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Hanqin
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ArticleSpatial and temporal patterns of carbon emissions from forest fires in China from 1950 to 2000(American Geophysical Union, 2006-03-11) Lu, Aifeng ; Tian, Hanqin ; Liu, Mingliang ; Liu, Jiyuan ; Melillo, Jerry M.We have estimated the emission of carbon (C) and carbon-containing trace gases including CO2, CO, CH4, and NMHC (nonmethane hydrocarbons) from forest fires in China for the time period from 1950 to 2000 by using a combination of remote sensing, forest fire inventory, and terrestrial ecosystem modeling. Our results suggest that mean annual carbon emission from forest fires in China is about 11.31 Tg per year, ranging from a minimum level of 8.55 Tg per year to a maximum level of 13.9 Tg per year. This amount of carbon emission is resulted from the atmospheric emissions of four trace gases as follows: (1) 40.66 Tg CO2 with a range from 29.21 to 47.53 Tg, (2) 2.71 Tg CO with a range from 1.48 to 4.30 Tg, (3) 0.112 Tg CH4 with a range from 0.06 to 0.2 Tg, and (4) 0.113 Tg NMHC with a range from 0.05 to 0.19 Tg. Our study indicates that fire-induced carbon emissions show substantial interannual and decadal variations before 1980 but have remained relatively low and stable since 1980 because of the application of fire suppression. Large spatial variation in fire-induced carbon emissions exists due to the spatial variability of climate, forest types, and fire regimes.
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PreprintThe terrestrial biosphere as a net source of greenhouse gases to the atmosphere( 2015-12-21) Tian, Hanqin ; Lu, Chaoqun ; Ciais, Philippe ; Michalak, Anna M. ; Canadell, Josep G. ; Saikawa, Eri ; Huntzinger, Deborah N. ; Gurney, Kevin R. ; Sitch, Stephen ; Zhang, Bowen ; Yang, Jia ; Bousquet, Philippe ; Bruhwiler, Lori ; Chen, Guangsheng ; Dlugokencky, Edward J. ; Friedlingstein, Pierre ; Melillo, Jerry M. ; Pan, Shufen ; Poulter, Benjamin ; Prinn, Ronald G. ; Saunois, Marielle ; Schwalm, Christopher R. ; Wofsy, Steven C.The terrestrial biosphere can release or absorb the greenhouse gases, carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) and therefore plays an important role in regulating atmospheric composition and climate1. Anthropogenic activities such as land use change, agricultural and waste management have altered terrestrial biogenic greenhouse gas fluxes and the resulting increases in methane and nitrous oxide emissions in particular can contribute to climate warming2,3. The terrestrial biogenic fluxes of individual greenhouse gases have been studied extensively4-6, but the net biogenic greenhouse gas balance as a result of anthropogenic activities and its effect on the climate system remains uncertain. Here we use bottom-up (BU: e.g., inventory, statistical extrapolation of local flux measurements, process-based modeling) and top-down (TD: atmospheric inversions) approaches to quantify the global net biogenic greenhouse gas balance between 1981-2010 as a result of anthropogenic activities and its effect on the climate system. We find that the cumulative warming capacity of concurrent biogenic CH4 and N2O emissions is about a factor of 2 larger than the cooling effect resulting from the global land CO2 uptake in the 2000s. This results in a net positive cumulative impact of the three GHGs on the planetary energy budget, with a best estimate of 3.9±3.8 Pg CO2 eq/yr (TD) and 5.4±4.8 Pg CO2 eq/yr (BU) based on the GWP 100 metric (global warming potential on a 100-year time horizon). Our findings suggest that a reduction in agricultural CH4 and N2O emissions in particular in Southern Asia may help mitigate climate change.
