas to oil ratio, poses stringent constraints to upstream gas processing technologies. Under such circumstances, oil and gas are processed in Floating Production Storage and Offloading rigs, whose topside facilities are limited in terms of weight and footprint of equipment. Energy demands, supplied by on-site generation, also reduce the availability of space and weight to oil and gas processing. This work evaluates carbon dioxide separation alternatives applicable to this challenging scenario in terms of technical, economic and environmental aspects, considering early enhanced oil recovery as the destination of carbon dioxide. The Brazilian Pre-Salt fields are used as case study due to their unusual high capacity gas processing on the production topside, a consequence of the high gas to oil ratio and carbon dioxide content. The set of studied carbon dioxide separation technologies encompasses membrane permeation, chemical absorption by aqueous methyl diethanolamine with piperazine, physical absorption with propylene carbonate and hybrid variants physical absorption and membranes, membranes and chemical absorption, and two stages membrane, technically assessed by process simulation. Due to the continuous injection of carbon dioxide to enhanced oil recovery, the reservoir content of carbon dioxide increases along production life-cycle, which means that the performances of technologies have to be compared under short-term, mid-term and long-term carbon dioxide content in the associated gas, respectively, of 10%, 30% and 50% (mol), for gas production of 6 million sm3/d. Chemical absorption exhibits the lowest hydrocarbon losses and the lowest specific electric power consumption at the expense of the highest footprint, for all investigated scenarios. The lowest life-cycle costs are for chemical absorption and two stages membrane, respectively $0.57 and $0.46 million/GJ of exported gas, while the largest cost belongs to the hybrid membrane and chemical absorption ($1.78 million/GJ of exported gas). Chemical absorption holds the lowest carbon dioxide emission per ton of injected carbon dioxide (0.15 t/t), seconded by membrane permeation (0.19 t/t). Hybrid membrane and chemical absorption inherits the small footprint of membrane permeation and, despite its highest life-cycle cost, is recommended for flexibility reasons due to increasing carbon dioxide content in the reservoir life-time in cases of ultra-deepwater fields with high gas to oil ratio, high carbon dioxide content and early carbon dioxide enhanced oil recovery. Contrarily to the widely acceptance of membrane permeation as a leading small footprint solution, the overall performance analysis, under the adopted premises, remarkably favors chemical absorption.

Global carbon export from the terrestrial biosphere controlled by erosion

Riverine export of particulate organic carbon (POC) to the ocean affects the atmospheric carbon inventory over a broad range of timescales. On geological timescales, the balance between sequestration of POC from the terrestrial biosphere and oxidation of rock-derived (petrogenic) organic carbon sets the magnitude of the atmospheric carbon and oxygen reservoirs. Over shorter timescales, variations in the rate of exchange between carbon reservoirs, such as soils and marine sediments, also modulate atmospheric carbon dioxide levels. The respective fluxes of biospheric and petrogenic organic carbon are poorly constrained, however, and mechanisms controlling POC export have remained elusive, limiting our ability to predict POC fluxes quantitatively as a result of climatic or tectonic changes. Here we estimate biospheric and petrogenic POC fluxes for a suite of river systems representative of the natural variability in catchment properties. We show that export yields of both biospheric and petrogenic POC are positively related to the yield of suspended sediment, revealing that POC export is mostly controlled by physical erosion. Using a global compilation of gauged suspended sediment flux, we derive separate estimates of global biospheric and petrogenic POC fluxes of 157(+74)(-50) and 43(+61)(-25) megatonnes of carbon per year, respectively. We find that biospheric POC export is primarily controlled by the capacity of rivers to mobilize and transport POC, and is largely insensitive to the magnitude of terrestrial primary production. Globally, physical erosion rates affect the rate of biospheric POC burial in marine sediments more strongly than carbon sequestration through silicate weathering. We conclude that burial of biospheric POC in marine sediments becomes the dominant long-term atmospheric carbon dioxide sink under enhanced physical erosion.

