Global CO2 Budget Research Articles

Quaternary glacial cycles: Karst processes and the global CO2 budget

Extensive research has been conducted investigating the relationship between karst processes, carbonate deposition and the global carbon cycle. However, little work has been done looking into the relationship between glaciations, subsequent sea level changes, and aerially exposed land masses in relation to karstic processes and the global carbon budget. During glaciations sea-level exposed the world’s carbonate platforms. With the sub-aerial exposure of the platforms, karst processes can occur, and the dissolution of carbonate material can commence, resulting in the drawdown of CO2 from the atmosphere as HCO3−. Furthermore, the material on the platform surfaces is primarily aragonite which is more readily soluble than calcite allowing karst processes to occur more quickly. During glaciations arctic carbonates and some of the temperate carbonates are blanketed in ice, effectively removing those areas from karst processes. Given the higher solubility of aragonite, and the extent of carbonate platforms exposed during glaciations, this dissolution balances the CO2 no longer taken up by karst processes at higher latitudes that were covered during the last glacial maximum The balance is within 0.001 GtC / yr, using soil pCO2 (0.005 GtC/yr assuming atmospheric pCO2) which is a difference of <1% of the total amount of atmospheric CO2 removed in a year by karst processes. Denudation was calculated using the maximum potential dissolution formulas of Gombert (2002). On a year to year basis the net amount of atmospheric carbon removed through karstic processes is equivalent between the last glacial maximum and the present day, however, the earth has spent more time in a glacial configuration during the Quaternary, which suggests that there is a net drawdown of atmospheric carbon during glaciations from karst processes, which may serve as a feedback to prolong glacial episodes. This research has significance for understanding the global carbon budget during the Quaternary. Keywords: Karst, Global Carbon Budget, Quaternary, Last Glacial Maximum, Carbonate Dissolution. DOI: 10.3986/ac.v42i2-3.661

Natural land carbon dioxide exchanges in the ECMWF integrated forecasting system: Implementation and offline validation

AbstractThe European Centre for Medium‐Range Weather Forecasts land surface model has been extended to include a carbon dioxide module. This relates photosynthesis to radiation, atmospheric carbon dioxide (CO2) concentration, soil moisture, and temperature. Furthermore, it has the option of deriving a canopy resistance from photosynthesis and providing it as a stomatal control to the transpiration formulation. Ecosystem respiration is based on empirical relations dependent on temperature, soil moisture, snow depth, and land use. The CO2 model is designed for the numerical weather prediction (NWP) environment where it benefits from good quality meteorological input (i.e., radiation, temperature, and soil moisture). This paper describes the CO2 model formulation and the way it is optimized making use of off‐line simulations for a full year of tower observations at 34 sites. The model is then evaluated against the same observations for a different year. A correlation coefficient of 0.65 is obtained between model simulations and observations based on 10 day averaged CO2 fluxes. For sensible and latent heat fluxes there is a correlation coefficient of 0.80. To study the impact on atmospheric CO2, coupled integrations are performed for the 2003 to 2008 period. The global atmospheric growth is well reproduced. The simulated interannual variability is shown to reproduce the observationally based estimates with a correlation coefficient of 0.70. The main conclusions are (i) the simple carbon dioxide model is highly suitable for the numerical weather prediction environment where environmental factors are controlled by data assimilation, (ii) the use of a carbon dioxide model for stomatal control has a positive impact on evapotranspiration, and (iii) even using a climatological leaf area index, the interannual variability of the global atmospheric CO2 budget is well reproduced due to the interannual variability in the meteorological forcing (i.e., radiation, precipitation, temperature, humidity, and soil moisture) despite the simplified or missing processes. This highlights the importance of meteorological forcing but also cautions the use of such a simple model for process attribution.

Time and space variations of the O2/N2 ratio in the troposphere over Japan and estimation of the global CO2 budget for the period 2000–2010

ABSTRACTSystematic measurements of the atmospheric O2/N2 ratio have been made using aircraft and ground-based stations in Japan since 1999. The observed seasonal cycles of the O2/N2 ratio and atmospheric potential oxygen (APO) vary almost in opposite phase to that of the CO2 concentration at all altitudes, and their amplitudes and phases are generally reduced and delayed, respectively, with increasing altitude. Simulations of APO using two atmospheric transport models reproduce general features of the observed seasonal cycle, but both models fail to reproduce the phase at an altitude ranging from 8 km to the tropopause. By analysing the observed secular trends of APO and CO2 concentration, and assuming a global net oceanic O2 outgassing of 0.2±0.5 GtC yr−1, we estimate global average terrestrial biospheric and oceanic CO2 uptake for the period 2000–2010 to be 1.0±0.8 and 2.5±0.7 GtC yr−1, respectively.

