Causal feedbacks in climate change
Nes, E.H. van; Scheffer, M. ; Brovkin, V. ; Lenton, T.M. ; Ye, H. ; Deyle, E. ; Sugihara, G. - \ 2015
Nature Climate Change 5 (2015). - ISSN 1758-678X - p. 445 - 448.
carbon-cycle - ice core - antarctic temperature - last deglaciation - atmospheric co2 - global climate - dioxide - record - model - lag
The statistical association between temperature and greenhouse gases over glacial cycles is well documented1, but causality behind this correlation remains difficult to extract directly from the data. A time lag of CO2 behind Antarctic temperature—originally thought to hint at a driving role for temperature2, 3—is absent4, 5 at the last deglaciation, but recently confirmed at the last ice age inception6 and the end of the earlier termination II (ref. 7). We show that such variable time lags are typical for complex nonlinear systems such as the climate, prohibiting straightforward use of correlation lags to infer causation. However, an insight from dynamical systems theory8 now allows us to circumvent the classical challenges of unravelling causation from multivariate time series. We build on this insight to demonstrate directly from ice-core data that, over glacial–interglacial timescales, climate dynamics are largely driven by internal Earth system mechanisms, including a marked positive feedback effect from temperature variability on greenhouse-gas concentrations.
Terrestrial cycling of (CO2)-C-13 by photosynthesis, respiration, and biomass burning in SiBCASA
Velde, I.R. van der; Miller, J.B. ; Schaefer, K. ; Werf, G.R. van der; Krol, M.C. ; Peters, W. - \ 2014
Biogeosciences 11 (2014). - ISSN 1726-4170 - p. 6553 - 6571.
carbon-isotope discrimination - surface parameterization sib2 - ecosystem respiration - interannual variability - biophysical parameters - stomatal conductance - co2 assimilation - atmospheric gcms - global fields - dioxide
We present an enhanced version of the SiBCASA terrestrial biosphere model that is extended with (a) biomass burning emissions from the SiBCASA carbon pools using remotely sensed burned area from the Global Fire Emissions Database (GFED), (b) an isotopic discrimination scheme that calculates 13C signatures of photosynthesis and autotrophic respiration, and (c) a separate set of 13C pools to carry isotope ratios into heterotrophic respiration. We quantify in this study the terrestrial exchange of CO2 and 13CO2 as a function of environmental changes in humidity and biomass burning. The implementation of biomass burning yields similar fluxes as CASA-GFED both in magnitude and spatial patterns. The implementation of isotope exchange gives a global mean discrimination value of 15.2‰, ranges between 4 and 20‰ depending on the photosynthetic pathway in the plant, and compares favorably (annually and seasonally) with other published values. Similarly, the isotopic disequilibrium is similar to other studies that include a small effect of biomass burning as it shortens the turnover of carbon. In comparison to measurements, a newly modified starch/sugar storage pool propagates the isotopic discrimination anomalies to respiration much better. In addition, the amplitude of the drought response by SiBCASA is lower than suggested by the measured isotope ratios. We show that a slight increase in the stomatal closure for large vapor pressure deficit would amplify the respired isotope ratio variability. Our study highlights the importance of isotope ratio observations of 13C to assess and improve biochemical models like SiBCASA, especially with regard to the allocation and turnover of carbon and the responses to drought.
Persistent growth of CO2 emissions and implications for reaching climate targets
Friedlingstein, P. ; Andrew, R.M. ; Rogelj, J. ; Schaeffer, M. ; Vuuren, D.P. van - \ 2014
Nature Geoscience 7 (2014). - ISSN 1752-0894 - p. 709 - 715.
cumulative carbon emissions - dioxide - temperature - variability - mitigation - scenarios - storage - system - policy - 2-degrees-c
Efforts to limit climate change below a given temperature level require that global emissions of CO2 cumulated over time remain below a limited quota. This quota varies depending on the temperature level, the desired probability of staying below this level and the contributions of other gases. In spite of this restriction, global emissions of CO2 from fossil fuel combustion and cement production have continued to grow by 2.5% per year on average over the past decade. Two thirds of the CO2 emission quota consistent with a 2 °C temperature limit has already been used, and the total quota will likely be exhausted in a further 30 years at the 2014 emissions rates. We show that CO2 emissions track the high end of the latest generation of emissions scenarios, due to lower than anticipated carbon intensity improvements of emerging economies and higher global gross domestic product growth. In the absence of more stringent mitigation, these trends are set to continue and further reduce the remaining quota until the onset of a potential new climate agreement in 2020. Breaking current emission trends in the short term is key to retaining credible climate targets within a rapidly diminishing emission quota.
