设计师的地球工程“工具箱”：危机给予风景园林师扭转、修复和再生地球气候的机会

著：（美）玛莎·施瓦茨 （美）伊迪丝·卡茨 译：李致 校：胡一可

1 大气脱碳

目前，“脱碳”一词还未家喻户晓。但若想避免气候变化灾难，经济部门必须在未来10年迅速减少化石燃料使用量和二氧化碳排放量，即实现“去碳化”发展。除此之外还需要采取一项不太为人所知的行动。我们必须清除100年来已经排放到大气中的二氧化碳（CO2）。换句话说，我们需要清理大气层。“人类一直在推迟二氧化碳的相关减排行动，现在不得不从大气中吸回大量二氧化碳，以避免全球变暖引发的灾害。”[1]2015年，《巴黎协定》和联合国承诺在21世纪下半叶将全球变暖限制在工业化前的水平——“远低于20℃”并“力求将升温控制在1.5℃以下”①。即便如此，排放量仍在继续上升。“除非我们采取有效行动，否则世界将迅速接近1.5℃的升温‘红线’，并且有可能冲破3℃。”[2]在实现2015年《巴黎协定》目标的所有途径中，联合国政府间气候变化专门委员会（IPCC）②将大规模的大气二氧化碳脱除（CDR）作为减排的辅助措施，以实现气候治理目标[3]。本研究重点讨论大气脱碳问题，这是地球工程学领域最重要的研究之一，地球工程学定义为“对影响地球气候的环境过程进行有意识地大规模干预，以试图减轻全球变暖的影响”[4]。具体而言，地球工程学研究尤其是CDR的应用，与风景园林及其脱碳作用密切相关。

1.1 “减缓”：对“适应”和“弹性”的超越

气候变化问题的紧迫性已引起全球范围内设计行业的关注。当前的设计教育和实践通常使用2种基本方法应对气候危机：弹性（快速恢复的能力）和适应力（应对自然变化的能力）③。这些方法很重要，且需要坚持实施，但它们无法解决根本问题。

1.2 “减缓”“适应”与“弹性”的区别

“减缓”从问题根源出发，减轻气候变化的恶性影响[5]。“气候减缓”意味着减少二氧化碳的排放或加强碳汇（生物圈、大气层、海洋），从而实现大气二氧化碳的长期清理。“减缓”也指通过冷却地球弱化全球变暖的影响。

“减缓”和“适应”的另一个区别在于空间尺度。“弹性”和“适应”通常应用于局部范围，而“减缓”可解决全球尺度上的问题。“适应”策略侧重治标，如更有效地利用稀缺水资源，或为了应对海平面上升而建设防洪设施；而脱碳领域中的“减缓”策略则通过减少二氧化碳排放而实现治本，以期在未来某个时间点稳定碳循环。

1.3 脱碳问题已成关注热点

科学家、经济学家、企业家和消息灵通的国家领导层逐渐意识到气候变化的代价，以及为了避免最坏的情况，人们必须在2030年之前采取强有力的行动。为了响应这一趋势，本研究为风景园林师提供了一系列可以充实“工具箱”的脱碳“工具”，并通过代表案例介绍其具体应用，以便在日后工作中进一步探索实践。在这个气候变化的新时代，风景园林师的工作重点在于土地和植被，而二者都能吸收并转化二氧化碳，可以说风景园林是最优秀的“脱碳专业”。“人类已知的其他机制，都无法做到像光合作用一样有效地解决全球变暖问题。”[6]笔者认为，风景园林师在减缓气候变化以及逆转、修复和再生气候方面发挥着非常重要的作用。

1.4 气候变化机制与风景园林

气候变化的机制和驱动因素提供了可以人为干预的关键点，风景园林师们可在地球系统多圈层间的相互作用、地球能量平衡和碳循环中发现设计机会，并从这些方面着手解决问题。

2 气候变化的影响：中国将面临什么?

