方 愷

1荷蘭萊頓大學(xué)環(huán)境科學(xué)系，萊頓 2333CC 2浙江大學(xué)環(huán)境與能源政策研究中心，杭州 310058

足跡家族研究綜述

方 愷1,2,*

1荷蘭萊頓大學(xué)環(huán)境科學(xué)系，萊頓 2333CC 2浙江大學(xué)環(huán)境與能源政策研究中心，杭州 310058

綜合測(cè)度人類社會(huì)的可持續(xù)發(fā)展?fàn)顟B(tài)是生態(tài)經(jīng)濟(jì)學(xué)者追求的重要目標(biāo)。足跡家族由生態(tài)足跡、碳足跡和水足跡等一系列足跡類指標(biāo)整合而成，旨在為決策者系統(tǒng)評(píng)估與權(quán)衡人類活動(dòng)的環(huán)境影響提供理論和技術(shù)支持。從理論探索、整合實(shí)踐和分類比較等三方面對(duì)足跡家族的研究現(xiàn)狀進(jìn)行了綜述；在此基礎(chǔ)上圍繞極具爭(zhēng)議的足跡定義、計(jì)算方法和加權(quán)方式等問題，深入分析了阻礙當(dāng)前研究進(jìn)一步推進(jìn)的關(guān)鍵性因素；指出未來應(yīng)從建立足跡類型學(xué)、完善跨區(qū)域投入產(chǎn)出模型、細(xì)化產(chǎn)品和機(jī)構(gòu)環(huán)境足跡標(biāo)準(zhǔn)等方面入手，推動(dòng)實(shí)現(xiàn)足跡家族的量化整合；并首次提出了足跡家族與行星邊界耦合的構(gòu)想，以期為監(jiān)測(cè)和預(yù)警人類活動(dòng)的生態(tài)閾值、促進(jìn)環(huán)境影響評(píng)價(jià)向可持續(xù)性評(píng)價(jià)轉(zhuǎn)變提供科學(xué)依據(jù)。

足跡家族；量化整合；指標(biāo)分類；行星邊界；進(jìn)展

現(xiàn)代生態(tài)學(xué)之父Odum[1]通過查考生態(tài)學(xué)(ecology)與經(jīng)濟(jì)學(xué)(economics)的希臘語詞源，認(rèn)為這2個(gè)分屬自然科學(xué)和社會(huì)科學(xué)的學(xué)科之間應(yīng)具有某些天然的聯(lián)系[2]。生態(tài)學(xué)家與經(jīng)濟(jì)學(xué)家之所以在某些問題上持對(duì)立觀點(diǎn)，是因?yàn)殡p方的研究視角都有一定的局限性。在這樣的背景下，生態(tài)經(jīng)濟(jì)學(xué)(ecological economics)應(yīng)運(yùn)而生。作為連接生態(tài)學(xué)與經(jīng)濟(jì)學(xué)的交叉學(xué)科，生態(tài)經(jīng)濟(jì)學(xué)具有彌合分歧、促進(jìn)融合的重要意義[3]。

以生態(tài)足跡、碳足跡和水足跡等為代表的足跡類指標(biāo)，是生態(tài)經(jīng)濟(jì)學(xué)研究的重要對(duì)象和手段，正日益受到學(xué)界、政府乃至公眾的廣泛關(guān)注[4]。隨著人類對(duì)環(huán)境問題的復(fù)雜性、整體性與全球性特征的認(rèn)識(shí)不斷加深，任何單一足跡指標(biāo)已無法滿足環(huán)境影響綜合評(píng)估的需要[5]。足跡家族概念的提出，標(biāo)志著足跡研究重心正逐步由單指標(biāo)的定量測(cè)度向多指標(biāo)的集成整合演進(jìn)[6]。足跡家族研究開展僅短短數(shù)年，但已經(jīng)取得了一批重要的階段性成果。本文在系統(tǒng)梳理足跡家族研究進(jìn)展的基礎(chǔ)上，聚焦限制當(dāng)前研究進(jìn)一步深入的主要問題，并據(jù)此展望未來發(fā)展方向，以期為我國(guó)學(xué)者開展相關(guān)研究提供參考。