Reduced carbon uptake during the 2010 Northern Hemisphere summer from GOSAT
Guerlet, S. ; Basu, S. ; Butz, A. ; Krol, M.C. ; Hahne, P. ; Houweling, S. ; Hasekamp, O.P. ; Aben, I. - \ 2013
Geophysical Research Letters 40 (2013)10. - ISSN 0094-8276 - p. 2378 - 2383.
column observing network - calibration - transport - dioxide - europe
Column-averaged dry air mole fractions of carbon dioxide (XCO2) measured by the Greenhouse Gases Observing Satellite (GOSAT) reveal significant interannual variation (IAV) of CO(2)uptake during the Northern Hemisphere summer between 2009 and 2010. The XCO(2)drawdown in 2010 is shallower than in 2009 by 2.4ppm and 3.0ppm over North America and Eurasia, respectively. Reduced carbon uptake in the summer of 2010 is most likely due to the heat wave in Eurasia driving biospheric fluxes and fire emissions. A joint inversion of GOSAT and surface data estimates an integrated biospheric and fire emission anomaly in April-September of 0.89 0.20 PgC over Eurasia. In contrast, inversions of surface measurements alone fail to replicate the observed XCO(2)IAV and underestimate emission IAV over Eurasia. This shows the value of GOSAT XCO(2)in constraining the response of land-atmosphere exchange of CO2 to climate events.
|CO2 capture by biomimetic adsorption: enzyme mediated co2 absorption for post-combustion carbon sequestration and storage process
Russo, M.E. ; Olivieri, G. ; Salatino, P. ; Marzocchella, A. - \ 2013
Environmental Engineering and Management Journal (EEMJ) 12 (2013)8. - ISSN 1582-9596 - p. 1595 - 1601.
butanol production - inhibitor removal - mass-transfer - anhydrase ii - hydration - kinetics - dioxide - reactor - microreactor - diffusivity
The huge emission of greenhouse gases from fossil-fuelled power plants is emphasizing the need for efficient Carbon Capture and Storage (CCS) technologies. The biomimetic CO2 absorption in aqueous solutions has been recently investigated as a promising innovative alternative for post-combustion CCS. The carbonic anhydrase (CA) - a broad group of ubiquitous enzymes - may catalyse the CO2 hydration reaction and then to promote CO2 absorption rate into aqueous solutions. Nevertheless the research on this issue is quite active, the reliable designing of absorption units still requires more details. The present study proposes the design of a random packing absorption column operated with alkaline solvents supplied with CA. The height of the packed bed to fulfil the 80% of CO2 abatement from a flue gas stream was as large as 15-20 m. A comprehensive discussion of effects of operating conditions and of CA features on unit performance is reported.
Carbon Nanofiber-Supported K2CO3 as an Efficient Low-Temperature Regenerable CO2 Sorbent for Post-Combustion Capture
Meis, N.N.A.H. ; Frey, A.M. ; Bitter, J.H. ; Jong, K.P. de - \ 2013
Industrial & Engineering Chemistry Research 52 (2013)36. - ISSN 0888-5885 - p. 12812 - 12818.
metal-organic frameworks - fixed-bed operations - solid base catalysts - flue-gas - dioxide - adsorption - recovery - adsorbents - sorption - k2co3-on-carbon
This study focuses on regenerable sorbents for post-combustion CO2 capture at low temperature (373 K). K2CO3 loaded on three different supports, carbon nanofibers (CNF), alumina (¿-Al2O3), and activated carbon (AC), was investigated. K2CO3–CNF revealed excellent properties as CO2 sorbent, displaying capacities of 1.2–1.6 mmol g–1 and fast desorption kinetics at low temperatures (423 K). This temperature was too low to completely regenerate K2CO3–Al2O3 and K2CO3–AC, and consequently, these sorbents lost 8% and 50%, respectively, of their capacity after the first absorption–desorption cycle. K2CO3–CNF could be regenerated to restore 80% of its capacity with a low energy input, estimated at 2–3 GJ/ton CO2, which is competitive to currently used amines.
