設(shè)計(jì)師的地球工程“工具箱”：危機(jī)給予風(fēng)景園林師扭轉(zhuǎn)、修復(fù)和再生地球氣候的機(jī)會

著：（美）瑪莎·施瓦茨 （美）伊迪絲·卡茨 譯：李致 校：胡一可

1 大氣脫碳

目前，“脫碳”一詞還未家喻戶曉。但若想避免氣候變化災(zāi)難，經(jīng)濟(jì)部門必須在未來10年迅速減少化石燃料使用量和二氧化碳排放量，即實(shí)現(xiàn)“去碳化”發(fā)展。除此之外還需要采取一項(xiàng)不太為人所知的行動。我們必須清除100年來已經(jīng)排放到大氣中的二氧化碳（CO2）。換句話說，我們需要清理大氣層。“人類一直在推遲二氧化碳的相關(guān)減排行動，現(xiàn)在不得不從大氣中吸回大量二氧化碳，以避免全球變暖引發(fā)的災(zāi)害?！盵1]2015年，《巴黎協(xié)定》和聯(lián)合國承諾在21世紀(jì)下半葉將全球變暖限制在工業(yè)化前的水平——“遠(yuǎn)低于20℃”并“力求將升溫控制在1.5℃以下”①。即便如此，排放量仍在繼續(xù)上升?！俺俏覀儾扇∮行袆?，否則世界將迅速接近1.5℃的升溫‘紅線’，并且有可能沖破3℃。”[2]在實(shí)現(xiàn)2015年《巴黎協(xié)定》目標(biāo)的所有途徑中，聯(lián)合國政府間氣候變化專門委員會（IPCC）②將大規(guī)模的大氣二氧化碳脫除（CDR）作為減排的輔助措施，以實(shí)現(xiàn)氣候治理目標(biāo)[3]。本研究重點(diǎn)討論大氣脫碳問題，這是地球工程學(xué)領(lǐng)域最重要的研究之一，地球工程學(xué)定義為“對影響地球氣候的環(huán)境過程進(jìn)行有意識地大規(guī)模干預(yù)，以試圖減輕全球變暖的影響”[4]。具體而言，地球工程學(xué)研究尤其是CDR的應(yīng)用，與風(fēng)景園林及其脫碳作用密切相關(guān)。

1.1 “減緩”：對“適應(yīng)”和“彈性”的超越

氣候變化問題的緊迫性已引起全球范圍內(nèi)設(shè)計(jì)行業(yè)的關(guān)注。當(dāng)前的設(shè)計(jì)教育和實(shí)踐通常使用2種基本方法應(yīng)對氣候危機(jī)：彈性（快速恢復(fù)的能力）和適應(yīng)力（應(yīng)對自然變化的能力）③。這些方法很重要，且需要堅(jiān)持實(shí)施，但它們無法解決根本問題。

1.2 “減緩”“適應(yīng)”與“彈性”的區(qū)別

“減緩”從問題根源出發(fā)，減輕氣候變化的惡性影響[5]?！皻夂驕p緩”意味著減少二氧化碳的排放或加強(qiáng)碳匯（生物圈、大氣層、海洋），從而實(shí)現(xiàn)大氣二氧化碳的長期清理?！皽p緩”也指通過冷卻地球弱化全球變暖的影響。

“減緩”和“適應(yīng)”的另一個(gè)區(qū)別在于空間尺度?！皬椥浴焙汀斑m應(yīng)”通常應(yīng)用于局部范圍，而“減緩”可解決全球尺度上的問題?！斑m應(yīng)”策略側(cè)重治標(biāo)，如更有效地利用稀缺水資源，或?yàn)榱藨?yīng)對海平面上升而建設(shè)防洪設(shè)施；而脫碳領(lǐng)域中的“減緩”策略則通過減少二氧化碳排放而實(shí)現(xiàn)治本，以期在未來某個(gè)時(shí)間點(diǎn)穩(wěn)定碳循環(huán)。

1.3 脫碳問題已成關(guān)注熱點(diǎn)

科學(xué)家、經(jīng)濟(jì)學(xué)家、企業(yè)家和消息靈通的國家領(lǐng)導(dǎo)層逐漸意識到氣候變化的代價(jià)，以及為了避免最壞的情況，人們必須在2030年之前采取強(qiáng)有力的行動。為了響應(yīng)這一趨勢，本研究為風(fēng)景園林師提供了一系列可以充實(shí)“工具箱”的脫碳“工具”，并通過代表案例介紹其具體應(yīng)用，以便在日后工作中進(jìn)一步探索實(shí)踐。在這個(gè)氣候變化的新時(shí)代，風(fēng)景園林師的工作重點(diǎn)在于土地和植被，而二者都能吸收并轉(zhuǎn)化二氧化碳，可以說風(fēng)景園林是最優(yōu)秀的“脫碳專業(yè)”?！叭祟愐阎钠渌麢C(jī)制，都無法做到像光合作用一樣有效地解決全球變暖問題?！盵6]筆者認(rèn)為，風(fēng)景園林師在減緩氣候變化以及逆轉(zhuǎn)、修復(fù)和再生氣候方面發(fā)揮著非常重要的作用。

1.4 氣候變化機(jī)制與風(fēng)景園林

氣候變化的機(jī)制和驅(qū)動因素提供了可以人為干預(yù)的關(guān)鍵點(diǎn)，風(fēng)景園林師們可在地球系統(tǒng)多圈層間的相互作用、地球能量平衡和碳循環(huán)中發(fā)現(xiàn)設(shè)計(jì)機(jī)會，并從這些方面著手解決問題。

2 氣候變化的影響：中國將面臨什么?

按照一些標(biāo)準(zhǔn)，中國仍屬于發(fā)展中國家，但中國已經(jīng)實(shí)現(xiàn)工業(yè)化，甚至在2019年與美國并列成為全球最大的二氧化碳排放國，兩國合計(jì)排放量占全球的40%[7]。中國30年來的經(jīng)濟(jì)快速增長，在提高其世界經(jīng)濟(jì)強(qiáng)國地位的同時(shí)，也加劇了氣候變化危機(jī)。燃煤廠造成的大氣污染、河流污染和日漸枯竭的地下水資源，都是經(jīng)濟(jì)飛速發(fā)展的后果。隨著二氧化碳排放和氣溫上升，氣候變化對中國的負(fù)面影響還會進(jìn)一步擴(kuò)大。

中國廣泛存在著以下4種類型的氣候影響，并呈現(xiàn)分布不均勻的特點(diǎn)：

1）冰川融化和淡水流失；2）溫度上升、熱浪加劇和空氣污染；3）荒漠化對食物和棲息地的影響；4）海平面上升和沿海地區(qū)洪災(zāi)。

2.1 中國與“亞洲水塔”

氣候變化最明顯且最嚴(yán)重的后果之一就是對“亞洲水塔”的影響——中國青藏高原上的冰川。青藏高原是亞洲若干條重要河流的發(fā)源地，這些河流流經(jīng)中國、尼泊爾、阿富汗、巴基斯坦、印度、孟加拉國、不丹、緬甸和湄公河半島，并為周邊地區(qū)帶來淡水資源，因此青藏高原冰川作為“亞洲水塔”也是20多億人口生存的關(guān)鍵。青藏高原地區(qū)包含全球14%以上的冰川和積雪，僅次于北極和南極，又被稱為“第三極”。然而，氣溫上升卻致使冰川的消融和退縮。

2.2 華北平原（NCP）出現(xiàn)熱浪

熱浪有可能對中國造成致命影響，特別是在華北平原。若不采取嚴(yán)格措施控制排放而任其發(fā)展，預(yù)計(jì)華北平原將成為全球“熱”點(diǎn)地帶。預(yù)計(jì)最早在2070年，相較于地球其他地區(qū)，氣溫上升將嚴(yán)重威脅中國居民的生命財(cái)產(chǎn)安全[8-9]。

2.3 荒漠化

伴隨著淡水枯竭，中國北方地區(qū)荒漠化將進(jìn)一步加重?；哪欢x為“土地類型從沃土變?yōu)楹档氐囊环N土地”[10]。戈壁灘是地球上擴(kuò)張最快的沙漠，其成因不止一種，目前仍以每年約3 621 km（2 250英里）的速度向南延伸，相當(dāng)于美國西海岸到東海岸面積的80%！干旱的土地取代了適宜居住的農(nóng)業(yè)用地，沙塵暴侵襲，人們流離失所，進(jìn)而影響經(jīng)濟(jì)發(fā)展。經(jīng)濟(jì)快速增長被認(rèn)為是用材林被大肆砍伐的原因之一，這也使得森林遭到大規(guī)模破壞，而最終導(dǎo)致荒漠化。據(jù)估計(jì)，目前中國約有27%的土地被沙漠覆蓋?；哪率垢卦絹碓缴?，由此導(dǎo)致的糧食短缺已經(jīng)成為中國切實(shí)關(guān)注的問題。

2.4 上升的海平面

不斷上升的海平面是中國面臨的另一個(gè)主要威脅。中國是沿海地區(qū)人口最多的國家，海平面上升必然帶來巨大影響[11]。預(yù)計(jì)到2050年，中國將有9 300萬人受到海平面上升的威脅，涉及上海、深圳、天津、廣州、江蘇省和珠三角等地區(qū)。在未來的30年內(nèi)，這些地方可能會經(jīng)歷嚴(yán)重的洪澇災(zāi)害，擾亂全球經(jīng)濟(jì)和供應(yīng)鏈，影響當(dāng)今全球25%的經(jīng)濟(jì)增長[12]。

3 地球工程學(xué)

3.1 地球工程學(xué)簡述

地球工程學(xué)指有意識地對地球氣候進(jìn)行大規(guī)模干預(yù)，以緩和全球變暖問題的學(xué)科[4]。

3.2 地球工程學(xué)分支

地球工程學(xué)干預(yù)有2個(gè)分支：太陽輻射管理和二氧化碳脫除（CDR）。前者通過增加反照率或地球的反射率影響地球的能源系統(tǒng)，即進(jìn)出能量之間的平衡；后者則與地球的碳循環(huán)相互作用，即碳在大氣層中的移動和轉(zhuǎn)化，變成植物、有機(jī)體和地殼巖石，如此循環(huán)往復(fù)（圖1）。