Comparison of Model-simulated Atmospheric Carbon Dioxide with GOSAT Retrievals

Global atmospheric CO₂ distributions were simulated with a chemical transport model (GEOS-Chem) and compared with space-borne observations of CO₂ column density by GOSAT from April 2009 to January 2010. The GEOS-Chem model simulated 3-D global atmospheric CO₂ at 2°×2.5°horizontal resolution using global CO₂ surface sources/sinks as well as 3-D emissions from aviation and the atmospheric oxidation of other carbon species. The seasonal cycle and spatial distribution of GEOS-Chem CO₂ columns were generally comparable with GOSAT columns over each continent with a systematic positive bias of ~1.0%. Data from the World Data Center for Greenhouse Gases (WDCGG) from twelve ground stations spanning 90°S-82°N were also compared with the modeled data for the period of 2004-2009 inclusive. The ground-based data show high correlations with the GEOS-Chem simulation (0.66≤R₂≤0.99) but the model data have a negative bias of ~1.0%, which is primarily due to the model initial conditions. Together these two comparisons can be used to infer that GOSAT CO₂ retrievals underestimate CO₂ column concentration by ~2.0%, as demonstrated in recent validation work using other methods. We further estimated individual source/sink contributions to the global atmospheric CO₂ budget and trends through 7 tagged CO₂ tracers (fossil fuels, ocean exchanges, biomass burning, biofuel burning, net terrestrial exchange, shipping, aviation, and CO oxidation) over 2004-2009. The global CO₂ trend over this period (2.1 ppmv/year) has been mainly driven by fossil fuel combustion and cement production (3.2 ppmv/year), reinforcing the fact that rigorous CO₂ reductions from human activities are necessary in order to stabilize atmospheric CO₂ levels.