Carbon and nitrogen mass balance during flue gas treatment with Dunaliella salina
Harter, T. ; Bossier, P. ; Verreth, J.A.J. ; Bodé, S. ; Ha, D. van der; Debeer, A.E. ; Boon, N. ; Boeckx, P. ; Vyverman, W. ; Nevejan, N. - \ 2013
Journal of Applied Phycology 25 (2013)2. - ISSN 0921-8971 - p. 359 - 368.
life-cycle assessment - nitric-oxide - tubular photobioreactor - denitrifying bacteria - biodiesel production - organic-carbon - biological co2 - green-algae - microalgae - dioxide
The biotreatment of flue gases with algae cultures is a promising option to sequestrate CO2, yet the emission of other greenhouse gases (GHG) from the cultures can hamper their environmental benefit. Quantitative data on the sequestration potential for CO2 and NO x in relation to the direct production of CH4 and N2O are urgently required. The present study assessed the flows of carbon (C) and nitrogen (N) through cultures of the green alga Dunaliella salina, supplied with biodiesel flue gas, by means of mass balancing. D. salina was grown in artificially lighted, field- (42-L bubble column reactor) and laboratory-scale cultures (23 °C, pH 7.5). In the bubble column reactor, algae grew with an average specific growth rate of 0.237 day-1 under flue gas supplementation (6.3 % (v/v) CO2, 1.2 ppmv NO x ), and CO2 was retained to 39 % in the system. The specific sequestration rate for CO2 was low, with 0.13 g CO2 L-1 day-1. Cultures emitted up to 13.03 µg CH4 L-1 day-1 and 4261 µg N2O L-1 day-1. The moderate retention of NO x -N was outweighed by emissions of N2O-N, and total N in the system decreased by 15.48 % during the 9-day trial. Results suggest that GHG production was mainly the outcome of anaerobic microbial processes and their emission was lower in pre-sterilized cultures. Under the tested conditions, up to six times more CO2 equivalents were emitted during flue gas treatment. Therefore, the direct GHG emissions of algae culture systems, intended for flue gas treatment (i.e. open ponds) need to be reviewed critically.
The European land and inland water CO2, CO, CH4 and N2O balance between 2001 and 2005
Luyssaert, S. ; Abril, G. ; Andres, R. ; Bastviken, D. ; Bellassen, V. ; Bergamaschi, P. ; Bousquet, P. ; Chevallier, F. ; Ciais, P. ; Corazza, M. ; Dechow, R. ; Erb, K.H. ; Etiope, G. ; Fortems-Cheiney, A. ; Grassi, G. ; Hartmann, J. ; Jung, M. ; Lathiere, J. ; Lohila, A. ; Mayorga, E. ; Moosdorf, N. ; Njakou, D.S. ; Otto, J. ; Papale, D. ; Peters, W. ; Peylin, P. ; Raymond, P. ; Rodenbeck, C. ; Saarnio, S. ; Schulze, E.D. ; Szopa, S. ; Thompson, R. ; Verkerk, P.J. ; Vuichard, N. ; Wang, R. ; Wattenbach, M. ; Zaehle, S. - \ 2012
Biogeosciences 9 (2012)8. - ISSN 1726-4170 - p. 3357 - 3380.
north-atlantic oscillation - net ecosystem exchange - organic-carbon changes - atmospheric co2 - climate-change - nitrous-oxide - terrestrial biosphere - dioxide - fluxes - emissions
Globally, terrestrial ecosystems have absorbed about 30% of anthropogenic greenhouse gas emissions over the period 2000-2007 and inter-hemispheric gradients indicate that a significant fraction of terrestrial carbon sequestration must be north of the Equator. We present a compilation of the CO2, CO, CH4 and N2O balances of Europe following a dual constraint approach in which (1) a land-based balance derived mainly from ecosystem carbon inventories and (2) a land-based balance derived from flux measurements are compared to (3) the atmospheric data-based balance derived from inversions constrained by measurements of atmospheric GHG (greenhouse gas) concentrations. Good agreement between the GHG balances based on fluxes (1294 +/- 545 Tg C in CO2-eq yr(-1)), inventories (1299 +/- 200 Tg C in CO2-eq yr(-1)) and inversions (1210 +/- 405 Tg C in CO2-eq yr(-1)) increases our confidence that the processes underlying the European GHG budget are well understood and reasonably sampled. However, the uncertainty remains large and largely lacks formal estimates. Given that European net land to atmosphere exchanges are determined by a few dominant fluxes, the uncertainty of these key components needs to be formally estimated before efforts could be made to reduce the overall uncertainty. The net land-to-atmosphere flux is a net source for CO2, CO, CH4 and N2O, because the anthropogenic emissions by far exceed the biogenic sink strength. The dual-constraint approach confirmed that the European biogenic sink removes as much as 205 +/- 72 Tg C yr(-1) from fossil fuel burning from the atmosphere. However, This C is being sequestered in both terrestrial and inland aquatic ecosystems. If the C-cost for ecosystem management is taken into account, the net uptake of ecosystems is estimated to decrease by 45% but still indicates substantial C-sequestration. However, when the balance is extended from CO2 towards the main GHGs, C-uptake by terrestrial and aquatic ecosystems is offset by emissions of non-CO2 GHGs. As such, the European ecosystems are unlikely to contribute to mitigating the effects of climate change.