CDR參與地球的碳循環(huán)。根據(jù)二氧化碳從大氣中分離的方式，可分為自然脫除（NCDR）、物理脫除和化學(xué)脫除。

太陽能地球工程通過技術(shù)手段與地球能量平衡相互作用，減少太陽輻射，從而降低地球的溫度。

4 21世紀(jì)風(fēng)景園林師的職責(zé)

地球工程學(xué)的兩個(gè)分支雖然為設(shè)計(jì)師們提供了諸多選擇，但并不是萬能的，還需要其他方法加以輔助。若想做出重要貢獻(xiàn)，風(fēng)景園林師最大的機(jī)遇則在于二氧化碳自然脫除（NCDR）或大氣二氧化碳清除方法，通過影響地球碳循環(huán)應(yīng)對氣候問題。

4.1 CDR：二氧化碳自然脫除（NCDR）

許多自然過程能夠“吸收”并儲存大氣中的二氧化碳，如土地、土壤和植被，這也是風(fēng)景園林師通常采用的方法?！稖p排：扭轉(zhuǎn)全球變暖最強(qiáng)計(jì)劃》（以下簡稱《減排》）[6]是一本脫碳行動研究清單，介紹了80種解決氣候危機(jī)的途徑，其目的是展示如何在未來30年里消除1 031 Gt（1.031萬億t）的大氣二氧化碳，使地球回到平衡狀態(tài)。該書較周全地將各方法以Gt為單位（1 Gt= 10億t，或相當(dāng)于40萬個(gè)奧運(yùn)會規(guī)模的泳池容量）進(jìn)行效用歸類。書中提到的陸上氣候應(yīng)對方案在前20種中占60%，在前80種中占30%；這意味著基于陸地的方案是最有效的大氣二氧化碳脫除途徑。為什么陸上氣候應(yīng)對方案屬于地球工程學(xué)？因?yàn)槿绻@些方案應(yīng)用范圍足夠大，便可在能量平衡（熱量控制）和碳循環(huán)（減少大氣中的二氧化碳）兩方面干預(yù)全球大氣狀況，這正是《減排》中的觀點(diǎn)。除此之外，下文所述的一系列脫碳工具同樣適用于各種尺度，并皆可產(chǎn)生良好效果。

4.1.1 自然脫除工具1：植樹造林

二氧化碳年捕獲潛力：5億～36億t；當(dāng)前成本預(yù)估：每噸花費(fèi)5～50美元[1]。

造林，指在至少50年沒有樹木的地區(qū)播種或種植樹木并形成林地或森林。樹木不僅外形優(yōu)美，還可以通過光合作用吸收二氧化碳，并將其轉(zhuǎn)化為根、莖、葉等生物量。只要樹木存活，便可一直封存二氧化碳。但是當(dāng)樹木被分解或燃燒后，又會重新釋放內(nèi)部封存的二氧化碳。因此，造林脫碳也意味著需要加強(qiáng)對森林的管理，防止二氧化碳的大量外泄?？赏ㄟ^火災(zāi)管理降低風(fēng)險(xiǎn)，或者將砍伐的樹木用作生物燃料。此外，在大型建筑工程中用木材制品代替鋼鐵和混凝土產(chǎn)品，也可以在相當(dāng)長的時(shí)間內(nèi)保持碳封存。

植樹造林代表案例：

1）2019北京大興國際機(jī)場臨空經(jīng)濟(jì)區(qū)中央公園競賽?，斏な┩叽暮匣锶嗽O(shè)計(jì)事務(wù)所設(shè)計(jì)，位于中國北京市大興區(qū)。

①場地面積747 hm2，設(shè)計(jì)面積361 hm2；②設(shè)計(jì)競賽于2020年落幕；③方案計(jì)劃種植11.2萬棵樹；④二氧化碳封存、空氣污染物修復(fù)、降噪和小氣候營造；⑤重要的雨水蓄存區(qū)。

方案建立了大規(guī)模的綠化和集水區(qū)，結(jié)合現(xiàn)有的森林碎片和運(yùn)河，采取中央公共公園的形式，并支持多樣化的公共項(xiàng)目。作為機(jī)場大型基礎(chǔ)設(shè)施的組成部分，在景觀設(shè)計(jì)方面不僅通過二氧化碳自然封存和生物封存緩解氣候危機(jī)，還利用“彈性”策略適應(yīng)場地預(yù)估的氣候影響（圖2～4）。

2）速造小型環(huán)境保護(hù)林，宮脅昭設(shè)計(jì)。

① 場地面積約6個(gè)停車位大小，種植300棵樹；②造林成本相當(dāng)于1部一代蘋果手機(jī)；③ 植物生長速度提高10倍，密度提高30倍；④ 選擇最合適的鄉(xiāng)土樹種；⑤ 種苗種植間距較小，為獲取陽光而爭相拔高；⑥ 營養(yǎng)豐富的土壤提供養(yǎng)料；⑦ 10年內(nèi)演變?yōu)槊芰帧?/p>

日本植物學(xué)家宮脅昭（Akira Miyawaki）的研究給予了植樹造林工作極大的啟發(fā)。他基于德國的一種技術(shù)，發(fā)明出“潛在自然植被”造林法。該方法“通常選擇缺乏有機(jī)質(zhì)的退化土地，密植幾十種鄉(xiāng)土樹種和其他鄉(xiāng)土植物。隨著種苗生長，自然選擇開始發(fā)揮作用，最終形成生物多樣性豐富且適應(yīng)性強(qiáng)的密林”[6]……宮脅造林法可營造森林或密集的植物群落，一般情況下耗時(shí)較短，但在生物多樣性、彈性和茂密程度上遠(yuǎn)高于傳統(tǒng)植樹造林法構(gòu)建的森林，同時(shí)也能夠更有效地吸收碳[6]（圖 5）。

3）楊柳青大運(yùn)河國家文化公園大師邀請賽，瑪莎·施瓦茨合伙人設(shè)計(jì)事務(wù)所設(shè)計(jì)，是中國天津2020年總體規(guī)劃的一部分。

① 占地188 hm2；② 密林具備二氧化碳封存及空氣凈化等功效；③ 人工濕地管控雨水；④ 綠色基礎(chǔ)設(shè)施具有經(jīng)濟(jì)效益，每年可節(jié)省9萬美元。

該方案將作為城市中最廣闊的綠色基礎(chǔ)設(shè)施。面對氣溫上升和氣溫波動等問題，茂密的林冠層可營造出舒適的微氣候。人工濕地作為碳匯，以減少天津的水土流失，同時(shí)結(jié)合下沉式花園房，提供可持續(xù)的雨水溢流修復(fù)（圖6、7）。

4）濟(jì)南CBD街道景觀，Sasaki 景觀設(shè)計(jì)事務(wù)所設(shè)計(jì)。

①位于中國濟(jì)南；設(shè)計(jì)完成時(shí)間為2018年2月；② 項(xiàng)目占地320 hm2；③新增3萬棵樹（相當(dāng)于50英畝約20 hm2森林）、灌木及多年生植物；④ 每年可吸收7 Gt（70億t）二氧化碳。

Sasaki團(tuán)隊(duì)的濟(jì)南CBD項(xiàng)目，提出了將街道作為公共空間的前沿理念，并營造“城市森林”作為街道系統(tǒng)的基礎(chǔ)。中央商務(wù)區(qū)共有30條街道，Sasaki負(fù)責(zé)設(shè)計(jì)其中的14條，總長26 km。街道類型十分豐富，大到城市干道、城市交通樞紐，小到社區(qū)公園頂棚、步行道和休閑環(huán)路。每一種街道類型都被賦予了不同的寬度、限速標(biāo)準(zhǔn)、尺度比例和植物色系，其鄰近區(qū)域也有不同的用途和規(guī)劃。方案建議新增3萬棵樹，相當(dāng)于20多hm2的森林。

1 地球工程學(xué)分支圖Geoengineering taxonomy diagram

2 大興中央公園鳥瞰圖Daxing aerial perspective

3 紅絲帶路和集水區(qū)Red Ribbon Path and water catchment

4 人工林風(fēng)環(huán)境分析Wind study for forest plantations

大規(guī)模植被的累積效應(yīng)將在降溫、健康以及生物多樣性和生態(tài)等方面發(fā)揮積極作用。該方案有助于重構(gòu)鄉(xiāng)土植物群落并凸顯其特色，同時(shí)喚醒場所精神和人們的地域文化記憶（圖8、9）。

5）智慧森林城市，位于墨西哥坎昆，斯坦法諾·博埃里（Stefani Boeri）設(shè)計(jì)。

① 項(xiàng)目區(qū)內(nèi)有13萬居民；② 占地557 hm2，其中一半以上將用于綠化；③ 種植750萬株植物，共350種；④ 26萬棵喬木；⑤ 每年封存5 800 t二氧化碳。

建筑師斯坦法諾·博埃里是城市森林的擁護(hù)者，他的作品中最引人注目的就是城市森林這種垂直布局形式。這項(xiàng)新提案展示了他對21世紀(jì)城市主義最雄心勃勃的思考，其內(nèi)容涉及環(huán)境公平、智能技術(shù)、可持續(xù)能源和密集種植計(jì)劃。大型公園、花園屋頂、綠色立面和樹木林立的街道景觀交織在一起，博埃里將城市轉(zhuǎn)變?yōu)橹参飯@，顛覆了人們對一般意義下“硬景觀”城市風(fēng)貌的設(shè)想。該提案也為循環(huán)經(jīng)濟(jì)提供了支撐，可實(shí)現(xiàn)糧食、水和能源的自給自足（圖10、11）。

4.1.2 自然脫除工具2：城市綠化

城市景觀中大部分是硬質(zhì)景觀，綠地比例較小。若想依據(jù)氣候變化重塑空間，城市街道和一些待開發(fā)利用的空間則是最普遍的選擇。

代表案例：哈佛設(shè)計(jì)研究生院實(shí)踐教授瑪莎·施瓦茨的2016年Option Studio課程設(shè)計(jì)：“固碳都市：城市作為應(yīng)對氣候變化的機(jī)器”。

