Central and individual air-conditioning systems — A comparison of environmental impacts and resource consumption in a life cycle perspective

This paper compares individual (split) and central systems of air-conditioning in a life cycle perspective, taking into account the environmental impacts and resource consumption during resource extraction, material production, production of the air-conditioning units, their use, disposal and recycling. Life cycle assessment (LCA) is used in conducting this comparison.

Central systems have a longer lifetime than individual systems, lower electricity consumption and maintenance requirements during the use phase, and a higher recycling potential during the disposal phase. However, to transfer cool air, central systems use a large quantity of water pipes or air ducts, the production of which contributes significantly to resource use. The LCA study reveals that, on the whole, the central systems generally use less resources than split systems and result in lower environmental impacts.

The paper suggests a need for producers of air-conditioners to consider a change from being suppliers of air-conditioning hardware to being suppliers of cool air in order to overcome the initial cost constraints of central systems and realize their environmental and economic improvement potential to the benefit of the environment, and the industry as well as customers.     

Assessing carbon footprint in the life cycle of accommodation services: the case of an international tourist hotel

The accommodation sector is the most demanding energy consumer among all building stock categories. This study quantifies an international tourist hotel in Taiwan to holistically estimate the greenhouse gas emissions of hotel accommodation services through a complete life cycle inventory. The study also investigates the difference between the carbon emissions of the baseline and reduction years to understand the effects of carbon emission reduction on the hotel industry. Results show that energy consumption is the main source of carbon footprint. However, the carbon emissions of other activities, such as the production and transportation of hotel amenities and laundry services, are 15.90% for the baseline year and 16.03% for the reduction year. These values are larger than the 5% cutoff rule according to PAS 2050. Thus, these factors should also be considered in assessing the carbon emissions of accommodation services. Hotel occupancy rate significantly affects carbon emissions during a one-night stay in a standard room as the functional unit. The selection of the functional unit should be considered in the hotel strategy. Although this case study involves an international tourist hotel in Taiwan, the findings and recommendations for improvements can be applied elsewhere.     

Life cycle assessment of the winter wheat-summer maize production system on the North China Plain

A life cycle assessment (LCA) method was used to examine the environmental impact of the winter wheat-summer maize production system on the North China Plain. The LCA considered the entire system required to produce 1 ton each of winter wheat and summer maize. The analysis included raw material extraction and transportation, agrochemical production and transportation, and arable farming in the field. First, all emissions and resource consumption connected to the different processes were listed in a life cycle inventory (LCI) and related to a common unit (1 ton of grain). Subsequently, a life cycle impact assessment (LCIA) was conducted, in which the inventory data were aggregated into indicators for environmental effects, including energy depletion, climate change, acidification, aquatic eutrophication, human toxicity, aquatic and terrestrial ecotoxicity. For winter wheat systems, energy depletion and acidification were the most relevant environmental impacts, and energy depletion and aquatic eutrophication were the primary concerns for summer maize systems. The results revealed that the most important source of environmental impact in the winter wheat-summer maize production system in Huantai County was the production and application of nitrogen fertilisers. The environmental impacts of winter wheat were much stronger than those of summer maize due to higher inputs and lower use efficiency of agrochemicals.     

Identification and assessment of environmental burdens of Chinese copper production from a life cycle perspective

The environmental burdens of Chinese copper production have been identified and quantified in the context of typical technologies, materials supplies and environmental emissions by a life cycle approach. Primary and secondary copper production using copper ores and scraps, respectively, were analyzed in detail. The flash and bath smelting approaches and the recycling of copper scraps were selected as representative copper production processes. A quantitative analysis was also conducted to assess the influence of material transport distance in copper production. Life cycle assessment （LCA） results showed that resources depletion and human health contribute significantly to environmental burdens in Chinese copper production. In addition, the secondary copper production has dramatically lower environmental burdens than the primary production. There is no obvious distinction in overall environmental burdens in primary copper production by flash or bath smelting approach. However, resources depletion is lower and the damage to human health is higher for flash smelting approach. Ecosystem quality damage is slight for both approaches. Environ- mental burdens from the mining stage contribute most in all life cycle stages in primary copper production. In secondary copper production, the electrolytic refining stage dominates. Based on the life cycle assessment results, some suggestions for improving environmental performance were proposed to meet the sustainable development of Chinese copper industry.     

