Publications
55 results found
Jeong S, Newman S, Zhang J, et al., 2016, Estimating methane emissions in California's urban and rural regions using multitower observations, JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, Vol: 121, Pages: 13031-13049, ISSN: 2169-897X
Thomas RT, Prentice IC, Graven H, et al., 2016, Increased light-use efficiency in northern terrestrial ecosystems indicated by CO2 and greening observations, Geophysical Research Letters, Vol: 43, Pages: 11339-11349, ISSN: 1944-8007
Observations show an increasing amplitude in the seasonal cycle of CO2 (ASC) north of 45°N of 56 ± 9.8% over the last 50 years and an increase in vegetation greenness of 7.5–15% in high northern latitudes since the 1980s. However, the causes of these changes remain uncertain. Historical simulations from terrestrial biosphere models in the Multiscale Synthesis and Terrestrial Model Intercomparison Project are compared to the ASC and greenness observations, using the TM3 atmospheric transport model to translate surface fluxes into CO2 concentrations. We find that the modeled change in ASC is too small but the mean greening trend is generally captured. Modeled increases in greenness are primarily driven by warming, whereas ASC changes are primarily driven by increasing CO2. We suggest that increases in ecosystem-scale light use efficiency (LUE) have contributed to the observed ASC increase but are underestimated by current models. We highlight potential mechanisms that could increase modeled LUE.
Graven HD, 2016, The carbon cycle in a changing climate, Physics Today, Vol: 69, Pages: 48-54, ISSN: 0031-9228
Thomas R, Graven H, Hoskins B, et al., 2016, What is meant by ‘balancing sources and sinks of greenhouse gases’ to limit global temperature rise?, Grantham Institute Briefing Note, Imperial College London, 3
In an effort to limit global temperature rise to well below 2˚C, the COP21 Paris Agreement stipulates that a ‘balance’ between anthropogenic (man-made) sources and sinks of greenhouse gases must be reached by 2050-2100. An overall greenhouse gas ‘balance’ must consider individual gases in terms of how strongly they absorb solar infrared radiation, their concentration in the atmosphere, and their lifetime in the atmosphere.• Long-lived greenhouse gases, including carbon dioxide (CO2), accumulate in the atmosphere and continue to affect the climate for many centuries. To stabilise the concentrations of these long-lived gases, and thereby their effect on the climate, their sources must be progressively reduced towards zero. • For short-lived greenhouse gases that remain in the atmosphere for less than 100 years, including methane, stable or decreasing concentrations could be achieved within decades if emissions were stabilised or decreased. However, these gases currently only contribute about 20% of the total warming from greenhouse gases, so their reduction alone cannot successfully stabilise global temperature.• An overall ‘balance’ of sources and sinks of greenhouse gases could be facilitated by deliberate removal of CO2 from the atmosphere, for example, by combining biomass energy production with carbon capture and storage. Most current greenhouse gas emission scenarios that keep global temperature rise below 2˚C include some deliberate removal of CO2 to compensate for continued emissions of CO2 and other greenhouse gases
Jones CD, Arora V, Friedlingstein P, et al., 2016, The C4MIP experimental protocol for CMIP6, Geoscientific Model Development Discussions, Vol: 9, Pages: 2853-2880, ISSN: 1991-962X
Coordinated experimental design and implemen-tation has become a cornerstone of global climate modelling.Model Intercomparison Projects (MIPs) enable systematicand robust analysis of results across many models, by reduc-ing the influence of ad hoc differences in model set-up or ex-perimental boundary conditions. As it enters its 6th phase,the Coupled Model Intercomparison Project (CMIP6) hasgrown significantly in scope with the design and documenta-tion of individual simulations delegated to individual climatescience communities.The Coupled Climate–Carbon Cycle Model Intercompar-ison Project (C4MIP) takes responsibility for design, docu-mentation, and analysis of carbon cycle feedbacks and in-teractions in climate simulations. These feedbacks are poten-tially large and play a leading-order contribution in determin-ing the atmospheric composition in response to human emis-sions of CO2and in the setting of emissions targets to sta-bilize climate or avoid dangerous climate change. For overa decade, C4MIP has coordinated coupled climate–carboncycle simulations, and in this paper we describe the C4MIPsimulations that will be formally part of CMIP6. While theclimate–carbon cycle community has created this experimen-tal design, the simulations also fit within the wider CMIP ac-tivity, conform to some common standards including docu-mentation and diagnostic requests, and are designed to com-plement the CMIP core experiments known as the Diagnos-tic, Evaluation and Characterization of Klima (DECK).C4MIP has three key strands of scientific motivation andthe requested simulations are designed to satisfy their needs:(1) pre-industrial and historical simulations (formally partof the common set of CMIP6 experiments) to enable modelevaluation, (2) idealized coupled and partially coupled sim-ulations with 1 % per year increases in CO2to enable di-agnosis of feedback strength and its components, (3) futurescenario simulations