① 調(diào)研場地：波士頓的4個(gè)鄉(xiāng)鎮(zhèn)（超過218 km2）；② 使用I-Tree的衡量指標(biāo)：計(jì)劃種植450萬棵樹；溫室氣體排放量為46萬t/年；需水量為22 890 156 034加侖（1加侖≈3.8 L）；節(jié)省能源開支206 963 526美元（約13.705億人民幣）。

工作坊與哈佛森林（由哈佛大學(xué)擁有和管理的3 000英畝即大約1 214 hm2的生態(tài)研究區(qū)，譯者注）的管理團(tuán)隊(duì)合作，哈佛森林團(tuán)隊(duì)人員對馬薩諸塞州進(jìn)行了深入的研究，在2060年前將該州組織成一個(gè)自我維持的實(shí)體。工作坊專注于整個(gè)大波士頓地區(qū)，其目標(biāo)是展示一個(gè)老舊的高密度城市通過重新組織和設(shè)計(jì)街道和其他公共開放空間，以應(yīng)對2060年全球變暖的影響。方案中提出了“混合系統(tǒng)”，該系統(tǒng)由自然、生物以及人造裝置和技術(shù)組成，可應(yīng)對氣候變化，同時(shí)研究城市綠化并以此為“混合系統(tǒng)”的核心部分。

此外，學(xué)生們預(yù)測了2060年波士頓4個(gè)城鎮(zhèn)的氣候變化，包括：暴雨和洪水；進(jìn)入干旱期；熱島效應(yīng)；6區(qū)和7區(qū)為種植區(qū)；海平面上升0.6 m（2英尺），風(fēng)暴潮達(dá)到約2.4 m（8英尺）。

與哈佛森林合作并制定設(shè)計(jì)假設(shè)：① 在公共和私人土地上植樹造林造成了“環(huán)境不公平”；② 通過馬薩諸塞州能源與環(huán)境部的“門戶城市計(jì)劃”；③ 2060年，自動駕駛將成為交通運(yùn)輸?shù)闹髁?，因此可回收地面空間用于城市綠化；④ 禁止在1-95環(huán)路內(nèi)使用私家車；波士頓的公共交通將延伸到TOD的環(huán)路上，允許通勤者停放私家車；⑤ 綠色防浪堤用來對抗上升的海平面；⑥ 合流制排水系統(tǒng)將實(shí)現(xiàn)雨水零溢流；⑦ 盡可能將屋頂涂成白色以增加城市反照率（圖12～14）。

4.1.3 自然脫除工具3：濱海濕地

在咸淡水交匯處、海岸線邊緣，存在著地球上規(guī)模最大但未得到充分重視的自然碳匯之一——“藍(lán)碳”資源，如鹽沼濕地。鹽沼內(nèi)長有紅樹林和海草，在土壤、植物及其根系之間長期的相互作用下，鹽沼具有比熱帶森林更強(qiáng)的碳封存能力，若不加以保護(hù)，它們可能會釋放大量的溫室氣體。濱海濕地也充當(dāng)海洋生物和飛行動物（魚類和候鳥）理想的棲息地和覓食地。除此之外，海岸帶生態(tài)系統(tǒng)還可以作為抵御風(fēng)暴潮的天然屏障，防止內(nèi)陸城市發(fā)生洪水，人們常常忽視它們在吸收二氧化碳方面可發(fā)揮的巨大作用，最近的一項(xiàng)研究已經(jīng)證實(shí)，濱海濕地系統(tǒng)是幫助解決氣候變化的最佳途徑之一。另外，近期另一項(xiàng)重要研究的作者之一詹妮弗·霍華德（Jennifer Howard）也總結(jié)道：“濱海生態(tài)系統(tǒng)可能是減少排放的一個(gè)重要組成部分，我們正努力向外界傳達(dá)這一重要訊息……”[13]

5 孟買宮脅森林Miyawaki Mumbai forest

6 天津楊柳青大運(yùn)河國家文化公園方案鳥瞰圖Tianjin aerial view

7 綠意縈繞的大運(yùn)河Tianjin canal with afforested territories

8 濟(jì)南CBD街景規(guī)劃Jinan CBD Streetscape plan

11 智慧森林城市中的水道Canal in Smart Forest City

10 智慧森林城市規(guī)劃方案平面放大圖Enlarged area of plan Smart Forest City

代表案例：舊金山灣“混合海岸線”，由克里斯蒂娜·希爾設(shè)計(jì)。

① 針對防洪需求和海平面上升問題設(shè)計(jì)新的“邊緣帶”；② 4 hm2“圩田”單元；③ 結(jié)合濱海特征建設(shè)人工濕地和住宅。

加州大學(xué)伯克利分校副教授克里斯蒂娜·希爾從大尺度出發(fā)，對舊金山海岸線及其生態(tài)系統(tǒng)的規(guī)劃策略展開研究。受海平面上升的威脅，預(yù)計(jì)舊金山海岸在接下來的50～75年將發(fā)生巨大變化。在土地規(guī)劃策略方面，希爾采取了一種獨(dú)特的方法：接受《財(cái)產(chǎn)法》在美國扮演的基本角色并支持私有制，她試圖將該方法與保護(hù)主義者以及合宜的生態(tài)設(shè)計(jì)相結(jié)合?；诖?，她提出了名為“混合邊緣”的解決方案。該方案受荷蘭圍墾系統(tǒng)的啟發(fā)，并融合了住房、人工濕地和海岸特征。最終，該區(qū)域會轉(zhuǎn)變?yōu)橐粋€(gè)新的可管理“邊緣帶”，可提供經(jīng)濟(jì)適用房并具備經(jīng)濟(jì)驅(qū)動力，因此該方案也不依賴于政府的資助：私人開發(fā)商可以發(fā)揮主導(dǎo)作用（圖15）。

12 街道類型：市中心固碳區(qū)Sequestropolis downtown street typology

13 高層CBD街道平面圖Sequestropolis CBD high-rise street plan

14 商業(yè)街固碳分析Sequestropolis Commercial street section

15 舊金山灣所在位置San Francisco Bay site

16“混合海岸線”方案設(shè)計(jì)流程Hybrid edge design process sequence

希爾在海岸線上布置了一個(gè)僅占4 hm2的微型圩田，規(guī)模遠(yuǎn)小于荷蘭的圍墾地。圩田周圍設(shè)置堤壩（圖16紫色區(qū)域），可以蓄存雨水并抵御洪水（橙色區(qū)域）。在圩田周圍引入干凈的沉淀物，從而構(gòu)建濕地“淺灘”（綠色區(qū)域）。濕地系統(tǒng)可充當(dāng)棲息地，也可抵擋海浪侵蝕，甚至可以進(jìn)一步建造海灘（黃色），為人們提供游憩場所。當(dāng)然，植物和土壤的碳封存作用也不言而喻。經(jīng)濟(jì)適用房建在圩田區(qū)內(nèi)（圖17）。

4.1.4 自然脫除工具4：土地利用

作為風(fēng)景園林師，我們經(jīng)常被邀請為城市、城鎮(zhèn)、社區(qū)（包括郊區(qū)在內(nèi)）以及發(fā)展中國家做大尺度的土地規(guī)劃。但不論面對的任務(wù)如何，我們都應(yīng)當(dāng)著手促成新的議程：將土地利用實(shí)踐納入提案，特別是實(shí)現(xiàn)土地和土壤的碳封存作用。

代表案例：土地利用變化報(bào)告，來自2014年哈佛森林研究課題。

該研究遵從以下幾項(xiàng)原則，通過合理的土地利用實(shí)現(xiàn)馬薩諸塞州的自給自足。

① 增加土壤下滲率是本次設(shè)計(jì)的重要任務(wù)，以補(bǔ)充波士頓賴以生存的地下水資源；② 土地利用必須保證馬薩諸塞州的糧食供應(yīng)；③ 增加土地連通性，充分發(fā)揮各生態(tài)系統(tǒng)的生態(tài)效益。

17 圩田住宅示意Polder housing

18 沙漠試驗(yàn)場顯示沿著帶狀硅酸鹽巖（橙色和深灰色）建設(shè)配套沙漠綠化帶可加快巖石風(fēng)化過程Desert Test Site showing linear strand pattern of silicate rock (orange and dark grey) for enhanced weathering side-by-side with strands of desert greening

為應(yīng)對2060年整個(gè)馬薩諸塞州的氣候變化影響，該研究制定了4種方案。方案1著眼于近期趨勢；方案2強(qiáng)調(diào)機(jī)會增長；方案3為區(qū)域的自力更生；方案4將森林作為基礎(chǔ)設(shè)施。其中“將森林作為基礎(chǔ)設(shè)施景觀”方案描繪了未來的政策、市場、州和地方規(guī)劃，將激勵(lì)措施的重點(diǎn)放在增加“生活設(shè)施”上。在能為馬薩諸塞州帶來的9項(xiàng)自然福利中，該方案有7項(xiàng)獲得了最高分。

4.1.5 自然脫除工具5：土壤固碳

土壤固碳策略優(yōu)勢頗多，它可以改善退化的土壤，提高生物產(chǎn)量，凈化地表水和地下水，并通過抵消化石燃料的碳排放降低大氣中二氧化碳的富集率。

代表案例：諾里公司的脫碳市場項(xiàng)目。

諾里脫碳劑不僅可消除碳足跡，也可幫助農(nóng)民采用可持續(xù)的耕作方式除碳，對土壤固碳進(jìn)行監(jiān)測和量化，通過這種方式助力整個(gè)脫碳市場的啟動和運(yùn)作。