The Warming papers: the scientific foundation for the climate change forecast

Preface. Part I Climate Physics. 1 The Effect. On the Temperatures of the Terrestrial Sphere and Interplanetary Space (Jean-Baptiste Joseph Fourier (1824)). 2 Wagging the Dog. On the Absorption and Radiation of Heat by Gases and Vapours, and on the Physical Connexion of Radiation, Absorption, and Conduction (John Tyndall (1861)). 3 By the Light of the Silvery Moon. On the Influence of Carbonic Acid in the Air upon the Temperature of the Ground (Svante Arrhenius (1896)). 4 Radiative Transfer. The Influence of the 15 m Carbon-dioxide Band on the Atmospheric Infra-red Cooling Rate (G. N. Plass (1956)). 5 The Balance of Energy. Thermal Equilibrium of the Atmosphere with a Given Distribution of Relative Humidity (Syukuro Manabe and Richard T. Wetherald (1967)). The Effect of Solar Radiation Variations on the Climate of the Earth (M. I. Budyko (1968)). A Global Climatic Model Based on the Energy Balance of the Earth-Atmosphere System (William D. Sellers (1968)). 6 The Birth of the General Circulation Climate Model. The Effects of Doubling the CO2Concentration on the Climate of a General Circulation Model (Syukuro Manabe and Richard T. Wetherald (1975)). Climate Sensitivity: Analysis of Feedback Mechanisms (J. Hansen, A. Lacis, D. Rind, G. Russell, P. Stone, I. Fung, R. Ruedy, and J. Lerner (1984)). 7 Aerosols. Climate Response to Increasing Levels of Gases and Sulphate Aerosols (J. F. B. Mitchell, T. C. Johns, J. M. Gregory and S. F. B. Tett (1995)). 8 Ocean Heat Uptake and Committed Warming. Earth's Energy Imbalance: Confirmation and Implications (James Hansen, Larissa Nazarenko, Reto Ruedy, Makiko Sato, Josh Willis, Anthony Del Genio, Dorothy Koch, Andrew Lacis, Ken Lo, Surabi Menon, Tica Novakov, Judith Perlwitz, Gary Russell, Gavin A. Schmidt and Nicholas Tausnev (2005)). 9 Taking Earth's Temperature. Global Temperature Variations Between 1861 and 1984 (P. D. Jones, T. M. L. Wigley and P. B. Wright (1986)). Contribution of Stratospheric Cooling to Satellite-Inferred Troposphoric Temperature Trends (Qiang Fu, Celeste M. Johanson, Stephen G. Warren and Dian J. Seidel (2004)). Northern Hemisphere Temperatures During the Past Millennium: Inferences, Uncertainties, and Limitations (Michael E. Mann, Raymond S. Bradley and Malcolm K. Hughes (1999)). 10 Ice Sheets and Sea Level. Surface Melt-Induced Acceleration of Greenland Ice-Sheet Flow (H. Jay Zwally, Waleed Abdalati, Tom Herring, Kristine Larson, Jack Saba and Konrad Steffen (2002)). 11 The Public Statement. Man-Made Carbon Dioxide and the Greenhouse Effect (J. S. Sawyer (1972)). Carbon Dioxide and Climate: A Scientific Assessment (Jule G. Charney, Akio Arakawa, D. James Baker, Bert Bolin, Robert E. Dickinson, Richard M. Goody, Cecil E. Leith, Henry M. Stommel and Carl I. Wunsch (1979)). Part II The Carbon Cycle. 12 The Sky is Rising! The Artificial Production of Carbon Dioxide and its Influence on Temperature (G. S. Callendar (1938)). 13 Denial and Acceptance. Carbon Dioxide Exchange Between Atmosphere and Ocean and the Question of an Increase of Atmospheric CO2during the Past Decades (Roger Revelle and Hans E. Suess (1957)). Distribution of Matter in the Sea and Atmosphere: Changes in the Carbon Dioxide Content of the Atmosphere and Sea due to Fossil Fuel Combustion (Bert Bolin and Erik Eriksson (1958)). 14 Bookends. The Concentration and Isotopic Abundances of Carbon Dioxide in the Atmosphere (Charles D. Keeling (1960)). Is Carbon Dioxide from Fossil Fuel Changing Man's Environment? (Charles D. Keeling (1970)). 15 One If by Land. Changes of Land Biota and Their Importance for the Carbon Cycle (Bert Bolin (1977)). Observational Constraints on the Global Atmospheric CO2 Budget (Pieter P. Tans, Inez Y. Fung and Taro Takahashi (1990)). Acceleration of Global Warming Due to Carbon-Cycle Feedbacks in a Coupled Climate Model (Peter M. Cox, Richard A. Betts, Chris D. Jones, Steven A. Spall and Ian J. Totterdell (2000)). 16 Two If by Sea. Neutralization of Fossil Fuel CO2 by Marine Calcium Carbonate (W. S. Broecker and T. Takahashi (1977)). Effects of Fuel and Forest Conservation on Future Levels of Atmospheric Carbon Dioxide (James C. G. Walker and James F. Kasting (1992)). Abrupt Deep-Sea Warming, Palaeoceanographic Changes and Benthic Extinctions at the End of the Palaeocene (J. P. Kennett and L. D. Stott (1991)). 17 On Ocean pH. Anthropogenic Carbon and Ocean pH (Ken Caldeira and Michael E. Wickett (2003)). Reduced Calcification of Marine Plankton in Response to Increased Atmospheric CO2 (Ulf Riebesell, Ingrid Zondervan, Bjorn Rost, Philippe D. Tortell, Richard E. Zeebe and Francois M. M. Morel (2000)). 18 Tiny Bubbles. Evidence From Polar Ice Cores for the Increase in Atmospheric CO2 in the Past Two Centuries (A. Neftel, E. Moor, H. Oeschger and B. Stauffer (1985)). Vostok Ice Core Provides 160,000-Year Record of Atmospheric CO2(J. M. Barnola, D. Raynaud, Y. S. Korotkevich and C. Lorius (1987)). Index.

Inferring terrestrial photosynthetic light use efficiency of temperate ecosystems from space

[1] Terrestrial ecosystems absorb about 2.8 Gt C yr?1, which is estimated to be about a quarter of the carbon emitted from fossil fuel combustion. However, the uncertainties of this sink are large, on the order of ±40%, with spatial and temporal variations largely unknown. One of the largest factors contributing to the uncertainty is photosynthesis, the process by which plants absorb carbon from the atmosphere. Currently, photosynthesis, or gross ecosystem productivity (GEP), can only be inferred from flux towers by measuring the exchange of CO2 in the surrounding air column. Consequently, carbon models suffer from a lack of spatial coverage of accurate GEP observations. Here, we show that photosynthetic light use efficiency (?), hence photosynthesis, can be directly inferred from spaceborne measurements of reflectance. We demonstrate that the differential between reflectance measurements in bands associated with the vegetation xanthophyll cycle and estimates of canopy shading obtained from multiangular satellite observations (using the CHRIS/PROBA sensor) permits us to infer plant photosynthetic efficiency, independently of vegetation type and structure (r2 = 0.68, compared to flux measurements). This is a significant advance over previous approaches seeking to model global-scale photosynthesis indirectly from a combination of growth limiting factors, most notably pressure deficit and temperature. When combined with modeled global-scale photosynthesis, satellite-inferred ? can improve model estimates through data assimilation. We anticipate that our findings will guide the development of new spaceborne approaches to observe vegetation carbon uptake and improve current predictions of global CO2 budgets and future climate scenarios by providing regularly timed calibration points for modeling plant photosynthesis consistently at a global scale.