上海、北京和天津碳排放的比较

以北京、天津、上海为例,探讨了城市碳排放趋势预测的研究方法。采用最优增长率模型,研究了经济平稳增长的条件下,各市未来的能源碳排放趋势。考虑了水泥工业的碳排放量,并采用CO2FIX模型计算各市森林碳汇量,从而得到各市净碳排放量。结果表明：北京、天津、上海的能源碳排放量都呈倒U型曲线,上海的碳排放量远高于北京和天津两市。北京、天津、上海的水泥碳排放量都呈增加趋势,其中北京每年的水泥碳排放量最大,且增长率也是3个城市中最大的。北京和天津的累计森林碳汇量不断上升,上海的累计森林碳汇量几乎为零。北京、上海、天津的净碳排放量仍呈倒U型曲线增长,但与不考虑水泥碳排放和森林碳汇时的情况差别不大。由此可见,北京、上海、天津应重点减少能源碳排放,有效控制水泥产业碳排放,逐步扩大植树造林面积,从多方面采取措施降低碳排放。     

Benefits and challenges of streamlined life-cycle assessment for SMEs – findings from case studies on climate change impacts

ABSTRACT

Small and medium-sized enterprises (SMEs) have a substantial role in the economy and job creation, but they are a remarkable source of environmental impacts. SMEs often lack skills and resources to compile environmental impact assessments; Streamlined Life Cycle Analysis (LCA) can provide efficient tools for this. An application of streamlined LCA relying heavily on database data, LCA clinic, was developed and tested on 23 SMEs in Finland. The climate change impacts were mainly caused by the production of raw materials, electricity and heating, whereas packaging and transportation were not influential. A significant amount of emissions were indirect, i.e. caused by production of raw materials. Thus, decreasing emissions from raw material production or selecting raw materials with a smaller environmental load could be a more efficient way to decrease emissions than reducing direct emissions such as those from electricity use. Lack of data in the LCA-databases was considered a challenge. An access to regionally customised datasets is important for the implementation of LCA clinics. Company feedback indicated that LCA clinics were useful in climate-friendly product design and increased environmental awareness, but did not lead to immediate actions to reduce emissions because of inadequate investment capabilities. Company managers had limited possibilities to use the results in marketing as comparative assessments would require a full LCA. Many company managers were willing to pay a fee sufficient to cover the costs of an LCA clinic, but some considered that the costs should be covered by external funding sources.     

中国燃煤电厂碳排放量计算及分析

人类活动造成的温室气体排放已经对自然生态造成了巨大的影响。如果无法有效解决气候变化问题,到2030年将有超过1亿人因此而失去生命,且全球经济增长将削减3.2%。有效地控制和减少温室气体的排放是人类急需解决的问题。目前中国温室气体排放总量已经超越美国成为全球第一大温室气体排放国,中国的能源结构决定了中国燃煤发电是中国CO2主要排放源之一,因此实现燃煤发电碳减排对降低中国碳排放总量,减少温室气体排放具有重要意义。准确地计算燃煤电厂产生的碳排放量是进行碳排放权交易、低碳火电厂在经济上具有可行性,最终实现燃煤电厂碳减排的前提条件之一。本研究根据世界资源研究所提供的计算工具首先界定了本研究对于碳排放计算的范围,其次阐述了不同电厂应针对其使用的燃煤进行工业分析的精细化程度不同而采用不同的计算方法,最后对两组不同机组类型的中国火电厂进行了碳排放量计算和对比分析。根据以上分析得出了大容量、高参数的燃煤发电机组相比小容量发电机组不仅能提高能源利用效率,同时也能相对减少因生产电能而产生的CO2排放。其次,燃煤电厂CO2排放中煤炭固定燃烧占有绝对比例,脱硫及外购电力所占比例较小,但排放的绝对总量并不小。再次,由于大容量、高参数机组与小容量发电机组相比在生产单位电能所消耗的燃煤量更少、其排放的废弃中的CO2浓度相对较高,应此更适合安装碳捕捉系统,有助于提高捕捉效率,降低捕捉CO2的成本。因此,建议在未来建设碳捕捉系统时应优先选择大容量、高参数机组。本研究的创新点在于在上述研究的基础上考虑单个燃煤电厂的煤质、考虑电厂脱硫、外购电力的因素,根据电厂对煤质不同程度的工业分析采用不同的计算方法,目的在于更?     