按照一些标准，中国仍属于发展中国家，但中国已经实现工业化，甚至在2019年与美国并列成为全球最大的二氧化碳排放国，两国合计排放量占全球的40%[7]。中国30年来的经济快速增长，在提高其世界经济强国地位的同时，也加剧了气候变化危机。燃煤厂造成的大气污染、河流污染和日渐枯竭的地下水资源，都是经济飞速发展的后果。随着二氧化碳排放和气温上升，气候变化对中国的负面影响还会进一步扩大。

中国广泛存在着以下4种类型的气候影响，并呈现分布不均匀的特点：

1）冰川融化和淡水流失；2）温度上升、热浪加剧和空气污染；3）荒漠化对食物和栖息地的影响；4）海平面上升和沿海地区洪灾。

2.1 中国与“亚洲水塔”

气候变化最明显且最严重的后果之一就是对“亚洲水塔”的影响——中国青藏高原上的冰川。青藏高原是亚洲若干条重要河流的发源地，这些河流流经中国、尼泊尔、阿富汗、巴基斯坦、印度、孟加拉国、不丹、缅甸和湄公河半岛，并为周边地区带来淡水资源，因此青藏高原冰川作为“亚洲水塔”也是20多亿人口生存的关键。青藏高原地区包含全球14%以上的冰川和积雪，仅次于北极和南极，又被称为“第三极”。然而，气温上升却致使冰川的消融和退缩。

2.2 华北平原（NCP）出现热浪

热浪有可能对中国造成致命影响，特别是在华北平原。若不采取严格措施控制排放而任其发展，预计华北平原将成为全球“热”点地带。预计最早在2070年，相较于地球其他地区，气温上升将严重威胁中国居民的生命财产安全[8-9]。

2.3 荒漠化

伴随着淡水枯竭，中国北方地区荒漠化将进一步加重。荒漠化被定义为“土地类型从沃土变为旱地的一种土地”[10]。戈壁滩是地球上扩张最快的沙漠，其成因不止一种，目前仍以每年约3 621 km（2 250英里）的速度向南延伸，相当于美国西海岸到东海岸面积的80%！干旱的土地取代了适宜居住的农业用地，沙尘暴侵袭，人们流离失所，进而影响经济发展。经济快速增长被认为是用材林被大肆砍伐的原因之一，这也使得森林遭到大规模破坏，而最终导致荒漠化。据估计，目前中国约有27%的土地被沙漠覆盖。荒漠化致使耕地越来越少，由此导致的粮食短缺已经成为中国切实关注的问题。

2.4 上升的海平面

不断上升的海平面是中国面临的另一个主要威胁。中国是沿海地区人口最多的国家，海平面上升必然带来巨大影响[11]。预计到2050年，中国将有9 300万人受到海平面上升的威胁，涉及上海、深圳、天津、广州、江苏省和珠三角等地区。在未来的30年内，这些地方可能会经历严重的洪涝灾害，扰乱全球经济和供应链，影响当今全球25%的经济增长[12]。

3 地球工程学

3.1 地球工程学简述

地球工程学指有意识地对地球气候进行大规模干预，以缓和全球变暖问题的学科[4]。

3.2 地球工程学分支

地球工程学干预有2个分支：太阳辐射管理和二氧化碳脱除（CDR）。前者通过增加反照率或地球的反射率影响地球的能源系统，即进出能量之间的平衡；后者则与地球的碳循环相互作用，即碳在大气层中的移动和转化，变成植物、有机体和地壳岩石，如此循环往复（图1）。

CDR参与地球的碳循环。根据二氧化碳从大气中分离的方式，可分为自然脱除（NCDR）、物理脱除和化学脱除。

太阳能地球工程通过技术手段与地球能量平衡相互作用，减少太阳辐射，从而降低地球的温度。

4 21世纪风景园林师的职责

地球工程学的两个分支虽然为设计师们提供了诸多选择，但并不是万能的，还需要其他方法加以辅助。若想做出重要贡献，风景园林师最大的机遇则在于二氧化碳自然脱除（NCDR）或大气二氧化碳清除方法，通过影响地球碳循环应对气候问题。