The carbon balance of Africa: synthesis of recent research studies

The African continent contributes one of the largest uncertainties to the global CO(2) budget, because very few long-term measurements are carried out in this region. The contribution of Africa to the global carbon cycle is characterized by its low fossil fuel emissions, a rapidly increasing population causing cropland expansion, and degradation and deforestation risk to extensive dryland and savannah ecosystems and to tropical forests in Central Africa. A synthesis of the carbon balance of African ecosystems is provided at different scales, including observations of land-atmosphere CO(2) flux and soil carbon and biomass carbon stocks. A review of the most recent estimates of the net long-term carbon balance of African ecosystems is provided, including losses from fire disturbance, based upon observations, giving a sink of the order of 0.2 Pg C yr(-1) with a large uncertainty around this number. By comparison, fossil fuel emissions are only of the order of 0.2 Pg C yr(-1) and land-use emissions are of the order of 0.24 Pg C yr(-1). The sources of year-to-year variations in the ecosystem carbon-balance are also discussed. Recommendations for the deployment of a coordinated carbon-monitoring system for African ecosystems are given.

A process model for simulating net primary productivity (NPP) based on the interaction of water-heat process and nitrogen: a case study in Lantsang valley

Terrestrial carbon cycle and the global atmospheric CO2 budget are important foci in global climate change research. Simulating net primary productivity (NPP) of terrestrial ecosystems is important for carbon cycle research. In this study, a plant-atmosphere-soil continuum nitrogen (N) cycling model was developed and incorporated into the Boreal Ecosystem Productivity Simulator (BEPS) model. With the established database (leaf area index, land cover, daily meteorology data, vegetation and soil) at a 1 km resolution, daily maps of NPP for Lantsang valley in 2007 were produced, and the spatial-temporal patterns of NPP and mechanisms of its responses to soil N level were further explored. The total NPP and mean NPP of Lantsang valley in 2007 were 66.5 Tg C and 416 g·m−2·a−1 C, respectively. In addition, statistical analysis of NPP of different land cover types was conducted and investigated. Compared with BEPS model (without considering nitrogen effect), it was inferred that the plant carbon fixing for the upstream of Lantsang valley was also limited by soil available nitrogen besides temperature and precipitation. However, nitrogen has no evident limitation to NPP accumulation of broadleaf forest, which mainly distributed in the downstream of Lantsang valley.

Indoor and outdoor urban atmospheric CO2: Stable carbon isotope constraints on mixing and mass balance

Abstract From July to November 2009, concentrations of CO2 in 78 samples of ambient air collected in 18 different interior spaces on a university campus in Dallas, Texas (USA) ranged from 386 to 1980 ppm. Corresponding δ13C values varied from −8.9‰ to −19.4‰. The CO2 from 22 samples of outdoor air (also collected on campus) had a more limited range of concentrations from 385 to 447 ppm (avg. = 408 ppm), while δ13C values varied from −10.1‰ to −8.4‰ (avg.=-9.0‰). In contrast to ambient indoor and outdoor air, the concentrations of CO2 exhaled by 38 different individuals ranged from 38,300 to 76,200 ppm (avg. = 55,100 ppm), while δ13C values ranged from −24.8‰ to −17.7‰ (avg. = −21.8‰). The residence times of the total air in the interior spaces of this study appear to have been on the order of 10 min with relatively rapid approaches (∼30 min) to steady-state concentrations of ambient CO2 gas. Collectively, the δ13C values of the indoor CO2 samples were linearly correlated with the reciprocal of CO2 concentration, exhibiting an intercept of −21.8‰, with r2 = 0.99 and p The average concentration of outdoor Dallas atmospheric CO2 was ∼17 ppm higher than the average of CO2 concentrations measured on the same campus 10 a ago. In addition, Dallas outdoor CO2 concentrations at both times were higher than the contemporaneous global atmospheric CO2 concentrations. This observation, plus the fact that the increase of ∼17 ppm in the average concentration of Dallas outdoor CO2 was comparable to the global increase of ∼18 ppm over the same 10-a interval, is consistent with a significant role for urban CO2 “factories” in the global atmospheric CO2 budget.

