Global Carbon Budget 2017

Le Quéré C., Andrew R.M., Friedlingstein P., Sitch S., Pongratz J., Manning A.C., Ivar Korsbakken J., Peters G.P., Canadell J.G., Jackson R.B., Boden T.A., Tans P.P., Andrews O.D., Arora V.K., Bakker D.C.E., Barbero L., Becker M., Betts R.A., Bopp L., Chevallier F., Chini L.P., Ciais P., Cosca C.E., Cross J., Currie K., Gasser T., Harris I., Hauck J., Haverd V., Houghton R.A., Hunt C.W., Hurtt G., Ilyina T., Jain A.K., Kato E., Kautz M., Keeling R.F., Klein Goldewijk K., Körtzinger A., Landschützer P., Lefèvre N., Lenton A., Lienert S., Lima I., Lombardozzi D., Metzl N., Millero F., Monteiro P.M.S., Munro D.R., Nabel J.E.M.S., Nakaoka S.-I., Nojiri Y., Antonio Padin X., Peregon A., Pfeil B., Pierrot D., Poulter B., Rehder G., Reimer J., Rödenbeck C., Schwinger J., Séférian R., Skjelvan I., Stocker B.D., Tian H., Tilbrook B., Tubiello F.N., Laan-Luijkx I.T.V., Werf G.R.V., Van Heuven S., Viovy N., Vuichard N., Walker A.P., Watson A.J., Wiltshire A.J., Zaehle S., Zhu D. (2018) Global Carbon Budget 2017. Earth System Science Data. 10: 405-448.
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Doi: 10.5194/essd-10-405-2018

Resum:

Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere-the "global carbon budget"-is important to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe data sets and methodology to quantify the five major components of the global carbon budget and their uncertainties. CO2 emissions from fossil fuels and industry (EFF) are based on energy statistics and cement production data, respectively, while emissions from land-use change (ELUC), mainly deforestation, are based on land-cover change data and bookkeeping models. The global atmospheric CO2 concentration is measured directly and its rate of growth (GATM) is computed from the annual changes in concentration. The ocean CO2 sink (SOCEAN) and terrestrial CO2 sink (SLAND) are estimated with global process models constrained by observations. The resulting carbon budget imbalance (BIM), the difference between the estimated total emissions and the estimated changes in the atmosphere, ocean, and terrestrial biosphere, is a measure of imperfect data and understanding of the contemporary carbon cycle. All uncertainties are reported as ±1δ. For the last decade available (2007-2016), EFF was 9.4±0.5 GtC yr-1, ELUC 1.3±0.7 GtC yr-1, GATM 4.7±0.1 GtC yr-1, SOCEAN 2.4±0.5 GtC yr-1, and SLAND 3.0±0.8 GtC yr-1, with a budget imbalance BIM of 0.6 GtC yr-1 indicating overestimated emissions and/or underestimated sinks. For year 2016 alone, the growth in EFF was approximately zero and emissions remained at 9.9±0.5 GtC yr-1. Also for 2016, ELUC was 1.3±0.7 GtC yr-1, GATM was 6.1±0.2 GtC yr-1, SOCEAN was 2.6±0.5 GtC yr-1, and SLAND was 2.7±1.0 GtC yr-1, with a small BIM of-0.3 GtC. GATM continued to be higher in 2016 compared to the past decade (2007-2016), reflecting in part the high fossil emissions and the small SLAND consistent with El Ninõ conditions. The global atmospheric CO2 concentration reached 402.8±0.1 ppm averaged over 2016. For 2017, preliminary data for the first 6-9 months indicate a renewed growth in EFF of C2.0% (range of 0.8 to 3.0 %) based on national emissions projections for China, USA, and India, and projections of gross domestic product (GDP) corrected for recent changes in the carbon intensity of the economy for the rest of the world. This living data update documents changes in the methods and data sets used in this new global carbon budget compared with previous publications of this data set (Le Quéré et al., 2016, 2015b, a, 2014, 2013). All results presented here can be downloaded from https://doi.org/10.18160/GCP-2017 (GCP, 2017). © 2018 Author(s).