1 研究現(xiàn)狀與進(jìn)展

1.1 足跡家族理論探索

國(guó)際上的足跡研究由3大學(xué)術(shù)群體共同主導(dǎo)：全球足跡網(wǎng)絡(luò)(Global Footprint Network, GFN)主導(dǎo)生態(tài)足跡[7]；水足跡網(wǎng)絡(luò)(Water Footprint Network, WFN)主導(dǎo)水足跡[8]；生命周期評(píng)價(jià)(Life Cycle Assessment, LCA)主導(dǎo)碳足跡[9]。足跡家族概念的提出，是一次將系統(tǒng)論觀點(diǎn)引入生態(tài)經(jīng)濟(jì)學(xué)理論的有益嘗試，有助于打破目前這種單打獨(dú)斗、各自為戰(zhàn)的局面，加強(qiáng)學(xué)術(shù)群體之間的溝通與交流。

1.2 足跡家族整合實(shí)踐

足跡整合是足跡家族研究的重點(diǎn)與難點(diǎn)。國(guó)際上一些學(xué)者以此為切入點(diǎn)進(jìn)行了有益的嘗試(表1)，歸納起來主要包括以下幾方面：

(1) 組成多樣化 理論上，任何2類及以上的足跡指標(biāo)都可以組成特定的足跡家族[6]。在整合實(shí)踐中，足跡家族研究大多包含了碳足跡和水足跡，以及生態(tài)足跡、能源足跡和土地足跡等足跡中的一種或幾種類型。

(2) 模型規(guī)范化 多數(shù)研究基于LCA或一系列MRIO模型，對(duì)不同足跡指標(biāo)的計(jì)算過程進(jìn)行規(guī)范化、可視化操作，以便實(shí)現(xiàn)足跡類指標(biāo)的方法學(xué)融合，從而保證計(jì)算結(jié)果的一致性與可比性。

(4) 數(shù)據(jù)網(wǎng)絡(luò)化 在Ewing[20]、Galli[21]等一批國(guó)際學(xué)者研究的基礎(chǔ)上，歐盟建立起EUREAPA在線數(shù)據(jù)庫[24]，完成了全球45個(gè)國(guó)家和地區(qū)及其57個(gè)產(chǎn)業(yè)部門的生態(tài)足跡、碳足跡和水足跡計(jì)算，所有數(shù)據(jù)均免費(fèi)下載并可模擬不同情景下的足跡變化趨勢(shì)。

表1 足跡指標(biāo)整合研究文獻(xiàn)綜述Table 1 Literature review of the studies on integrating footprint indicators

*DDT: 目標(biāo)距離法Distance-to-Target；**MRIO: 跨區(qū)域投入產(chǎn)出Multiregional Input-Output；***IPCC: 政府間氣候變化專門委員會(huì)Intergovernmental Panel on Climate Change；****NPP: 凈初級(jí)生產(chǎn)力Net Primary Production

1.3 足跡指標(biāo)比較與分類

正如家庭成員存在角色分工一樣，不同足跡指標(biāo)在足跡家族中的地位與作用也有顯著差異[6]。綜合當(dāng)前足跡比較研究的主要成果(表2)，可以得出以下結(jié)論：①每類足跡指標(biāo)都只能反映環(huán)境影響的一個(gè)方面，故不宜單純依靠某類指標(biāo)進(jìn)行決策；②足跡指標(biāo)往往具有此消彼長(zhǎng)的關(guān)系，降低某一足跡可能導(dǎo)致其他足跡指標(biāo)的增高，因此需要權(quán)衡不同減排方案的潛在影響；③足跡指標(biāo)在決策支持方面具有互補(bǔ)性，通盤考量才能較為全面、客觀地評(píng)估人類活動(dòng)的環(huán)境影響；④隨著LCA廣泛應(yīng)用于足跡指標(biāo)的量化，有必要系統(tǒng)分析基于LCA方法的足跡指標(biāo)與基于非LCA方法的足跡指標(biāo)在清單分析、環(huán)境影響評(píng)價(jià)等方面的方法學(xué)差異，辯證看待LCA與足跡研究之間的關(guān)系[31]。