Global monthly averaged CO2 fluxes recovered using a geostatistical inverse modeling approach: 1. Results using atmospheric measurements

This study presents monthly CO2 fluxes from 1997 to 2001 at a 3.75° latitude × 5° longitude resolution, inferred using a geostatistical inverse modeling approach. The approach focuses on quantifying the information content of measurements from the NOAA‐ESRL cooperative air sampling network with regard to the global CO2 budget at different spatial and temporal scales. The geostatistical approach avoids the use of explicit prior flux estimates that have formed the basis of previous synthesis Bayesian inversions and does not prescribe spatial patterns of flux for large, aggregated regions. Instead, the method relies strongly on the atmospheric measurements and the inferred spatial autocorrelation of the fluxes to estimate sources and sinks and their associated uncertainties at the resolution of the atmospheric transport model. Results show that grid‐scale estimates exhibit high uncertainty and relatively little small‐scale variability, but generally reflect reasonable fluxes in areas that are relatively well constrained by measurements. The aggregated continental‐scale fluxes are better constrained, and estimates are consistent with results from previous synthesis Bayesian inversion studies for many regions. Observed differences at the continental scale are primarily attributable to the choice of a priori assumptions in the current work relative to those in other synthesis Bayesian studies. Overall, the results indicate that the geostatistical inverse modeling approach is able to estimate global fluxes using the limited atmospheric measurement network without relying on assumptions about a priori estimates of the flux distribution. As such, the method provides a means of isolating the information content of the atmospheric measurements, and thus serves as a valuable tool for reconciling top‐down and bottom‐up estimates of CO2 flux variability.

CO2 absorption by alkaline soils and its implication to the global carbon cycle

Motivated by the rapid increase in atmospheric CO2 due to human activities since the Industrial Revolution, and the climate changes it produced, the world’s concerned scientific community has made a huge effort to investigate the global carbon cycle. However, the results reveal that the global CO2 budget cannot be balanced, unless a “missing sink” is invoked. Although numerous studies claimed to find the “missing sink”, none of those claims has been widely accepted. This current study showed that alkaline soil on land are absorbing CO2 at a rate of 0.3–3.0μmolm−2s−1 with an inorganic, non-biological process. The intensity of this CO2 absorption is determined by the salinity, alkalinity, temperature and water content of the saline/alkaline soils, which are widely distributed on land. Further studies revealed that high salinity or alkalinity positively affected the CO2 absorbing intensity, while high temperature and water content had a negative effect on the CO2 absorbing intensity of these soils. This inorganic, non-biological process of CO2 absorption by alkaline soils might have significant implications to the global carbon budget accounting.

Preface to special section on New Approaches to Quantifying Exchanges of Carbon and Energy Across a Range of Scales

