Measurements of midday vertical atmospheric CO 2 distributions reveal annual-mean vertical CO 2 gradients that are inconsistent with atmospheric models that estimate a large transfer of terrestrial carbon from tropical to northern... more
Measurements of midday vertical atmospheric CO 2 distributions reveal annual-mean vertical CO 2 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 CO 2 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 CO 2 emissions plays a smaller role than previously thought and that, after subtracting land-use emissions, tropical ecosystems may currently be strong sinks for CO 2 .
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Atmospheric methane (CH<sub>4</sub>) increased from ~900 ppb (parts per billion, or nanomoles per mole of dry air) in 1900 to ~1800 ppb during the 2000s at a rate unprecedented in any observational records. However, the causes... more
Atmospheric methane (CH<sub>4</sub>) increased from ~900 ppb (parts per billion, or nanomoles per mole of dry air) in 1900 to ~1800 ppb during the 2000s at a rate unprecedented in any observational records. However, the causes of the CH<sub>4</sub> increase are poorly understood. Here we use initial emissions from bottom-up inventories for anthropogenic sources, emissions from wetlands and rice paddies simulated by a terrestrial biogeochemical model, and an atmospheric general circulation model (AGCM)-based chemistry-transport model (i.e. ACTM) to simulate atmospheric CH<sub>4</sub> concentrations for 1910 to 2010. The ACTM simulations are compared with the CH<sub>4</sub> concentration records reconstructed from Antarctic and Arctic ice cores and firn air samples, and from direct measurements since the 1980s at multiple sites around the globe. The differences between ACTM simulations and observed CH<sub>4</sub> concentratio...
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The global methane (CH<sub>4</sub>) budget is becoming an increasingly important component for managing realistic pathways to mitigate climate change. This relevance, due to a shorter atmospheric lifetime and a stronger... more
The global methane (CH<sub>4</sub>) budget is becoming an increasingly important component for managing realistic pathways to mitigate climate change. This relevance, due to a shorter atmospheric lifetime and a stronger warming potential than carbon dioxide, is challenged by the still unexplained changes of atmospheric CH<sub>4</sub> over the past decade. Emissions and concentrations of CH<sub>4</sub> are continuing to increase making CH<sub>4</sub> the second most important human-induced greenhouse gas after carbon dioxide. Two major difficulties in reducing uncertainties come from the large variety of diffusive CH<sub>4</sub> sources that overlap geographically, and from the destruction of CH<sub>4</sub> by the very short-lived hydroxyl radical (OH). To address these difficulties, we have established a consortium of multi-disciplinary scientists under the umbrella of the Global…
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ABSTRACT In 2000 the European Community started an extensive research program, CARBOEUROPE, which aims at budgeting Eurasian carbon emissions. CARBOEUROPE consists of several projects performing long term observations of atmospheric CO2... more
ABSTRACT In 2000 the European Community started an extensive research program, CARBOEUROPE, which aims at budgeting Eurasian carbon emissions. CARBOEUROPE consists of several projects performing long term observations of atmospheric CO2 and its stable isotope ratios (13C/12C, 18O/16O) at ground level sites but also by flask sampling during regular aircraft profiling (EuroSiberian CarbonFlux [start in 1998], AEROCARB, TCOS-Siberia). Analysis of air is performed by different laboratories in Western Europe and Australia. In order to merge thecomplete set of observational data, thus providing a robust and reliable basis for modelling studies, good laboratory intercomparison is a crucial pre-requisite. Although all laboratories are linked to international calibration scales, different analysis techniques used in the different laboratories may cause offsets for real air analysis which must not be interpreted as bio-geochemical signals. In order to identify and quantify possible offsets between laboratories (to be eventually applied on the atmospheric data) a number of intercomparison exercises has been performed (see Table 1). These consist of so-called Round Robins of artificial and natural air in high pressure tanks, exchange of pure CO2 for mass spectrometer intercomparison, so-called sausage flask intercomparison and ongoing intercomparison by some pairs of laboratories on flasks filled at dedicated sampling sites (here Cape Grim Baseline Observatory) or during aircraft flights (Orleans, Zotino). In the first instance, the comparisons provide a diagnostic tool to identify systematic errors. In many cases correction of data for systematic errors is possible on the basis of independent information that describes the nature and magnitude of the error. For persisting offsets between laboratories, the frequent comparisons monitor the difference and permit an accurate estimate of uncertainty in merged data sets. For specific applications in which the absolute value is not a critical parameter, offsets that prove to be predictable may be used to adjust data sets to obtain higher precision of spatial and temporal differences in merged data sets.