4.1 CDR：二氧化碳自然脱除（NCDR）

许多自然过程能够“吸收”并储存大气中的二氧化碳，如土地、土壤和植被，这也是风景园林师通常采用的方法。《减排：扭转全球变暖最强计划》（以下简称《减排》）[6]是一本脱碳行动研究清单，介绍了80种解决气候危机的途径，其目的是展示如何在未来30年里消除1 031 Gt（1.031万亿t）的大气二氧化碳，使地球回到平衡状态。该书较周全地将各方法以Gt为单位（1 Gt= 10亿t，或相当于40万个奥运会规模的泳池容量）进行效用归类。书中提到的陆上气候应对方案在前20种中占60%，在前80种中占30%；这意味着基于陆地的方案是最有效的大气二氧化碳脱除途径。为什么陆上气候应对方案属于地球工程学？因为如果这些方案应用范围足够大，便可在能量平衡（热量控制）和碳循环（减少大气中的二氧化碳）两方面干预全球大气状况，这正是《减排》中的观点。除此之外，下文所述的一系列脱碳工具同样适用于各种尺度，并皆可产生良好效果。

4.1.1 自然脱除工具1：植树造林

二氧化碳年捕获潜力：5亿～36亿t；当前成本预估：每吨花费5～50美元[1]。

造林，指在至少50年没有树木的地区播种或种植树木并形成林地或森林。树木不仅外形优美，还可以通过光合作用吸收二氧化碳，并将其转化为根、茎、叶等生物量。只要树木存活，便可一直封存二氧化碳。但是当树木被分解或燃烧后，又会重新释放内部封存的二氧化碳。因此，造林脱碳也意味着需要加强对森林的管理，防止二氧化碳的大量外泄。可通过火灾管理降低风险，或者将砍伐的树木用作生物燃料。此外，在大型建筑工程中用木材制品代替钢铁和混凝土产品，也可以在相当长的时间内保持碳封存。

植树造林代表案例：

1）2019北京大兴国际机场临空经济区中央公园竞赛。玛莎·施瓦茨合伙人设计事务所设计，位于中国北京市大兴区。

①场地面积747 hm2，设计面积361 hm2；②设计竞赛于2020年落幕；③方案计划种植11.2万棵树；④二氧化碳封存、空气污染物修复、降噪和小气候营造；⑤重要的雨水蓄存区。

方案建立了大规模的绿化和集水区，结合现有的森林碎片和运河，采取中央公共公园的形式，并支持多样化的公共项目。作为机场大型基础设施的组成部分，在景观设计方面不仅通过二氧化碳自然封存和生物封存缓解气候危机，还利用“弹性”策略适应场地预估的气候影响（图2～4）。

2）速造小型环境保护林，宫胁昭设计。

① 场地面积约6个停车位大小，种植300棵树；②造林成本相当于1部一代苹果手机；③ 植物生长速度提高10倍，密度提高30倍；④ 选择最合适的乡土树种；⑤ 种苗种植间距较小，为获取阳光而争相拔高；⑥ 营养丰富的土壤提供养料；⑦ 10年内演变为密林。

日本植物学家宫胁昭（Akira Miyawaki）的研究给予了植树造林工作极大的启发。他基于德国的一种技术，发明出“潜在自然植被”造林法。该方法“通常选择缺乏有机质的退化土地，密植几十种乡土树种和其他乡土植物。随着种苗生长，自然选择开始发挥作用，最终形成生物多样性丰富且适应性强的密林”[6]……宫胁造林法可营造森林或密集的植物群落，一般情况下耗时较短，但在生物多样性、弹性和茂密程度上远高于传统植树造林法构建的森林，同时也能够更有效地吸收碳[6]（图 5）。

3）杨柳青大运河国家文化公园大师邀请赛，玛莎·施瓦茨合伙人设计事务所设计，是中国天津2020年总体规划的一部分。

① 占地188 hm2；② 密林具备二氧化碳封存及空气净化等功效；③ 人工湿地管控雨水；④ 绿色基础设施具有经济效益，每年可节省9万美元。

该方案将作为城市中最广阔的绿色基础设施。面对气温上升和气温波动等问题，茂密的林冠层可营造出舒适的微气候。人工湿地作为碳汇，以减少天津的水土流失，同时结合下沉式花园房，提供可持续的雨水溢流修复（图6、7）。

4）济南CBD街道景观，Sasaki 景观设计事务所设计。

①位于中国济南；设计完成时间为2018年2月；② 项目占地320 hm2；③新增3万棵树（相当于50英亩约20 hm2森林）、灌木及多年生植物；④ 每年可吸收7 Gt（70亿t）二氧化碳。