此外，足跡指標(biāo)的分類研究也是近年來的熱點(diǎn)之一。常見的生態(tài)足跡、碳足跡、水足跡、能源足跡[32]、生物多樣性足跡[33]、化學(xué)足跡[34]、氮足跡[35]和磷足跡[36]均旨在評(píng)估由資源消費(fèi)或廢料排放導(dǎo)致的某一類具體環(huán)境影響，可視為影響導(dǎo)向型足跡；而如產(chǎn)品足跡[37]、部門足跡[38]、國(guó)家足跡[39]則致力于研究特定尺度對(duì)象的局部或全局環(huán)境影響，屬于對(duì)象導(dǎo)向型足跡。從嚴(yán)格意義上來說，任何足跡應(yīng)用研究均需要同時(shí)指明所屬的對(duì)象類型和影響類型，如某一產(chǎn)品的碳足跡、部門的水足跡、國(guó)家的生態(tài)足跡等。

表2 足跡指標(biāo)比較研究文獻(xiàn)綜述Table 2 Literature review of comparative studies of footprint indicators

2 主要問題與爭(zhēng)論

2.1 足跡概念的定義

圍繞如何定義“足跡”概念而展開的爭(zhēng)論由來已久(表3)。起初，人們習(xí)慣將其等同于Wackernagel[7]所定義的生態(tài)足跡，即人類的生物資源消費(fèi)和化石能源碳排放所需占用的生態(tài)生產(chǎn)性土地和水域面積。Hammond[41]據(jù)此斷言足跡必須以空間物理量為單位，并改稱碳足跡為碳質(zhì)量。而隨著碳足跡和水足跡等指標(biāo)的引入，足跡概念的外延日趨寬泛和多樣化，很多學(xué)者將其視為表征資源消費(fèi)水平或環(huán)境影響強(qiáng)度的指標(biāo)。近年來，一系列經(jīng)濟(jì)社會(huì)領(lǐng)域足跡指標(biāo)的興起，如經(jīng)濟(jì)足跡[13]、社會(huì)足跡[13]、天堂足跡[48]、雇傭足跡[49]等，使得上述定義的合理性再次遭受質(zhì)疑。為此，UNEP/SETAC[44]、Peters[45]、Steen-Olsen[46]分別從全球可持續(xù)性和消費(fèi)者負(fù)責(zé)等視角重新審視足跡概念?？梢灶A(yù)見，隨著足跡家族成員陣容的擴(kuò)大，足跡概念的內(nèi)涵與外延也將繼續(xù)深化和擴(kuò)展，體現(xiàn)可持續(xù)發(fā)展環(huán)境、經(jīng)濟(jì)、社會(huì)三重支柱的廣義足跡概念更能反映該領(lǐng)域發(fā)展的實(shí)際趨勢(shì)。

表3 足跡定義文獻(xiàn)綜述Table 3 Literature review of the definitions of the footprint concept

*GDP: 國(guó)內(nèi)生產(chǎn)總值Gross Domestic Product

2.2 計(jì)算方法的選取

足跡類指標(biāo)的計(jì)算方法雖然眾多，但均有一定的適用條件。因此，找尋規(guī)范化的計(jì)算路徑頗有意義。目前，有關(guān)足跡計(jì)算的方法學(xué)討論主要集中在生態(tài)足跡、碳足跡和水足跡，以這3類足跡指標(biāo)為例(表4)，同時(shí)適用的量化方法主要包括以下幾種：

(1) LCA 產(chǎn)業(yè)生態(tài)學(xué)的重要分析方法，用于評(píng)估產(chǎn)品系統(tǒng)物質(zhì)流輸入、輸出的一系列潛在環(huán)境影響[73-74]。由于LCA覆蓋“從搖籃到墳?zāi)埂钡漠a(chǎn)品全生命周期，有助于破除“有煙囪才有污染”的末端治理觀念，加之技術(shù)框架成熟、分析過程規(guī)范、定量結(jié)果可靠，目前已成為足跡類指標(biāo)特別是碳足跡計(jì)算的常規(guī)方法?；谶^程的LCA是一種自下而上(bottom-up)的分析方法，在確定系統(tǒng)邊界的過程中不可避免地存在截?cái)嗾`差，對(duì)數(shù)據(jù)精度的要求也較高，因此基本不適用于區(qū)域及以上尺度足跡研究。