4.1.6 自然脫除工具6：增強(qiáng)風(fēng)化固碳/巖石固碳

二氧化碳年捕獲力：20億～40億t；當(dāng)前成本預(yù)估：50～200美元/t。

地質(zhì)過程是碳循環(huán)中較慢的一環(huán)，涉及巖石與大氣中的氣體發(fā)生化學(xué)反應(yīng)，而在此過程中巖石可長期吸收二氧化碳。某些類型的物質(zhì)，如硅酸鹽巖石，當(dāng)溶解在雨水中時(shí)會與弱酸性二氧化碳發(fā)生劇烈的催化反應(yīng)，使巖石發(fā)生變化。二氧化碳嵌入礦物巖石分子結(jié)構(gòu)，最終將其轉(zhuǎn)變?yōu)樘妓猁}礦物，這些二氧化碳可被封存數(shù)千年?？茖W(xué)家們一直在探索如何使用強(qiáng)反應(yīng)硅酸鹽巖石（例如橄欖石或菱錳礦）來加速自然風(fēng)化過程。這種材料在農(nóng)田、熱帶地區(qū)或海灘上的應(yīng)用始終是試驗(yàn)重點(diǎn)。

代表案例：

1）維斯塔計(jì)劃（Project Vesta）。

維斯塔計(jì)劃可加速古老的自然進(jìn)程。該計(jì)劃的任務(wù)是進(jìn)一步研究增強(qiáng)風(fēng)化并推動其全球部署。用橄欖石制成綠沙海灘；海浪可加快二氧化碳捕獲速度，同時(shí)能使海洋脫酸④。

風(fēng)景園林師的工作遍布世界各地，如果應(yīng)用方案在某一項(xiàng)目中可行，那么這種低技術(shù)策略就有價(jià)值。巖石的碳封存比例約為：1 t的橄欖石置換2/3 t的二氧化碳，同時(shí)必須考慮采礦和運(yùn)輸?shù)某杀?，這是關(guān)鍵的制約因素[6]。

2）瑪莎·施瓦茨合伙人事務(wù)所的沙漠試驗(yàn)場。

試驗(yàn)場采用增強(qiáng)風(fēng)化策略，將硅酸鹽礦物圖案置于地面，通過灌溉催化化學(xué)反應(yīng)，從而捕獲空氣中的二氧化碳。該項(xiàng)目與英國科學(xué)家保羅·倫弗斯（Paul Renforth）合作，通過實(shí)際應(yīng)用推進(jìn)干旱氣候下增強(qiáng)風(fēng)化作用的技術(shù)（圖18）。

4.2 二氧化碳物理脫除和指標(biāo)

除了自然脫碳技術(shù)，風(fēng)景園林師還可以采用其他新材料及新工具，從源頭控制二氧化碳的排放或?qū)⑵溟L期封存，也許還能夠方便計(jì)算設(shè)計(jì)方案的除碳效率。

4.2.1 物理脫除工具7：低碳水泥和混凝土

人們往往會忽視另一個(gè)二氧化碳排放源——建筑材料。事實(shí)上，1 t混凝土在制造過程中可釋放1 t二氧化碳。如果將混凝土工業(yè)比喻成一個(gè)國家，那么世界第三大二氧化碳排放國非它莫屬?；炷凉I(yè)的碳排放量占全球的5%～8%：“混凝土是地球上除水資源以外使用最廣泛的材料?！盵14]許多公司正在研制低碳混凝土。索利達(dá)（Solida）公司利用一種先進(jìn)的混合基礎(chǔ)材料，使混凝土在固化過程中能夠吸收二氧化碳。建筑師也開始使用低碳混凝土，而風(fēng)景園林師們可以在外部設(shè)計(jì)要素中使用低碳混凝土，如橋梁、道路、步行道、墻壁、路緣和人行道等常見節(jié)點(diǎn)。

4.2.2 物理脫除工具8：重型木結(jié)構(gòu)和交叉層壓木材

重型木結(jié)構(gòu)或交叉層壓木材（CLT）是新型建筑材料的一種，具有結(jié)構(gòu)的完整性和環(huán)境友好性，可積累和封存二氧化碳。重型木結(jié)構(gòu)是大型工程木材產(chǎn)品的總稱，通過木材膠合、加壓、機(jī)械壓制而成。其材料堅(jiān)固且耐火，如果森林資源可持續(xù)，那么該材料的成本效益較高。重型木結(jié)構(gòu)材料同樣適用于景觀行業(yè)，作為鋼鐵和混凝土的低碳替代品，其生產(chǎn)過程利用的是可再生資源，不會造成化石燃料污染。

4.2.3 物理脫除工具9：用量化手段證明觀點(diǎn)

為應(yīng)對科學(xué)和經(jīng)濟(jì)挑戰(zhàn)，碳計(jì)算器應(yīng)運(yùn)而生，用以評估設(shè)計(jì)方案緩解氣候變化的功效。“氣候積極設(shè)計(jì)”的“探路者”（Pathfinder）工具可提供相關(guān)數(shù)據(jù)，幫助設(shè)計(jì)師計(jì)算景觀方案中的碳足跡。通過交互式的“探路者”工具完善設(shè)計(jì)方案，以確保增加碳捕獲量并減少建筑材料中的碳含量，從而實(shí)現(xiàn)設(shè)計(jì)目標(biāo)：建筑過程中碳的吸收量大于排放量，并在短時(shí)間內(nèi)實(shí)現(xiàn)“負(fù)碳”。同時(shí)，通過使用“探路者”，設(shè)計(jì)師可以將這些好處傳達(dá)給客戶和致力于減排的志愿者。通過參與，每個(gè)人都可以為應(yīng)對氣候變化的解決方案以及2030年的挑戰(zhàn)做出積極貢獻(xiàn)。

4.3 二氧化碳化學(xué)脫除工具10：直接空氣捕獲（DAC）技術(shù)

前文所述的內(nèi)容屬于NCDR的范疇。自然脫碳必不可少，需要納入風(fēng)景園林行業(yè)的適用范圍，但必須承認(rèn)，我們已經(jīng)越來越接近氣候變化臨界點(diǎn)。觸發(fā)臨界點(diǎn)的可能性極高，因此需要討論2種基于高科技的地球工程方案；其中一種方案名為直接空氣捕獲（DAC）比自然脫碳更高效，另一種方案則通過降溫緩解全球變暖問題，以應(yīng)對氣溫上升的緊迫性和全球性生態(tài)行動的缺乏。

直接空氣捕獲（DAC）是一種地球工程技術(shù)，可直接從大氣中捕獲二氧化碳，然后將其埋于地下。捕獲設(shè)備吸入空氣后，經(jīng)過一系列的化學(xué)反應(yīng)，將提純的二氧化碳加壓并泵入地下巖層，進(jìn)行化學(xué)轉(zhuǎn)化，最終可封存于地下數(shù)千年。作為“工具箱”中的一員，一個(gè)DAC工廠每年可以吸收100萬t二氧化碳，相當(dāng)于4萬棵樹吸收的量。然而，需要清除的二氧化碳高達(dá)數(shù)十億t，因此需要大規(guī)模地?cái)U(kuò)大DAC機(jī)器的生產(chǎn)才能較快地看到效果?？茖W(xué)家、工程師和企業(yè)家們正在研究這項(xiàng)技術(shù)，尋找各種更便宜、更有效的方法，以達(dá)到相當(dāng)規(guī)模的氣候應(yīng)用。風(fēng)景園林師可以借助DAC實(shí)驗(yàn)裝置推動研究、測試和開發(fā)，并協(xié)助宣傳DAC的研發(fā)應(yīng)用。

4.4 太陽能輻射管理（SRM）/太陽能地球工程（SG）

該方法人為改變地球的反射率，將陽光反射回太空而改變地球上的光照量，進(jìn)而降低地球溫度。許多太陽能地球工程技術(shù)都基于這一原理。

4.4.1 太陽能地球工程與時(shí)間期限

盡管上述種種方法組合都能應(yīng)對氣候變化，但其發(fā)揮效用的前提是必須在10年內(nèi)開展行動。事實(shí)是，自然與社會發(fā)展緩慢，而氣候變化的速度卻遠(yuǎn)比預(yù)想的更快?？茖W(xué)家指出，我們正在為減緩全球變暖的速度而努力，若升溫幅度超過1.5～2 ℃的臨界值，將無法逆轉(zhuǎn)，其后果極其嚴(yán)重。但鑒于目前相關(guān)政策滯后，為了在國際上形成有效的應(yīng)對機(jī)制，學(xué)術(shù)界加大了地球工程技術(shù)的科研力度和經(jīng)費(fèi)投入[15]。

4.4.2 調(diào)整反照率

一些反照率調(diào)整方法技術(shù)含量低，可應(yīng)用于城市空間的硬質(zhì)表面（如屋頂、街道、城市硬景觀和墻壁等）降低城市熱島效應(yīng)。

4.4.3 工具11：地面反照率

調(diào)整地面反照率的方法之一是改變建筑物表面或鋪裝材料的顏色，從而減少吸光量、增加反光量；或者在建筑物上增加垂直綠墻，可以起到雙重作用——既可以營造涼爽微氣候，又可以為城市空間增加綠意、吸收二氧化碳。

4.4.4 工具12：植被反照率——會反光的植物

基因科學(xué)家正在開發(fā)更多的反光植物，這些植物可以用于農(nóng)業(yè)，也可以用于大面積的景觀種植。

4.5 太陽能地球工程技術(shù)

這些先進(jìn)技術(shù)多涉及大規(guī)模的全球干預(yù)。①太空遮陽板（太空鏡）；② 海洋云彩增亮（添加粒子，增強(qiáng)云彩反射性）；③ 海洋微氣泡工程（增強(qiáng)海洋表面反射性）；④ 卷云薄化（允許熱量從大氣層排出，回到被云層截留的空間；⑤ 平流層氣溶膠注入（SAI）。

4.5.1 最具爭議性的觀點(diǎn)

SAI效率高且成本相對較低，因此是太陽能地球工程中研究最多的技術(shù)之一。雖然未被列入“工具箱”，但它是唯一能給地球降溫的方法，可為人類向可再生能源經(jīng)濟(jì)轉(zhuǎn)型和大氣脫碳行動爭取時(shí)間。SAI以火山噴發(fā)的原理為模型，據(jù)觀察發(fā)現(xiàn)火山噴發(fā)可增加地球的反照率從而降低地球溫度。例如，1991年皮納圖博（Pinatubo）火山噴發(fā)后，由于大量硫酸鹽噴入大氣，測得當(dāng)時(shí)的氣溫下降了1.00 ℃。