Forest inventories for carbon change assessments
Mohren, G.M.J. ; Hasenauer, H. ; Köhl, M. ; Nabuurs, G.J. - \ 2012
Current Opinion in Environmental Sustainability 4 (2012)6. - ISSN 1877-3435 - p. 686 - 695.
tropical forests - european forests - climate-change - root biomass - ecosystems - dioxide - sequestration - harmonization - mitigation - management
We give a general overview of forest inventory developments and their potential to estimate forest carbon budgets and GHG emissions. Forest inventories mostly focus on timber resources, but can be extended to cover other forest characteristics, such as forest biomass. From forest biomass, ecosystem carbon content can be derived. Forest inventory comprises of ground-based and space-based techniques, and the combination of the two provides a versatile scheme for carbon storage assessment. Large uncertainties remain in the estimation of soil carbon, as well as in the attribution and assessment of mitigation associated with the use of forest products, for example in substituting for high-energy building materials. Together, significant uncertainty remains in assessing and reporting of carbon storage and greenhouse mitigation with respect to forest-related land use and land use change.
Longer growing seasons do not increase net carbon uptake in Northeastern Siberian tundra
Parmentier, F.J.W. ; Molen, M.K. van der; Huissteden, J. van; Karsanaev, S. ; Kononov, A.V. ; Suzdalov, D. ; Maximov, T.C. ; Dolman, A.J. - \ 2011
Journal of Geophysical Research: Biogeosciences 116 (2011). - ISSN 2169-8953 - 11 p.
eddy covariance - ecosystem exchange - climate-change - arctic tundra - co2 exchange - respiration - flux - vegetation - dioxide - cycle
With global warming, snowmelt is occurring earlier and growing seasons are becoming longer around the Arctic. It has been suggested that this would lead to more uptake of carbon due to a lengthening of the period in which plants photosynthesize. To investigate this suggestion, 8 consecutive years of eddy covariance measurements at a northeastern Siberian graminoid tundra site were investigated for patterns in net ecosystem exchange, gross primary production (GPP) and ecosystem respiration (Reco). While GPP showed no clear increase with longer growing seasons, it was significantly increased in warmer summers. Due to these warmer temperatures however, the increase in uptake was mostly offset by an increase in Reco. Therefore, overall variability in net carbon uptake was low, and no relationship with growing season length was found. Furthermore, the highest net uptake of carbon occurred with the shortest and the coldest growing season. Low uptake of carbon mostly occurred with longer or warmer growing seasons. We thus conclude that the net carbon uptake of this ecosystem is more likely to decrease rather than to increase under a warmer climate. These results contradict previous research that has showed more net carbon uptake with longer growing seasons. We hypothesize that this difference is due to site-specific differences, such as climate type and soil, and that changes in the carbon cycle with longer growing seasons will not be uniform around the Arctic
CO2, dO2/N2 and APO: observations from the Lutjewad, Mace Head and F3 platform flask sampling network
Laan-Luijkx, I.T. van der; Karstens, U. ; Steinbach, J. ; Gerbig, C. ; Sirignano, C. ; Neubert, R.E.M. ; Laan, S. van der; Meijer, H.A.J. - \ 2010
Atmospheric Chemistry and Physics 10 (2010)21. - ISSN 1680-7316 - p. 10691 - 10704.
atmospheric oxygen measurements - global carbon-cycle - gas-chromatograph - o-2/n-2 ratio - o-2 - air - variability - dioxide - sinks - emissions
We report results from our atmospheric flask sampling network for three European sites: Lutjewad in the Netherlands, Mace Head in Ireland and the North Sea F3 platform. The air samples from these stations are analyzed for their CO2 and O2 concentrations. In this paper we present the CO2 and O2 data series from these sites between 1998 and 2009, as well as the atmospheric potential oxygen (APO). The seasonal pattern and long term trends agree to a large extent between our three measurement locations. We however find a changing gradient between Mace Head and Lutjewad, both for CO2 and O2. To explain the potential contribution of fossil fuel emissions to this changing gradient we use an atmospheric transport model in combination with CO2 emission data and information on the fossil fuel mix per region. Using the APO trend from Mace Head we obtain an estimate for the global oceanic CO2 uptake of 1.8 ± 0.8 PgC/year.