Sasaki团队的济南CBD项目，提出了将街道作为公共空间的前沿理念，并营造“城市森林”作为街道系统的基础。中央商务区共有30条街道，Sasaki负责设计其中的14条，总长26 km。街道类型十分丰富，大到城市干道、城市交通枢纽，小到社区公园顶棚、步行道和休闲环路。每一种街道类型都被赋予了不同的宽度、限速标准、尺度比例和植物色系，其邻近区域也有不同的用途和规划。方案建议新增3万棵树，相当于20多hm2的森林。

1 地球工程学分支图Geoengineering taxonomy diagram

2 大兴中央公园鸟瞰图Daxing aerial perspective

3 红丝带路和集水区Red Ribbon Path and water catchment

4 人工林风环境分析Wind study for forest plantations

大规模植被的累积效应将在降温、健康以及生物多样性和生态等方面发挥积极作用。该方案有助于重构乡土植物群落并凸显其特色，同时唤醒场所精神和人们的地域文化记忆（图8、9）。

5）智慧森林城市，位于墨西哥坎昆，斯坦法诺·博埃里（Stefani Boeri）设计。

① 项目区内有13万居民；② 占地557 hm2，其中一半以上将用于绿化；③ 种植750万株植物，共350种；④ 26万棵乔木；⑤ 每年封存5 800 t二氧化碳。

建筑师斯坦法诺·博埃里是城市森林的拥护者，他的作品中最引人注目的就是城市森林这种垂直布局形式。这项新提案展示了他对21世纪城市主义最雄心勃勃的思考，其内容涉及环境公平、智能技术、可持续能源和密集种植计划。大型公园、花园屋顶、绿色立面和树木林立的街道景观交织在一起，博埃里将城市转变为植物园，颠覆了人们对一般意义下“硬景观”城市风貌的设想。该提案也为循环经济提供了支撑，可实现粮食、水和能源的自给自足（图10、11）。

4.1.2 自然脱除工具2：城市绿化

城市景观中大部分是硬质景观，绿地比例较小。若想依据气候变化重塑空间，城市街道和一些待开发利用的空间则是最普遍的选择。

代表案例：哈佛设计研究生院实践教授玛莎·施瓦茨的2016年Option Studio课程设计：“固碳都市：城市作为应对气候变化的机器”。

① 调研场地：波士顿的4个乡镇（超过218 km2）；② 使用I-Tree的衡量指标：计划种植450万棵树；温室气体排放量为46万t/年；需水量为22 890 156 034加仑（1加仑≈3.8 L）；节省能源开支206 963 526美元（约13.705亿人民币）。

工作坊与哈佛森林（由哈佛大学拥有和管理的3 000英亩即大约1 214 hm2的生态研究区，译者注）的管理团队合作，哈佛森林团队人员对马萨诸塞州进行了深入的研究，在2060年前将该州组织成一个自我维持的实体。工作坊专注于整个大波士顿地区，其目标是展示一个老旧的高密度城市通过重新组织和设计街道和其他公共开放空间，以应对2060年全球变暖的影响。方案中提出了“混合系统”，该系统由自然、生物以及人造装置和技术组成，可应对气候变化，同时研究城市绿化并以此为“混合系统”的核心部分。

此外，学生们预测了2060年波士顿4个城镇的气候变化，包括：暴雨和洪水；进入干旱期；热岛效应；6区和7区为种植区；海平面上升0.6 m（2英尺），风暴潮达到约2.4 m（8英尺）。

与哈佛森林合作并制定设计假设：① 在公共和私人土地上植树造林造成了“环境不公平”；② 通过马萨诸塞州能源与环境部的“门户城市计划”；③ 2060年，自动驾驶将成为交通运输的主流，因此可回收地面空间用于城市绿化；④ 禁止在1-95环路内使用私家车；波士顿的公共交通将延伸到TOD的环路上，允许通勤者停放私家车；⑤ 绿色防浪堤用来对抗上升的海平面；⑥ 合流制排水系统将实现雨水零溢流；⑦ 尽可能将屋顶涂成白色以增加城市反照率（图12～14）。