硫酸鹽顆粒具有很強(qiáng)的反射性，可將入射的陽光反射回外層空間，從而增加地球反照率。以宇宙中的星體為例，金星作為夜空中最亮的天體，其反射率是月球的7倍，這是由于它具備稠密、含硫的大氣層。除硫酸鹽之外，專家還在測試具有反射光和溶解性能的粒子，也許會發(fā)現(xiàn)更好的解決方案。

因此人造制品成為可能，不僅效果立竿見影，而且費(fèi)用低。該方法需要飛機(jī)群飛抵平流層釋放硫黃顆粒。雖不能一勞永逸，但能為脫碳、節(jié)能爭取時(shí)間。專用飛行器和分散系統(tǒng)需要幾年的時(shí)間部署到位，其成本相當(dāng)于一部好萊塢大片[16]。這項(xiàng)技術(shù)通過冷卻地球來避免最糟糕的情況發(fā)生，是目前的一個(gè)理想備選方案。

4.5.2 SAI的風(fēng)險(xiǎn)和收益

SAI也許是一個(gè)非常強(qiáng)大的工具，但也存在一定風(fēng)險(xiǎn)?？茖W(xué)家將深入研究模擬其風(fēng)險(xiǎn)和效果，以進(jìn)一步確定該技術(shù)對全球不同地區(qū)可能產(chǎn)生的影響。風(fēng)險(xiǎn)增加的原因是許多國家都具備部署SAI的能力，而管理是最大的問題。無論SAI的技術(shù)及應(yīng)用潛力有多大，都需要擴(kuò)大以氣候變化為主流話題的研討，針對其風(fēng)險(xiǎn)和效果進(jìn)行辯論。此外，提高公眾參與度，通過集體的判斷和決策推動SAI的建設(shè)與發(fā)展，使受過教育且知情的公民能夠參與氣候工程專題的相關(guān)決策。

5 結(jié)語

“我們正生活在這樣一個(gè)時(shí)代，所有人都在問自己有關(guān)未來的問題。COVID-19動搖了人類的信念和習(xí)慣，并引發(fā)了各種質(zhì)疑的聲音。”[17]新冠疫情讓我們關(guān)注到一個(gè)事實(shí)，人類正經(jīng)受自然的威脅。人類無法控制自然，相反，是自然控制了人類。除了潛在的核災(zāi)難，氣候危機(jī)是人類前所未有的生存威脅?？梢詫⑿鹿谝咔榭闯墒巧鐣驼仨殤?yīng)對氣候變化這一歷史性挑戰(zhàn)的彩排。作為設(shè)計(jì)師，隨著劇情的推進(jìn)，又該如何處理處理一系列難題？人類的思想將受到挑戰(zhàn)，工作模式也將改變。氣候在變化，設(shè)計(jì)也需要革新。我們想做的不僅僅是“活著”和解決眼前的麻煩，而是希望能進(jìn)一步扭轉(zhuǎn)、修復(fù)氣候狀況，讓地球重?zé)ü獠省Ｉ衔囊颜故玖孙L(fēng)景園林師如何為21世紀(jì)大氣脫碳工程做出的重要貢獻(xiàn)。風(fēng)景園林師們有“工具箱”作為智囊，可以在生態(tài)系統(tǒng)到地球系統(tǒng)等不同尺度中實(shí)現(xiàn)自我認(rèn)知，也期望能夠更進(jìn)一步發(fā)揮專業(yè)價(jià)值，超越“彈性”和“適應(yīng)”策略，利用“工具箱”減緩氣候變化。在新使命的推動下，設(shè)計(jì)師必須思考在各種規(guī)模和尺度下可開展的工作——從地方到國家，乃至全球；同時(shí)在工作中運(yùn)用專業(yè)知識、技能和想象力進(jìn)行不同層面的交流并采取行動。最后，我們必須為現(xiàn)實(shí)的可能性做好準(zhǔn)備，即使用地球工程的先進(jìn)技術(shù)對地球能源系統(tǒng)進(jìn)行干預(yù)，以避免氣候變化最壞情況的發(fā)生。相關(guān)技術(shù)的研究、爭論、統(tǒng)籌和監(jiān)管也需要風(fēng)景園林師的關(guān)注和參與。最重要的是風(fēng)景園林師需要積極參與各個(gè)層面的工作，竭盡所能分享知識，幫助更多人了解氣候治理的重要性并加入隊(duì)伍中來。我們需要攜手合作、保護(hù)地球，實(shí)現(xiàn)自然生態(tài)系統(tǒng)的再生，從而恢復(fù)氣候平衡。

注釋：

① 引自在第21屆聯(lián)合國氣候變化大會上通過的《巴黎協(xié)定》。

② 引自2019年聯(lián)合國政府間氣候變化專門委員會（IPCC）《全球增暖1.5 ℃特別報(bào)告》。.

③ 麻省理工學(xué)院建筑學(xué)院開設(shè)了適應(yīng)氣候的Mass Timber課程以及A Threshold Winery in climatic and economic shift；哈佛設(shè)計(jì)研究生院開設(shè)了Dam Studio Climate Change Along the Mystic River探索氣候變化的解決方案；Core Studio從“問題”到“適應(yīng)”探索氣候變化和適應(yīng)；耶魯大學(xué)開設(shè)了高階設(shè)計(jì)工作坊Learning from Piura:Building Resilience in an Era of Climate Change.BIG建筑事務(wù)所提出的曼哈頓下城適應(yīng)海平面上升的方案。

④ 引自維斯塔計(jì)劃（Project Vesta）。網(wǎng)站www.project vesta.org。

圖片來源：

圖1由伊迪絲·卡茨繪制；圖2～4、6、7、18來源自瑪莎·施瓦茨合伙人設(shè)計(jì)事務(wù)所；圖5來自2019年2月24日印度《孟買鏡報(bào)》；圖8、9來自Sasaki；圖10、11來自斯坦法諾·博埃里事務(wù)所；圖12～14來自瑪莎·施瓦茨；圖15～17來自克里斯蒂娜·希爾。

（編輯/劉昱霏）

The Designer’s Geoengineering Toolkit: Crisis Creates Opportunities for Landscape Architects to Reverse, Repair and Regenerate The Earth’s Climate

Authors: (USA) Martha Schwartz, (USA) Edith Katz Translator: LI Zhi Proofreader: HU Yike

1 Decarbonization

At present,decarbonizationis not a household word.However, it will be in the next decade as sectors of the economy must transition rapidly from the use of fossil fuels to reduce carbon dioxide emissions or, ‘decarbonize,’ if we are to avoid climate change calamity.But a lesser understood action is also required.We have to remove carbon dioxide (CO2) from the atmosphere which has already been emitted over the past 100 years.In other words, our atmosphere needs to be cleaned up too.“The world has delayed reducing carbon emissions for so long that humanity will need to suck enormous amounts of carbon dioxide back out of the atmosphere to avoid catastrophic global warming.”[1]In 2015, the Paris agreement and the United Nations committed to limiting global warming by the second half of the century to “well below 2 ℃ ” and “to pursue to keep warming below 1.5℃ ” above pre-industrial levels①.However, emissions continue to rise.“The world is rapidly approaching 1.5℃ of warming and is on track for 3 ℃ unless we take action.”[2]In all the pathways to achieve the 2015 Paris goals,the IPCC②relies upon large-scale atmospheric carbon dioxide removal (CDR), as a complement to emissions reductions to achieve the climate targets[3].This paper focuses uponatmosphericdecarbonizationas one of the most important areas of study within the field of geoengineering which is defined as “the deliberate large-scale manipulation of an environmental process that affects the earth’s climate, in an attempt to mitigate the effects of global warming.”[4]Geoengineering research and application of CDR, specifically, has a powerful relationship to the profession of landscape architecture and our role in decarbonization of the atmosphere.

1.1 Beyond Adaptation and Resiliency: Mitigation

Design professions world-wide have taken up the urgent and dramatic issue of climate change.In design education and practice today, two basic approaches are used to meet the challenges of the climate crisis:resiliency(the capacity to recover quickly from difficulties) andadaptation(modifications that cope with the impacts)③.While these practices are important and will need to be deployed well into the future, they do not go far enough in tackling the root of the problem.

1.2 Mitigation Compared to Adaptation and Resiliency

Mitigation addresses the causes of the problem to alleviate the severity of the impacts[5].When referring to climate mitigation, this means reduction in CO2emissions, or enhancing carbon sinks (biosphere, atmosphere, ocean) for long-term atmospheric CO2removal.It also refers to reducing the effects of global warming by cooling the Earth.

The other differentiation betweenmitigationandadaptation, is their spatial scales.Resilienceandadaptationmeasures are usually done at smaller,more local scales whilemitigationmeasures work to address a global scale.Adaptation strategies try to ameliorate negative impacts for example, using scarce water resources more efficiently, or building flood defenses to sea level rise; mitigation, in this case (decarbonization), by addressing the root of the problem in drawing down CO2will eventually help stabilize the carbon cycle at some point in time.

1.3 Decarbonization is at a High Level of Concern

Scientists, economists, industrialists, and wellinformed state leaderships are becoming more aware of the future costs of climate change and the daunting scale of alterations we must undergo by 2030, in order to avoid worst case scenarios.To assist in the global effort, it is the purpose of this discussion to present a range of ‘tools’ in adecarbonizing‘toolkit’for designers and offer representative projects which illustrate their use so that landscape architects can begin to explore these methods in their own projects and practices.In this new era of climate change, landscape architects,whose remit focuses on the land and vegetation,both of which capture and transform CO2, should be recognized as the ‘decarbonizingprofession’par excellence.“No other mechanism known to humankind is as effective in addressing global warming as capturing carbon dioxide from the air through photosynthesis.”[6]It is our assertion that landscape architects have a very important role to perform in climate mitigation as well as the reversal, repair and regeneration of the planet’s climate over time.

1.4 Mechanics of Climate Change and Landscape Architecture

The mechanics and drivers of climate change offer key points where landscape architects can intervene to produce positive results.Understanding the interactions of the multiple spheres in the earth system, the earth energy balance and the carbon cycle present opportunities wherein landscape architects can operate to beneficial effect.