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ArticleChina's terrestrial carbon balance : contributions from multiple global change factors(American Geophysical Union, 2011-03-31) Tian, Hanqin ; Melillo, Jerry M. ; Lu, Chaoqun ; Kicklighter, David W. ; Liu, Mingliang ; Ren, Wei ; Xu, Xiaofeng ; Chen, Guangsheng ; Zhang, Chi ; Pan, Shufen ; Liu, Jiyuan ; Running, Steven W.The magnitude, spatial, and temporal patterns of the terrestrial carbon sink and the underlying mechanisms remain uncertain and need to be investigated. China is important in determining the global carbon balance in terms of both carbon emission and carbon uptake. Of particular importance to climate-change policy and carbon management is the ability to evaluate the relative contributions of multiple environmental factors to net carbon source and sink in China's terrestrial ecosystems. Here the effects of multiple environmental factors (climate, atmospheric CO2, ozone pollution, nitrogen deposition, nitrogen fertilizer application, and land cover/land use change) on net carbon balance in terrestrial ecosystems of China for the period 1961–2005 were modeled with newly developed, detailed historical information of these changes. For this period, results from two models indicated a mean land sink of 0.21 Pg C per year, with a multimodel range from 0.18 to 0.24 Pg C per year. The models' results are consistent with field observations and national inventory data and provide insights into the biogeochemical mechanisms responsible for the carbon sink in China's land ecosystems. In the simulations, nitrogen deposition and fertilizer applications together accounted for 61 percent of the net carbon storage in China's land ecosystems in recent decades, with atmospheric CO2 increases and land use also functioning to stimulate carbon storage. The size of the modeled carbon sink over the period 1961–2005 was reduced by both ozone pollution and climate change. The modeled carbon sink in response to per unit nitrogen deposition shows a leveling off or a decline in some areas in recent years, although the nitrogen input levels have continued to increase.
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PreprintOptimizing resource use efficiencies in the food-energy-water nexus for sustainable agriculture : from conceptual model to decision support system( 2018-04) Tian, Hanqin ; Lu, Chaoqun ; Pan, Shufen ; Yang, Jia ; Miao, Ruiqing ; Ren, Wen ; Yu, Qiang ; Fu, Bojie ; Jin, Fei-Fei ; Lu, Yonglong ; Melillo, Jerry M. ; Ouyang, Zhiyun ; Palm, Cheryl A. ; Reilly, John M.Increased natural and anthropogenic stresses have threatened the Earth’s ability to meet growing human demands of food, energy and water (FEW) in a sustainable way. Although much progress has been made in the provision of individual component of FEW, it remains unknown whether there is an optimized strategy to balance the FEW nexus as a whole, reduce air and water pollution, and mitigate climate change on national and global scales. Increasing FEW conflicts in the agroecosystems make it an urgent need to improve our understanding and quantification of how to balance resource investment and enhance resource use efficiencies in the FEW nexus. Therefore, we propose an integrated modeling system of the FEW nexus by coupling an ecosystem model, an economic model, and a regional climate model, aiming to mimic the interactions and feedbacks within the ecosystem-human-climate systems. The trade-offs between FEW benefit and economic cost in excess resource usage, environmental degradation, and climate consequences will be quantitatively assessed, which will serve as sustainability indicators for agricultural systems (including crop production, livestock and aquaculture). We anticipate that the development and implementation of such an integrated modeling platform across world’s regions could build capabilities in understanding the agriculture-centered FEW nexus and guiding policy and land management decision making for a sustainable future.
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PreprintPattern and variation of C:N:P ratios in China’s soils : a synthesis of observational data( 2009-09-01) Tian, Hanqin ; Chen, Guangsheng ; Zhang, Chi ; Melillo, Jerry M. ; Hall, Charles A. S.Inspired by previous studies that have indicated consistent or even well-constrained relationships among carbon (C), nitrogen (N) and phosphorus (P) in soils, we have endeavored to explore general soil C:N:P ratios in China on a national scale, as well as the changing patterns of these ratios with soil depth, developmental stages and climate; we also attempted to determine if well-constrained C:N:P stoichiometrical ratios exist in China’s soil. Based on an inventory data set of 2,384 soil profiles, our analysis indicated that the mean C:N, C:P and N:P ratios for the entire soil depth (as deep as 250 cm for some soil profiles) in China were 11.9, 61 and 5.2, respectively, showing a C:N:P ratio of ~60:5:1. C:N ratios showed relatively small variation among different climatic zones, soil orders, soil depth and weathering stages, while C:P and N:P ratios showed a high spatial heterogeneity and large variations in different climatic zones, soil orders, soil depth and weathering stages. No well-constrained C:N:P ratios were found for the entire soil depth in China. However, for the 0-10 cm organic-rich soil, where has the most active organism-environment interaction, we found a well-constrained C:N ratio (14.4, molar ratio) and relatively consistent C:P (136) and N:P (9.3) ratios, with a general C:N:P ratio of 134:9:1. Finally, we suggested that soil C:N, C:P and N:P ratios in organic-rich topsoil could be a good indicator of soil nutrient status during soil development.