Impacts of inter-sectoral trade on carbon emissions—a case of China in 2007

With the increase in international trade, more attention has been given to quantifying the impacts of international trade on energy use and carbon emissions. Input-output analysis is a suitable tool for assessing resources or pollutants embodied in trade and it has become a critical tool for performing such analysis. This study estimated the national and sectoral carbon emissions embodied in Chinese international trade using the latest available China input-output table of 2007. The results showed that a significant exporting behavior of embodied carbon emissions existed in China??s trade. Over 1/3 of the emissions in Chinese domestic production processes were generated for exports in 2007. The net balance of emissions embodied in exports and imports accounted for nearly 30% of China??s domestic emissions, which means that any policy made to increase the exports would result in a significant growth of China??s domestic emissions. Since over half of China??s export trade is processing trade, the re-exported emissions could not be overlooked; otherwise, it would hard to capture the actual emissions generated abroad to obtain China??s domestic consumption. The enlargement of export scale is a primary driven factor to the rapid growth of China??s exported emissions. It is necessary for China to adjust its economic and industrial structure to reduce the dependence of economic growth on the export trade. However, when adjusting industry structures or making policies on carbon emission reduction, it will be more reasonable to consider the relationship between production and consumption, rather than just focus on the emission values of sectors?? direct production, as a large part of carbon emissions emitted by the principal direct polluters were generated to obtain the products which were required by other sectors.     

城市生活垃圾生命周期管理

生命周期评价是一种全面的环境管理工具，具有潜在的发展前景。０它通过对产品，产品系统，工艺活动整个生命周期的环境影响环境改善的机会进行评价。根据国际环境毒理与化学学会１９９３年和ＩＳＯ１４０００环境管理体系中关于生命周期评价的技术框架，本文应生命周期评价在城市生产垃圾管理系统中的作用及管理系统的清单分析，影响评价和改善评价进行研究。     

基于生命周期评价理论的建筑物环境影响评价系统

建筑物对环境有着巨大的影响。基于生命周期评价(LCA)理论,从材料的开采生产,建筑物的建造、运行直至建筑物被拆除来研究建筑物的环境影响。在一个涉及建筑材料、建筑设备以及建设场地的环境影响数据库的基础上,开发了一个建筑物的环境影响的评价模型BEPAS(BuildingEnvironmentalPerformanceAnalysisSystem)。模型从3个方面:建筑设备运行、建筑材料和建筑场地来研究建筑的环境影响。最后,测算了一个案例,分析了其环境影响水平。     

湿地碳循环研究综述

湿地由于其巨大的碳库储存能力而成为碳循环研究的热点之一.从湿地CO_2/CH_4释放时空格局,CO_2/CH_4释放影响因子,碳"源""汇"评估及人类活动影响四个方而综述了国内外湿地碳循环方面的研究工作.认为当前对湿地碳排放过程各种潜在的影响因素比较清楚,但碳排放过程各种影响因子之间存在的交互作用有待于进一步深入研究.在进行不同湿地类型碳循环研究的同时,应加强包括微生物、植物根系等地下碳动态研究,加强碳、氮耦合研究.在评估人类活动对湿地碳循环的影响过程中,要综合考虑植被碳库、土壤碳库及土壤碳排的变化.另外,无论从认识不同湿地类型碳过程特征及机理的角度,还是从减少全球或区域碳收支估测不确定性的角度来看,加强数据缺乏地区的湿地类型的碳平衡及相关碳过程的研究都具有重要意义.     

中国农田固碳减排发展现状及其战略对策

自20世纪80年代以来,农田固碳减排的动态变化日益成为全球的研究热点,它对于正确评价农业产业对全球气候变化的影响具有重要的理论意义。采取农业分区的方法,将我国划分为4个不同的农业区,并从区域植被覆盖、地理气候、品种、土壤性质、种植制度和施肥情况等方面,综合分析了各区域农田固碳减排的基本现状。通过对我国农田固碳减排的各个影响因素进行系统阐述,探明了耕作措施、水田种植面积、秸秆还田、施肥情况、轮作制度、土地利用方式和农田生态系统等是影响我国农田固碳减排的主要关键因素。同时,针对目前我国农田固碳减排的基本状况,提出了适合我国农田固碳减排的主要对策。文章认为,应从加强农田碳循环和土壤碳汇效应、合理调整农田土地利用结构、加强农田管理技术体系创新、加强农田生物固碳减排技术研究和注重降低农业生产温室气体的排放等方面开展系统研究,从而进一步增强农田的土壤固碳能力和减少温室气体的排放,达到我国农田固碳减排的最终目的。     