[1] Estimating carbon and energy exchanges in the soilplant-atmosphere continuum across spatial and temporal scales is a primary focus of coordinated interagency collaborations (i.e., U.S. Global Change Research Program, Climate Change Science Program, and the Carbon Cycle InterAgency Working Group) that are outlined in North American Carbon Plan [Wofsy and Harriss, 2002], Carbon Cycle Science Plan [Sarmiento and Wofsy, 1999], Intergovernmental Panel on Global Climate Change [Intergovernmental Panel on Global Climate Change, 1995] and other position papers. Eddy covariance (EC) has served well to define these exchanges over scales of 10–100 ha in relatively simple terrain under well-mixed conditions. These data have contributed to significant advances in our understanding of important ecosystem processes and quantifying the key biotic and abiotic processes that control these rates [Loescher et al., 2003, 2005; Law et al., 2002, 2003; Anthoni et al., 1999, 2002; Bowling et al., 2001; Clark et al., 1999; Goulden et al., 1996], and useful in developing regional approaches to constraining the global CO2 budget [Townsend et al., 2002; Battle et al., 2000]. However, extension to complex terrain and measurement under nonideal meteorological conditions requires new approaches. New approaches are also needed to increase our ability to scale these exchanges. The focus of this thematic issue is to quantify uncertainty in energy and carbon fluxes, and introduce new approaches for extending the measurements to larger scales. [2] This thematic issue presents a suite papers covering a wide range of topics including estimation of uncertainties in flux measurements, examination of problems associated with nighttime fluxes, extraction of physiological parameters from flux measurements, methodological issues with measurements, use of isotopic measurements, and regionalization. The section begins with Loescher et al. [2006] outlining the uncertainties associated with EC measurements (e.g., random and systematic errors, gap filling, and flows not accounted for), how these errors scale with time and space, and how these errors compare to the errors associated with traditional estimates of ecosystem respiration and net primary productivity. [3] Estimating the uncertainty in EC data can be challenging because the variability in 30-min EC estimates increase with the magnitude of the estimate, i.e., heteroscedastic quantities. Moreover, it is now a criterion to provide an estimate of uncertainty in EC estimates when reporting data from any (and all) AmeriFlux site. Hagen et al. [2006] provide a robust methodology to accomplish these goals. By using bootstrapping and an artificial neural network, these authors found by that the uncertainty in EC was 100% for 30-min estimates, but was reduced with longer temporal scales (annual estimates) to 10%. Their research site was micrometeorologically ideal (average and uniform surface roughness, flat topography), so other unaccounted flows did not likely contribute to this study. [4] The combination of thermally stratified, decoupled nocturnal boundary layers and structurally complex forest structures make nighttime EC estimates difficult to estimate and create the conditions when drainage of CO2 below the height of the measured turbulent flux can occur. Goulden et al. [2006] used remotely sensed data to examine potential nighttime CO2 drainage patterns in an Amazon forest and surrounding landscape, and identify when drainage flows develop and become significant. Juang et al. [2006] provide a promising inverse approach (Eulerian rather than Langrangian) using below-canopy air temperature to model ecosystem respiration. Lai et al. [2006] use stable carbon and oxygen isotopes of respired CO2 to partition the abiotic controls on ecosystem-level uptake and respiration from a C3/C4 grassland. [5] Using eddy covariance data to estimate annual integrals is hampered by incomplete data sets due to enviable data gaps due to calibrations, instrument failure, precipitation, and power problems. Gap filling strategies have included look-up tables, interpolations or estimates of uptake and respiration (e.g., those based on Ball-Berry and Q10 equations). Gove and Hollinger [2006] present an innovative methodology to gap fill data that relies on the heteroscedastic nature of EC-derived 30-min, and optimizes parameters used in uptake and respiration equations. [6] Wolf et al. [2006] invert a model and constrain the governing equations by measured EC data to estimate key ecosystem parameters from uncertainties associated with light use efficiency models that primarily stem from the JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, D14S91, doi:10.1029/2006JD007135, 2006

Is carbon within the global terrestrial biosphere becoming more oxidized? Implications for trends in atmospheric O2

AbstractMeasurements of atmospheric O2 and CO2 concentrations serve as a widely used means to partition global land and ocean carbon sinks. Interpretation of these measurements has assumed that the terrestrial biosphere contributes to changing O2 levels by either expanding or contracting in size, and thus serving as either a carbon sink or source (and conversely as either an oxygen source or sink). Here, we show how changes in atmospheric O2 can also occur if carbon within the terrestrial biosphere becomes more reduced or more oxidized, even with a constant carbon pool. At a global scale, we hypothesize that increasing levels of disturbance within many biomes has favored plant functional types with lower oxidative ratios and that this has caused carbon within the terrestrial biosphere to become increasingly more oxidized over a period of decades. Accounting for this mechanism in the global atmospheric O2 budget may require a small increase in the size of the land carbon sink. In a scenario based on the Carnegie–Ames–Stanford Approach model, a cumulative decrease in the oxidative ratio of net primary production (NPP) (moles of O2 produced per mole of CO2 fixed in NPP) by 0.01 over a period of 100 years would create an O2 disequilibrium of 0.0017 and require an increased land carbon sink of 0.1 Pg C yr−1 to balance global atmospheric O2 and CO2 budgets. At present, however, it is challenging to directly measure the oxidative ratio of terrestrial ecosystem exchange and even more difficult to detect a disequilibrium caused by a changing oxidative ratio of NPP. Information on plant and soil chemical composition complement gas exchange approaches for measuring the oxidative ratio, particularly for understanding how this quantity may respond to various global change processes over annual to decadal timescales.