4.1.3 自然脱除工具3：滨海湿地

在咸淡水交汇处、海岸线边缘，存在着地球上规模最大但未得到充分重视的自然碳汇之一——“蓝碳”资源，如盐沼湿地。盐沼内长有红树林和海草，在土壤、植物及其根系之间长期的相互作用下，盐沼具有比热带森林更强的碳封存能力，若不加以保护，它们可能会释放大量的温室气体。滨海湿地也充当海洋生物和飞行动物（鱼类和候鸟）理想的栖息地和觅食地。除此之外，海岸带生态系统还可以作为抵御风暴潮的天然屏障，防止内陆城市发生洪水，人们常常忽视它们在吸收二氧化碳方面可发挥的巨大作用，最近的一项研究已经证实，滨海湿地系统是帮助解决气候变化的最佳途径之一。另外，近期另一项重要研究的作者之一詹妮弗·霍华德（Jennifer Howard）也总结道：“滨海生态系统可能是减少排放的一个重要组成部分，我们正努力向外界传达这一重要讯息……”[13]

5 孟买宫胁森林Miyawaki Mumbai forest

6 天津杨柳青大运河国家文化公园方案鸟瞰图Tianjin aerial view

7 绿意萦绕的大运河Tianjin canal with afforested territories

8 济南CBD街景规划Jinan CBD Streetscape plan

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

10 智慧森林城市规划方案平面放大图Enlarged area of plan Smart Forest City

代表案例：旧金山湾“混合海岸线”，由克里斯蒂娜·希尔设计。

① 针对防洪需求和海平面上升问题设计新的“边缘带”；② 4 hm2“圩田”单元；③ 结合滨海特征建设人工湿地和住宅。

加州大学伯克利分校副教授克里斯蒂娜·希尔从大尺度出发，对旧金山海岸线及其生态系统的规划策略展开研究。受海平面上升的威胁，预计旧金山海岸在接下来的50～75年将发生巨大变化。在土地规划策略方面，希尔采取了一种独特的方法：接受《财产法》在美国扮演的基本角色并支持私有制，她试图将该方法与保护主义者以及合宜的生态设计相结合。基于此，她提出了名为“混合边缘”的解决方案。该方案受荷兰围垦系统的启发，并融合了住房、人工湿地和海岸特征。最终，该区域会转变为一个新的可管理“边缘带”，可提供经济适用房并具备经济驱动力，因此该方案也不依赖于政府的资助：私人开发商可以发挥主导作用（图15）。

12 街道类型：市中心固碳区Sequestropolis downtown street typology

13 高层CBD街道平面图Sequestropolis CBD high-rise street plan

14 商业街固碳分析Sequestropolis Commercial street section

15 旧金山湾所在位置San Francisco Bay site

16“混合海岸线”方案设计流程Hybrid edge design process sequence

希尔在海岸线上布置了一个仅占4 hm2的微型圩田，规模远小于荷兰的围垦地。圩田周围设置堤坝（图16紫色区域），可以蓄存雨水并抵御洪水（橙色区域）。在圩田周围引入干净的沉淀物，从而构建湿地“浅滩”（绿色区域）。湿地系统可充当栖息地，也可抵挡海浪侵蚀，甚至可以进一步建造海滩（黄色），为人们提供游憩场所。当然，植物和土壤的碳封存作用也不言而喻。经济适用房建在圩田区内（图17）。

4.1.4 自然脱除工具4：土地利用

作为风景园林师，我们经常被邀请为城市、城镇、社区（包括郊区在内）以及发展中国家做大尺度的土地规划。但不论面对的任务如何，我们都应当着手促成新的议程：将土地利用实践纳入提案，特别是实现土地和土壤的碳封存作用。

代表案例：土地利用变化报告，来自2014年哈佛森林研究课题。

该研究遵从以下几项原则，通过合理的土地利用实现马萨诸塞州的自给自足。

① 增加土壤下渗率是本次设计的重要任务，以补充波士顿赖以生存的地下水资源；② 土地利用必须保证马萨诸塞州的粮食供应；③ 增加土地连通性，充分发挥各生态系统的生态效益。

17 圩田住宅示意Polder housing

18 沙漠试验场显示沿着带状硅酸盐岩（橙色和深灰色）建设配套沙漠绿化带可加快岩石风化过程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

为应对2060年整个马萨诸塞州的气候变化影响，该研究制定了4种方案。方案1着眼于近期趋势；方案2强调机会增长；方案3为区域的自力更生；方案4将森林作为基础设施。其中“将森林作为基础设施景观”方案描绘了未来的政策、市场、州和地方规划，将激励措施的重点放在增加“生活设施”上。在能为马萨诸塞州带来的9项自然福利中，该方案有7项获得了最高分。