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ArticleGlobal carbon budget 2017(Copernicus Publications on behalf of the European Geosciences Union, 2018-03-12) Le Quere, Corinne ; Andrew, Robbie M. ; Friedlingstein, Pierre ; Sitch, Stephen ; Pongratz, Julia ; Manning, Andrew C. ; Korsbakken, Jan Ivar ; Peters, Glen P. ; Canadell, Josep G. ; Jackson, Robert B. ; Boden, Thomas A. ; Tans, Pieter P. ; Andrews, Oliver D. ; Arora, Vivek K. ; Bakker, Dorothee ; Barbero, Leticia ; Becker, Meike ; Betts, Richard A. ; Bopp, Laurent ; Chevallier, Frédéric ; Chini, Louise Parsons ; Ciais, Philippe ; Cosca, Catherine E. ; Cross, Jessica N. ; Currie, Kim I. ; Gasser, Thomas ; Harris, Ian ; Hauck, Judith ; Haverd, Vanessa ; Houghton, Richard A. ; Hunt, Christopher W. ; Hurtt, George ; Ilyina, Tatiana ; Jain, Atul K. ; Kato, Etsushi ; Kautz, Markus ; Keeling, Ralph F. ; Klein Goldewijk, Kees ; Körtzinger, Arne ; Landschützer, Peter ; Lefèvre, Nathalie ; Lenton, Andrew ; Lienert, Sebastian ; Lima, Ivan D. ; Lombardozzi, Danica ; Metzl, Nicolas ; Millero, Frank J. ; Monteiro, Pedro M. S. ; Munro, David R. ; Nabel, Julia E. M. S. ; Nakaoka, Shin-ichiro ; Nojiri, Yukihiro ; Padin, X. Antonio ; Peregon, Anna ; Pfeil, Benjamin ; Pierrot, Denis ; Poulter, Benjamin ; Rehder, Gregor ; Reimer, Janet ; Rödenbeck, Christian ; Schwinger, Jorg ; Séférian, Roland ; Skjelvan, Ingunn ; Stocker, Benjamin D. ; Tian, Hanqin ; Tilbrook, Bronte ; Tubiello, Francesco N. ; van der Laan-Luijkx, Ingrid T. ; van der Werf, Guido R. ; van Heuven, Steven ; Viovy, Nicolas ; Vuichard, Nicolas ; Walker, Anthony P. ; Watson, Andrew J. ; Wiltshire, Andrew J. ; Zaehle, Sonke ; Zhu, DanAccurate 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 ±1σ. 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 Niño 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 +2.0 % (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).
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ArticleChina's changing landscape during the 1990s : large-scale land transformations estimated with satellite data(American Geophysical Union, 2005-01-27) Liu, Jiyuan ; Tian, Hanqin ; Liu, Mingliang ; Zhuang, Dafang ; Melillo, Jerry M. ; Zhang, ZengxiangLand-cover changes in China are being powered by demand for food for its growing population and by the nation's transition from a largely rural society to one in which more than half of its people are expected to live in cities within two decades. Here we use an analysis of remotely sensed data gathered between 1990 and 2000, to map the magnitude and pattern of changes such as the conversion of grasslands and forests to croplands and the loss of croplands to urban expansion. With high-resolution (30 m) imagery from Landsat TM for the entire country, we show that between 1990 and 2000 the cropland area increased by 2.99 million hectares and urban areas increased by 0.82 million hectares. In northern China, large areas of woodlands, grasslands and wetlands were converted to croplands, while in southern China large areas of croplands were converted to urban areas. The land-cover products presented here give the Chinese government and international community, for the first time, an unambiguous understanding of the degree to which the nation's landscape is being altered. Documentation of these changes in a reliable and spatially explicit way forms the foundation for management of China's environment over the coming decades.