Using the experience curve model to project carbon dioxide emissions through 2040

Projections of long-term carbon dioxide (CO2) emissions in the literature vary over a wide range depending on both socio-economic development and mitigation policy. Therefore, any attempt to improve the accuracy of such projections is important. We present a simple aggregate model to project the future carbon intensity of economic output, which is then used to forecast energy-related CO2 emissions through 2040 for seven countries and three regions of the world. Our projection results are compared to those from the International Energy Outlook 2013 report. We find that our projections are significantly higher than those reported in the International Energy Outlook 2013 report.

Developing long-term strategies to reduce energy use and CO2 emissions—analysis of three mitigation scenarios for iron and steel production in China

We perform a scenario analysis of three strategies for long-term energy savings and carbon dioxide (CO2) emission reductions in iron and steel production in China, using a linear optimization modeling framework industry sector energy efficiency modeling (ISEEM). The modeling includes annual projections for one base scenario representing business-as-usual (BAU) and three additional scenarios representing different strategies to reduce annual energy use and CO2 emissions from 2010 to 2050. Specifically, the three scenarios for cost-optimization modeling include changing the production share (PS), predefining emission reduction (ER) target, and stipulating carbon emission pricing (CP), respectively. While the three strategies are projected to result in similar annual energy savings by approximately 15 % compared to that of the BAU scenario in year 2050, the carbon emission pricing strategy brings about the highest annual energy savings in the medium term (e.g., 2025). In addition, adopting carbon emission pricing strategy will result in the highest emission reduction from BAU with much higher costs, i.e., by 20 % in 2025 and 41 % in 2050, while adopting either PS or ER strategies will result in a moderate level of emission reduction from BAU, i.e., by approximately 4 % in 2025 and 14 % in 2050. The analysis of China’s national strategies to reduce energy use and emissions provides important implications for global mitigation strategies.

A two-fold increase of carbon cycle sensitivity to tropical temperature variations

Earth system models project that the tropical land carbon sink will decrease in size in response to an increase in warming and drought during this century, probably causing a positive climate feedback. But available data are too limited at present to test the predicted changes in the tropical carbon balance in response to climate change. Long-term atmospheric carbon dioxide data provide a global record that integrates the interannual variability of the global carbon balance. Multiple lines of evidence demonstrate that most of this variability originates in the terrestrial biosphere. In particular, the year-to-year variations in the atmospheric carbon dioxide growth rate (CGR) are thought to be the result of fluctuations in the carbon fluxes of tropical land areas. Recently, the response of CGR to tropical climate interannual variability was used to put a constraint on the sensitivity of tropical land carbon to climate change. Here we use the long-term CGR record from Mauna Loa and the South Pole to show that the sensitivity of CGR to tropical temperature interannual variability has increased by a factor of 1.9 ± 0.3 in the past five decades. We find that this sensitivity was greater when tropical land regions experienced drier conditions. This suggests that the sensitivity of CGR to interannual temperature variations is regulated by moisture conditions, even though the direct correlation between CGR and tropical precipitation is weak. We also find that present terrestrial carbon cycle models do not capture the observed enhancement in CGR sensitivity in the past five decades. More realistic model predictions of future carbon cycle and climate feedbacks require a better understanding of the processes driving the response of tropical ecosystems to drought and warming.