天津市燃煤型热电企业初始碳核查方法初探

天津市开展初始碳核查旨在通过碳排放交易市场来控制当地的二氧化碳排放量,促进当地绿色低碳发展。以天津市燃煤型热电企业为初始碳核查对象,结合实际核查过程中遇到的"指南外"情况,探索一套适合于此类企业的碳核查方法,来准确核算其真实碳排放数据,为天津市碳排放交易市场及企业碳排放权配额分配的顺利开展奠定基础。     

不同灌溉方式冬小麦农田生态系统碳平衡研究

全球气候变暖趋势明显,陆地生态系统碳循环的研究成为目前的研究热点,而农田生态系统是陆地生态系统的重要组成部分,由于农田生态系统是受人类强烈调节与控制的复合系统,其碳循环受各类农作措施的影响极大。新疆地处干旱区,水分条件是农田碳循环的最重要限制因子。为此,分析不同灌溉方式对冬小麦（Triticum aestivuml）农田生态系统碳平衡的影响,从而提出有利于新疆冬小麦生产的固碳减排的灌溉方式。试验于2012—2013年在伊宁县科技示范园冬小麦试验田进行,选择伊农18冬小麦品种为供试材料,确定滴灌和漫灌为两个试验主因子并设置小区。试验自冬小麦返青开始至完全成熟结束,期间平均每7天采1次样,其中用典型样株法采集小麦植株,分根、茎、叶等不同器官单独烘干测定植株固碳量;用静态钠石灰吸收法测定冬小麦土壤呼吸;收集整理已发表国内外文献中的各类碳排放参数确定本研究中所需参数;采用王小彬的碳平衡计算方法分析不同灌溉方式农田生态系统碳平衡,据此对滴灌和漫灌两种灌溉方式的冬麦农田作物生物量固碳、土壤碳排放量和作物生产过程中物质投入的间接碳排放量,以及两种灌溉方式下冬麦农田生态系统净碳值进行分析。试验结果表明：滴灌条件下冬麦农田生态系统小麦的固碳量、土壤碳排放总量分别比漫灌小麦的高出15.38%和11.43%,冬小麦穗是差异形成的主要原因;而农业生产资料排碳总量比漫灌少排3.88%;但无论是滴灌还是漫灌,耗电碳排放量均占农业生产资料碳排放总量的59%以上,是农业生产资料碳排放的第一大来源。两种灌溉方式下冬小麦田生态系统的净碳值均呈现出固碳并存在显著差异（p〈0.01）,且滴灌冬麦农田生态系统净碳值比漫灌高25.39%。因此,新疆冬小麦生产中采用滴灌方式更有利于农田生态系统的固碳,     

湿地生态系统碳汇与碳源过程的控制因子和临界条件

湿地生态系统由于其自身的结构组分特征,已成为地球表层系统中最为重要的碳汇。但是近年来对于湿地系统的不合理开发利用、降水减少等原因使其碳＂汇＂功能减弱,湿地的碳蓄积能力下降且有转变为碳＂源＂的趋势。文章从湿地生态系统的水份、植物类型、土壤厚度、微生物（底物、pH、温度、氧化还原条件）等方面总结了影响湿地碳汇/源过程的控制因子和临界交替条件。湿地水位的高低决定湿地的氧气环境,与甲烷产生量成正相关,但却与二氧化碳产生量有一定的负相关关系。湿地植物通过通气组织与根系分泌物等影响湿地碳的吸收与排放通量,湿地植株的高度、覆盖率等也是影响湿地作为碳汇与碳源的重要因素。不同深度土层由于其产甲烷菌、甲烷氧化菌等微生物活性不同导致各个土层碳吸收、排放通量的差异,通常浅层土壤中的CO2、CH4的产生率高于深层土壤。微生物的活跃程度直接影响到湿地碳的吸收与排放,影响活跃程度的因素包括湿地底物、pH、温度与氧化还原条件等。湿地底物浓度的增加会在一定程度上提高甲烷的产生率,中性或者是弱碱性环境是产甲烷菌的最适宜条件,在一定范围内温度越高,甲烷产生量越大,而温度对于二氧化碳的影响则是通过改变光合作用来实现。氧化还原电位与甲烷产生量成负相关关系,-150 mV是产甲烷菌产生甲烷的最高电位。总体上,由于湿地生态系统的复杂性和碳吸收与排放过程的复杂,以上这些因子相互作用,且在一定条件下会相互转化。最后针对如何充分发挥湿地生态系统的碳＂汇＂功能,控制湿地向碳＂源＂转化的条件措施方面进行了讨论,包括间歇灌溉、种植多年生草本植物或木本植物等来增强湿地的固碳能力。     