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ArticleInteraction between pollution and climate change augments ecological risk to a coastal ecosystem(Taylor & Francis, 2018-07-31) Lu, Yonglong ; Wang, Ruoshi ; Shi, Yajuan ; Su, Chao ; Yuan, Jingjing ; Johnson, Andrew C. ; Jenkins, Alan ; Ferrier, Robert C. ; Chen, Deliang ; Tian, Hanqin ; Melillo, Jerry M. ; Song, Shuai ; Ellison, Aaron M.Pollution and climate change are among the most challenging issues for countries with developing economies, but we know little about the ecological risks that result when these pressures occur together. We explored direct effects of, and interactions between, environmental pollution and climate change on ecosystem health in the Bohai Sea region of Northern China. We developed an integrated approach to assess ecological risks to this region under four scenarios of climate change. Although ecological risks to the system from pollution alone have been declining, interactions between pollution and climate change have enhanced ecological risks to this coastal/marine ecosystem. Our results suggest that current policies focused strictly on pollution control alone should be changed to take into account the interactive effects of climate change so as to better forecast and manage potential ecological risks.
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ArticleGlobal Carbon Budget 2016(Copernicus Publications, 2016-11-14) Le Quere, Corinne ; Andrew, Robbie M. ; Canadell, Josep G. ; Sitch, Stephen ; Korsbakken, Jan Ivar ; Peters, Glen P. ; Manning, Andrew C. ; Boden, Thomas A. ; Tans, Pieter P. ; Houghton, Richard A. ; Keeling, Ralph F. ; Alin, Simone R. ; Andrews, Oliver D. ; Anthoni, Peter ; Barbero, Leticia ; Bopp, Laurent ; Chevallier, Frédéric ; Chini, Louise Parsons ; Ciais, Philippe ; Currie, Kim I. ; Delire, Christine ; Doney, Scott C. ; Friedlingstein, Pierre ; Gkritzalis, Thanos ; Harris, Ian ; Hauck, Judith ; Haverd, Vanessa ; Hoppema, Mario ; Klein Goldewijk, Kees ; Jain, Atul K. ; Kato, Etsushi ; Körtzinger, Arne ; Landschützer, Peter ; Lefèvre, Nathalie ; Lenton, Andrew ; Lienert, Sebastian ; Lombardozzi, Danica ; Melton, Joe R. ; Metzl, Nicolas ; Millero, Frank J. ; Monteiro, Pedro M. S. ; Munro, David R. ; Nabel, Julia E. M. S. ; Nakaoka, Shin-ichiro ; O'Brien, Kevin ; Olsen, Are ; Omar, Abdirahman M. ; Ono, Tsuneo ; Pierrot, Denis ; Poulter, Benjamin ; Rödenbeck, Christian ; Salisbury, Joseph E. ; Schuster, Ute ; Schwinger, Jorg ; Séférian, Roland ; Skjelvan, Ingunn ; Stocker, Benjamin D. ; Sutton, Adrienne J. ; Takahashi, Taro ; Tian, Hanqin ; Tilbrook, Bronte ; van der Laan-Luijkx, Ingrid ; van der Werf, Guido R. ; Viovy, Nicolas ; Walker, Anthony P. ; Wiltshire, Andrew J. ; Zaehle, SonkeAccurate 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 all major components of the global carbon budget, including their uncertainties, based on the combination of a range of data, algorithms, statistics, and model estimates and their interpretation by a broad scientific community. We discuss changes compared to previous estimates and consistency within and among components, alongside methodology and data limitations. 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 combined evidence from land-cover change data, fire activity associated with deforestation, and models. The global atmospheric CO2 concentration is measured directly and its rate of growth (GATM) is computed from the annual changes in concentration. The mean ocean CO2 sink (SOCEAN) is based on observations from the 1990s, while the annual anomalies and trends are estimated with ocean models. The variability in SOCEAN is evaluated with data products based on surveys of ocean CO2 measurements. The global residual terrestrial CO2 sink (SLAND) is estimated by the difference of the other terms of the global carbon budget and compared to results of independent dynamic global vegetation models. We compare the mean land and ocean fluxes and their variability to estimates from three atmospheric inverse methods for three broad latitude bands. All uncertainties are reported as ±1σ, reflecting the current capacity to characterise the annual estimates of each component of