Jones CD, Arora V, Friedlingstein P, et al., 2016, C4MIP - The Coupled Climate-Carbon Cycle Model Intercomparison Project: experimental protocol for CMIP6, Geoscientific Model Development, Vol: 9, Pages: 2853-2880, ISSN: 1991-9603
Coordinated experimental design and implementation has become a cornerstone of global climate modelling. Model Intercomparison Projects (MIPs) enable systematic and robust analysis of results across many models, by reducing the influence of ad hoc differences in model set-up or experimental boundary conditions. As it enters its 6th phase, the Coupled Model Intercomparison Project (CMIP6) has grown significantly in scope with the design and documentation of individual simulations delegated to individual climate science communities. The Coupled Climate–Carbon Cycle Model Intercomparison Project (C4MIP) takes responsibility for design, documentation, and analysis of carbon cycle feedbacks and interactions in climate simulations. These feedbacks are potentially large and play a leading-order contribution in determining the atmospheric composition in response to human emissions of CO2 and in the setting of emissions targets to stabilize climate or avoid dangerous climate change. For over a decade, C4MIP has coordinated coupled climate–carbon cycle simulations, and in this paper we describe the C4MIP simulations that will be formally part of CMIP6. While the climate–carbon cycle community has created this experimental design, the simulations also fit within the wider CMIP activity, conform to some common standards including documentation and diagnostic requests, and are designed to complement the CMIP core experiments known as the Diagnostic, Evaluation and Characterization of Klima (DECK). C4MIP has three key strands of scientific motivation and the requested simulations are designed to satisfy their needs: (1) pre-industrial and historical simulations (formally part of the common set of CMIP6 experiments) to enable model evaluation, (2) idealized coupled and partially coupled simulations with 1 % per year increases in CO2 to enable diagnosis of feedback strength and its components, (3) future scenario simulations to project how the Earth system will re
Turnbull JC, Graven H, Krakauer NY, 2016, Radiocarbon in the Atmosphere, RADIOCARBON AND CLIMATE CHANGE: MECHANISMS, APPLICATIONS AND LABORATORY TECHNIQUES, Editors: Schuur, Druffel, Trumbore, Publisher: SPRINGER INTERNATIONAL PUBLISHING AG, Pages: 83-137, ISBN: 978-3-319-25641-2
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- Citations: 13
Graven HD, 2015, Impact of fossil fuel emissions on atmospheric radiocarbon and various applications of radiocarbon over this century, Proceedings of the National Academy of Sciences of the United States of America, Vol: 112, Pages: 9542-9545, ISSN: 1091-6490
Radiocarbon analyses are commonly used in a broad range of fields, including earth science, archaeology, forgery detection, isotope forensics, and physiology. Many applications are sensitive to the radiocarbon ((14)C) content of atmospheric CO2, which has varied since 1890 as a result of nuclear weapons testing, fossil fuel emissions, and CO2 cycling between atmospheric, oceanic, and terrestrial carbon reservoirs. Over this century, the ratio (14)C/C in atmospheric CO2 (Δ(14)CO2) will be determined by the amount of fossil fuel combustion, which decreases Δ(14)CO2 because fossil fuels have lost all (14)C from radioactive decay. Simulations of Δ(14)CO2 using the emission scenarios from the Intergovernmental Panel on Climate Change Fifth Assessment Report, the Representative Concentration Pathways, indicate that ambitious emission reductions could sustain Δ(14)CO2 near the preindustrial level of 0‰ through 2100, whereas "business-as-usual" emissions will reduce Δ(14)CO2 to -250‰, equivalent to the depletion expected from over 2,000 y of radioactive decay. Given current emissions trends, fossil fuel emission-driven artificial "aging" of the atmosphere is likely to occur much faster and with a larger magnitude than previously expected. This finding has strong and as yet unrecognized implications for many applications of radiocarbon in various fields, and it implies that radiocarbon dating may no longer provide definitive ages for samples up to 2,000 y old.