2 Impacts of Climate Change: What Will China Face?

China is considered by some metrics as part of the Global South, despite the fact it is industrialized and in 2019, a top CO2emitter, along with the USA.Together, they were responsible for 40% of all global emissions[7].Thirty years of rapid economic growth has raised China’s world status as an economic power.But it also has exacerbated how it will be affected by climate change.Atmospheric pollution, produced by China’s coal burning plants, combined with polluted rivers and depleted aquifers are consequences of their swift economic development which will magnify the negative effects of climate change within China as emissions and temperatures increase.

Here are four main general categories of climate impacts that will be distributed unevenly across China and which will be explained in greater detail:

1) melting glaciers and loss of fresh water;2) rising temperatures / heat waves and increased air pollution; 3) desertification with resultant effects to food and habitation; 4) rising sea levels and coastal area inundation.

2.1 China and the ‘Water Tower of Asia’

One of the most glaring and monumental consequences of climate change starts with effects upon the ‘Water Tower of Asia,’ located on the Tibetan Plateau, in China, and high within the Himalayas.The water tower is critical to the survival of over two billion people as it is the headwaters for the main rivers which bring fresh water to China, Nepal, Afghanistan, Pakistan, India,Bangladesh, Bhutan, Myanmar and the Mekong peninsula.This area contains over 14%, the largest number of glaciers and snow, after the Arctic and Antarctic, giving it the nickname the ‘third pole’.However, rising temperatures are melting these glaciers and forcing them into retreat.

2.2 Heatwaves to the North China Plain (NCP)

Heatwaves threaten to have deadly impacts in China, especially on the North China Plain which is predicted to become a global hotspot if drastic measures to curb emissions are not taken and ‘business as usual’ continues.As early as 2070,China will face greats risks to human life from rising temperatures compared to any other location on Earth[8-9].

2.3 Desertification

Along with the threat of freshwater depletion is the resultant effect of desertification across China’s northern regions.Desertification is defined as a “l(fā)and type where previously fertile soil is transformed into arid land.”[10]Numerous reasons are to blame for the Gobi Desert being the fastest growing desert on Earth, extending southward into China at the rate of 2,250 miles each year.This extent compares to 80% of the width of the USA from coast to coast annually! Arid land replacing hospitable agricultural land is displacing people,creating enormous sandstorms, and impacting economic development.China’s growth spurt is cited as one reason that destroyed and denuded timber forests causing massive deforestation,leading to desertification.It is estimated that roughly 27% of China is now covered in desert.Food scarcity, due to desertification, has become a real concern for China, as a very small percentage of their land is arable and can produce crops.

2.4 Rising Sea Levels

Another major threat to China is rising sea levels which will have an enormous impact because it has the largest population living in coastal areas[11].In China alone, and by 2050, 93 million people would be affected by sea level rise in places like Shanghai, Shenzhen, Tianjin, Guangzhou, and the provinces of Jiangsu, Pearl River Delta megacity zone.In just 30 years these places could experience severe inundation and flooding, disrupting global economies and supply chains, affecting 25% of global economic growth today[12].

3 Geoengineering

3.1 Introduction to Geoengineering

Geoengineering is defined as the deliberate large- scale intervention in the Earth’s climate system, in order to moderate global warming[4].

3.2 Geoengineering Taxonomy

There are two distinct areas of geoengineering interventions.One branch, Solar Radiation Management, increases the albedo, or reflectivity of the Earths, affecting the earth’s energy system,the balance between in-coming and outgoing energy.The other branch, Carbon Dioxide Removal, interacts with the earth’s carbon cycle, the movement and transformation of carbon through the atmosphere, into plants and organisms, the earth and back again (Fig.1).

Carbon Dioxide Removal (CDR) engages with the Earth’s carbon cycle to draw down or decarbonize the atmosphere.Within CDR, methods are divided up between natural or biological carbon dioxide removal (NCDR), physical, and chemical,depending on how CO2is separated from the atmosphere.

Solar Geoengineering interacts with the Earth’s energy budget through technological means by decreasing the incoming solar radiation resulting in lowering the Earth’s temperature: or cooling the earth.

4 The Landscape Architect’s Remit for the 21st Century

Within the two branches of geoengineering are many options, but there is no ‘silver bullet’solution.A broad portfolio of tools will be needed.To make a significant contribution, the largest opportunity for landscape architects to mitigate climate causes and effects lie within the realm of Natural Carbon Dioxide Removal (NCDR), or atmospheric carbon dioxide clean-up methods,which effect the earth’s carbon cycle.

4.1 CDR: Natural Carbon Dioxide Removal(NCDR)

There are manynaturalprocesses that remove and store CO2, in ‘sinks,’ from the atmosphere.These methods include land, soil and vegetation which we, as landscape architects,deal with routinely.In the bookDrawdown:TheMostComprehensivePlanEverProposed toReverseGlobalWarming,”[6]is a list of 80 researched decarbonizing actions that can solve the climate crisis.The intention of the book is to show how 1,031 GT (gigatons) of atmospheric CO2can be removed over the next 30 years, the amount required, to bring the Earth back into planetary equilibrium.The book conveniently ranks methods in various categories according to their effectiveness in gigatons (1 gigaton=1 billion tons: or the equivalent of 400,000 Olympic size swimming pools filled with water.On Drawdown's list, land-based solutions ranked 60% of all the solutions within the top 20, and 30% of the top 80 solutions; meaning that landbased methods are the most effective and powerful ways to decarbonize atmospheric CO2.Why is this considered geoengineering? Because, as proposed inDrawdown, if these solutions are applied at large enough scale, they will affect the condition of the global atmosphere in both the energy budget (heat control) and carbon cycle (reduction of atmospheric CO2).However, many of the decarbonizing tools described below can still be implemented at various scales where their effects will accrue to be beneficial.

4.1.1 Afforestation Tool #1

Annual capture potential: between 0.5 and 3.6 billion metric tons.Current estimated cost between$5 to $50 per metric ton[1].

Sowing seeds or planting trees in an area that was devoid of any trees for at least 50 years to create a stand or forest is considered afforestation.Beside the natural beauty of trees is their ability to absorb CO2during photosynthesis and transform the gas into biomass as roots, leaves and stems.As long as the tree remains standing, the carbon is stored out of the atmosphere.However, when this biomass decomposes or is burned, it releases the CO2again.Thus, planting trees for decarbonization also means managing the forests to prevent the undesired release of large quantities of carbon dioxide.This can be done with proper fire management to limit the risks.Or, felled trees can be used for biofuels.Or, another method such as the use of trees in mass timber construction where steel and concrete products are replaced with wood products which keeps the carbon locked up for a very long time.

Representative Afforestation Projects:

1) Daxing International Airport Economic Zone Central Park Competition 2019, Martha Schwartz Partners, Beijing Daxing District, China.

① Research area 747 hm2./design area 361 hm2;② Design competition completed 2020; ③ 112,000 trees;④ CO2sequestration, air pollutant remediation,noise reduction and microclimate modification;⑤ Significant storm water storage area.

The landscape establishes large-scale afforestation and water catchment areas incorporating existing forest fragments and canals which take the form of a central public park with diverse public realm programs.As a large-scale infrastructural component to the airport, the landscape works to both mitigate the climate crisis through natural,biological CO2sequestration plus adapt to the site’s projected climate impacts promoting a resilient strategy (Fig.2-4).

2) Fast Mini Forests, Akira Miyawaki.

① Area the size of 6 parking spaces contains 300 trees; ②Cost as little as an I-phone to afforest; ③ Engender plant growth 10 times faster and 30 times more dense; ④ Best suitable native species selected; ⑤ Saplings planted so close that they compete for sunlight by growing taller;⑥ Nutrient-rich soil prepared to fuel growth of saplings; ⑦ Within 10 years area transformed into dense forest.

The work of the Japanese botanist,Akira Miyawaki, is inspirational for the task of afforestation.He has devised a method based upon a German technique calledpotentialnatural vegetation.This method “calls for dozens of native tree species and other indigenous flora to be planted close together, often on degraded land devoid of organic matter.As these saplings grow,natural selection plays out and a richly biodiverse,resilient forest results.”[6]…The effects of this practice forms forests, or dense plantings, in a fraction of the time required normally and they are many times more biodiverse, resilient and thick than conventional plantation planting while at the same time sequestering carbon more effectively[6](Fig.5).

3) Yangliuqing Grand Canal National Culture Park Competition, Martha Schwartz Partners,Tianjin, China.Masterplan 2020.

① 188 hm2; ② Dense forests provide CO2sequestration plus air pollutant cleansing;③ Constructed wetlands control storm water;④ Economic benefits from green infrastructure =savings $90,000 annually.

The entire proposed landscape serves as an extensive green infrastructure for the city.Dense forests canopies create comfortable micro-climates during rapidly shifting temperature rise and fluctuation.Constructed wetlands are employed as a carbon sink and to reduce soil erosion in Tianjin along with a combination of sunken garden rooms that provide sustainable storm water overflow remediation (Fig.6, 7).

4) Jinan CBD Streetscape, Sasaki Landscape Architects.

① Jinan, China.Design completed: Feb.2018.② 320 hm2.Urban site.③ 30,000 new trees(equivalent to 50 acres of forest) plus understory shrubs and perennials.④ 7 Gt.of CO2annual sequestration.

In this project, by Sasaki, for the CBD of Jinan, advanced thinking about the street as public realm and with it the creation of an urban forest as the matrix for the street system evolved.Sasaki was asked to design the streetscapes for 14 of the CBD’s 30 streets totally 26 kilometers of roadway.Streets varied from large scale arterials and major urban connectors to buffer roads, small scale park canopies, walks and pedestrian friendly recreational ring roads.Each street type was given a different range of widths, speed limits, scales and plant palettes along with adjacent uses and programming.The plan proposes the introduction of 30,000 trees:the equivalent of over 20 hectares of forest.

The cumulative effect of the introduction of such massive amounts of vegetation will have cooling, health and ecological benefits including biodiversity.Native plant communities were featured, where none before had been seen this urban setting, re-establishing the indigenous botanical locale that will enhance a sense of place,memory and culture (Fig.8, 9).