More Notes on Global Warming

I was puzzled when I read the exchange of letters on global warming in the January 2005 issue of Physics Today, (page 13). George Smith suggested that the recent carbon dioxide increase could be the result of a century of global warming—in particular, by the degassing of the ocean. Spencer Weart answered (correctly, but see below) that scientists with the Intergovernmental Panel on Climate Change (IPCC) have calculated the budget between the carbon input with the sinks in different reservoirs of the carbon cycle: ocean, forest, soil, and so forthBesides technicalities implying that the global CO2 budget still has second-order uncertainties, I’m surprised Weart didn’t cite first-order proofs demonstrating that the recent CO2 increase cannot be due to ocean warming. Those killing proofs are well-known in the climatology community—for example, in the IPCC—but it is crucial to emphasize them again for a wider audience.The recent CO2 increase—280 to 380 parts per million by volume between 1800 and 2005—is accompanied by three phenomena that completely rule out ocean warming as the main cause: ▸ Parallel decline of the 14C/12C ratio of atmospheric CO2. Strictly speaking, this is the “Suess effect,” first observed, and correctly interpreted, by Hans Suess of the University of California, San Diego, in the early 1950s. The Suess effect occurs because fossil fuels do not contain 14C precisely because they are fossil—much older than 10 half-lives of 14C.▸ Parallel decline of the 13C/12C ratio of atmospheric CO2. This phenomenon is linked to the fact that fossil fuels, forests, and soil carbon come from photosynthetic carbon, which is strongly depleted in 13C.▸ Parallel decline in the oxygen concentration of the atmosphere, which is the inescapable signature of an oxidation of carbon. If ocean warming were responsible for the CO2 increase, we should also observe an increase in atmospheric O2. Nonspecialists will not easily be impressed by model calculations and complex budgets that contain often large uncertainties. Moreover, I have seen dishonest skeptics using “old hat” arguments such as ocean CO2 outgassing to refute the responsibility of human activities in the recent CO2 increase and the forthcoming large global warming. One crucial note about the global budget of inputs and outputs that Weart should have stated: Known CO2 emissions from fossil fuels and deforestation largely exceed (by about a factor of two) what remains in the atmosphere. Hence, if warming were the cause of the CO2 increase, how would we account for the hundreds of gigatons of carbon generated by human activity?© 2005 American Institute of Physics.

Strategies for measurement of atmospheric column means of carbon dioxide from aircraft using discrete sampling

Automated flask sampling aboard small charter aircraft has been proposed as a low‐cost, reliable method to greatly increase the density of measurements of CO2 mixing ratios in continental regions in order to provide data for assessment of global and regional CO2 budgets. We use data from the CO2 Budget and Rectification‐Airborne 2000 campaign over North America to study the feasibility of using discrete (flask) sampling to determine column mean CO2 in the lowest 4 km of the atmosphere. To simulate flask sampling, data were selected from profiles of CO2 measured continuously with an onboard (in situ) analyzer. We find that midday column means can be determined without bias relative to true column means measured by the in situ analyzer to within 0.15 and better than 0.10 ppm by using 10 and 20 instantaneously collected flask samples, respectively. More precise results can be obtained by using a flask sampling strategy that linearly integrates over portions of the air column. Using less than 8–10 flasks can lead to significant sampling bias for some common profile shapes. Sampling prior to the breakup of the nocturnal stable layer will generally lead to large sampling bias because of the inability of aircraft to probe large CO2 gradients that often exist very close to the ground at night and during the early morning.

CO2Deficit in Temperate Forest Soils Receiving High Atmospheric N-Deposition

Evidence is provided for an internal CO2 sink in forest soils, that may have a potential impact on the global CO2-budget. Lowered CO2 fraction in the soil atmosphere, and thus lowered CO2 release to the aboveground atmosphere, is indicated in high N-deposition areas. Also at forest edges, especially of spruce forest, where additional N-deposition has occurred, the soil CO2 is lowered, and the gradient increases into the closed forest. Over the last three decades the capacity of the forest soil to maintain the internal sink process has been limited to a cumulative supply of approximately 1000 and 1500 kg N ha−1. Beyond this limit the internal soil CO2 sink becomes an additional CO2 source, together with nitrogen leaching. This stage of “nitrogen saturation” is still uncommon in closed forests in southern Scandinavia, however, it occurs in exposed forest edges which receive high atmospheric N-deposition. The soil CO2 gradient, which originally increases from the edge towards the closed forest, becomes reversed.

CO2 Deficit in Temperate Forest Soils Receiving High Atmospheric N-Deposition

Evidence is provided for an internal CO2 sink in forest soils, that may have a potential impact on the global CO2-budget. Lowered CO2 fraction in the soil atmosphere, and thus lowered CO2 release to the aboveground atmosphere, is indicated in high N-deposition areas. Also at forest edges, especially of spruce forest, where additional N-deposition has occurred, the soil CO2 is lowered, and the gradient increases into the closed forest. Over the last three decades the capacity of the forest soil to maintain the internal sink process has been limited to a cumulative supply of approximately 1000 and 1500 kg N ha(-1). Beyond this limit the internal soil CO2 sink becomes an additional CO2 source, together with nitrogen leaching. This stage of "nitrogen saturation" is still uncommon in closed forests in southern Scandinavia, however, it occurs in exposed forest edges which receive high atmospheric N-deposition. The soil CO2 gradient, which originally increases from the edge towards the closed forest, becomes reversed.