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After almost a decade with little change in the global atmospheric methane burden, measurements from the Advanced Global Atmospheric Gases Experiment (AGAGE) and the Australian Commonwealth Scientific and Industrial Research Organisation... more
After almost a decade with little change in the global atmospheric methane burden, measurements from the Advanced Global Atmospheric Gases Experiment (AGAGE) and the Australian Commonwealth Scientific and Industrial Research Organisation (CSIRO) networks show a period of significant renewed growth at all measurement sites since late-2006. We use these data, with a simple model of atmospheric chemistry and transport, to optimally estimate the required change in emissions under both inter-annually repeating and inter-annually varying hydroxyl radical concentration. We find that if the annual mean hydroxyl radical concentration did not change, a substantial increase in emissions was required in both hemispheres during 2006-2007. However, if a small drop in the hydroxyl radical concentration did occur, consistent with AGAGE methyl chloroform measurements, the emissions increase is reduced overall and is more strongly biased to the Northern Hemisphere.
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ABSTRACT Current estimates of the terrestrial carbon fluxes in Asia (&quot;Asia&quot; refers to lands as far west as the Urals and is divided into Boreal Eurasia, Temperate Eurasia and tropical Asia based on TransCom regions) show... more
ABSTRACT Current estimates of the terrestrial carbon fluxes in Asia (&quot;Asia&quot; refers to lands as far west as the Urals and is divided into Boreal Eurasia, Temperate Eurasia and tropical Asia based on TransCom regions) show large uncertainties particularly in the boreal and mid-latitudes and in China. In this paper, we present an updated carbon flux estimate for Asia by introducing aircraft CO2 measurements from the CONTRAIL (Comprehensive Observation Network for Trace gases by Airline) program into an inversion modeling system based on the CarbonTracker framework. We estimated the averaged annual total Asian terrestrial land CO2 sink was about -1.56 Pg C yr-1 over the period 2006-2010, which offsets about one-third of the fossil fuel emission from Asia (+4.15 Pg C yr-1). The uncertainty of the terrestrial uptake estimate was derived from a set of sensitivity tests and ranged from -1.07 to -1.80 Pg C yr-1, comparable to the formal Gaussian error of ±1.18 Pg C yr-1 (1-sigma). The largest sink was found in forests, predominantly in coniferous forests (-0.64 Pg C yr-1) and mixed forests (-0.14 Pg C yr-1); and the second and third large carbon sinks were found in grass/shrub lands and crop lands, accounting for -0.44 Pg C yr-1 and -0.20 Pg C yr-1, respectively. The peak-to-peak amplitude of inter-annual variability (IAV) was 0.57 Pg C yr-1 ranging from -1.71 Pg C yr-1 to -2.28 Pg C yr-1. The IAV analysis reveals that the Asian CO2 sink was sensitive to climate variations, with the lowest uptake in 2010 concurrent with summer flood/autumn drought and the largest CO2 sink in 2009 owing to favorable temperature and plentiful precipitation conditions. We also found the inclusion of the CONTRAIL data in the inversion modeling system reduced the uncertainty by 11% over the whole Asian region, with a large reduction in the southeast of Boreal Eurasia, southeast of Temperate Eurasia and most Tropical Asian areas.