Circular economy strategies for combating climate change and other environmental issues

Global industrialization and excessive dependence on nonrenewable energy sources have led to an increase in solid waste and climate change, calling for strategies to implement a circular economy in all sectors to reduce carbon emissions by 45% by 2030, and to achieve carbon neutrality by 2050. Here we review circular economy strategies with focus on waste management, climate change, energy, air and water quality, land use, industry, food production, life cycle assessment, and cost-effective routes. We observed that increasing the use of bio-based materials is a challenge in terms of land use and land cover. Carbon removal technologies are actually prohibitively expensive, ranging from 100 to 1200 dollars per ton of carbon dioxide. Politically, only few companies worldwide have set climate change goals. While circular economy strategies can be implemented in various sectors such as industry, waste, energy, buildings, and transportation, life cycle assessment is required to optimize new systems. Overall, we provide a theoretical foundation for a sustainable industrial, agricultural, and commercial future by constructing cost-effective routes to a circular economy.

     

Evaluating the environmental impacts of an urban wetland park based on emergy accounting and life cycle assessment: A case study in Beijing

In this paper, emergy accounting (EA) and life cycle assessment (LCA) methods are employed to investigate a typical urban wetland park, the Green Lake Urban Wetland Park (GLUWP) of Beijing, in terms of its environmental and capital inputs, ecosystem services and organic matter yields, environmental support, and sustainability. The LCA method is also used to obtain a quantitative estimation of the environmental impact of discharges during the entire life cycle of the GLUWP. Various emergy-based indices, such as emergy yield ratio (EYR), environmental load ratio (ELR), emergy sustainability index (ESI), net economic benefit (Np), and environmental impacts of process-based LCA, including global warming potential (GWP), eutrophication (EU), nonrenewable resource depletion (RU), energy consumption (EN), acidification potential (AP), photochemical oxidant creation potential (POCP), particulate matter (PM) and wastes (W), are calculated. The results show that the GLUWP has higher proportions of renewable resource input, less pressure on the environment, more environmental support and better ecological and economic benefits, which can be considered as an environment-friendly and long-term sustainable ecological practice, compared with another constructed wetland in Beijing. Meanwhile, the dominant environmental impact is induced by POCP with the construction phase contributing the most on the entire life cycle. It is expected that increasing green area, extensively using environment-friendly materials, optimizing construction techniques and reducing power consumption can promote the sustainability of the GLUWP.     

经济增长与农业碳排放关系的实证研究

研究首先基于农业投入与生产视角的6个主要方面碳源,测算了1993-2008年我国农业生产活动所导致的碳排放量,分析发现我国农业碳排放总量和强度分别年均增长率为4.08%、2.38%,但环比增速总体上处于阶段性下降态势。化肥、农药、农膜、农用柴油、灌溉、翻耕等导致碳排放年均递增率分别为3.45%、4.65%、7.20%、4.77%、1.22%、0.38%。进一步综合运用协整理论及误差修正模型,实证我国经济增长与农业碳排放之间的关系。结果表明：我国经济增长与农业碳排放总强度,以及经济增长与化肥、农药、农膜、农用柴油、翻耕等5类碳源导致的碳排放强度之间存在协整关系,且人均GDP每增加1%,农业碳排放总强度与化肥、农药、农膜、农用柴油、翻耕等碳源的碳排放强度分别增加1.72%、1.61%、1.18%、0.40%、2.48%和1.31%。最后,据此提出相关政策建议。     

Treibhausgas-Emissionen zukünftiger Erdgas-Bereitstellung für Deutschland

Background

Natural gas makes a significant contribution to the current energy supply and its importance, in relation to both the German and worldwide energy supplies, will increase further in decades to come. In addition to its high degree of efficiency, the low level of direct GHG combustion emissions is also an advantageous factor. However, around 90% of natural gas is methane (CH₄), which is the second most significant GHG due to its high greenhouse potential (21 times higher than CO₂). Therefore, high levels of direct gas losses of natural gas in its production, processing, transport and distribution could neutralise its low emission advantages. This is particularly apparent when considering the growing distances between production and use, the demanding production processes and the upcoming worldwide market for LNG (liquefied natural gas).

