Publications by authors named "Dave Chadwick"

13 Publications

  • Page 1 of 1

Mitigation of Multiple Environmental Footprints for China's Pig Production Using Different Land Use Strategies.

Environ Sci Technol 2021 04 1;55(8):4440-4451. Epub 2021 Apr 1.

College of Resources and Environmental Sciences; National Academy of Agriculture Green Development; Key Laboratory of Plant-Soil Interactions, Ministry of Education, China Agricultural University, Beijing 100193, China.

Pig production contributes considerably to land use and greenhouse gas (GHG) and reactive nitrogen (Nr) emissions. Land use strategies were widely proposed, but the spillover effects on biological flow are rarely explored. Here, we simultaneously assessed the carbon (C), nitrogen (N), and cropland footprints of China's pig production at the provincial scale in 2017. The environmental impacts of land use strategies were further evaluated. Results show that one kg live-weight pig production generated an average of 1.9 kg CO-equiv and 59 g Nr emissions, occupying 3.5 m cropland, with large regional variations. A large reduction in GHG (58-64%) and Nr (12-14%) losses and occupied cropland (10-11%) could be achieved simultaneously if combined strategies of intensive crop production, improved feed-protein utilization efficiency, and feeding co-products were implemented. However, adopting a single strategy may have environmental side-effects. Reallocating cropland that pigs used for feed to plant food alternatives would enhance human-edible energy (3-20 times) and protein delivery (1-5 times) and reduce C and N footprints, except for rice and vegetables. Reallocating cropland to beef and milk production would decrease energy and protein supply. Therefore, a proper combination of land use strategies is essential to alleviate land use changes and nutrient emissions without sacrificing food supply.
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http://dx.doi.org/10.1021/acs.est.0c08359DOI Listing
April 2021

Carbon footprint of maize production in tropical/subtropical region: a case study of Southwest China.

Environ Sci Pollut Res Int 2021 Jun 5;28(22):28680-28691. Epub 2021 Feb 5.

Key Laboratory of Efficient Utilization of Soil and Fertilizer Resources, Chongqing, 400715, China.

Maize production is critical in tropical/subtropical regions, especially in developing countries where maize is a staple food. However, its environmental costs remain unclear. Southwest China is a tropical/subtropical region with large-scale maize production in each of its sub-regions. In the present study, we used Southwest China as a case study to evaluate the greenhouse gas (GHG) emissions and carbon footprint (CF) of maize production during 1996-2015 using life cycle assessment to identify the driving factors behind the GHG emissions and CF and to propose potential mitigation strategies. The mean GHG emissions of maize production per year during 1996-2015 was 4132 kg CO-eq·ha, and the CF during this period was 961 kg CO-eq·Mg. The GHG emissions and CF in Southwest China were 2-4 times higher than those of other major maize-producing regions worldwide. The GHG emissions and CF were both significantly correlated with the N surplus. The N surplus was also linearly correlated with annual precipitation, annual temperature and growing degree days, but not significantly related with soil pH. Scenario testing showed that the CF of maize production in Southwest China could be reduced by 41%, i.e. to 437 kg CO-eq·Mg, by farmers adopting a comprehensive strategy including recommended fertiliser application rates, innovative fertilisers, and crop management to decrease GHG emissions and achieve the yield potential in the region. Integrated soil and crop management is essential for sustainable maize production in tropical/subtropical regions with complex and changeable ecological conditions, especially in developing countries where maize is a staple food.
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http://dx.doi.org/10.1007/s11356-021-12663-wDOI Listing
June 2021

Combined applications of organic and synthetic nitrogen fertilizers for improving crop yield and reducing reactive nitrogen losses from China's vegetable systems: A meta-analysis.

Environ Pollut 2021 Jan 23;269:116143. Epub 2020 Nov 23.