A global-scale simulation of the CO2 exchange between the atmosphere and the terrestrial biosphere with a mechanistic model including stable carbon isotopes, 1953–1999

This paper presents the results of a simulation with a mechanistic terrestrial ecosystem model, focusing on the atmosphere—biosphere exchange and stable isotope composition of carbon. The simulation was performed from 1953 to 1999 on the basis of observed climate data and atmospheric carbon dioxide (CO2) concentration and stable carbon isotope ratio (δ13C). The model, termed Sim-CYCLE, captures carbon dynamics from photosynthetic assimilation to microbial decomposition, including seasonal and interannual variability. Photosynthetic discrimination effect on δ13C was considered at three levels: (1) leaf-level fractionation, (2) canopy-level CO2 recycling and (3) continent-level C3/C4 pattern. The 47-yr simulation estimated that the average gross CO2 flux was 121 Pg C yr−1, and that the average photosynthetic δ13C discrimination coefficient (Δ) was 18.2%. A sensitivity analysis indicated that the estimated Δ depends heavily on the parameterization of stomatal conductance and C3/C4 composition. In spite of their small biomass, C4 plants contributed considerably to the biospheric productivity and belowground carbon supply. The estimated net CO2and isotopic exchange of the terrestrial ecosystems corresponded, at least qualitatively, with observed atmospheric CO2 and its δ13C seasonal patterns in the Northern Hemisphere. The gross CO2 fluxes of photosynthesis and respiration indicated a wide range of interannual variability, which was in a sufficient magnitude to induce anomalies in the atmospheric CO2 growth rate. The estimated Δ showed a wide range of latitudinal and longitudinal variations and seasonal oscillation, but little interannual change. However, during the 47-yr period, the estimated δ13C of carbon pools decreased by 0.3%, while the δ13C of atmospheric CO2 decreased by 0.7%. These results carry implications for the application of a top-down approach, i.e. the double-deconvolution method, to inferring the global terrestrial CO2 budget.

Effects of Heavy-Oil Contamination on CO2 Transfer across the Air-Water Interface.

The effects of heavy-oil surface contamination on the CO2 transfer across the air-water interface were investigated through laboratory experiments in an oscillating-grid tank. The CO2 transfer velocities across the air-water interface contaminated with heavy-oil were estimated for both tap water and saltwater. The results show that the CO2 transfer volocity across the non-breaking interface for tap water contaminated with heavy-oil is damped to 30% of that for tap water without heavy-oil contamination. The CO2 transfer velocity across the non-breaking interface for 3.5 wt% saltwater (or natural seawater) contaminated with heavy-oil is damped to 46% of that for 3.5 wt% saltwater (or natural seawater) without heavy-oil contamination. The reduction in the CO2 transfer velocity can well be explained by assuming the resistance equivalent for tap water and saltwater to mass transfer due to a thin oil film on the surface. When the interface is intensively broken, the CO2 transfer velocity across the air-water interface contaminated with heavy-oil approaches to that for tap water or saltwater without heavy-oil contamination. The reduction in the CO2 transfer velocity across the air-water interfaces suggests that the effects of the surface contamination should be taken into account in the General Circulation Model (GCM) for estimating the global CO2 budget.

Raised atmospheric CO2 levels and increased N deposition cause shifts in plant species composition and production in Sphagnum bogs

AbstractPart of the missing sink in the global CO2 budget has been attributed to the positive effects of CO2 fertilization and N deposition on carbon sequestration in Northern Hemisphere terrestrial ecosystems. The genus Sphagnum is one of the most important groups of plant species sequestrating carbon in temperate and northern bog ecosystems, because of the low decomposability of the dead material it produces. The effects of raised CO2 and increased atmospheric N deposition on growth of Sphagnum and other plants were studied in bogs at four sites across Western Europe. Contrary to expectations, elevated CO2 did not significantly affect Sphagnum biomass growth. Increased N deposition reduced Sphagnum mass growth, because it increased the cover of vascular plants and the tall moss Polytrichum strictum. Such changes in plant species composition may decrease carbon sequestration in Sphagnum‐dominated bog ecosystems.