Aim

This paper aims to analyse and illustrate the future GHG emissions of the whole process chain of natural gas (indirect emissions) to be supplied to the German border over the next 2 decades. This should allow the comparison of total GHG emissions (indirect and direct) of natural gas with the GHG emissions of other fossil fuels. By considering likely changes in gas origin as well as dynamic changes in the infrastructure and technology of gas production, processing and transport until 2030, all relevant factors are included. The study focuses on the emissions of Russian natural gas as Russia is already, and will be in the future, the most important gas supplier to the German and European gas markets.

Results and Discussion

The analysis illustrates a significant change in the gas supply over the next two decades. The EU Gas Fields are in decline and it is predicted that these will run dry. In parallel the share of Russian and Norwegian natural gas, and also the levels of LNG production (e.g. from Algeria or Egypt), will increase. Although the potential for GHG emissions tends to grow as a result of greater transport distances and demanding production and processing activities, high investment in necessary mitigation options (e.g. through replacing older and inefficient technology; updating to state-of-the-art technology) may neutralise the increase. The overall result of these counteracting trends will be to decrease GHG emissions, in a range of around 12% per TJ of direct emissions of natural gas, depending on the level of investment in the modernisation of the Russian gas infrastructure and the improvements of the LNG process. In the two given scenarios the indirect emissions of the natural gas used in Germany will decrease from about 23 million t CO₂-eq (2005) to 19.5 or 17.6 million t CO₂-eq in the year 2030. In spite of a significant higher gas consumption the emissions are reduced in the first scenario due to technical modifications. In the second scenario the emission reduction is based on the lower gas consumption.

Conclusions

At present, the indirect GHG emissions of the natural gas process chain are comparable to the indirect emissions produced by oil and coal. The emission trend of the natural gas process chain will markedly decrease if the mitigation options are followed consistently. However, in order to ensure the long-term security of natural gas supply for future decades, a high level of investment is essential. With regard to future emissions, the best available technology and, therefore, that which is most economically feasible in the long term, should be used. Under these conditions natural gas — as the fossil fuel with the lowest levels of GHG emissions — can play a major role in the transition to a renewable energy supply for the future.     

土壤生态系统中黑碳研究的几个关键问题

因人类活动的影响,全球大气C02浓度自1750年以来呈现逐步上升的趋势。农业生产活动与气候变化紧密相关,因土地利用方式的改变以及高度集约化的粮食、食物生产等农业活动都有可能增加CO2等温室气体的排放。如何遏制和减少大气中的CO2浓度是当前的热点问题,黑碳这一物质形式有可能为这一问题的缓解或解决提供新途径。生物质黑碳是生物质材料在低氧或无氧状态下经热裂解而形成的一种富含碳元素的有机连续体,其中碳（C）元素的含量高达70％-80％,并且大多以稳定的芳香环形式而存在。人类生存环境中所形成黑碳的80％以上最终都要归于土壤,且由于其较强的抗分解能力而长期滞留于土壤环境中。利用黑碳的这些特性及其碳封存能力,实施积极而有效的土壤管理措施,有可能增加土壤生态系统中的碳储存,从而为人类社会应对全球气候变化提供新的机遇。在文献资料调研的基础上,描述了土壤中黑碳的来源及其增加土壤碳储存、减缓陆地生态系统碳循环的潜力;阐释了量化土壤中黑碳的重要性以及精确测定土壤黑碳含量的关键所在;揭示了黑碳在土壤环境中的稳定性,探讨了外源黑碳与土壤本体有机碳的相互作用关系,并分析了黑碳对土壤温室气体排放的影响及其不确定性。揭示这些问题有助于客观评价黑碳能否作为一个有效的土壤有机碳库,也益于明确黑碳在全球碳循环以及中国农业减排过程中的作用与地位。