College of Resources and Environment, Academy of Agricultural Sciences, Southwest University, Chongqing, 400716, China; Interdisciplinary Research Center for Agriculture Green Development in Yangtze River Basin, Southwest University, Chongqing, 400716, China; Chongqing Key Laboratory of Efficient Utilization of Soil and Fertilizer Resources, Southwest University, Chongqing, 400716, China. Electronic address:

The combined application of organic and synthetic nitrogen (N) fertilizers is being widely recommended in China's vegetable systems to reduce reliance on synthetic N fertilizer. However, the effect of substituting synthetic fertilizer with organic fertilizer on vegetable productivity (yield, N uptake and nitrogen use efficiency) and reactive nitrogen (Nr) losses (NO emission, N leaching and NH volatilization) remains unclear. A meta-analysis was performed using peer-reviewed papers published from 2000 to 2019 to comprehensively assess the effects of combined application of organic and synthetic N fertilizers. The results indicate that overall, the vegetable yield, NO emission and NH volatilization were not significantly changed, whereas N leaching was reduced by 44.6% and soil organic carbon (SOC) concentration increased by 12.5% compared to synthetic N fertilizer alone. Specifically, when synthetic N substitution rates (SRs) were ≤70%, vegetable yields and SOC concentration were increased by 5.5%-5.6% and 13.1-18.0%, and N leaching was reduced by 41.6%-48.1%. At the high substitution rate (SR>70%), vegetable yield was reduced by 13.6%, NO emission was reduced by 14.3%, and SOC concentration increased by 16.4%. Mixed animal-plant sources of organic N preferentially increased vegetable yield and SOC concentration, and reduced NO emission and N leaching compared with single sources of organic-N. Greenhouse gas (GHG) emission was decreased by 28.4%-34.9% by combined applications of organic and synthetic N sources, relative to synthetic N fertilizer alone. We conclude that appropriate rates (SR ≤ 70%) of combined applications of organic and synthetic N fertilizers could improve vegetable yields, decrease Nr and GHG emission, and facilitate sustainable development of coupled vegetable-livestock systems.
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http://dx.doi.org/10.1016/j.envpol.2020.116143DOI Listing
January 2021

Revealing soil legacy phosphorus to promote sustainable agriculture in Brazil.

Sci Rep 2020 09 28;10(1):15615. Epub 2020 Sep 28.

School of Natural Sciences, Bangor University, Bangor, LL57 2UW, Gwynedd, UK.

Exploiting native soil phosphorus (P) and the large reservoirs of residual P accumulated over decades of cultivation, namely "legacy P", has great potential to overcome the high demand of P fertilisers in Brazilian cropping systems. Long-term field experiments have shown that a large proportion (> 70%) of the surplus P added via fertilisers remains in the soil, mainly in forms not readily available to crops. An important issue is if the amount of legacy P mobilized from soil is sufficient for the crop nutritional demand and over how long this stored soil P can be effectively 'mined' by crops in a profitable way. Here we mapped the spatial-temporal distribution of legacy P over the past 50 years, and discussed possible agricultural practices that could increase soil legacy P usage by plants in Brazil. Mineral fertiliser and manure applications have resulted in ~ 33.4 Tg of legacy P accumulated in the agricultural soils from 1967 to 2016, with a current annual surplus rate of 1.6 Tg. Following this same rate, soil legacy P may reach up to 106.5 Tg by 2050. Agricultural management practices to enhance soil legacy P usage by crops includes increasing soil pH by liming, crop rotation, double-cropping, inter-season cover crops, no-tillage system and use of modern fertilisers, in addition to more efficient crop varieties and inoculation with P solubilising microorganisms. The adoption of these practices could increase the use efficiency of P, substantially reducing the new input of fertilisers and thus save up to 31.8 Tg of P fertiliser use (US$ 20.8 billion) in the coming decades. Therefore, exploring soil legacy P is imperative to reduce the demand for mineral fertilisers while promoting long-term P sustainability in Brazil.
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http://dx.doi.org/10.1038/s41598-020-72302-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7522976PMC
September 2020

Measured ammonia emissions from tropical and subtropical pastures: A comparison with 2006 IPCC, 2019 Refinement to the 2006 IPCC, and EMEP/EEA (European Monitoring and Evaluation Programme and European Environmental Agency) inventory estimates.

J Dairy Sci 2020 Jul 21;103(7):6706-6715. Epub 2020 May 21.