Long-term surface carbon dioxide flux monitoring at the Ketzin carbon dioxide storage test site

Subsurface geologic storage of carbon dioxide calls for sophisticated monitoring tools with respect to long-term safety and environmental impact issues. Despite extensive research, many factors governing the fate of injected carbon dioxide (CO2) remain unclear. To identify possible risks through leakage of the CO2 storage reservoir, a program for monitoring of the CO2 flux at the surface was started at the Ketzin test site, which allows to distinguish between natural temporal and spatial flux variations and a potential leakage. To gain adequate long-term baseline data on the local background CO2 flux variations, CO2 soil gas flux, soil moisture, and temperature measurements were conducted once a month during a 6-yr period. Furthermore, soil samples were analyzed for their organic carbon and total nitrogen contents. The mean flux of all sampling sites before the CO2 injection (2005–2007) was 2.8 mol m2 s1 (ranging from 2.4 to 3.5), with a Q10 factor of 2.4, and in the years after commencing injection (2009–2010), 2.4 mol m2 s1 (ranging from 2.2 to 2.5), with the same Q10 factor. The CO2 flux rate is mainly controlled by the soil temperature. A significant influence of diurnal temperature variation and soil moisture was not detected. The spatial variability of the CO2 flux among the 20 sampling locations ranges from 1.0 to 4.5 mol m2 s1, depending on the organic carbon and total nitrogen content of the soil. Through comparison with the long-term measurements, unusual high CO2 fluxes can theoretically be distinguished from natural variations.

Planetary boundaries: Tangible targets are critical

Setting a limit on long-term atmospheric carbon dioxide concentrations merely distracts from the much more immediate challenge of limiting warming to 2 °C.

A Life Cycle Inventory of Structural Engineering Design Strategies for Greenhouse Gas Reduction

The paper presents the results of a life cycle inventory (LCI) for various structural engineering design strategies. The strategies focus on alternative design approaches the structural engineer can implement to minimize a building’s contribution to global climate change. The approaches investigated include material selection, recycling or reusing a structure, maximizing material efficiency, thermal mass effects, and future adaptability. Analysis including operational energy use shows thermal mass effects offer the greatest potential for reducing carbon dioxide emissions. Excluding operational energy use from the LCI shows that material selection is the most favorable design strategy. Consequently, the structural engineer has a significant role in mitigating both short-term and long-term carbon dioxide emissions of the built environment.

Predictors of Outcome After Exacerbation of Chronic Obstructive Pulmonary Disease

The outcome after hospitalization for an exacerbation of chronic obstructive pulmonary disease (COPD) is unfavorable and uncertainty exists about factors predicting short and long-term prognosis. To identify clinical predictors of length of hospital stay (LOS) and three-year mortality after COPD exacerbations requiring hospitalization. Retrospective analysis of prospectively collected data. All consecutive patients hospitalized with COPD exacerbation were enrolled. Disease severity was estimated by FEV(1,) body mass index (BMI), Medical Research Council (MRC) chronic dyspnoea scale, previous hospitalizations, need for long-term oxygen treatment (LTOT), arterial oxygen and carbon dioxide partial pressures (PaO(2) and PaCO(2)), pH and respiratory rate. Outcome was assessed by LOS and three-year mortality. Out of 81 patients enrolled, three-year mortality data were available for 61. LOS was related to BMI, MRC scale and respiratory rate. Three-year mortality was related to FEV(1), BMI, MRC scale, LTOT, and PaCO(2). Multiple logistic regression analysis demonstrated that MRC scale was the only independent determinant of LOS, [p = 0.001, odds ratio (OR) 7.67 (95% CI 2.50-23.41)], whereas MRC scale and BMI predicted three-year mortality, [p = 0.001, OR 8.28 (95% CI 2.25-30.47) and p = 0.006, OR 6.91 (95% CI 1.74-27.48), respectively]. Cox regression analysis demonstrated identical results. Using receiver-operator-optimized thresholds for these variables (MRC > 2 and BMI < 25 kg/m(2)), we propose a prediction model that accurately determines three-year mortality risk. In this study, MRC scale and BMI predicted outcome after COPD hospitalization. Pending further validation, this predictive model may contribute to identify patients with poor outcome even when spirometric data are unavailable.