4.1.5 自然脱除工具5：土壤固碳

土壤固碳策略优势颇多，它可以改善退化的土壤，提高生物产量，净化地表水和地下水，并通过抵消化石燃料的碳排放降低大气中二氧化碳的富集率。

代表案例：诺里公司的脱碳市场项目。

诺里脱碳剂不仅可消除碳足迹，也可帮助农民采用可持续的耕作方式除碳，对土壤固碳进行监测和量化，通过这种方式助力整个脱碳市场的启动和运作。

4.1.6 自然脱除工具6：增强风化固碳/岩石固碳

二氧化碳年捕获力：20亿～40亿t；当前成本预估：50～200美元/t。

地质过程是碳循环中较慢的一环，涉及岩石与大气中的气体发生化学反应，而在此过程中岩石可长期吸收二氧化碳。某些类型的物质，如硅酸盐岩石，当溶解在雨水中时会与弱酸性二氧化碳发生剧烈的催化反应，使岩石发生变化。二氧化碳嵌入矿物岩石分子结构，最终将其转变为碳酸盐矿物，这些二氧化碳可被封存数千年。科学家们一直在探索如何使用强反应硅酸盐岩石（例如橄榄石或菱锰矿）来加速自然风化过程。这种材料在农田、热带地区或海滩上的应用始终是试验重点。

代表案例：

1）维斯塔计划（Project Vesta）。

维斯塔计划可加速古老的自然进程。该计划的任务是进一步研究增强风化并推动其全球部署。用橄榄石制成绿沙海滩；海浪可加快二氧化碳捕获速度，同时能使海洋脱酸④。

风景园林师的工作遍布世界各地，如果应用方案在某一项目中可行，那么这种低技术策略就有价值。岩石的碳封存比例约为：1 t的橄榄石置换2/3 t的二氧化碳，同时必须考虑采矿和运输的成本，这是关键的制约因素[6]。

2）玛莎·施瓦茨合伙人事务所的沙漠试验场。

试验场采用增强风化策略，将硅酸盐矿物图案置于地面，通过灌溉催化化学反应，从而捕获空气中的二氧化碳。该项目与英国科学家保罗·伦弗斯（Paul Renforth）合作，通过实际应用推进干旱气候下增强风化作用的技术（图18）。

4.2 二氧化碳物理脱除和指标

除了自然脱碳技术，风景园林师还可以采用其他新材料及新工具，从源头控制二氧化碳的排放或将其长期封存，也许还能够方便计算设计方案的除碳效率。

4.2.1 物理脱除工具7：低碳水泥和混凝土

人们往往会忽视另一个二氧化碳排放源——建筑材料。事实上，1 t混凝土在制造过程中可释放1 t二氧化碳。如果将混凝土工业比喻成一个国家，那么世界第三大二氧化碳排放国非它莫属。混凝土工业的碳排放量占全球的5%～8%：“混凝土是地球上除水资源以外使用最广泛的材料。”[14]许多公司正在研制低碳混凝土。索利达（Solida）公司利用一种先进的混合基础材料，使混凝土在固化过程中能够吸收二氧化碳。建筑师也开始使用低碳混凝土，而风景园林师们可以在外部设计要素中使用低碳混凝土，如桥梁、道路、步行道、墙壁、路缘和人行道等常见节点。

4.2.2 物理脱除工具8：重型木结构和交叉层压木材

重型木结构或交叉层压木材（CLT）是新型建筑材料的一种，具有结构的完整性和环境友好性，可积累和封存二氧化碳。重型木结构是大型工程木材产品的总称，通过木材胶合、加压、机械压制而成。其材料坚固且耐火，如果森林资源可持续，那么该材料的成本效益较高。重型木结构材料同样适用于景观行业，作为钢铁和混凝土的低碳替代品，其生产过程利用的是可再生资源，不会造成化石燃料污染。