School of Natural Sciences, Bangor University, Bangor, Gwnedd, LL59 5TH, United Kingdom.

Agriculture is the largest source of ammonia (NH) emissions. As NH is an indirect greenhouse gas, NH measurements are crucial to improving greenhouse gas emission inventory estimates. Moreover, NH emissions have wider implications for environmental and human health. Only a few studies have measured NH emissions from pastures in the tropics and subtropics and none has compared emissions to inventory estimates. The objectives of this study were to (1) measure NH emissions from dairy pastures in tropical and subtropical regions; (2) calculate NH emissions factors (EF) for each campaign; and (3) compare measured EF with those based on the 2006 Intergovernmental Panel on Climate Change (IPCC) Tier 1, 2019 Refinement to the 2006 IPCC Tier 1, and the European Monitoring and Evaluation Programme/European Environmental Agency (EMPE/EEA) Tier 2 inventory estimates. Pasture NH emissions were measured on 3 dairy farms in Costa Rica. On each dairy, NH emissions were measured twice during the wet season and once during the dry season using a micrometeorological integrated horizontal-flux mass-balance method. Emissions were measured from excreta (dung and urine) deposited by grazing cattle and the subsequent application of organic (slurry) or synthetic fertilizer (ammonium nitrate or urea). Measured EF for all campaigns [from grazing cattle excreta and any subsequent slurry or fertilizer application; 4.9 ± 0.9% of applied nitrogen (mean ± SE)] were similar to those of the EMEP/EEA Tier 2 approach (6.1 ± 0.9%; mean ± SE) and 4 times lower than 2006 IPCC and 2019 Refinement to 2006 IPCC Tier 1 default estimates (17.7 ± 1.4 and 18.2 ± 0.9%, respectively; mean ± SE). Measured EF for excreta deposited on pasture and excreta both deposited on pasture and slurry application [3.9 ± 2.1 and 4.2 ± 2.1% (mean ± 95% CI), respectively] were 5 times lower than default EF assumed by 2006 IPCC and 2019 Refinement to 2006 IPCC methodology (both 20 and 21%, respectively), whereas EMEP/EAA estimates were similar [6.0 and 4.6 ± 0.3% (mean ± 95% CI), respectively]. This suggests an overestimation of EF from excreta deposited on pasture and slurry applications in tropical and subtropical regions by IPCC methodologies. Furthermore, rainfall, which is not included as a parameter in the current EMEP/EEA Tier 2 methodology, appeared to reduce NH emissions, suggesting that accounting for this in the inventory methodologies could improve inventory estimates.
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http://dx.doi.org/10.3168/jds.2019-17825DOI Listing
July 2020

Integrated systematic approach increase greenhouse tomato yield and reduce environmental losses.

J Environ Manage 2020 Jul 16;266:110569. Epub 2020 Apr 16.

College of Resources and Environment, Academy of Agricultural Sciences, Southwest University, Chongqing, 400716, China; Chongqing Key Laboratory of Efficient Utilization of Soil and Fertilizer Resources, Southwest University, Chongqing, 400716, China. Electronic address:

High input - high output greenhouse vegetable systems are responsible for nutrient surpluses and environmental losses. Integrated strategies that improve soil, crop and nutrient management are needed to ensure more sustainable production systems. We conducted a two-year field experiment to evaluate the potential of integrated soil-crop system management (ISSM) practices to improve the productivity and environmental outcomes from an intensive greenhouse tomato production system in the Yangtze River Basin, China. Four treatments were tested: i) farmers' practice (FP); ii) soil remediation (SR), where lime nitrogen with compost addition was the only management strategy; iii) a treatment that combined soil remediation with optimized crop planting density (SRCO), which increased planting density for improving crop yield; and iv) integrated soil-crop system management (ISSM), as a systematic integrated approach, which included the combined optimization of soil remediation, crop optimization, and nutrient management. In the integrated soil-crop system management treatment, nutrient management was optimized through adoption of the most appropriate type (formula) of fertilizer for the crop, rate and application timing of synthetic fertilizer, and by substituting poultry manure with compost. Our results indicated that the fruit yield of the integrated soil-crop system management treatment was 104 t ha, 13.4%-37.3% higher than that of the other three treatments. The mean reactive nitrogen loss (81.1 kg N ha) and the greenhouse gas emissions (6495 kg CO-eq ha) in the farmers' practice treatment were much higher than in the other three treatments (reactive nitrogen loss: 47.9-54.3 kg N ha; and greenhouse gas emissions: 4926-5468 kg CO-eq ha, respectively). The mean nitrogen and carbon footprints of the integrated soil-crop system management treatment were significantly lower than those of other treatments, as a result of both the lower fertilizer nitrogen use and the greater yield. This study indicates that integrated soil-crop system management could produce greater yields and increase net profit with reduced nitrogen inputs, whilst reducing the environmental cost associated with conventional farmers' practice in plastic-greenhouse vegetable production systems.
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http://dx.doi.org/10.1016/j.jenvman.2020.110569DOI Listing
July 2020