the global carbon budget. For the last decade available (2006–2015), EFF was 9.3 ± 0.5 GtC yr−1, ELUC 1.0 ± 0.5 GtC yr−1, GATM 4.5 ± 0.1 GtC yr−1, SOCEAN 2.6 ± 0.5 GtC yr−1, and SLAND 3.1 ± 0.9 GtC yr−1. For year 2015 alone, the growth in EFF was approximately zero and emissions remained at 9.9 ± 0.5 GtC yr−1, showing a slowdown in growth of these emissions compared to the average growth of 1.8 % yr−1 that took place during 2006–2015. Also, for 2015, ELUC was 1.3 ± 0.5 GtC yr−1, GATM was 6.3 ± 0.2 GtC yr−1, SOCEAN was 3.0 ± 0.5 GtC yr−1, and SLAND was 1.9 ± 0.9 GtC yr−1. GATM was higher in 2015 compared to the past decade (2006–2015), reflecting a smaller SLAND for that year. The global atmospheric CO2 concentration reached 399.4 ± 0.1 ppm averaged over 2015. For 2016, preliminary data indicate the continuation of low growth in EFF with +0.2 % (range of −1.0 to +1.8 %) based on national emissions projections for China and USA, and projections of gross domestic product corrected for recent changes in the carbon intensity of the economy for the rest of the world. In spite of the low growth of EFF in 2016, the growth rate in atmospheric CO2 concentration is expected to be relatively high because of the persistence of the smaller residual terrestrial sink (SLAND) in response to El Niño conditions of 2015–2016. From this projection of EFF and assumed constant ELUC for 2016, cumulative emissions of CO2 will reach 565 ± 55 GtC (2075 ± 205 GtCO2) for 1870–2016, about 75 % from EFF and 25 % from ELUC. This living data update documents changes in the methods and data sets used in this new carbon budget compared with previous publications of this data set (Le Quéré et al., 2015b, a, 2014, 2013). All observations presented here can be downloaded from the Carbon Dioxide Information Analysis Center (doi:10.3334/CDIAC/GCP_2016).
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ArticleCarbon budget of tidal wetlands, estuaries, and shelf waters of eastern North America(John Wiley & Sons, 2018-04-04) Najjar, Raymond G. ; Herrmann, Maria ; Alexander, Richard ; Boyer, Elizabeth W. ; Burdige, David J. ; Butman, David ; Cai, Wei-Jun ; Canuel, Elizabeth A. ; Chen, Robert F. ; Friedrichs, Marjorie A. M. ; Feagin, Russell A. ; Griffith, Peter C. ; Hinson, Audra L. ; Holmquist, James R. ; Hu, Xinping ; Kemp, William M. ; Kroeger, Kevin D. ; Mannino, Antonio ; McCallister, S. Leigh ; McGillis, Wade R. ; Mulholland, Margaret R. ; Pilskaln, Cynthia H. ; Salisbury, Joseph E. ; Signorini, Sergio R. ; St-Laurent, Pierre ; Tian, Hanqin ; Tzortziou, Maria ; Vlahos, Penny ; Wang, Zhaohui Aleck ; Zimmerman, Richard C.Carbon cycling in the coastal zone affects global carbon budgets and is critical for understanding the urgent issues of hypoxia, acidification, and tidal wetland loss. However, there are no regional carbon budgets spanning the three main ecosystems in coastal waters: tidal wetlands, estuaries, and shelf waters. Here we construct such a budget for eastern North America using historical data, empirical models, remote sensing algorithms, and process‐based models. Considering the net fluxes of total carbon at the domain boundaries, 59 ± 12% (± 2 standard errors) of the carbon entering is from rivers and 41 ± 12% is from the atmosphere, while 80 ± 9% of the carbon leaving is exported to the open ocean and 20 ± 9% is buried. Net lateral carbon transfers between the three main ecosystem types are comparable to fluxes at the domain boundaries. Each ecosystem type contributes substantially to exchange with the atmosphere, with CO2 uptake split evenly between tidal wetlands and shelf waters, and estuarine CO2 outgassing offsetting half of the uptake. Similarly, burial is about equal in tidal wetlands and shelf waters, while estuaries play a smaller but still substantial role. The importance of tidal wetlands and estuaries in the overall budget is remarkable given that they, respectively, make up only 2.4 and 8.9% of the study domain area. This study shows that coastal carbon budgets should explicitly include tidal wetlands, estuaries, shelf waters, and the linkages between them; ignoring any of them may produce a biased picture of coastal carbon cycling.