Lucas DD, Kwok CY, Cameron-Smith P, et al., 2015, Designing optimal greenhouse gas observing networks that consider performance and cost, Geoscientific Instrumentation, Methods and Data Systems, Vol: 4, Pages: 121-137, ISSN: 2193-0864
Emission rates of greenhouse gases (GHGs) enteringinto the atmosphere can be inferred using mathematicalinverse approaches that combine observations from a networkof stations with forward atmospheric transport models.Some locations for collecting observations are better thanothers for constraining GHG emissions through the inversion,but the best locations for the inversion may be inaccessibleor limited by economic and other non-scientific factors.We present a method to design an optimal GHG observingnetwork in the presence of multiple objectives that may bein conflict with each other. As a demonstration, we use ourmethod to design a prototype network of six stations to monitorsummertime emissions in California of the potent GHG1,1,1,2-tetrafluoroethane (CH2FCF3, HFC-134a). We use amultiobjective genetic algorithm to evolve network configurationsthat seek to jointly maximize the scientific accuracyof the inferred HFC-134a emissions and minimize the associatedcosts of making the measurements. The genetic algorithmeffectively determines a set of “optimal” observingnetworks for HFC-134a that satisfy both objectives (i.e., thePareto frontier). The Pareto frontier is convex, and clearlyshows the tradeoffs between performance and cost, and thediminishing returns in trading one for the other. Without dif-ficulty, our method can be extended to design optimal networksto monitor two or more GHGs with different emissionspatterns, or to incorporate other objectives and constraintsthat are important in the practical design of atmosphericmonitoring networks.
Lucas DD, Kwok CY, Cameron-Smith P, et al., 2015, Designing optimal greenhouse gas observing networks that consider performance and cost, GEOSCIENTIFIC INSTRUMENTATION METHODS AND DATA SYSTEMS, Vol: 4, Pages: 705-749, ISSN: 2193-0856
Goldberg SJ, Ball GI, Allen BC, et al., 2015, Refractory dissolved organic nitrogen accumulation in high-elevation lakes, Nature Communications, Vol: 6, ISSN: 2041-1723
The role of dissolved organic matter (DOM) as either a sink for inorganic nutrients or anadditional nutrient source is an often-neglected component of nutrient budgets in aquaticenvironments. Here, we examined the role of DOM in reactive nitrogen (N) storage in SierraNevada (California, USA) lakes where atmospheric deposition of N has shifted the lakestoward seasonal phosphorus (P)-limitation. Nuclear magnetic resonance (NMR) spectroscopyand isotope analyses performed on DOM isolated from Lake Tahoe reveal the accumulationof refractory proteinaceous material with a 100–200-year residence time. Incontrast, smaller lakes in the same watershed contain DOM with typical terrestrial characteristics,indicating that proteins in Lake Tahoe are autochthonously produced. These datasupport the role of DOM as a possible sink for reactive N in these lake ecosystems andidentify a potential role for DOM in affecting the inorganic nutrient stoichiometry of theseenvironments.