The role of terrestrial plants in limiting atmospheric CO2 decline over the past 24 million years

Environmental conditions during the past 24 million years are thought to have been favourable for enhanced rates of atmospheric carbon dioxide drawdown by silicate chemical weathering. Proxy records indicate, however, that the Earth's atmospheric carbon dioxide concentrations did not fall below about 200-250 parts per million during this period. The stabilization of atmospheric carbon dioxide concentrations near this minimum value suggests that strong negative feedback mechanisms inhibited further drawdown of atmospheric carbon dioxide by high rates of global silicate rock weathering. Here we investigate one possible negative feedback mechanism, occurring under relatively low carbon dioxide concentrations and in warm climates, that is related to terrestrial plant productivity and its role in the decomposition of silicate minerals. We use simulations of terrestrial and geochemical carbon cycles and available experimental evidence to show that vegetation activity in upland regions of active orogens was severely limited by near-starvation of carbon dioxide in combination with global warmth over this period. These conditions diminished biotic-driven silicate rock weathering and thereby attenuated an important long-term carbon dioxide sink. Although our modelling results are semi-quantitative and do not capture the full range of biogeochemical feedbacks that could influence the climate, our analysis indicates that the dynamic equilibrium between plants, climate and the geosphere probably buffered the minimum atmospheric carbon dioxide concentrations over the past 24 million years.

Semi-continuous Cultivation of Haematococcus pluvialis for Commercial Production

The objectives of the present study on the growth of Haematococcus pluvialis were to indicate the effects of a long-term semi-continuous cultivation, sterilization, carbon dioxide, and different culture media by using artesian well water. This investigation was an enterprise in order to commercialize the production economically. When the effect of CO(2) was investigated in basal culture medium, the influence of sterilization was also researched in Rudic's culture medium in vertical panel-type photobioreactors for 31 days of semi-continuous cultivation. The maximum cell concentration of 10.55 x 10(5) cells ml(-1), which corresponds to the growth rate of 0.271 day(-1) with the areal productivity of 3.531 g m(-2) day(-1), was found in non-sterilized RM medium on the 24th day of the third run of semi-continuous cultivation at a renewal rate of 50% in a vertical panel-type photobioreactor.

Understanding Long-Term Energy Use and Carbon Dioxide Emissions in the USA

We compile a database of energy uses, energy sources, and carbon dioxide emissions for the USA for the period 1850-2002. We use a model to extrapolate the missing observations on energy use by sector. Overall emission intensity rose between 1850 and 1917, and fell between 1917 and 2002. The leading cause for the rise in emission intensity was the switch from wood to coal, but population growth, economic growth, and electrification contributed as well. After 1917, population growth, economic growth and electrification pushed emissions up further, and there was no net shift from fossil to non-fossil energy sources. From 1850 to 2002, emissions were reduced by technological and behavioural change (particularly in transport, manufacturing and households), structural change in the economy, and a shift from coal to oil and gas. These trends are stronger than electrification, explaining the fall in emissions relative to GDP. (This abstract was borrowed from another version of this item.)

Surface energy-balance closure over rangeland grass using the eddy covariance method and surface renewal analysis

The performance of surface renewal (SR) analysis for estimating sensible heat ( H), latent heat ( L w E) and carbon dioxide ( L p F p) flux, and the closure of the surface energy-balance equation were analyzed in an experiment at a rangeland grass site in the foothills of the Sierra Nevada Mountains (Ione, CA, USA). Both the L w E and H fluxes in late fall, winter, and early spring (the wet period) were relevant in the energy-balance, but from early spring to fall (dry period), most of the available net surface-energy contributed to sensible heat flux. The site is influenced by regional advection and some degree of dissimilarity between temperature and the other two scalars was observed. To our knowledge, this is the first paper evaluating the capability of SR analysis to (1) close the energy-balance on a long-term experiment and (2) estimate carbon dioxide flux. The SR analysis performance was evaluated in terms of the correlation with fluxes from the eddy covariance (EC) method and its capability to close the surface energy-balance. Regardless of the weather conditions, the EC closure underestimated the available energy by about 10%, but the performance was slightly better during dry rather than humid conditions. In contrast, the SR closure was always good and did not favor wetness conditions. Despite the lack of similarity, the energy partitioning provided by SR analysis was reliable for all three scalars. SR analysis provided reliable Bowen ratio estimates. Under stable atmospheric conditions fluxes were too small to evaluate either method.