A critical review of the impacts of cover crops on nitrogen leaching, net greenhouse gas balance and crop productivity.

Glob Chang Biol 2019 08 13;25(8):2530-2543. Epub 2019 May 13.

Institute of Biological and Environmental Sciences, School of Biological Sciences, University of Aberdeen, Aberdeen, UK.

Cover crops play an increasingly important role in improving soil quality, reducing agricultural inputs and improving environmental sustainability. The main objectives of this critical global review and systematic analysis were to assess cover crop practices in the context of their impacts on nitrogen leaching, net greenhouse gas balances (NGHGB) and crop productivity. Only studies that investigated the impacts of cover crops and measured one or a combination of nitrogen leaching, soil organic carbon (SOC), nitrous oxide (N O), grain yield and nitrogen in grain of primary crop, and had a control treatment were included in the analysis. Long-term studies were uncommon, with most data coming from studies lasting 2-3 years. The literature search resulted in 106 studies carried out at 372 sites and covering different countries, climatic zones and management. Our analysis demonstrates that cover crops significantly (p < 0.001) decreased N leaching and significantly (p < 0.001) increased SOC sequestration without having significant (p > 0.05) effects on direct N O emissions. Cover crops could mitigate the NGHGB by 2.06 ± 2.10 Mg CO -eq ha  year . One of the potential disadvantages of cover crops identified was the reduction in grain yield of the primary crop by ≈4%, compared to the control treatment. This drawback could be avoided by selecting mixed cover crops with a range of legumes and non-legumes, which increased the yield by ≈13%. These advantages of cover crops justify their widespread adoption. However, management practices in relation to cover crops will need to be adapted to specific soil, management and regional climatic conditions.
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http://dx.doi.org/10.1111/gcb.14644DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6851768PMC
August 2019

The environmental costs and benefits of high-yield farming.

Nat Sustain 2018 Sep;1(9):477-485

Conservation Science Group, Department of Zoology, Downing St, Cambridge CB2 3EJ, UK.

How we manage farming and food systems to meet rising demand is pivotal to the future of biodiversity. Extensive field data suggest impacts on wild populations would be greatly reduced through boosting yields on existing farmland so as to spare remaining natural habitats. High-yield farming raises other concerns because expressed per unit area it can generate high levels of externalities such as greenhouse gas (GHG) emissions and nutrient losses. However, such metrics underestimate the overall impacts of lower-yield systems, so here we develop a framework that instead compares externality and land costs per unit production. Applying this to diverse datasets describing the externalities of four major farm sectors reveals that, rather than involving trade-offs, the externality and land costs of alternative production systems can co-vary positively: per unit production, land-efficient systems often produce lower externalities. For GHG emissions these associations become more strongly positive once forgone sequestration is included. Our conclusions are limited: remarkably few studies report externalities alongside yields; many important externalities and farming systems are inadequately measured; and realising the environmental benefits of high-yield systems typically requires additional measures to limit farmland expansion. Yet our results nevertheless suggest that trade-offs among key cost metrics are not as ubiquitous as sometimes perceived.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6237269PMC
September 2018

Designing Vulnerable Zones of Nitrogen and Phosphorus Transfers To Control Water Pollution in China.