Climate control of terrestrial carbon exchange across biomes and continents
Yi, C. ; Jacobs, C.M.J. ; Moors, E.J. ; Elbers, J.A. - \ 2010
Environmental Research Letters 5 (2010)3. - ISSN 1748-9326 - 10 p.
eddy-covariance measurements - long-term - interannual variability - spatial variability - soil respiration - deciduous forest - water-vapor - fluxes - dioxide - uncertainty
Understanding the relationships between climate and carbon exchange by terrestrial ecosystems is critical to predict future levels of atmospheric carbon dioxide because of the potential accelerating effects of positive climate–carbon cycle feedbacks. However, directly observed relationships between climate and terrestrial CO2 exchange with the atmosphere across biomes and continents are lacking. Here we present data describing the relationships between net ecosystem exchange of carbon (NEE) and climate factors as measured using the eddy covariance method at 125 unique sites in various ecosystems over six continents with a total of 559 site-years. We find that NEE observed at eddy covariance sites is (1) a strong function of mean annual temperature at mid- and high-latitudes, (2) a strong function of dryness at mid- and low-latitudes, and (3) a function of both temperature and dryness around the mid-latitudinal belt (45°N). The sensitivity of NEE to mean annual temperature breaks down at ~ 16 °C (a threshold value of mean annual temperature), above which no further increase of CO2 uptake with temperature was observed and dryness influence overrules temperature influence
Simulating carbon exchange using a regional atmospheric model coupled to an advanced land-surface model
Maat, H.W. ter; Hutjes, R.W.A. ; Miglietta, F. - \ 2010
Biogeosciences 7 (2010)8. - ISSN 1726-4170 - p. 2397 - 2417.
kooldioxide - broeikasgassen - landgebruik - modellen - carbon dioxide - greenhouse gases - land use - models - valencia coastal region - mesoscale circulations - complex terrain - boundary-layer - gas-exchange - rain-forest - co2 - dioxide - fluxes - sea
A large scale mismatch exists between our understanding and quantification of ecosystem atmosphere exchange of carbon dioxide at local scale and continental scales. This paper will focus on the carbon exchange on the regional scale to address the following 5 question: What are the main controlling factors determining atmospheric carbon dioxide content at a regional scale? We use the Regional Atmospheric Modelling System (RAMS), coupled with a land surface scheme simulating carbon, heat and momentum fluxes (SWAPS-C), and including also sub models for urban and marine fluxes, which in principle include the main controlling mechanisms and capture the relevant dynamics 10 of the system. To validate the model, observations are used which were taken during an intensive observational campaign in the central Netherlands in summer 2002. These included flux-site observations, vertical profiles at tall towers and spatial fluxes of various variables taken by aircraft. The coupled regional model (RAMS-SWAPS-C) generally does a good job in sim15 ulating results close to reality. The validation of the model demonstrates that surface fluxes of heat, water and CO2 are reasonably well simulated. The comparison against aircraft data shows that the regional meteorology is captured by the model. Comparing spatially explicit simulated and observed fluxes we conclude that in general simulated latent heat fluxes are underestimated by the model to the observations which exhibit 20 large standard deviation for all flights. Sensitivity experiments demonstrated the relevance of the urban emissions of carbon dioxide for the carbon balance in this particular region. The same test also show the relation between uncertainties in surface fluxes and those in atmospheric concentrations.
Ectomycorrhizal fungi associated with Pinus sylvestris seedlings respond differently to increased carbon and nitrogen availability: implications for ecosystem responses to global change.