(2) IOA 與LCA相反，是一種典型的自上而下(top-down)分析方法，由Leontief[75]提出并用于國(guó)民經(jīng)濟(jì)核算。該方法通過編制投入產(chǎn)出表，運(yùn)用線性代數(shù)構(gòu)建數(shù)學(xué)模型，既清晰地揭示了社會(huì)最終需求與各生產(chǎn)和再生產(chǎn)部門之間投入產(chǎn)出的復(fù)雜聯(lián)系[76]，又節(jié)省了大量的人力物力成本。不過該方法只能反映部門平均水平，難以針對(duì)具體產(chǎn)品。隨著人類產(chǎn)業(yè)活動(dòng)引發(fā)的生態(tài)環(huán)境問題日益嚴(yán)重，IOA也被用于研究溫室氣體排放和自然資源(水、土地、原材料等)利用的結(jié)構(gòu)與數(shù)量等環(huán)境問題，相繼與生態(tài)足跡、碳足跡和水足跡等足跡指標(biāo)結(jié)合，成為部門、區(qū)域和國(guó)家尺度上足跡計(jì)算的主要方法。

(3) 混合方法(hybrid method) 兼具LCA和IOA的優(yōu)勢(shì)，既能保證研究精度又能節(jié)省人力物力，因而有著更為廣泛的適用范圍[20,45,66]。值得注意的是，表4所謂的方法學(xué)大類“自下而上”和“自上而下”，盡管理論上計(jì)算過程完全相反[77]，但實(shí)際界定并不十分清晰。以生態(tài)足跡的經(jīng)典計(jì)算方法NFA為例[7,57]，GFN原先認(rèn)為其屬于IOA(自上而下)的一個(gè)特例[78]，后又將其歸入過程分析(自下而上)的范疇[79]，可見自下而上與自上而下兩種方法之間存在交叉重疊，這一部分不妨也視為混合方法。

上述3類方法的適用范圍如圖1所示。盡管各尺度上的足跡指標(biāo)均有對(duì)應(yīng)的計(jì)算方法，但仍然缺乏一個(gè)橫跨材料尺度到全球尺度的普適性方法。如何破解尺度轉(zhuǎn)換性障礙是足跡家族研究面臨的重大挑戰(zhàn)。

2.3 權(quán)重系數(shù)的確定

權(quán)重賦值始終是指標(biāo)整合研究中一個(gè)極具爭(zhēng)議的話題[80-81]。足跡家族力圖揭示可持續(xù)發(fā)展復(fù)雜系統(tǒng)的運(yùn)行機(jī)制，不可避免地需要通過指標(biāo)加權(quán)來綜合評(píng)估和權(quán)衡人類活動(dòng)的影響。表5對(duì)比了7類足跡指標(biāo)內(nèi)部各自的加權(quán)方式，發(fā)現(xiàn)均采用的是線性加權(quán)聚合，遵循“總體等于部分之和”的思想，這顯然與系統(tǒng)論的核心理念“總體不等于部分之和”相抵觸[86]。此外，由于權(quán)重的確定多少會(huì)帶有一些主觀性[80]，所以無論是生態(tài)足跡的均衡因子加權(quán)，還是水足跡的等量加權(quán)，都存在質(zhì)疑和批評(píng)聲[87-88]。但碳足跡是一個(gè)例外，其權(quán)重賦值基于反映環(huán)境機(jī)理的GWP特征化模型，能夠客觀地描述不同溫室氣體對(duì)氣候變化的潛在影響，因而具有廣泛的科學(xué)共識(shí)[16,80,88]。

表4 生態(tài)足跡、碳足跡和水足跡在不同尺度研究中的方法歸納[14]Table 4 Summary of the approaches to the ecological, carbon and water footprints across scales[14]

*IOA: 投入產(chǎn)出分析Input-Output Analysis；**NFA: 國(guó)家足跡核算National Footprint Accounts；***MEA：千年生態(tài)系統(tǒng)評(píng)估Millennium Ecosystem Assessment;凡文獻(xiàn)未詳細(xì)說明采用何種方法，均粗略劃分為“自下而上”或“自上而下”

圖1 不同尺度生態(tài)足跡、碳足跡和水足跡的適用方法 Fig.1 The range of applicability for different footprint approaches across scales