Environ Sci Technol 2018 08 30;52(16):8987-8988. Epub 2018 Jul 30.

Key Laboratory of Agricultural Water Resources, Center for Agricultural Resources Research , Institute of Genetic and Developmental Biology, The Chinese Academy of Sciences , 286 Huaizhong Road , Shijiazhuang 050021 , Hebei China.

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http://dx.doi.org/10.1021/acs.est.8b02651DOI Listing
August 2018

Nitrogen losses to the environment following food-based digestate and compost applications to agricultural land.

Environ Pollut 2017 Sep 1;228:504-516. Epub 2017 Jun 1.

ADAS Boxworth, Battlegate Road, Boxworth, Cambridge, CB23 4NN, UK.

The anaerobic digestion of food waste for energy recovery produces a nutrient-rich digestate which is a valuable source of crop available nitrogen (N). As with any 'new' material being recycled to agricultural land it is important to develop best management practices that maximise crop available N supply, whilst minimising emissions to the environment. In this study, ammonia (NH) and nitrous oxide (NO) emissions to air and nitrate (NO) leaching losses to water following digestate, compost and livestock manure applications to agricultural land were measured at 3 sites in England and Wales. Ammonia emissions were greater from applications of food-based digestate (c.40% of total N applied) than from livestock slurry (c.30% of total N applied) due to its higher ammonium-N content (mean 5.6 kg/t compared with 1-2 kg/t for slurry) and elevated pH (mean 8.3 compared with 7.7 for slurry). Whilst bandspreading was effective at reducing NH emissions from slurry compared with surface broadcasting it was not found to be an effective mitigation option for food-based digestate in this study. The majority of the NH losses occurred within 6 h of spreading highlighting the importance of rapid soil incorporation as a method for reducing NH emissions. Nitrous oxide losses from food-based digestates were low, with emission factors all less than the IPCC default value of 1% (mean 0.45 ± 0.15%). Overwinter NO leaching losses from food-based digestate were similar to those from pig slurry, but much greater than from pig farmyard manure or compost. Both gaseous N losses and NO leaching from green and green/food composts were low, indicating that, in these terms, compost can be considered as an 'environmentally benign' material. These findings have been used in the development of best practice guidelines which provide a framework for the responsible use of digestates and composts in agriculture.
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http://dx.doi.org/10.1016/j.envpol.2017.05.023DOI Listing
September 2017

Mitigating Greenhouse Gas and Ammonia Emissions from Swine Manure Management: A System Analysis.

Environ Sci Technol 2017 04 29;51(8):4503-4511. Epub 2017 Mar 29.

Environment Centre Wales, School of Environment, Natural Resources and Geography, Deiniol Rd., Bangor University , Bangor LL57 2UW, United Kingdom.

Gaseous emissions from animal manure are considerable contributor to global ammonia (NH) and agriculture greenhouse gas (GHG) emissions. Given the demand to promote mitigation of GHGs while fostering sustainable development of the Paris Agreement, an improvement of management systems is urgently needed to help mitigate climate change and to improve atmospheric air quality. This study presents a meta-analysis and an integrated assessment of gaseous emissions and mitigation potentials for NH, methane (CH), and nitrous oxide (NO) (direct and indirect) losses from four typical swine manure management systems (MMSs). The resultant emission factors and mitigation efficiencies allow GHG and NH emissions to be estimated, as well as mitigation potentials for different stages of swine operation. In particular, changing swine manure management from liquid systems to solid-liquid separation systems, coupled with mitigation measures, could simultaneously reduce GHG emissions by 65% and NH emissions by 78%. The resultant potential reduction in GHG emissions from China's pig production alone is greater than the entire GHG emissions from agricultural sector of France, Australia, or Germany, while the reduction in NH emissions is equivalent to 40% of the total NH emissions from the European Union. Thus, improved swine manure management could have a significant impact on global environment issues.
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http://dx.doi.org/10.1021/acs.est.6b06430DOI Listing
April 2017

Environmental balance of the UK biogas sector: An evaluation by consequential life cycle assessment.