Alberton, O. ; Kuyper, T.W. - \ 2009
Global Change Biology 15 (2009)1. - ISSN 1354-1013 - p. 166 - 175.
elevated atmospheric co2 - progressive n limitation - douglas-fir seedlings - terrestrial ecosystems - deposition gradient - mycorrhizal fungal - community change - soil biota - dioxide - metaanalysis
The ectomycorrhizal (ECM) symbiosis can cause both positive and negative feedback with trees under elevated CO2. Positive feedback arises if the additional carbon (C) increases both nutrient uptake by the fungus and nutrient transfer to the plant, whereas negative feedback results from increased nutrient uptake and immobilization by the fungus and reduced transfer to the plant. Because species of ECM fungi differ in their C and nitrogen (N) demand, understanding fungal species-specific responses to variation in C and N supply is essential to predict impacts of global change. We investigated fungal species-specific responses of ECM Scots pine (Pinus sylvestris) seedlings under ambient and elevated CO2 (350 or 700 ¿L L¿1 CO2) and under low and high mineral N availability. Each seedling was associated with one of the following ECM species: Hebeloma cylindrosporum, Laccaria bicolor and Suillus bovinus. The experiment lasted 103 days. During the final 27 days, seedlings were labeled with 14CO2 and 15N. Most plant and fungal parameters were significantly affected by fungal species, CO2 level and N supply. Interactions between fungal species and CO2 were also regularly significant. At low N availability, elevated CO2 had the smallest impact on the photosynthetic performance of seedlings inoculated with H. cylindrosporum and the largest impact on seedlings with S. bovinus. At ambient CO2, increasing N supply had the smallest impact on seedlings inoculated with S. bovinus and the largest on seedlings inoculated with H. cylindrosporum. At low N availability, extraradical hyphal length increased after doubling CO2 level, but this was significant only for L. bicolor. At ambient CO2, increasing N levels reduced hyphal length for both H. cylindrosporum and S. bovinus, but not for L. bicolor. We discuss the potential interplay of two major elements of global change, elevated CO2 and increased N availability, and their effects on plant growth. We conclude that increased N supply potentially relieves mycorrhiza-induced progressive N limitation under elevated CO2
Increasing carbon storage in intact African tropical forests
Lewis, S.L. ; Lopez-Gonzalez, G. ; Sonké, B. ; Affum-Baffoe, K. ; Ewango, C.E.N. - \ 2009
Nature 457 (2009). - ISSN 0028-0836 - p. 1003 - 1006.
long-term plots - atmospheric transport - rain-forest - co2 - climate - biomass - disturbances - dioxide - impacts - balance
The response of terrestrial vegetation to a globally changing environment is central to predictions of future levels of atmospheric carbon dioxide1, 2. The role of tropical forests is critical because they are carbon-dense and highly productive3, 4. Inventory plots across Amazonia show that old-growth forests have increased in carbon storage over recent decades5, 6, 7, but the response of one-third of the world's tropical forests in Africa8 is largely unknown owing to an absence of spatially extensive observation networks9, 10. Here we report data from a ten-country network of long-term monitoring plots in African tropical forests. We find that across 79 plots (163 ha) above-ground carbon storage in live trees increased by 0.63 Mg C ha-1 yr-1 between 1968 and 2007 (95% confidence interval (CI), 0.22¿0.94; mean interval, 1987¿96). Extrapolation to unmeasured forest components (live roots, small trees, necromass) and scaling to the continent implies a total increase in carbon storage in African tropical forest trees of 0.34 Pg C yr-1 (CI, 0.15¿0.43). These reported changes in carbon storage are similar to those reported for Amazonian forests per unit area6, 7, providing evidence that increasing carbon storage in old-growth forests is a pan-tropical phenomenon. Indeed, combining all standardized inventory data from this study and from tropical America and Asia5, 6, 11 together yields a comparable figure of 0.49 Mg C ha-1 yr-1 (n = 156; 562 ha; CI, 0.29¿0.66; mean interval, 1987¿97). This indicates a carbon sink of 1.3 Pg C yr-1 (CI, 0.8¿1.6) across all tropical forests during recent decades. Taxon-specific analyses of African inventory and other data12 suggest that widespread changes in resource availability, such as increasing atmospheric carbon dioxide concentrations, may be the cause of the increase in carbon stocks13, as some theory14 and models2, 10, 15 predict.