5) Smart Forest City, Cancun, Mexico, Stefani Boeri.

① 130,000 inhabitants; ② 557 hm2.more than half of which will be vegetated; ③ 7.5 million plants, 350 species; ④ 260,000 trees; ⑤ 5,800 tons of CO2annual sequestration.

The architect, Stefani Boeri is a champion of the urban forest, most notably placed vertically on his buildings.But this more recent proposal exhibits his most ambitious thinking on urbanism for the 21st century with an agenda for environmental equity, smart technologies,sustainable energy and an intensive planting program.With a rich intermingling of large parks, garden roofs green facades and tree lined streetscapes Boeri reverses the normal expectation of the ‘hard-scape’ city by turning it into a botanical garden.The proposal also designed support for circular economies to make its food,water and energy self-sufficient (Fig.10, 11).

4.1.2 Urban Afforestation (NCDR) Tool #2

Within the urban landscape, which is mostly hardscape with a smaller percentage of green space, streets and underutilized spaces offer the largest piece of infrastructure a city has that can be reshaped in response to climate change.

Sequestropolis: The City as Machine to Combat Climate Change, Option Studio 2016,Harvard Graduate School of Design, Martha Schwartz, Professor in Practice.

① Test sites: 4 townships within Boston,over 218 km2; ② Metrics using, I-Tree were applied to determine: 4.5 million trees proposed;GHG removed 460,000 tons / annually; Water captured 22,890,156,034 gallons; Energy savings$206,963,526.

Working in collaboration with Harvard Forest, which had done an in-depth study of Massachusetts, except for the urban areas, to organize the state into a self-sustaining entity by the year 2060, the studio focused upon the urban area of Boston.Its goal was to show how an older,existing, and dense city, can reconfigure itself by reorganizing and re-designing their streets and other public realm open spaces to address the impacts of global warming predicted for 2060.Urban afforestation was explored, as the central concept to promote an ‘hybrid system,’ composed of natural, biological and man-made devices and technologies, which could function at climate relevant scales.Students researched climate change predictions for 4 Townships in Boston 2060 which included: High velocity rain events and flooding;Periods of drought; Heat Island effect, Transition from Zones 6 - 7 for plants, Sea level rise of 2 feet with storm surge of 8 feet.

Working along with Harvard Forest,assumptions were formed that framed the design:① Environmental inequity through afforestation on public and private lands; ② Through the Massachusetts Department of Energy and the Environment’s“Gateway Cities Program; ③ Automated vehicles(AVs) will be the dominant mode of private transportation in 2060 meaning that space could be‘harvested’ for urban afforestation;④ Transport Zones Private cars within the 1-95 ring road will be disallowed; and Public transport in Boston will extend out to the ring road to TOD’s and enable commuters to park privately owned cars;⑤ Sea Level Rise will be dealt with by a flood wall; ⑥ Zero storm water run-off will be added to the existing combined sewer; ⑦ Increase urban albedo by painting roofs white wherever possible(Fig.12-14).

4.1.3 Coastal Wetland Sinks NCDR Tool #3

One of the largest yet underappreciated natural carbon sinks on the planet are ‘blue carbon’ resources that occur along the edges of coastlines where land and salt water converge.This is where the salt grass marshes, the mangroves and sea grasses live.

Relative to their land area, they have the ability to absorb and sequester CO2many times the rate that tropical forests do, in the long-term,in the aboveground plant life, the roots and the soils below.The corollary, of course is, if they are not protected they could release vast storages of greenhouse gases into the atmosphere.Coastal wetlands are also rich nurseries and feeding grounds for marine and air life: fish and migratory birds.These systems also function as natural defenses to storm surges that can prevent cities inland from flooding.Although often overlooked for the immense role they can perform in carbon dioxide sequestration, a recent study has confirmed that coastal wetland systems are one of the best ways to help solve climate change.Jennifer Howard, coauthor of an important study has summarized: “We are trying to emphasize that coastal ecosystems could be an important component of reducing emissions through conservation and restoration of these systems...”[13]

Representative Coastal Wetland Project: San Francisco Bay Hybrid Edge, Christina Hill.

①New designed edge for sea rise and flood control; ② 4 hm2polder unit; ③ Combines constructed wetlands, housing and coastal features.

Associate Professor, Kristina Hill at U.C.Berkeley, explores large scale planning strategies for the coastline of San Francisco and its coastal wetland ecosystems.The threat of sea level rise to San Francisco is predicted to result in dramatic changes to its coast in the next 50 to 75 years.Hill has taken a unique approach to her land planning strategies: one which accepts the fundamental role which property laws play in America, favoring private owners, and she tries to align this situation with conservationists and sound ecological design.She explores a solution she terms a ‘hybrid edge’based upon the Dutch polder system which incorporates housing, constructed wetlands and coastal features.The result is a new managed edge populated with affordable housing opportunities and an economic driver so that the solution does not depend upon government financing: private developers can take the lead (Fig.15).

Hill studies a micro-polder that populates the coastline with a system comprised of merely 4 ha:much smaller than the Dutch prototype (purple area in Fig.16).She surrounds these polders with levees that control the water, permit storage of storm water and control flooding (orange).Around the polders, wetlands are constructed (green)through the methodology of ‘shallowing’ the Bay at the edge by bringing in a clean sediment.The wetlands build habitat, shelter wave energy from the sea; and even allow the construction of beaches(yellow) to provide human recreational access to the shorelines: not to mention sequester CO2in their plant life and soils.Affordable housing built within the polders (Fig.17).

4.1.4 Land Use NCDR Tool #4

As landscape architects, we often are asked to do large scale land planning for cities, towns and communities that frequently include ex-urban areas,or work in developing countries.In either instance,we should begin to catalyze a new agenda: one that incorporates land use practices into the proposals specifically acknowledging the role that land and soils can perform in sequestering CO2.

Representative Land Use Project: Changes to the Land, Harvard Forest Study in 2014.

The principles of the study focus on how land-use can make Massachusetts be more selfsustaining in the following ways.

①Landscape as crucial to allowing water to percolate into the soils to replenish the aquifer that Boston depends on for fresh water.② Land must be available to produce food for the population of Massachusetts.③ Land must be connected so to be able to provide ecological benefits for the ecosystems within Massachusetts.

The study created four scenarios to address climate change effects for the entire state of Massachusetts in 2060.Scenario 1 looked at recent trends, Scenario 2 opportunistic growth, Scenario 3 regional self-reliance and Scenario 4 forests as infrastructure.The forests as infrastructure landscape scenario mapped a future in which policies, markets, state and local planning, and incentives focus on increasing the commonwealth’s“l(fā)iving infrastructure.” This scenario scored best for 7 out of 9 nature-based benefits to the state.

4.1.5 Soil Sequestration NCDR Tool #5

Soil sequestration is a strategy which has numerous benefits.It improves degraded soils, enhances biomass production, purifies surface and ground waters plus reduces the rate of enrichment of atmospheric CO2by offsetting emissions due to fossil fuels.

Representative Soil Sequestration Project:Nori, Carbon Removal Marketplace.

When you buy carbon removals in the Nori marketplace, you are not only negating your carbon footprint.You are helping start an entire market for carbon removal by paying farmers to use sustainable farming practices which remove atmospheric carbon and store it in their soil where it is monitored and quantified.

4.1.6 Enhanced Weather / Rock Sequestration NCDR Tool #6

Annual capture potential: between 2 and 4 billion metric tons.Current estimated costs of capture: between $50 and $200 per metric ton.

Geologic processes, that are part of the slower carbon cycle, involve rocks on the earth which chemically react with atmospheric gasses and sequester millions of tons of CO2from the air over very long periods of time.Certain types of material, like silicate rocks are highly interactive with the mildly acidic carbon dioxide when dissolved in rainwater which catalyzes the reaction transforming the rocks.During this process of material transformation, the mineral rocks embed CO2into their molecular structure ultimately turning into a carbonate material where the CO2stays locked up for millennia.Scientists have been exploring ways to accelerate this natural process of weathering using highly reactive silicate rocks such as olivine or dunnite.Applications of this material on agricultural lands, in the tropics or on coastal beaches has been a focus for experimentation.

Representative Enhanced Weathering Projects:

1) Project Vesta.

Project Vesta accelerates the ancient natural process.Their mission is to further the science of enhanced weathering and galvanize global deployment.They make green-sand beaches with olivine; where, wave action speeds up the carbon dioxide capture process while de-acidifying the oceans④.

For landscape architects, working all over the world, such low-tech tactics could be meaningful if the application is feasible within a given project.Significant limiting factors that must be considered are the cost and energy required for mining and transporting the minerals in relation to the sequestration ratio which is: approximately one ton of olivine can displace two -thirds of a ton of carbon dioxide[6].

2) Desert Test Site, Martha Schwartz Partners.

Site study using enhanced weathering where patterns of silicate minerals are placed in patterns on the ground, watered by irrigation to catalyze the chemical reaction to capture CO2from the air.The project collaborated with UK Scientist, Paul Renforth,to advance ways to conduct enhanced weathering in arid climates within an applied design (Fig.18).

4.2 Physical Carbon Dioxide Removal and Metrics

In addition to decarbonizing techniques for land, coasts, or vegetative based methods, landscape architects can adopt new materials and tools which affect carbon dioxide emissions to limit their input into the atmosphere in the first place or help to keep them sequestered long-term or help them calculate the effects of their designs on carbon.

4.2.1 Low Carbon Cement and Concrete Tool #7

A much-overlooked source of atmospheric CO2is a material that has helped to build the world.A killer fact is that 1 ton of concrete releases 1 ton of CO2into the atmosphere during its manufacturing.If the concrete industry were a country it would be the third largest emitter.As it is, the concrete industry is responsible for 5 -8% of carbon emissions worldwide: “Concrete is the most used material on the planet after water.”[14]Numerous companies are developing a low carbon concrete option.One innovation, by the company, Solida, utilizes an advanced blend of the basic materials and during the curing process the concrete actually absorbs CO2.Architects are beginning to employ low carbon concrete in buildings and landscape architects can use it in exterior elements like bridges, roadways, walkways,walls, curbs and walks, to mention only a few of the typical elements that are required for site development.

