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只从大气中除去二氧化碳不足以改变全球变暖(GT)

已有 1814 次阅读 2023-4-28 07:27 |个人分类:Scientific Translation|系统分类:科普集锦


 

Carbon dioxide removal is an ineffective time machine 

By David T. Ho 

 https://www.nature.com/articles/d41586-023-00953-x.pdf?pdf=button%20sticky


脱碳必须先行,否则除碳几乎毫无用处。

二氧化碳去除 (carbon dioxide removal, CDR) 是将“净”变成“净零排放”的关键。政府间气候变化专门委员会评估的将全球变暖限制在比工业化前水平高 1.5–2 °C 的所有途径,都需要从立即开始快速脱碳(decarbonization)做起。但这些途径还需要从大气中去除 CO 2 ,因为我们无法在规定的时间范围内完全消除碳排放。即使在最乐观的情况下,航空和航运等“难以减少”的行业仍将是温室气体的主要来源。残留排放(residual emissions)将意味着我们无法实现零排放目标,我们将需要 CDR 来实现净零排放目标。从历史上看,这意味着种植或维护树木,但从大气中去除 CO 2并将其储存在地下、海洋或产品中会更有效。

 

Decarbonization must come first, or carbon removal will be next to useless. 

Carbon dioxide removal (CDR) is what puts the ‘net’ into ‘net zero emissions’. All pathways to limit 

global warming to 1.5–2 °C above pre-industrial levels that have been assessed by the Intergovernmental Panel on

Climate Change require rapid decarbonization to start now. But they also require the removal of CO2 from 

the atmosphere because we won’t be able to eliminate carbon emissions entirely on the required time scales. ‘Hard to abate’ sectors such as aviation and shipping will 

remain large sources of greenhouse gases even in the most optimistic scenarios. 

Residual emissions will mean that we cannot achieve a zero-emissions goal, and we will need CDR to reach a net-zero target. Historically, this has meant planting or 

maintaining trees, but removing CO2 from the atmosphere 

and storing it in the ground, the ocean or in products 

will be more durable. 

 

承诺将各种 CDR 技术作为当今气候解决方案的企业如雨后春笋般涌现。其他人则热衷于购买碳信用额——本质上是投资植树或其他未来的 CDR 容量——作为他们当前脱碳承诺的一部分。

我的职业生涯一直在研究自然碳循环,并且在最近几年开发了检查 CDR 是否有效的方法。我仔细审查了数十个提案;我也是马斯克基金会资助的 1 亿美元 XPRIZE 碳清除竞赛的审稿人。从长远来看,我不否认需要开发 CDR 方法。我欢迎各国政府向该领域投入急需的资源。在对“直接空气捕获”( direct air capture ,DAC) 技术(通过化学方法从大气中吸收 CO 2 )进行了一些小规模示范后,2022 年美国两党基础设施法已拨款 35 亿美元用于开发四个 DAC 中心。但我很清楚,在人类社会几乎完全消除其污染活动之前,部署它们来去除大气中的CO 2是毫无意义的。

However, businesses are springing up that promise various CDR techniques as climate solutions for today. Others are enthusiastically buying carbon credits — essentially, 

investments in planting trees, or other future CDR 

capacity — as part of their current decarbonization 

commitments. 

I have spent my career studying the natural carbon cycle 

and, in recent years, developing methods for checking that CDR works. I have scrutinized dozens of proposals, and 

I was a reviewer for the US$100-million XPRIZE Carbon Removal competition funded by the Musk Foundation. I don’t 

deny the need to develop CDR methods over the longer term. And I welcome governments committing much-needed resources to this area. After some small-scale demonstrations of 

‘direct air capture’ (DAC) technology, which suck CO2 

out of the atmosphere by chemical means, the 2022 US 

Bipartisan Infrastructure Law has devoted $3.5 billion to developing four DAC hubs. But it’s clear to me that 

deploying them to remove CO2 from the atmosphere is 

pointless until society has almost completely eliminated 

its polluting activities. 

 

时间旅行

要了解为什么,请将 CDR 视为时间机器(a time machine)。以提议的美国 DAC 中心为例。每个设施最终预计每年提取 100 万吨CO 2 。

2022 年,全球排放了 405 亿吨CO 2 ( P. Friedlingstein et al. Earth Syst. Sci. Data 14, 4811–4900; 2022)。照此速度,每一年以其全部潜力运行,每个DAC 中心枢纽都会及时将大气清理到 13 分钟之前的状况,但在消除这 13 分钟的 CO 2 所花费的(一年)时间里,大气里又多了一年的(人类)碳排放。

在这同时,如果地球上的每个人都种一棵树——80 亿棵树——

一旦树木成熟,每年都会让我们回到大约 43 小时之前的状况。时间机器类比揭示了 CDR 目前是多么徒劳。我们必须将叙事转变为紧急事项(shift the narrative as a matter of urgency)。

未来几年,资金将大量涌入气候解决方案,我们需要很好地引导资金。今天,当排放量仍然很高时,我们必须停止谈论部署 CDR 作为解决方案——就好像它以某种方式取代了激进的、立即的减排。

Time travel 

To understand why, think of CDR as a time machine. Take 

the proposed US DAC hubs, for example. Each facility is 

eventually expected to extract one million tonnes of CO2 

each year. 