Carbon and nitrogen cycles in European ecosystems respond differently to global warming
Beier, C. ; Emmett, B.A. ; Penuelas, J. ; Schmidt, I.K. ; Tietema, A. ; Estiarte, M. ; Gundersen, P. ; Llorens, L. ; Riis-Nielsen, T. ; Sowerby, A. ; Gorissen, A. - \ 2008
Science of the Total Environment 407 (2008)1. - ISSN 0048-9697 - p. 692 - 697.
climate-change - soil respiration - drought - temperature - forests - feedbacks - gradient - dioxide - impacts - plants
The global climate is predicted to become significantly warmer over the next century. This will affect ecosystem processes and the functioning of semi natural and natural ecosystems in many parts of the world. However, as various ecosystem processes may be affected to a different extent, balances between different ecosystem processes as well as between different ecosystems may shift and lead to major unpredicted changes. In this study four European shrubland ecosystems along a north¿south temperature gradient were experimentally warmed by a novel nighttime warming technique. Biogeochemical cycling of both carbon and nitrogen was affected at the colder sites with increased carbon uptake for plant growth as well as increased carbon loss through soil respiration. Carbon uptake by plant growth was more sensitive to warming than expected from the temperature response across the sites while carbon loss through soil respiration reacted to warming in agreement with the overall Q10 and response functions to temperature across the sites. Opposite to carbon, the nitrogen mineralization was relatively insensitive to the temperature increase and was mainly affected by changes in soil moisture. The results suggest that C and N cycles respond asymmetrically to warming, which may lead to progressive nitrogen limitation and thereby acclimation in plant production. This further suggests that in many temperate zones nitrogen deposition has to be accounted for, not only with respect to the impact on water quality through increased nitrogen leaching where N deposition is high, but also in predictions of carbon sequestration in terrestrial ecosystems under future climatic conditions. Finally the results indicate that on the short term the above-ground processes are more sensitive to temperature changes than the below ground processes
Weak northern and strong tropical land carbon uptake from vertical profiles of atmospheric CO2
Stephens, B.B. ; Gurney, K.R. ; Tans, P.P. ; Sweeney, C. ; Peters, W. - \ 2007
Science 316 (2007)5832. - ISSN 0036-8075 - p. 1732 - 1735.
long-term - terrestrial biosphere - forest ecosystems - plant-growth - transport - sink - sequestration - inversions - emissions - dioxide
Measurements of midday vertical atmospheric CO2 distributions reveal annual-mean vertical CO2 gradients that are inconsistent with atmospheric models that estimate a large transfer of terrestrial carbon from tropical to northern latitudes. The three models that most closely reproduce the observed annual-mean vertical CO2 gradients estimate weaker northern uptake of ¿1.5 petagrams of carbon per year (Pg C year¿1) and weaker tropical emission of +0.1 Pg C year¿1 compared with previous consensus estimates of ¿2.4 and +1.8 Pg C year¿1, respectively. This suggests that northern terrestrial uptake of industrial CO2 emissions plays a smaller role than previously thought and that, after subtracting land-use emissions, tropical ecosystems may currently be strong sinks for CO2.
Full accounting of the greenhouse gas (CO2, N2O, CH4) budget of nine European grassland sites
Soussana, J.F. ; Allard, V. ; Pilegaard, K. ; Ambus, P. ; Amman, C. ; Campbell, C. ; Ceschia, E. ; Clifton-Brown, J. ; Czobel, S. ; Domingues, R. ; Flechard, C. ; Fuhrer, J. ; Hensen, A. ; Horvath, L. ; Jones, M. ; Kasper, G.J. ; Martin, C. ; Nagy, Z. ; Neftel, A. ; Raschi, A. ; Baronti, S. - \ 2007
Agriculture, Ecosystems and Environment 121 (2007)39479. - ISSN 0167-8809 - p. 121 - 134.