通過分析足跡指標(biāo)內(nèi)部的加權(quán)方式，對(duì)足跡間權(quán)重賦值的啟示有以下幾點(diǎn)：①目前的線性加權(quán)特別是等量加權(quán)，具有很大的主觀性和不確定性，故很難反映復(fù)雜環(huán)境系統(tǒng)的客觀實(shí)際；②部分足跡指標(biāo)的核算賬戶有重疊(如碳足跡與能源足跡)，進(jìn)一步限制了足跡間加和的可能性；③解決各類足跡指標(biāo)的計(jì)量單位不一致問題(如生態(tài)足跡基于面積、碳足跡基于質(zhì)量、水足跡基于體積)，一個(gè)可行的途徑是結(jié)果標(biāo)準(zhǔn)化，對(duì)應(yīng)的參考系既可以是特定的產(chǎn)品系統(tǒng)，也可以是某一區(qū)域乃至全球；④為降低二次加權(quán)(足跡內(nèi)部和足跡之間)的不確定性，在采用如DDT等方法進(jìn)行足跡間加權(quán)之前，在各類足跡內(nèi)部的清單物質(zhì)(如生態(tài)足跡中的土地類型、碳足跡中的溫室氣體)的分析及加和過程中，最好用科學(xué)的特征化因子取代人為權(quán)重系數(shù)。

3 研究展望

3.1 足跡類型學(xué)研究

隨著新興足跡的不斷涌現(xiàn)(圖2)，足跡類型學(xué)研究顯得愈加重要。值得一提的是，我國(guó)學(xué)者近年來在海洋足跡[89]、化工足跡[90]、污染足跡[91-92]以及基于生態(tài)系統(tǒng)服務(wù)的生態(tài)足跡[93-94]等方面做了大量有益的探索，豐富和擴(kuò)大了足跡家族的內(nèi)涵與外延。有必要全面分析和歸納現(xiàn)有的足跡指標(biāo)，考察其特性與共性，對(duì)某些有鮮明共性的指標(biāo)進(jìn)行歸類，從而建立一批具有特定功能指向的足跡家族，以適應(yīng)多角度、多層次評(píng)估人類活動(dòng)影響的需要。例如，碳足跡雖然標(biāo)榜指示氣候變化，但事實(shí)上溫室效應(yīng)僅是氣候變化的一個(gè)重要部分[45]，其他如土地利用變化引發(fā)的碳源/匯改變，臭氧層空洞導(dǎo)致的紫外線輻射增加，硫化物、氮氧化物以及其他顆粒物對(duì)大氣理化性質(zhì)的影響等，長(zhǎng)期而言均會(huì)對(duì)氣候造成一定影響。因此，由這些對(duì)應(yīng)環(huán)境足跡組成的足跡家族將比單單碳足跡更好地反映人為氣候變化效應(yīng)。

表5 各類足跡指標(biāo)的加權(quán)方式Table 5 Summary of the weighting schemes for different footprints

*碳足跡的組成采用京都議定書所推薦的6大類溫室氣體，GWP: 全球暖化潛值Global Warming Potential;這里取100a時(shí)間跨度，其單位為碳質(zhì)量當(dāng)量(kg CO2-eq.)；**等量加權(quán)(equal weighting)即指所有組分的權(quán)重系數(shù)均為1，此時(shí)權(quán)重系數(shù)略去不寫；***能源足跡的權(quán)重系數(shù)是指每1000kg不同類型燃料折算成足跡時(shí)需要乘以的系數(shù)[83]；****非生物資源足跡主要考慮金屬和礦物等的稀缺性，ADP: 非生物消耗潛值A(chǔ)biotic Depletion Potential;根據(jù)1999年主要非生物資源的全球儲(chǔ)量及當(dāng)年開采速度進(jìn)行計(jì)算[85]，其單位為銻質(zhì)量當(dāng)量(kg Sb-eq.)；*****由于相關(guān)資料缺乏，生物多樣性足跡等量加權(quán)所有可能威脅物種數(shù)量的因素