4.2.3 物理脱除工具9：用量化手段证明观点

为应对科学和经济挑战，碳计算器应运而生，用以评估设计方案缓解气候变化的功效。“气候积极设计”的“探路者”（Pathfinder）工具可提供相关数据，帮助设计师计算景观方案中的碳足迹。通过交互式的“探路者”工具完善设计方案，以确保增加碳捕获量并减少建筑材料中的碳含量，从而实现设计目标：建筑过程中碳的吸收量大于排放量，并在短时间内实现“负碳”。同时，通过使用“探路者”，设计师可以将这些好处传达给客户和致力于减排的志愿者。通过参与，每个人都可以为应对气候变化的解决方案以及2030年的挑战做出积极贡献。

4.3 二氧化碳化学脱除工具10：直接空气捕获（DAC）技术

前文所述的内容属于NCDR的范畴。自然脱碳必不可少，需要纳入风景园林行业的适用范围，但必须承认，我们已经越来越接近气候变化临界点。触发临界点的可能性极高，因此需要讨论2种基于高科技的地球工程方案；其中一种方案名为直接空气捕获（DAC）比自然脱碳更高效，另一种方案则通过降温缓解全球变暖问题，以应对气温上升的紧迫性和全球性生态行动的缺乏。

直接空气捕获（DAC）是一种地球工程技术，可直接从大气中捕获二氧化碳，然后将其埋于地下。捕获设备吸入空气后，经过一系列的化学反应，将提纯的二氧化碳加压并泵入地下岩层，进行化学转化，最终可封存于地下数千年。作为“工具箱”中的一员，一个DAC工厂每年可以吸收100万t二氧化碳，相当于4万棵树吸收的量。然而，需要清除的二氧化碳高达数十亿t，因此需要大规模地扩大DAC机器的生产才能较快地看到效果。科学家、工程师和企业家们正在研究这项技术，寻找各种更便宜、更有效的方法，以达到相当规模的气候应用。风景园林师可以借助DAC实验装置推动研究、测试和开发，并协助宣传DAC的研发应用。

4.4 太阳能辐射管理（SRM）/太阳能地球工程（SG）

该方法人为改变地球的反射率，将阳光反射回太空而改变地球上的光照量，进而降低地球温度。许多太阳能地球工程技术都基于这一原理。

4.4.1 太阳能地球工程与时间期限

尽管上述种种方法组合都能应对气候变化，但其发挥效用的前提是必须在10年内开展行动。事实是，自然与社会发展缓慢，而气候变化的速度却远比预想的更快。科学家指出，我们正在为减缓全球变暖的速度而努力，若升温幅度超过1.5～2 ℃的临界值，将无法逆转，其后果极其严重。但鉴于目前相关政策滞后，为了在国际上形成有效的应对机制，学术界加大了地球工程技术的科研力度和经费投入[15]。

4.4.2 调整反照率

一些反照率调整方法技术含量低，可应用于城市空间的硬质表面（如屋顶、街道、城市硬景观和墙壁等）降低城市热岛效应。

4.4.3 工具11：地面反照率

调整地面反照率的方法之一是改变建筑物表面或铺装材料的颜色，从而减少吸光量、增加反光量；或者在建筑物上增加垂直绿墙，可以起到双重作用——既可以营造凉爽微气候，又可以为城市空间增加绿意、吸收二氧化碳。

4.4.4 工具12：植被反照率——会反光的植物

基因科学家正在开发更多的反光植物，这些植物可以用于农业，也可以用于大面积的景观种植。

4.5 太阳能地球工程技术

这些先进技术多涉及大规模的全球干预。①太空遮阳板（太空镜）；② 海洋云彩增亮（添加粒子，增强云彩反射性）；③ 海洋微气泡工程（增强海洋表面反射性）；④ 卷云薄化（允许热量从大气层排出，回到被云层截留的空间；⑤ 平流层气溶胶注入（SAI）。

4.5.1 最具争议性的观点

SAI效率高且成本相对较低，因此是太阳能地球工程中研究最多的技术之一。虽然未被列入“工具箱”，但它是唯一能给地球降温的方法，可为人类向可再生能源经济转型和大气脱碳行动争取时间。SAI以火山喷发的原理为模型，据观察发现火山喷发可增加地球的反照率从而降低地球温度。例如，1991年皮纳图博（Pinatubo）火山喷发后，由于大量硫酸盐喷入大气，测得当时的气温下降了1.00 ℃。