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ArticleNet exchanges of CO2, CH4, and N2O between China's terrestrial ecosystems and the atmosphere and their contributions to global climate warming(American Geophysical Union, 2011-05-13) Tian, Hanqin ; Xu, Xiaofeng ; Lu, Chaoqun ; Liu, Mingliang ; Ren, Wei ; Chen, Guangsheng ; Melillo, Jerry M. ; Liu, JiyuanChina's terrestrial ecosystems have been recognized as an atmospheric CO2 sink; however, it is uncertain whether this sink can alleviate global warming given the fluxes of CH4 and N2O. In this study, we used a process-based ecosystem model driven by multiple environmental factors to examine the net warming potential resulting from net exchanges of CO2, CH4, and N2O between China's terrestrial ecosystems and the atmosphere during 1961–2005. In the past 45 years, China's terrestrial ecosystems were found to sequestrate CO2 at a rate of 179.3 Tg C yr−1 with a 95% confidence range of (62.0 Tg C yr−1, 264.9 Tg C yr−1) while emitting CH4 and N2O at rates of 8.3 Tg C yr−1 with a 95% confidence range of (3.3 Tg C yr−1, 12.4 Tg C yr−1) and 0.6 Tg N yr−1 with a 95% confidence range of (0.2 Tg N yr−1, 1.1 Tg N yr−1), respectively. When translated into global warming potential, it is highly possible that China's terrestrial ecosystems mitigated global climate warming at a rate of 96.9 Tg CO2eq yr−1 (1 Tg = 1012 g), substantially varying from a source of 766.8 Tg CO2eq yr−1 in 1997 to a sink of 705.2 Tg CO2eq yr−1 in 2002. The southeast and northeast of China slightly contributed to global climate warming; while the northwest, north, and southwest of China imposed cooling effects on the climate system. Paddy land, followed by natural wetland and dry cropland, was the largest contributor to national warming potential; forest, followed by woodland and grassland, played the most significant role in alleviating climate warming. Our simulated results indicate that CH4 and N2O emissions offset approximately 84.8% of terrestrial CO2 sink in China during 1961–2005. This study suggests that the relieving effects of China's terrestrial ecosystems on climate warming through sequestering CO2 might be gradually offset by increasing N2O emission, in combination with CH4 emission.
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ArticleEvaluation of simulated soil carbon dynamics in Arctic-Boreal ecosystems(IOP Publishing, 2020-02-07) Huntzinger, Deborah N. ; Schaefer, Kevin ; Schwalm, Christopher R. ; Fisher, Joshua B. ; Hayes, Daniel ; Stofferahn, Eric ; Carey, Joanna C. ; Michalak, Anna M. ; Wei, Yaxing ; Jain, Atul K. ; Kolus, Hannah ; Mao, Jiafu ; Poulter, Benjamin ; Shi, Xiaoying ; Tang, Jianwu ; Tian, HanqinGiven the magnitude of soil carbon stocks in northern ecosystems, and the vulnerability of these stocks to climate warming, land surface models must accurately represent soil carbon dynamics in these regions. We evaluate soil carbon stocks and turnover rates, and the relationship between soil carbon loss with soil temperature and moisture, from an ensemble of eleven global land surface models. We focus on the region of NASA's Arctic-Boreal vulnerability experiment (ABoVE) in North America to inform data collection and model development efforts. Models exhibit an order of magnitude difference in estimates of current total soil carbon stocks, generally under- or overestimating the size of current soil carbon stocks by greater than 50 PgC. We find that a model's soil carbon stock at steady-state in 1901 is the prime driver of its soil carbon stock a hundred years later—overwhelming the effect of environmental forcing factors like climate. The greatest divergence between modeled and observed soil carbon stocks is in regions dominated by peat and permafrost soils, suggesting that models are failing to capture the frozen soil carbon dynamics of permafrost regions. Using a set of functional benchmarks to test the simulated relationship of soil respiration to both soil temperature and moisture, we find that although models capture the observed shape of the soil moisture response of respiration, almost half of the models examined show temperature sensitivities, or Q10 values, that are half of observed. Significantly, models that perform better against observational constraints of respiration or carbon stock size do not necessarily perform well in terms of their functional response to key climatic factors like changing temperature. This suggests that models may be arriving at the right result, but for the wrong reason. The results of this work can help to bridge the gap between data and models by both pointing to the need to constrain initial carbon pool sizes, as well as highlighting the importance of incorporating functional benchmarks into ongoing, mechanistic modeling activities such as those included in ABoVE.