此外，足跡類型學(xué)研究也將為探尋更加科學(xué)、合理和有針對(duì)性的足跡概念奠定基礎(chǔ)。任何定義都有其適用的邊界條件，即便是同一名稱的足跡指標(biāo)，也應(yīng)根據(jù)采用的具體方法界定其所屬類型。這無疑有賴于對(duì)足跡指標(biāo)背后方法學(xué)異同的精準(zhǔn)辨析。以水足跡為例，除了常規(guī)的WFN水足跡外，Pfister[95]、Ridoutt[68]提出基于水稀缺性指數(shù)(Water Scarcity Index, WSI)計(jì)算本地水足跡。WSI可以視為類似于GWP的特征化因子，所以基于WSI的水足跡應(yīng)與碳足跡、而不是WFN水足跡歸為一類。當(dāng)然，足跡分類并非一成不變，應(yīng)該根據(jù)研究需要靈活進(jìn)行。有理由相信，通過推進(jìn)足跡類型學(xué)，整個(gè)足跡家族研究的深度和廣度都將得到拓展。

圖2 足跡指標(biāo)發(fā)展的時(shí)間軸Fig.2 Timeline of the development of footprint indicators

3.2 基于MRIO模型的足跡指標(biāo)量化研究

IOA自創(chuàng)立以來，在定量研究區(qū)域經(jīng)濟(jì)及其環(huán)境問題方面發(fā)揮了主導(dǎo)作用。在此基礎(chǔ)上，區(qū)域間投入產(chǎn)出(Interregional Input-Output, IRIO)和MRIO等IOA擴(kuò)展模型相繼提出，旨在精準(zhǔn)描繪部門間和區(qū)域間的全部投入產(chǎn)出關(guān)系。與IRIO相比，MRIO對(duì)數(shù)據(jù)資料要求較少，計(jì)算區(qū)域內(nèi)技術(shù)系數(shù)和區(qū)域間貿(mào)易系數(shù)的過程也大幅簡(jiǎn)化[96-97]。作為經(jīng)濟(jì)學(xué)原理成功應(yīng)用于環(huán)境研究的范例，MRIO模型能夠清晰追蹤環(huán)境影響的地理空間分布信息[97]，從而為量化廢料排放或資源消費(fèi)的跨區(qū)域轉(zhuǎn)移與分布提供了一條切實(shí)可行的途徑?？傊?，MRIO模型已成為中、宏觀尺度上足跡類指標(biāo)計(jì)算的重要方法[14,98]。

圖3 基于MRIO系列模型的多足跡量化研究指標(biāo)網(wǎng)絡(luò) Fig.3 Indicator network of the multi-footprinting quantitative analyses based on a series of MRIO models節(jié)點(diǎn)間的緊密度隨實(shí)線、長(zhǎng)虛線和短虛線遞減。土地足跡和能源足跡分別對(duì)應(yīng)生態(tài)足跡中的生物生產(chǎn)性土地和碳吸收地部分。

采用文獻(xiàn)計(jì)量學(xué)手段，對(duì)基于標(biāo)準(zhǔn)MRIO、環(huán)境擴(kuò)展MRIO(EE-MRIO)或混合環(huán)境擴(kuò)展MRIO(hybrid EE-MRIO)模型的多足跡指標(biāo)(≥2)研究論文進(jìn)行全面分析，發(fā)現(xiàn)當(dāng)前MRIO足跡研究呈現(xiàn)碳足跡與水足跡雙核驅(qū)動(dòng)的指標(biāo)分布網(wǎng)絡(luò)，且此2節(jié)點(diǎn)間的聯(lián)系也最為緊密(圖3)。這也基本上反映了不同足跡指標(biāo)在足跡家族中的地位差異?？傊_展基于MRIO模型的足跡指標(biāo)量化研究，既可以保證計(jì)算方法的一致性與兼容性，又能為指標(biāo)結(jié)果的標(biāo)準(zhǔn)化和權(quán)重化奠定基礎(chǔ)，是目前中、宏觀尺度足跡家族量化整合的首選模型。