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ABSTRACT We present a comprehensive estimate of nitrous oxide (N[subscript 2]O) emissions using observations and models from 1995 to 2008. High-frequency records of tropospheric N[subscript 2]O are available from measurements at Cape... more
ABSTRACT We present a comprehensive estimate of nitrous oxide (N[subscript 2]O) emissions using observations and models from 1995 to 2008. High-frequency records of tropospheric N[subscript 2]O are available from measurements at Cape Grim, Tasmania; Cape Matatula, American Samoa; Ragged Point, Barbados; Mace Head, Ireland; and at Trinidad Head, California using the Advanced Global Atmospheric Gases Experiment (AGAGE) instrumentation and calibrations. The Global Monitoring Division of the National Oceanic and Atmospheric Administration/Earth System Research Laboratory (NOAA/ESRL) has also collected discrete air samples in flasks and in situ measurements from remote sites across the globe and analyzed them for a suite of species including N[subscript 2]O. In addition to these major networks, we include in situ and aircraft measurements from the National Institute of Environmental Studies (NIES) and flask measurements from the Tohoku University and Commonwealth Scientific and Industrial Research Organization (CSIRO) networks. All measurements show increasing atmospheric mole fractions of N[subscript 2]O, with a varying growth rate of 0.1–0.7% per year, resulting in a 7.4% increase in the background atmospheric mole fraction between 1979 and 2011. Using existing emission inventories as well as bottom-up process modeling results, we first create globally gridded a priori N[subscript 2]O emissions over the 37 years since 1975. We then use the three-dimensional chemical transport model, Model for Ozone and Related Chemical Tracers version 4 (MOZART v4), and a Bayesian inverse method to estimate global as well as regional annual emissions for five source sectors from 13 regions in the world. This is the first time that all of these measurements from multiple networks have been combined to determine emissions. Our inversion indicates that global and regional N[subscript 2]O emissions have an increasing trend between 1995 and 2008. Despite large uncertainties, a significant increase is seen from the Asian agricultural sector in recent years, most likely due to an increase in the use of nitrogenous fertilizers, as has been suggested by previous studies.
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A major consideration for producing atmospheric records from firn and ice cores is the effect of diffusion on the age and isotopic composition of the air. By selecting a site on Law Dome where the diffusive column is only 40 metres deep,... more
A major consideration for producing atmospheric records from firn and ice cores is the effect of diffusion on the age and isotopic composition of the air. By selecting a site on Law Dome where the diffusive column is only 40 metres deep, we have obtained firn air with an age spectral width (analogous to the standard deviation of the age
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ABSTRACT We have measured mixing ratios and stable isotope ratios of H2 and CH4 in 29 samples of air collected from 1992 and 2004 at the Australian Cape Grim baseline air monitoring station and stored in the air archive in Aspendale. The... more
ABSTRACT We have measured mixing ratios and stable isotope ratios of H2 and CH4 in 29 samples of air collected from 1992 and 2004 at the Australian Cape Grim baseline air monitoring station and stored in the air archive in Aspendale. The D/H ratios of H2 and CH4 were determined using a new technique involving continuous-flow isotope ratio mass spectrometry. The H2 mixing ratios of archived air samples show an excellent agreement with the in situ measurements, implying that artifacts that could occur during the collection and subsequent storage are absent. The D/H ratio of the H2 (deltaD-H2) has increased by about 20 per mil and its mixing ratio by about 10 ppb from 1992 to 2004. Influence of the Indonesian fires in 1997 is visible as the value of deltaD-H2 reaches lowest values in 1998 during the southern hemispheric winter. As biomass burning emits H2 of a low deuterium content, the decrease of deltaD- H2 could be associated with its direct emission into the atmosphere. However, a large scale decrease of OH radical concentrations due to the reaction with large amounts of CO emitted from biomass burning may also lead to an increase of H2 and concomitant decrease of deltaD-H2 as observed. During the period from 1992 to 2004, the D/H ratio of CH4 (deltaD-CH4) has increased by about 8 per mil, which is about 2.5 times smaller than the increasing rate of deltaD-H2. The larger increase of deuterium in H2 compared to CH4 suggests that photochemical oxidation of CH4 may serve as the single major source of H2 considering both the overall isotopic fractionation factor of 1.3 during the photochemical chain reactions from CH4 to H2and the isotopic fractionation factor of 0.58 for the oxidation of H2 itself.