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ArticleFood benefit and climate warming potential of nitrogen fertilizer uses in China(IOP Publishing, 2012-10-31) Tian, Hanqin ; Lu, Chaoqun ; Melillo, Jerry M. ; Ren, Wei ; Huang, Yao ; Xu, Xiaofeng ; Liu, Mingliang ; Zhang, Chi ; Chen, Guangsheng ; Pan, Shufen ; Liu, Jiyuan ; Reilly, John M.Chemical nitrogen (N) fertilizer has long been used to help meet the increasing food demands in China, the top N fertilizer consumer in the world. Growing concerns have been raised on the impacts of N fertilizer uses on food security and climate change, which is lack of quantification. Here we use a carbon–nitrogen (C–N) coupled ecosystem model, to quantify the food benefit and climate consequence of agronomic N addition in China over the six decades from 1949 to 2008. Results show that N fertilizer-induced crop yield and soil C sequestration had reached their peaks, while nitrous oxide (N2O) emission continued rising as N was added. Since the early 2000s, stimulation of excessive N fertilizer uses to global climate warming through N2O emission was estimated to outweigh their climate benefit in increasing CO2 uptake. The net warming effect of N fertilizer uses, mainly centered in the North China Plain and the middle and lower reaches of Yangtze River Basin, with N2O emission completely counteracting or even exceeding, by more than a factor of 2, the CO2 sink. If we reduced the current N fertilizer level by 60% in 'over-fertilized' areas, N2O emission would substantially decrease without significantly influencing crop yield and soil C sequestration.
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ArticleEffects of tropospheric ozone pollution on net primary productivity and carbon storage in terrestrial ecosystems of China(American Geophysical Union, 2007-11-17) Ren, Wei ; Tian, Hanqin ; Liu, Mingliang ; Zhang, Chi ; Chen, Guangsheng ; Pan, Shufen ; Felzer, Benjamin S. ; Xu, XiaofengWe investigated the potential effects of elevated ozone (O3) along with climate variability, increasing CO2, and land use change on net primary productivity (NPP) and carbon storage in China's terrestrial ecosystems for the period 1961–2000 with a process-based Dynamic Land Ecosystem Model (DLEM) forced by the gridded data of historical tropospheric O3 and other environmental factors. The simulated results showed that elevated O3 could result in a mean 4.5% reduction in NPP and 0.9% reduction in total carbon storage nationwide from 1961 to 2000. The reduction of carbon storage varied from 0.1 Tg C to 312 Tg C (a decreased rate ranging from 0.2% to 6.9%) among plant functional types. The effects of tropospheric O3 on NPP were strongest in east-central China. Significant reductions in NPP occurred in northeastern and central China where a large proportion of cropland is distributed. The O3 effects on carbon fluxes and storage are dependent upon other environmental factors. Therefore direct and indirect effects of O3, as well as interactive effects with other environmental factors, should be taken into account in order to accurately assess the regional carbon budget in China. The results showed that the adverse influences of increasing O3 concentration across China on NPP could be an important disturbance factor on carbon storage in the near future, and the improvement of air quality in China could enhance the capability of China's terrestrial ecosystems to sequester more atmospheric CO2. Our estimation of O3 impacts on NPP and carbon storage in China, however, must be used with caution because of the limitation of historical tropospheric O3 data and other uncertainties associated with model parameters and field experiments.