4.2.2 Mass Timber and Cross Laminated Timber(CLT) Tool #8

Mass timber or CLT, Cross Laminated Timber, offers structural integrity plus environmental attributes which make this one of the most innovative new materials that keeps the CO2embodied in trees from sequestration exactly where it should remain.Mass timber describes a number of large engineered wood products that typically involve the compression of multiple layers into solid wood panels.Mass timber is fire resistant,it is strong, it is sustainable if the wood from the forests is sustainably taken and makes construction cost efficient.Outdoor applications for landscape architects are feasible.It is a lower carbon alternative to steel and concrete which draws on a renewable resource and it doesn’t require the burning of fossil fuels for its production.

4.2.3 Making Your Point Through Metrics Tool #9

The Climate Positive Design Carbon Calculator tool responds to the scientific and economic challenge to evaluate the implications of designs relative to their efficacy to mitigate climate change.Climate Positive Design’s Pathfinder tool delivers data that can help designers determine a landscape design’s carbon footprint.By using the Pathfinder tool, which is interactive, designers can improve their design to ensure it increases carbon capture and reduces embodied carbon in the construction materials to meet the goal of any project: to sequester more carbon than they emit during construction and ‘daylight’ to being ‘carbon negative’ in as short a time span as possible.By using the Pathfinder tool, a landscape architect can convey these benefits to clients and others who are participants in the fight to curb emissions.By participating, you can actively contribute to climate change solutions and the 2030 challenge.

4.3 Chemical/Mechanical Carbon Dioxide Removal: Direct Air Capture (DAC) Tool # 10

Thus far, we have surveyed some of the nature-based tools that can be employed in landscape architecture and which fall into the category of Natural Carbon Dioxide Removal(NCDR).While these efforts are urgently needed and necessary to be included within the toolkit, the growing possibility of overreaching climate change tipping points must also be acknowledged.The high likelihood of this happening thus requires the discussion of two high-tech geoengineering options; one which can take down atmospheric CO2more quickly than nature-based methods and the second, can cool down the Earth to avoid catastrophic global warming, thus addressing the urgency of climbing temperatures and lack of global action.

Direct Air Capture (DAC) refers to a geoengineering technology which removes CO2from the atmosphere and sequesters it by putting it back underground from where it came.A machine does this by pulling in air which undergoes a series of chemical reactions, extracts the carbon dioxide in a very pure form which is then pressurized and pumped underground into geologic rock formations, undergoing chemical transformations,where it can remain for millennia.As a tool in the landscape portfolio, one DAC plant does the work of 40,000 trees by drawing down 1 million tons of CO2annually.However, because there are gigatons(billions of tons) of CO2that must be removed,there is significant number of DAC needed to make any impact quickly.These machines would need to be scaled up enormously.Various approaches to this technology are being developed by scientists, engineers and entrepreneurs and they are all pushing to find ways that will make this technology cheaper and more efficient, so it can be applied at climate relevant scales.Landscape architects could help with experimental installations to promote research, testing and development, as well as advocacy for the development and use of DAC.

4.4 Solar Radiation Management (SRM) / Solar Geoengineering (SG)

This approach limits the amount of sunlight reaching the earth by reflecting it back into space to intentionally change the Earth’s albedo, or reflectivity, which in turn, cools the Earth.There are many technologies within this class of solar geoengineering all based upon this principle.

4.4.1 Solar Geoengineering and the Issue of Time

While a portfolio of all the approaches mentioned previously must be part of any scenario that begins to avert catastrophic climate change,these actions would have to happen immediately and rapidly within this decade.The fact is that nature and society move slowly, and climate change is moving more rapidly than predicted.Scientists warn that we are on a path to avoid overshooting the 1.5 - 2.0℃tipping point, wherein global warming can no longer be reversed, and the consequences will be extremely severe.Concerns with the lack of political progress, and global responsiveness has therefore increased interest and funding within the scientific community to develop advanced technologicalgeoengineeringapproaches to climate change[15].

4.4.2 Albedo Modification

Some albedo modification methods are lowtech.They can be used by designers especially to lower Urban Heat Island effects when applied to the many hard surfaces that comprise a city space:the roofs, streets, urban hardscapes and walls.

4.4.3 Surface Albedo Modification Tool #11

Changing the color of building surfaces or paving materials so that they are less absorptive and more reflective is one strategy.Or, adding vertical green walls to buildings can do double service cooling the microclimate and adding a living vegetative, CO2absorbing component to an urban space.

4.4.4 Vegetative Albedo Modification - Reflective plants Tool #12

Genetic scientists are developing more reflective plants which could be used in agriculture or by landscape architects in their palettes in large scale plantations.

4.5 Advanced Solar GE Technologies

The majority of these advanced technologies involve large global scaled interventions.

① Sunshade geoengineering (mirrors in space); ② Marine Cloud Brightening (add particles to make clouds more reflective); ③ Ocean Micro-Bubble engineering (make ocean surfaces more reflective); ④ Cirrus Cloud Thinning (allow heat to exit the atmosphere back into space where it is currently being trapped by clouds).⑤ Stratospheric Aerosol Injection.

4.5.1 Most Controversial Idea Yet!

SAI is one of the most researched technologies in this branch of advanced technological solar geoengineering due to its high effectiveness and relatively low cost.Although it isn’t really a tool in the toolkit, it is the only idea on the table that can cool down the earth to buy us the time we need to make the transition to renewable energy economies and remove atmospheric CO2.SAI is modelled on the natural principle of volcanic eruptions which have been observed to increase the Earth’s albedo and decrease the temperature of the Earth’s Global Temperature.Global temperatures measured after the 1991 Pinatubo eruption, for example, were measured to drop as much as 1.0℃due to sulfates that were ejected into the atmosphere from the explosion.

Sulfate particles are very reflective and bounce incoming sunlight back into outer space,increasing the Earth’s albedo.An example of that in the cosmos, is the planet Venus, the brightest object in the night sky.It’ reflectivity is seven times that of the Moon, due to its dense, sulfur-laden atmosphere.Other types of particles are also being tested for their properties to reflect sunlight and dissolve besides sulfates which may lead to an even better solution.

So it is possible to do this artificially, with immediate effect and for very cheap.It requires fleets of planes flying high into the stratosphere depositing trails of sulphur particles.It is not a permanent fix, but it would buy time we likely will need for the transition to decarbonized, energy economies.“The specialized aircraft and dispersal systems required to get started could be deployed in a few years for the price of a Hollywood blockbuster.”[16]Currently, this technology is the only feasible solution on the table that can reduce the worst-case scenarios by cooling the Earth.That given, it is an idea that must be considered.

4.5.2 Risks and Benefits of SAI

SAI is potentially a very powerful and beneficial tool, but it can also carry significant risks.Atmospheric and climate scientists continue to research and model the risks and benefits to better determine how this technology might act upon different global regions.The risks are heightened due to a number of nations around the world would be able to deploy SAI.Thus governance is one of the largest issues.Regardless how one feels about the potentials of this technology and its application, a forum is needed to broaden the discussion about SAI into mainstream conversation about climate change response, where a debate about therisksandbenefitscan occur.Groundwork needs to be laid amongst civil society’s actors, to bring collective discernment and decision-making power to its development so that educated and informed public participation in decision-making on the topic of climate engineering is enabled.

5 Conclusion

“We are living through a period when all of us are asking ourselves questions about the future.Covid-19 has shaken up our beliefs and habits and is opening up all sorts of questioning.”[17]The pandemic has brought our attention to the fact that we are all linked together in the face of planetary threats.And that humans are not in control of Nature.It is the other way around.And there has never been an existential threat as great as the climate crisis which is now facing us except,possibly, nuclear holocaust.Think of Covid as a dress rehearsal for the historic climate change challenge that global societies and governments must navigate, and how will we, as designers,engage massive problems as this drama unfolds?Our thinking will be challenged.Our models of working will shift.The climate is changing - so must design.We want to do more than survive and cope with the problem.We want to reverse and repair the climate to thrive.We have shown how as landscape architects we can make a significant contribution to this century’s atmospheric carbon dioxide clean-up project.We have a tool kit to employ.We can educate ourselves fromecosystem-scaleunderstanding toEarthSystemscale understanding.We can aspire to another level of agency which goes beyond adaptation or resiliency to also mitigate climate change with our toolkit.With this new mission, we must envision our work at all scales from local to national and even globally; where we can use our knowledge,skills and imagination to communicate and act at all levels.Finally, we must be prepared for the very real possibility, that advanced technological solutions to influence the Earth’s energy systems,geoengineering, will be required to avoid the worsecase scenarios of climate change.Whether those technologies are researched, debated, governed, and administered is also an area for our participation and concern.What is most important is our participation, at any level, to share our knowledge and activate others who are not aware of our predicament.We need to clasp hands and work together, to regenerate and protect our natural systems, so to bring Earth’s climate back in balance.

Notes:

①TheParisAgreement:essentialelements.UNFCC.(United Nations Climate Change).

②SpecialReportGlobalWarming1.5℃.(IPCC Intergovernmental Panel on Climate Change 2019).

③ MIT School of Architecture offered courses on Mass Timber for climate adaptation, A Threshold Winery in climatic and economic shift, Harvard GSD offered the Dam Studio Climate Change Along the Mystic River to explore solutions adapting to climate change; Core Studio from Episode to Adaptation exploring climate change and adaptation; Yale University offered an advanced design studio Learning from Piura: Building Resilience in an Era of Climate Change.BIG Architect’s proposal for lower Manhattan’s adaptation to the rise in sea level.

④ Project Vesta.www.project vesta.org.

Sources of Figures:

Fig.1?Edith Katz; Fig.2-4, 6, 7, 18?Courtesy Martha Schwartz Partners; Fig.5?MumbaiMirror.2019-02-24; Fig.8, 9?Sasaki;Fig.10, 11? Boeri Architects; Fig.12-14?Martha Schwartz;Fig.15-17?Kristina Hill.