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Quantifying soil moisture impacts on light use efficiency across biomes

Stocker B.D., Zscheischler J., Keenan T.F., Prentice I.C., Peñuelas J., Seneviratne S.I. (2018) Quantifying soil moisture impacts on light use efficiency across biomes. New Phytologist. 218: 1430-1449.
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Doi: 10.1111/nph.15123

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Terrestrial primary productivity and carbon cycle impacts of droughts are commonly quantified using vapour pressure deficit (VPD) data and remotely sensed greenness, without accounting for soil moisture. However, soil moisture limitation is known to strongly affect plant physiology. Here, we investigate light use efficiency, the ratio of gross primary productivity (GPP) to absorbed light. We derive its fractional reduction due to soil moisture (fLUE), separated from VPD and greenness changes, using artificial neural networks trained on eddy covariance data, multiple soil moisture datasets and remotely sensed greenness. This reveals substantial impacts of soil moisture alone that reduce GPP by up to 40% at sites located in sub-humid, semi-arid or arid regions. For sites in relatively moist climates, we find, paradoxically, a muted fLUE response to drying soil, but reduced fLUE under wet conditions. fLUE identifies substantial drought impacts that are not captured when relying solely on VPD and greenness changes and, when seasonally recurring, are missed by traditional, anomaly-based drought indices. Counter to common assumptions, fLUE reductions are largest in drought-deciduous vegetation, including grasslands. Our results highlight the necessity to account for soil moisture limitation in terrestrial primary productivity data products, especially for drought-related assessments. © 2018 The Authors. New Phytologist © 2018 New Phytologist Trust

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Ecosystem responses to elevated CO<inf>2</inf>governed by plant–soil interactions and the cost of nitrogen acquisition

Terrer, C., Vicca, S., Stocker, B.D., Hungate, B.A., Phillips, R.P., Reich, P.B., Finzi, A.C., Prentice, I.C. (2018) Ecosystem responses to elevated CO2governed by plant–soil interactions and the cost of nitrogen acquisition. New Phytologist. 217: 507-522.
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Doi: 10.1111/nph.14872

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Impacts of global change on Mediterranean forests and their services

Peñuelas, J., Sardans, J., Filella, I., Estiarte, M., Llusià, J., Ogaya, R., Carnicer, J., Bartrons, M., Rivas-Ubach, A., Grau, O., Peguero, G., Margalef, O., Pla-Rabés, S., Stefanescu, C., Asensio, D., Preece, C., Liu, L., Verger, A., Barbeta, A., Achotegui-Castells, A., Gargallo-Garriga, A., Sperlich, D., Farré-Armengol, G., Fernández-Martínez, M., Liu, D., Zhang, C., Urbina, I., Camino-Serrano, M., Vives-Ingla, M., Stocker, B.D., Balzarolo, M., Guerrieri, R., Peaucelle, M., Marañón-Jiménez, S., Bórnez-Mejías, K., Mu, Z., Descals, A., Castellanos, A., Terradas, J. (2017) Impacts of global change on Mediterranean forests and their services. Forests. 8: 0-0.
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Doi: 10.3390/f8120463

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Greening of the Earth and its drivers

Zhu Z., Piao S., Myneni R.B., Huang M., Zeng Z., Canadell J.G., Ciais P., Sitch S., Friedlingstein P., Arneth A., Cao C., Cheng L., Kato E., Koven C., Li Y., Lian X., Liu Y., Liu R., Mao J., Pan Y., Peng S., Peuelas J., Poulter B., Pugh T.A.M., Stocker B.D., Viovy N., Wang X., Wang Y., Xiao Z., Yang H., Zaehle S., Zeng N. (2016) Greening of the Earth and its drivers. Nature Climate Change. 6: 791-795.
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Doi: 10.1038/nclimate3004

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Global environmental change is rapidly altering the dynamics of terrestrial vegetation, with consequences for the functioning of the Earth system and provision of ecosystem services. Yet how global vegetation is responding to the changing environment is not well established. Here we use three long-term satellite leaf area index (LAI) records and ten global ecosystem models to investigate four key drivers of LAI trends during 1982-2009. We show a persistent and widespread increase of growing season integrated LAI (greening) over 25% to 50% of the global vegetated area, whereas less than 4% of the globe shows decreasing LAI (browning). Factorial simulations with multiple global ecosystem models suggest that CO2 fertilization effects explain 70% of the observed greening trend, followed by nitrogen deposition (9%), climate change (8%) and land cover change (LCC) (4%). CO2 fertilization effects explain most of the greening trends in the tropics, whereas climate change resulted in greening of the high latitudes and the Tibetan Plateau. LCC contributed most to the regional greening observed in southeast China and the eastern United States. The regional effects of unexplained factors suggest that the next generation of ecosystem models will need to explore the impacts of forest demography, differences in regional management intensities for cropland and pastures, and other emerging productivity constraints such as phosphorus availability. © 2016 Macmillan Publishers Limited.

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