Sci Total Environ 2016 08 19;560-561:241-53. Epub 2016 Apr 19.

School of Environment, Natural Resources and Geography, Bangor, Gwynedd LL57 2UW, UK.

Anaerobic digestion (AD) is expanding rapidly in the UK. Previous life cycle assessment (LCA) studies have highlighted the sensitivity of environmental outcomes to feedstock type, fugitive emissions, biomethane use, energy conversion efficiency and digestate management. We combined statistics on current and planned AD deployment with operational data from a survey of biogas plant operators to evaluate the environmental balance of the UK biogas sector for the years 2014 and 2017. Consequential LCA was applied to account for all major environmental credits and burdens incurred, including: (i) substitution of composting, incineration, sewer disposal, field decomposition and animal feeding of wastes; (ii) indirect land use change (ILUC) incurred by the cultivation of crops used for biogas production and to compensate for bakery and brewery wastes diverted from animal feed. In 2014, the UK biogas sector reduced greenhouse gas (GHG) emissions by 551-755Gg CO2e excluding ILUC, or 238-755Gg CO2e including ILUC uncertainty. Fossil energy depletion was reduced by 8.9-10.8PJe, but eutrophication and acidification burdens were increased by 1.8-3.4Gg PO4e and 8.1-14.6Gg SO2e, respectively. Food waste and manure feedstocks dominate GHG abatement, largely through substitution of in-vessel composting and manure storage, whilst food waste and crop feedstocks dominate fossil energy credit, primarily through substitution of natural gas power generation. Biogas expansion is projected to increase environmental credits and loadings by a factor of 2.4 by 2017. If all AD bioelectricity replaced coal generation, or if 90% of biomethane replaced transport diesel or grid natural gas, GHG abatement would increase by 131%, 38% and 20%, respectively. Policies to encourage digestion of food waste and manures could maximize GHG abatement, avoiding the risk of carbon leakage associated with use of crops and wastes otherwise used to feed livestock. Covering digestate stores could largely mitigate net eutrophication and acidification burdens.
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http://dx.doi.org/10.1016/j.scitotenv.2016.03.236DOI Listing
August 2016

New technologies reduce greenhouse gas emissions from nitrogenous fertilizer in China.

Proc Natl Acad Sci U S A 2013 May 13;110(21):8375-80. Epub 2013 May 13.

Key Laboratory of Plant-Soil Interactions, Ministry of Education, and Center for Resources, Environment, and Food Security, China Agricultural University, Beijing 100193, China.

Synthetic nitrogen (N) fertilizer has played a key role in enhancing food production and keeping half of the world's population adequately fed. However, decades of N fertilizer overuse in many parts of the world have contributed to soil, water, and air pollution; reducing excessive N losses and emissions is a central environmental challenge in the 21st century. China's participation is essential to global efforts in reducing N-related greenhouse gas (GHG) emissions because China is the largest producer and consumer of fertilizer N. To evaluate the impact of China's use of N fertilizer, we quantify the carbon footprint of China's N fertilizer production and consumption chain using life cycle analysis. For every ton of N fertilizer manufactured and used, 13.5 tons of CO2-equivalent (eq) (t CO2-eq) is emitted, compared with 9.7 t CO2-eq in Europe. Emissions in China tripled from 1980 [131 terrogram (Tg) of CO2-eq (Tg CO2-eq)] to 2010 (452 Tg CO2-eq). N fertilizer-related emissions constitute about 7% of GHG emissions from the entire Chinese economy and exceed soil carbon gain resulting from N fertilizer use by several-fold. We identified potential emission reductions by comparing prevailing technologies and management practices in China with more advanced options worldwide. Mitigation opportunities include improving methane recovery during coal mining, enhancing energy efficiency in fertilizer manufacture, and minimizing N overuse in field-level crop production. We find that use of advanced technologies could cut N fertilizer-related emissions by 20-63%, amounting to 102-357 Tg CO2-eq annually. Such reduction would decrease China's total GHG emissions by 2-6%, which is significant on a global scale.
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http://dx.doi.org/10.1073/pnas.1210447110DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3666697PMC
May 2013
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