Elevated CO2 concentration affects leaf photosynthesis-nitrogen relationships in Pinus taeda over nine years in FACE

To investigate whether long-term elevated carbon dioxide concentration ([CO(2)]) causes declines in photosynthetic enhancement and leaf nitrogen (N) owing to limited soil fertility, we measured photosynthesis, carboxylation capacity and area-based leaf nitrogen concentration (N(a)) in Pinus taeda L. growing in a long-term free-air CO(2) enrichment (FACE) facility at an N-limited site. We also determined how maximum rates of carboxylation (V(cmax)) and electron transport (J(max)) varied with N(a) under elevated [CO(2)]. In trees exposed to elevated [CO(2)] for 5 to 9 years, the slope of the relationship between leaf photosynthetic capacity (A(net-Ca)) and N(a) was significantly reduced by 37% in 1-year-old needles, whereas it was unaffected in current-year needles. The slope of the relationships of both V(cmax) and J(max) with N(a) decreased in 1-year-old needles after up to 9 years of growth in elevated [CO(2)], which was accompanied by a 15% reduction in N allocation to the carboxylating enzyme. Nitrogen fertilization (110 kg N ha(-1)) in the ninth year of exposure to elevated [CO(2)] restored the slopes of the relationships of V(cmax) and J(max) with N(a) to those of control trees (i.e., in ambient [CO(2)]). The J(max):V(cmax) ratio was unaffected by either [CO(2)] or N fertilization. Changes in the apparent allocation of N to photosynthetic components may be an important adjustment in pines exposed to elevated [CO(2)] on low-fertility sites. We conclude that fundamental relationships between photosynthesis or its component processes with N(a) may be altered in aging pine needles after more than 5 years of exposure to elevated atmospheric [CO(2)].

Towards a low-carbon future in China's building sector—A review of energy and climate models forecast

This article investigates the potentials of energy saving and greenhouse gases emission mitigation offered by implementation of building energy efficiency policies in China. An overview of existing literature regarding long-term energy-demand and carbon dioxide (CO 2) emission forecast scenarios is presented. Energy consumption in buildings could be reduced by 100–300 million tons of oil equivalent (mtoe) in 2030 compared with the business-as-usual (BAU) scenario, which means that 600–700 million metric tons of CO 2 emissions could be saved by implementing appropriate energy policies within an adapted institutional framework. The main energy-saving potentials in buildings can be achieved by improving a building's thermal performance and district heating system efficiency. The analyses also reveal that the energy interchange systems are effective especially in the early stage of penetration. Our analysis on the reviewed models suggests that more ambitious efficiency improvement policies in both supply- and demand-side as well as the carbon price should be taken into account in the policy scenarios to address drastic reduction of CO 2 emission in the building sector to ensure climate security over the next decades.

Forest patch modeling: using high performance computing to simulate aboveground interactions among individual trees

Functional-structural plant models (FSPMs) typically integrate suites of detailed physiological and phenological processes to simulate the growth of individual plants. Recent advances in high-performance computing have allowed FSPMs to be extended to patches of interacting trees. Here, we describe a parallel modelling strategy to run simultaneous individual tree models across an 8 × 8 patch of trees. The 64 'core' trees are surrounded by multiple rings of neighbour trees to remove edge effects. A sensitivity analysis of the patch model demonstrates that computational factors such as the number of independently simulated trees (9 v. 36) or number of neighbour rings (3 v. 6) did not significantly influence model estimates of tree volume growth. Updated submodels for phenology and redistribution of overwinter carbohydrate storage allow the simulation to be more responsive to above ground competition among trees in a patch over multiple growing seasons. An 8-year patch-scale simulation of aspen clones 216 and 259 was conducted using high-resolution environmental data from the Aspen FACE Experiment, a long-term free-air carbon dioxide enrichment (FACE) study. Tree heights and volumes were comparable to 8-year growth measurements made at the Aspen FACE site.