In 2022, the world emitted 40.5 billion tonnes of CO2 

(P. Friedlingstein et al. Earth Syst. Sci. Data 14, 4811–4900; 2022). At that rate, for every year of operation at its full potential, each hub would take the atmosphere 

back in time by almost 13 minutes, but in the time it took to remove those 13 minutes of CO2, the world would have spewed another full year of CO2 into the atmosphere.
Meanwhile, if everyone on Earth planted a tree — 8 billion trees — 

it would take us back in time by about 43 hours every year, once 

the trees had matured.
The time-machine analogy reveals just how futile CDR 

currently is.We have to shift the narrative as a matter of urgency. 

 

Money is going to flood into climate solutions over the 

next few years, and we need to direct it well. We must 

stop talking about deploying CDR as a solution today, when 

emissions remain high — as if it somehow replaces 

radical, immediate emission cuts. 

 

未来

如果我们在未来 20~30 年内成功地脱碳,情况就不同了。

如果我们将排放量减少到目前水平的 10% 左右——每年40 亿吨

CO 2 ——一个能够去除 100 万吨的DAC工厂将是一个时间机器,让我们回到 2 个多小时而不是 13 分钟之前的状况。到那时,假设它们完全由可再生能源供电,则需要 4,000 个设施才能在任何一年达到净零排放。

实际上,残余排放量可能占我们当前总量的 18%(H. J. Buck et al. Nature Clim. Change https://doi.org/j4jg; 2023),因此我们将不得不大幅扩大 CDR 以达到净零排放。不过,构建 7,290 个 DAC 集线器或部署其他 CDR 技术可能是可行的。

与此同时,需要研究寻找最大限度地减少土地使用和能源消耗,并且可以快速、廉价地扩大规模的 CDR 方法。现在这样做是必不可少的,以便我们在未来拥有可用的技术,何时有效以及何时可以使用它来消除遗留排放以解决代际公平问题(to address intergenerational justice)。

并非所有在实验室中有效的技术都适用于现实世界。有些可能会给生物多样性和环境带来沉重的代价。开发验证 CDR 是否有效的方法是一项重大挑战。很多年之后,我们才有科学来告诉我们哪些方法有效,以及它们是否损害或有益于环境。

人类从未在全球、大陆甚至区域范围内消除过大气污染物——我们只是关闭了源头,让大自然来清理。氯氟烃和平流层臭氧破坏、二氧化硫和酸雨、硫和氮氧化物以及光化学烟雾就是这种情况。我们必须做好 CDR 失败的准备,让我们在数千年内依靠环境来稳定大气中的 CO 2 。这是支持快速脱碳的另一个论据。

挑战的规模是巨大的。我们必须先让碳时钟慢下来,然后才能让它倒转。

Back to the future 

It’s a different story if we successfully decarbonize 

enough in the coming 20–30 years. 

If we reduced emissions to around 10% of current levels — 4 billion tonnes of CO2 a year — a DAC plant capable of 

removing one million tonnes would be a time machine taking us back just over 2 hours instead of 13 minutes. At that 

point, it would take 4,000 facilities to reach net zero in any given year, presuming they were fully powered by 

renewable energy. 

In reality, residual emissions will probably be 18% of our current total (H. J. Buck et al. Nature Clim. Change https://doi.org/j4jg; 2023), so we will have to scale up CDR 

substantially to reach net zero. Still, it might be 

feasible to build 7,290 DAC hubs or deploy other CDR 

technology. 

In the meantime, research is needed to seek CDR methods 

that minimize land use and energy consumption, and can be scaled up rapidly and cheaply. Doing that now is 

essential, so that we have the technology available in the future, when it will be effective, and when it can be used to remove legacy emissions to address intergenerational 

justice. 

Not all techniques that work in the laboratory will work 

in the real world. Some might come with heavy costs for 

biodiversity and the environment. Developing methods to 

verify that CDR works is a major challenge. It will be 

many years before we have the science to tell us which 

methods work and whether they harm or benefit 

the environment. 

Humanity has never removed an atmospheric pollutant 

at a global, continental or, even, regional scale — 

we have only ever shut down the source and let nature 

 

do the clearing up. This is the case for chlorofluorocarbons and stratospheric ozone destruction, for sulfur dioxide and acid rain, and for sulfur and nitrogen oxides and 

photochemical smog. We must be prepared for CDR to be a 

failure, leaving us to rely on the environment

to stabilize atmospheric CO2 over thousands of years. This is another argument for rapid decarbonization. 

The scale of the challenge is immense. We must slow the 

carbon clock to a crawl before we can turn it back. 

 

 

David T. Ho是夏威夷大学马诺阿分校的海洋学教授。

电子邮件: ho@hawaii.edu 

David T. Ho is a professor of oceanography at the University of Hawaii at Manoa.
e-mail: ho@hawaii.edu 




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