We report measurements of N2O isotopologues on 25 free tropospheric whole air samples collected and archived between 1978 and 2005 from Cape Grim, Tasmania, and 11 firn air measurements from Law Dome, Antarctica. The measurements on... more
We report measurements of N2O isotopologues on 25 free tropospheric whole air samples collected and archived between 1978 and 2005 from Cape Grim, Tasmania, and 11 firn air measurements from Law Dome, Antarctica. The measurements on archived air show significant decreasing trends in the nitrogen and oxygen isotopic compositions over the last 30 years and are the first direct observations
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We present measurements and analysis of the isotopic composition (delta15Nbulk, delta15Nalpha, delta15Nbeta, and delta18O) of nitrous oxide in 50 samples of tropospheric air collected at Cape Grim, Tasmania between 1978 and 2005 and in 11... more
We present measurements and analysis of the isotopic composition (delta15Nbulk, delta15Nalpha, delta15Nbeta, and delta18O) of nitrous oxide in 50 samples of tropospheric air collected at Cape Grim, Tasmania between 1978 and 2005 and in 11 samples of firn air from Law Dome, Antarctica, with mean ages dating from 1940 to the 1990s. Over this 65 year period, the isotopic compositions
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Concentrations of carbon dioxide (CO2), methane (CH4), carbon monoxide (CO), nitrous oxide (N2O) and hydrogen (H2), and the stable carbon (δ 13 C-CO2) and oxygen (δ 18 O-CO2) isotopic composition of CO2 have been measured in air samples... more
Concentrations of carbon dioxide (CO2), methane (CH4), carbon monoxide (CO), nitrous oxide (N2O) and hydrogen (H2), and the stable carbon (δ 13 C-CO2) and oxygen (δ 18 O-CO2) isotopic composition of CO2 have been measured in air samples collected from Cabo de Rama (also known as Cape Rama), on the west coast of India (CRI), for the period 1993- 2002.
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Carbon monoxide (CO) plays a key role in global atmospheric chemistry by being the main sink of atmospheric hydroxyl radicals (OH). Records of past [CO] from both hemispheres are essential for understanding past changes in atmospheric... more
Carbon monoxide (CO) plays a key role in global atmospheric chemistry by being the main sink of atmospheric hydroxyl radicals (OH). Records of past [CO] from both hemispheres are essential for understanding past changes in atmospheric [OH]. Earlier attempts at reconstruction of northern hemisphere (NH) [CO] suffered from apparent in-situ CO production in ice and firn. We present a record
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Franklin R Guenther 1, Walter R Miller 1, David L Duewer 1, Gwi Suk Heo 2, Yong-Doo Kim 2, Adriaan MH van der Veen 3, Leonid Konopelko 4, Yury Kustikov 4, Nina Shor 4, Chris Brookes 5, Martin Milton 5, Florbela Dias 6 and Han Qiao 7
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... LP Steele. Marine and Atmospheric Research, Commonwealth Scientific and Industrial Research Organization, Aspendale, Victoria, Australia. PC Novelli. ... RF Weiss. Scripps Institution of Oceanography, University of California, San... more
... LP Steele. Marine and Atmospheric Research, Commonwealth Scientific and Industrial Research Organization, Aspendale, Victoria, Australia. PC Novelli. ... RF Weiss. Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, USA. P. Salameh. ...