3.3 產(chǎn)品和機(jī)構(gòu)環(huán)境足跡標(biāo)準(zhǔn)研究

歐盟于近期發(fā)布了產(chǎn)品環(huán)境足跡(Product Environmental Footprint, PEF)和機(jī)構(gòu)環(huán)境足跡(Organization Environmental Footprint, OEF)標(biāo)準(zhǔn)方法導(dǎo)則[99-100]，首次提出從生命周期的角度規(guī)范化地評(píng)估產(chǎn)品和機(jī)構(gòu)的整體環(huán)境影響。無論是OEF還是PEF都與足跡家族的概念緊密相連：PEF可以有效避免因依賴單一指標(biāo)(如碳足跡)而導(dǎo)致的環(huán)境負(fù)擔(dān)轉(zhuǎn)嫁問題[101]，未來還可能以標(biāo)簽的形式貼在每件出廠產(chǎn)品上，從環(huán)保角度為消費(fèi)者選購(gòu)商品提供參考；OEF由于涉及對(duì)所研究機(jī)構(gòu)(工廠、企業(yè)、學(xué)校、社區(qū)等)生命周期系統(tǒng)邊界的明確定義，并以此為基礎(chǔ)分析整個(gè)系統(tǒng)內(nèi)部及其與外部的復(fù)雜物質(zhì)流動(dòng)和交換，因而較之PEF更具挑戰(zhàn)性[102]。

值得注意的是，上述兩份導(dǎo)則乍一發(fā)布就引發(fā)了兩種截然不同的看法：支持者認(rèn)為相較于現(xiàn)有LCA方法優(yōu)勢(shì)明顯[38]；反對(duì)者則認(rèn)為與目前的LCA標(biāo)準(zhǔn)相抵觸，不僅無益于方法統(tǒng)一，反而會(huì)加深學(xué)科內(nèi)部的分歧與對(duì)立[37]。筆者認(rèn)為，若要真正實(shí)踐PEF和OEF，在影響類型的選取、權(quán)重系數(shù)的確定等問題上都需要更加詳盡的操作細(xì)則。此外，厘清PEF與現(xiàn)有產(chǎn)品LCA[103-104]等領(lǐng)域的關(guān)系將會(huì)對(duì)合理界定足跡概念起到借鑒作用，比如不少關(guān)于產(chǎn)品貿(mào)易隱含碳、虛擬水、虛擬土地的研究盡管沒有采用“足跡”式稱謂，但基本思路與碳足跡、水足跡、生態(tài)足跡相似甚至完全一致，是否一并納入足跡研究范疇值得思考。

3.4 足跡家族與行星邊界耦合研究

足跡家族表征人類活動(dòng)作用于地球環(huán)境系統(tǒng)的影響，屬于靜態(tài)的回顧性評(píng)估，缺乏實(shí)際的決策咨詢價(jià)值，無法回答產(chǎn)生影響的壓力源是否可控[14,105]。鑒于此，可以考慮將承載力的研究成果引入目前研究。行星邊界(planetary boundaries)是近年來承載力領(lǐng)域最重要的一項(xiàng)成果，由Rockstr?m[106-107]于2009年提出，旨在為全球尺度的重要環(huán)境問題劃定“生態(tài)紅線”。如表6所示，行星邊界共設(shè)置了10項(xiàng)地球環(huán)境系統(tǒng)過程的生物物理參數(shù)閾值，并對(duì)工業(yè)革命以前和現(xiàn)在的水平進(jìn)行估算，據(jù)此判斷人類活動(dòng)的“越界”程度。由于行星邊界實(shí)現(xiàn)了對(duì)地球拐點(diǎn)的定量預(yù)測(cè)預(yù)警，Nature及其子刊曾辟專欄加以評(píng)論。國(guó)內(nèi)迄今未見相關(guān)的文獻(xiàn)報(bào)道，令人遺憾。