硫酸盐颗粒具有很强的反射性，可将入射的阳光反射回外层空间，从而增加地球反照率。以宇宙中的星体为例，金星作为夜空中最亮的天体，其反射率是月球的7倍，这是由于它具备稠密、含硫的大气层。除硫酸盐之外，专家还在测试具有反射光和溶解性能的粒子，也许会发现更好的解决方案。

因此人造制品成为可能，不仅效果立竿见影，而且费用低。该方法需要飞机群飞抵平流层释放硫黄颗粒。虽不能一劳永逸，但能为脱碳、节能争取时间。专用飞行器和分散系统需要几年的时间部署到位，其成本相当于一部好莱坞大片[16]。这项技术通过冷却地球来避免最糟糕的情况发生，是目前的一个理想备选方案。

4.5.2 SAI的风险和收益

SAI也许是一个非常强大的工具，但也存在一定风险。科学家将深入研究模拟其风险和效果，以进一步确定该技术对全球不同地区可能产生的影响。风险增加的原因是许多国家都具备部署SAI的能力，而管理是最大的问题。无论SAI的技术及应用潜力有多大，都需要扩大以气候变化为主流话题的研讨，针对其风险和效果进行辩论。此外，提高公众参与度，通过集体的判断和决策推动SAI的建设与发展，使受过教育且知情的公民能够参与气候工程专题的相关决策。

5 结语

“我们正生活在这样一个时代，所有人都在问自己有关未来的问题。COVID-19动摇了人类的信念和习惯，并引发了各种质疑的声音。”[17]新冠疫情让我们关注到一个事实，人类正经受自然的威胁。人类无法控制自然，相反，是自然控制了人类。除了潜在的核灾难，气候危机是人类前所未有的生存威胁。可以将新冠疫情看成是社会和政府必须应对气候变化这一历史性挑战的彩排。作为设计师，随着剧情的推进，又该如何处理处理一系列难题？人类的思想将受到挑战，工作模式也将改变。气候在变化，设计也需要革新。我们想做的不仅仅是“活着”和解决眼前的麻烦，而是希望能进一步扭转、修复气候状况，让地球重焕光彩。上文已展示了风景园林师如何为21世纪大气脱碳工程做出的重要贡献。风景园林师们有“工具箱”作为智囊，可以在生态系统到地球系统等不同尺度中实现自我认知，也期望能够更进一步发挥专业价值，超越“弹性”和“适应”策略，利用“工具箱”减缓气候变化。在新使命的推动下，设计师必须思考在各种规模和尺度下可开展的工作——从地方到国家，乃至全球；同时在工作中运用专业知识、技能和想象力进行不同层面的交流并采取行动。最后，我们必须为现实的可能性做好准备，即使用地球工程的先进技术对地球能源系统进行干预，以避免气候变化最坏情况的发生。相关技术的研究、争论、统筹和监管也需要风景园林师的关注和参与。最重要的是风景园林师需要积极参与各个层面的工作，竭尽所能分享知识，帮助更多人了解气候治理的重要性并加入队伍中来。我们需要携手合作、保护地球，实现自然生态系统的再生，从而恢复气候平衡。

注释：

① 引自在第21届联合国气候变化大会上通过的《巴黎协定》。

② 引自2019年联合国政府间气候变化专门委员会（IPCC）《全球增暖1.5 ℃特别报告》。.

③ 麻省理工学院建筑学院开设了适应气候的Mass Timber课程以及A Threshold Winery in climatic and economic shift；哈佛设计研究生院开设了Dam Studio Climate Change Along the Mystic River探索气候变化的解决方案；Core Studio从“问题”到“适应”探索气候变化和适应；耶鲁大学开设了高阶设计工作坊Learning from Piura:Building Resilience in an Era of Climate Change.BIG建筑事务所提出的曼哈顿下城适应海平面上升的方案。

④ 引自维斯塔计划（Project Vesta）。网站www.project vesta.org。

图片来源：

图1由伊迪丝·卡茨绘制；图2～4、6、7、18来源自玛莎·施瓦茨合伙人设计事务所；图5来自2019年2月24日印度《孟买镜报》；图8、9来自Sasaki；图10、11来自斯坦法诺·博埃里事务所；图12～14来自玛莎·施瓦茨；图15～17来自克里斯蒂娜·希尔。

（编辑/刘昱霏）

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 “land 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“living 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.