Yang Jia

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Yang
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Jia
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  • Preprint
    The 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.
  • Preprint
    Optimizing 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.