Sitch S, Friedlingstein P, Gruber N, et al., 2015, Recent trends and drivers of regional sources and sinks of carbon dioxide, BIOGEOSCIENCES, Vol: 12, Pages: 653-679, ISSN: 1726-4170
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- Citations: 541
Graven HD, Keeling RF, Piper SC, et al., 2013, Enhanced Seasonal Exchange of CO<sub>2</sub> by Northern Ecosystems Since 1960, SCIENCE, Vol: 341, Pages: 1085-1089, ISSN: 0036-8075
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- Citations: 277
Yver CE, Graven HD, Lucas DD, et al., 2013, Evaluating transport in the WRF model along the California coast, ATMOSPHERIC CHEMISTRY AND PHYSICS, Vol: 13, Pages: 1837-1852, ISSN: 1680-7316
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- Citations: 26
Turnbull J, Graven H, Miller J, et al., 2013, ATMOSPHERIC RADIOCARBON WORKSHOP REPORT, RADIOCARBON, Vol: 55, Pages: 1470-1474, ISSN: 0033-8222
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- Citations: 2
Miller J, Lehman S, Wolak C, et al., 2013, INITIAL RESULTS OF AN INTERCOMPARISON OF AMS-BASED ATMOSPHERIC <SUP>14</SUP>CO<sub>2</sub> MEASUREMENTS, RADIOCARBON, Vol: 55, Pages: 1475-1483, ISSN: 0033-8222
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- Citations: 11
Wanninkhof R, Park G-H, Takahashi T, et al., 2013, Global ocean carbon uptake: magnitude, variability and trends, BIOGEOSCIENCES, Vol: 10, Pages: 1983-2000, ISSN: 1726-4170
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- Citations: 251
Khatiwala S, Tanhua T, Fletcher SM, et al., 2013, Global ocean storage of anthropogenic carbon, BIOGEOSCIENCES, Vol: 10, Pages: 2169-2191, ISSN: 1726-4170
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- Citations: 311
Graven HD, Xu X, Guilderson TP, et al., 2013, COMPARISON OF INDEPENDENT Δ<SUP>14</SUP>CO<sub>2</sub> RECORDS AT POINT BARROW, ALASKA, RADIOCARBON, Vol: 55, Pages: 1541-1545, ISSN: 0033-8222
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- Citations: 7
Graven HD, Gruber N, Key R, et al., 2012, Changing controls on oceanic radiocarbon: New insights on shallow-to-deep ocean exchange and anthropogenic CO<sub>2</sub> uptake, JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS, Vol: 117, ISSN: 2169-9275
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- Citations: 90
Graven HD, Guilderson TP, Keeling RF, 2012, Observations of radiocarbon in CO<sub>2</sub> at La Jolla, California, USA 1992-2007: Analysis of the long-term trend, JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, Vol: 117, ISSN: 2169-897X
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- Citations: 14
Graven HD, Guilderson TP, Keeling RF, 2012, Observations of radiocarbon in CO<sub>2</sub> at seven global sampling sites in the Scripps flask network: Analysis of spatial gradients and seasonal cycles, JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, Vol: 117, ISSN: 2169-897X
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- Citations: 87
Graven HD, Gruber N, 2011, Continental-scale enrichment of atmospheric <SUP>14</SUP>CO<sub>2</sub> from the nuclear power industry: potential impact on the estimation of fossil fuel-derived CO<sub>2</sub>, ATMOSPHERIC CHEMISTRY AND PHYSICS, Vol: 11, Pages: 12339-12349, ISSN: 1680-7316
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- Citations: 57
Graven HD, Stephens BB, Guilderson TP, et al., 2009, Vertical profiles of biospheric and fossil fuel-derived CO<sub>2</sub> and fossil fuel CO<sub>2</sub> : CO ratios from airborne measurements of Δ<SUP>14</SUP>C, CO<sub>2</sub> and CO above Colorado, USA, TELLUS SERIES B-CHEMICAL AND PHYSICAL METEOROLOGY, Vol: 61, Pages: 536-546, ISSN: 1600-0889
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- Citations: 39
Graven HD, Guilderson TP, Keeling RF, 2007, Methods for high-precision <SUP>14</SUP>C AMS measurement of atmospheric CO<sub>2</sub> at LLNL, RADIOCARBON, Vol: 49, Pages: 349-356, ISSN: 0033-8222
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- Citations: 32
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