native tallgrass prairie - nitrous-oxide emissions - net ecosystem exchange - soil carbon - agricultural soils - primary productivity - land management - respiration - sequestration - dioxide
The full greenhouse gas balance of nine contrasted grassland sites covering a major climatic gradient over Europe was measured during two complete years. The sites include a wide range of management regimes (rotational grazing, continuous grazing and mowing), the three main types of managed grasslands across Europe (sown, intensive permanent and semi-natural grassland) and contrasted nitrogen fertilizer supplies. At all sites, the net ecosystem exchange (NEE) of CO2 was assessed using the eddy covariance technique. N2O emissions were monitored using various techniques (GC-cuvette systems, automated chambers and tunable diode laser) and CH4 emissions resulting from enteric fermentation of the grazing cattle were measured in situ at four sites using the SF6 tracer method. Averaged over the two measurement years, net ecosystem exchange (NEE) results show that the nine grassland plots displayed a net sink for atmospheric CO2 of -240 +/- 70 g C m(-2) year(-1) (mean confidence interval at p > 0.95). Because of organic C exports (from cut and removed herbage) being usually greater than C imports (from manure spreading), the average C storage (net biome productivity, NBP) in the grassland plots was estimated at -104 +/- 73 g cm(-2) year(-1) that is 43% of the atmospheric CO2 sink. On average of the 2 years, the grassland plots displayed annual N2O and CH4 (from enteric fermentation by grazing cattle) emissions, in CO2-C equivalents, of 14 +/- 4.7 and 32 +/- 6.8 g CO2-C equiv. m(-2) year(-1), respectively. Hence, when expressed in CO2-C equivalents, emissions of N2O and CH4 resulted in a 19% offset of the NEE sink activity. An attributed GHG balance has been calculated by subtracting from the NBP: (i) N2O and CH4 emissions occurring within the grassland plot and (ii) off-site emissions of CO2 and CH4 as a result of the digestion and enteric fermentation by cattle of the cut herbage. On average of the nine sites, the attributed GHG balance was not significantly different from zero (-85 +/- 77 g CO2-C equiv. m(-2) year(-1)).
Hierarchical saturation of soil carbon pools near a natural CO2 spring
Kool, D.M. ; Chung, H. ; Tate, K.R. ; Ross, D.J. ; Newton, P.C.D. ; Six, J. - \ 2007
Global Change Biology 13 (2007)6. - ISSN 1354-1013 - p. 1282 - 1293.
elevated atmospheric co2 - long-term exposure - organic-matter - nitrogen limitation - no-tillage - aggregate stability - agricultural soils - grassland - dioxide - sequestration
Soil has been identified as a possible carbon (C) sink to mitigate increasing atmospheric CO2 concentration. However, several recent studies have suggested that the potential of soil to sequester C is limited and that soil may become saturated with C under increasing CO2 levels. To test this concept of soil C saturation, we studied a gley and organic soil at a grassland site near a natural CO2 spring. Total and aggregate-associated soil organic C (SOC) concentration showed a significant increase with atmospheric CO2 concentration. An asymptotic function showed a better fit of SOC and aggregation with CO2 level than a linear model. There was a shift in allocation of total C from smaller size fractions to the largest aggregate fraction with increasing CO2 concentration. Litter inputs appeared to be positively related to CO2 concentration. Based on modeled function parameters and the observed shift in the allocation of the soil C from small to large aggregate-size classes, we postulate that there is a hierarchy in C saturation across different SOC pools. We conclude that the asymptotic response of SOC concentration at higher CO2 levels indicates saturation of soil C pools, likely because of a limit to physical protection of SOC.
Cost Evaluation of CO2 Sequestration by Aqueous Mineral Carbonation
Huijgen, W.J.J. ; Comans, R.N.J. ; Witkamp, G.J. - \ 2007
Energy Conversion and Management 48 (2007)7. - ISSN 0196-8904 - p. 1923 - 1935.
dioxide - disposal
A cost evaluation of CO2 sequestration by aqueous mineral carbonation has been made using either wollastonite (CaSiO3) or steel slag as feedstock. First, the process was simulated to determine the properties of the streams as well as the power and heat consumption of the process equipment. Second, a basic design was made for the major process equipment, and total investment costs were estimated with the help of the publicly available literature and a factorial cost estimation method. Finally, the sequestration costs were determined on the basis of the depreciation of investments and variable and fixed operating costs. Estimated costs are 102 and 77 Euro/ton CO2 net avoided for wollastonite and steel slag, respectively. For wollastonite, the major costs are associated with the feedstock and the electricity consumption for grinding and compression (54 and 26 Euro/ton CO2 avoided, respectively). A sensitivity analysis showed that additional influential parameters in the sequestration costs include the liquid-to-solid ratio in the carbonation reactor and the possible value of the carbonated product. The sequestration costs for steel slag are significantly lower due to the absence of costs for the feedstock. Although various options for potential cost reduction have been identified, CO2 sequestration by current aqueous carbonation processes seems expensive relative to other CO2 storage technologies. The permanent and inherently safe sequestration of CO2 by mineral carbonation may justify higher costs, but further cost reductions are required, particularly in view of (current) prices of CO2 emission rights. Niche applications of mineral carbonation with a solid residue such as steel slag as feedstock and/or a useful carbonated product hold the best prospects for an economically feasible CO2 sequestration process. (c) 2007 Elsevier Ltd. All rights reserved.