表6 行星邊界概念框架[106-107]Table 6 Conceptual framework for planetary boundaries

當(dāng)然，與很多生態(tài)環(huán)境領(lǐng)域研究成果一樣，行星邊界理論也招致了激烈的抨擊和質(zhì)疑[108-110]。一個(gè)關(guān)鍵性的問題在于其對(duì)現(xiàn)狀參數(shù)的估計(jì)全部基于專家知識(shí)，因而帶有較大的主觀成分，而現(xiàn)狀影響評(píng)估恰恰是足跡類指標(biāo)的強(qiáng)項(xiàng)。因此，將足跡家族與行星邊界結(jié)合起來，有望真正實(shí)現(xiàn)由環(huán)境影響評(píng)價(jià)向可持續(xù)性評(píng)價(jià)的轉(zhuǎn)變[111]：一方面，足跡研究相對(duì)成熟的量化手段能夠?yàn)樾行沁吔缣峁└涌陀^、準(zhǔn)確的現(xiàn)狀評(píng)估結(jié)果作參照；另一方面，行星邊界又為足跡家族預(yù)測(cè)人類活動(dòng)的臨界值、劃定剩余的安全操作空間提供了可能。足跡家族與行星邊界耦合研究亟需一批不同專業(yè)知識(shí)背景(如生態(tài)學(xué)、環(huán)境科學(xué)、資源科學(xué)、地球科學(xué)、系統(tǒng)科學(xué)、社會(huì)科學(xué)等)的專家學(xué)者廣泛參與，跨學(xué)科、跨團(tuán)隊(duì)的國(guó)際學(xué)術(shù)合作勢(shì)在必行。

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Footprint family: current practices, challenges and future prospects

FANG Kai1,2,*

1InstituteofEnvironmentalSciences(CML),LeidenUniversity,Leiden2333CC,Netherlands2EnvironmentalandEnergyPolicyCenter,ZhejiangUniversity,Hangzhou310058,China

It is increasingly widely accepted that anthropogenic impacts on the earth′s systems should stay within critical thresholds for humanity to preserve the planet as a pleasant living place and as a source of welfare.It is therefore a high priority for ecological economists to identify and quantify the state of sustainable development of the human society.Efforts have been made to build up a footprint family in which a suite of footprint-style indicators, such as the ecological, carbon, and water footprints, are combined to measure the environmental impacts associated with human activities in multiple dimensions.The footprint family concept stems from the firm belief that environmental issues are getting increasingly complex, and that wise policies in most cases cannot be formulated without some form of trade-offs among an ever-expanding number of stressors.This highlights the importance of identifying ways to quantitatively integrate different footprints and to minimize the total footprint from a system perspective, rather than emphasizing “net zero” solutions to individual footprints.As a fast-growing interdisciplinary topic, a number of footprint family studies have received great attention over recent years since its first appearance in the literature.By labeling current studies with theoretical exploration, integrated practice, and comparison and classification, a comprehensive review of the footprint family research is provided.Challenges remain in developing a truly integrated footprint family, especially in defining the footprint concept in a generally accepted way.The scarcity of calculation methods that are valid for various footprints on multiple scales ranging from a product, an organization, a nation, and even globally, and the uncertainty of dealing with weighting both within and between footprints, provide obstacles as well.To remove all these obstacles, the remainder of this paper presents a research agenda for updating the footprint family framework in future work.We call for the investigation of footprint typology, the development of multiregional input-output models, the concretization of operational guidelines for product and organizational environmental footprints, and the combination of footprint family and planetary boundaries.We believe that many well-grounded footprint models have the potential to consolidate the scientific foundation of planetary boundaries by providing a robust and reliable assessment of current environmental impacts and, conversely, that the planetary boundary concept could allow footprints to benchmark against thresholds for environmental impacts that humanity is placing on the planet, as a clear recognition of sustainable limits to human interference is lacking in many of the existing footprint accounts.Thus, we come to the conviction that the joint use of a footprint family and planetary boundaries would contribute to the assessment of global sustainability from a broader point of view, in which current environmental impacts and forecasted threshold boundaries can be synchronously quantified and compared.In this manner, the footprint-boundary alignment makes it possible for policy makers to monitor the extent to which critical thresholds are being approached or exceeded, and to warn about critical transitions that may have profoundly undesirable consequences for environmental quality, ecosystem stability, and human health in large parts of the world.

footprint family;quantitative integration;indicator classification;planetary boundaries;advance

國(guó)家公派留學(xué)基金項(xiàng)目(20113005)

2014-07-03; < class="emphasis_bold">網(wǎng)絡(luò)出版日期:

日期:2015-05-21

10.5846/stxb201407031373

*通訊作者Corresponding author.E-mail: fang@cml.leidenuniv.nl

方愷.足跡家族研究綜述.生態(tài)學(xué)報(bào),2015,35(24):7974-7986.

Fang K.Footprint family: current practices, challenges and future prospects.Acta Ecologica Sinica,2015,35(24):7974-7986.