A note on the top-down and bottom-up gradient functions over a forested site

The dimensionless bottom-up and top-down gradient functions in the convective boundary layer (CBL) are evaluated utilizing long-term well-calibrated carbon dioxide mixing ratio and flux measurements from multiple levels of a 447-m tall tower over a forested area in northern Wisconsin, USA. The estimated bottom- up and top-down functions are qualitatively consistent with those from large-eddy simulation (LES) results and theoretical expectations. Newly fitted gradient functions are proposed based on observations for this forested site. The integrated bottom-up function over the lowest 4% of the CBL depth estimated from the tower data is about five times larger than that from LES results for a 'with-canopy' case, and is smaller than that from LES results for a 'no-canopy' case by a factor of 0.7. We discuss the uncertainty in the evaluated gradient functions due to stability, wind direction, and uncertainty in the entrainment flux and show that while all of these have a significant impact on the gradient functions, none can explain the differences between the mod- elled and observed functions. The effects of canopy features and atmospheric stability may need to be considered in the gradient function relations.

Performance Evaluation of the Indoor Air Quality (IAQ) Assessment

Maintaining acceptable indoor air quality (IAQ) has become a public issue, policymakers have had developed strategies to address the performance of it. Pollutant concentrations measured during the occupied period of a space is a key parameter to determine IAQ. Apart from a number of sampling schemes concerning the measurement time of the average pollutant level, an 8-hour continuous measurement has been widely adopted in local IAQ assessments, with a balance of accuracy and measurement effort. It is believed that the longer the measurement time, the higher the accuracy and confidence level of the measurement can be achieved. However, the probable errors of the measurement regarding the measurement periods were not addressed clearly in those assessments. This study, taking a long-term carbon dioxide (CO2 ) measurement in a typical open-plan office building as a reference, develops a database to examine the probable errors of different sampling schemes. The results show that the probable errors of measureme...

Understanding Long-Term Energy Use and Carbon Dioxide Emissions in the USA

We compile a database of energy uses, energy sources, and carbon dioxide emissions for the USA for the period 1850-2002. We use a model to extrapolate the missing observations on energy use by sector. Overall emission intensity rose between 1850 and 1917, and fell between 1917 and 2002. The leading cause for the rise in emission intensity was the switch from wood to coal, but population growth, economic growth, and electrification contributed as well. After 1917, population growth, economic growth and electrification pushed emissions up further, and there was no net shift from fossil to non-fossil energy sources. From 1850 to 2002, emissions were reduced by technological and behavioural change (particularly in transport, manufacturing and households), structural change in the economy, and a shift from coal to oil and gas. These trends are stronger than electrification, explaining the fall in emissions relative to GDP.

Measurement of long-term average carbon dioxide concentrations using passive diffusion sampling

A diffusive sampling device is proposed for long-term determination of average airborne concentration of CO2 in urban and industrial areas, as well as in indoor sites. A hydro-alcoholic barium hydroxide solution is employed as a CO2 reagent sink. The analytical method is based on the determination of the solute barium hydroxide remained after the acid–base reaction, in which its insoluble carbonate salt precipitates. Indoor laboratory experiments show that this technique exhibits a good precision and reproducibility. A 6-week internal consistency test demonstrates that this device has a constant uptake rate, allowing us to propose it as a suitable and inexpensive tool in performing the monitoring of urban and industrial sites over long periods and in indoor–outdoor studies, like those involved in the sick-building syndrome problem.