【经济学人】负排放技术：关于气候变化你所不知道的事情 [英国媒体]

Negative-emissions technology

负排放技术

What they don’t tell you about climate change

关于气候变化你所不知道的事情

Stopping the flow of carbon dioxide into the atmosphere is not enough. It has to be sucked out, too

停止向大气排放二氧化碳还不够，必须将它们吸出大气



TWO years ago the world pledged to keep global warming “well below” 2°C hotter than pre-industrial times. Climate scientists and campaigners purred. Politicians patted themselves on the back. Despite the Paris agreement’s ambiguities and some setbacks, including President Donald Trump’s decision to yank America out of the deal, the air of self-congratulation was still on show among those who gathered in Bonn this month for a follow-up summit.

两年前，世界承诺以工业化前的气温为基准，把全球变暖幅度控制在“远低于”2℃以下。气候学家和活动人士兴奋不已，政客们沾沾自喜。尽管《巴黎协定》含糊其辞和出现倒退，比如川普总统决定让美国退出协定，但本月在波恩召开的后续峰会上，参与者仍表现得沾沾自喜。

Yet the most damaging thing about America’s renewed spasm of climate-change rejection may not be the effect on its own emissions, which could turn out to be negligible. It is the cover America has given other countries to avoid acknowledging the problems of the agreement America is abandoning.

但是，美国再次突然否认气候变暖，最具破坏性的可能不是对自身排放的影响，其排放可能微不足道，而是掩护其他国家避免承认美国放弃的协定存在问题。

The Paris agreement assumes, in effect, that the world will find ways to suck CO2 out of the air. That is because, in any realistic scenario, emissions cannot be cut fast enough to keep the total stock of greenhouse gases sufficiently small to limit the rise in temperature successfully. But there is barely any public discussion of how to bring about the extra “negative emissions” needed to reduce the stock of CO2 (and even less about the more radical idea of lowering the temperature by blocking out sunlight). Unless that changes, the promise of limiting the harm of climate change is almost certain to be broken.

《巴黎协定》设想世界将设法从大气中吸出二氧化碳。因为任何现实情况下，减排速度不足以有效减少温室气体总量来限制升温。但如何通过额外“负排放”来减少二氧化碳总量几乎没有公开讨论（通过阻挡阳光来降温的极端想法更无人问津）。除非有所改变，否则减少气候变暖造成危害的承诺必将成为泡影。

Don’t be so positive

别太自信

Fully 101 of the 116 models the Intergovernmental Panel on Climate Change uses to chart what lies ahead assume that carbon will be taken out of the air in order for the world to have a good chance of meeting the 2°C target. The total amount of CO2 to be soaked up by 2100 could be a staggering 810bn tonnes, as much as the world’s economy produces in 20 years at today’s rate (see article). Putting in place carbon-removal schemes of this magnitude would be an epic endeavour even if tried-and-tested techniques existed.

“政府间气候变化专门委员会”采用116个模型预测未来状况，整整101个模型显示世界要想达到2℃目标，就得从大气中除碳。预计到2100年，除碳总量将达到惊人的8100亿吨，按当前排放速度，相当于世界经济二十年的排放量。纵然有经实践检验的技术，落实此等规模的除碳计划也算史诗级壮举。

They do not. A few power stations and industrial facilities capture CO2 that would otherwise end up in the air and store it away underground, a practice known as carbon capture and storage. But this long-touted approach to cutting emissions still operates on only a very small scale, dealing with just a few tens of millions of tonnes of CO2 a year. And such schemes merely lower emissions; they do not reverse them.

这种计划尚不存在。少数发电厂和工业设施捕集本会排放到大气中的二氧化碳，然后封存到地下，这称为碳捕集与封存。但这种长期备受追捧的减排方式处理规模仍很小，每年仅处理数千万吨二氧化碳，而且这类计划只能减少而非彻底改变碳排放。

What might? One option is to plant more forests (which act as a carbon sink) or to replace the deep-ploughing of fields with shallow tillage (which helps soils absorb and retain more CO2). Another is to apply carbon capture and storage to biomass-burning power plants, stashing the carbon sucked up by crops or trees burnt as fuel. Fancier ideas exist. Carbon could be seized directly from the air, using chemical filters, and stored. Or minerals could be ground up and sowed over land or sea, accelerating from aeons to years the natural weathering process that binds them to CO2 to form carbonate rocks.

如何才能做到？一种方式是植树造林（起到碳汇作用）或用浅耕代替深耕（利于土壤吸收和固定更多二氧化碳）。另一种方式是让生物质燃烧型发电厂采用碳捕集与封存技术，将用作燃料的农作物或树木吸收的二氧化碳封存起来。还有更加奇特的想法，使用化学过滤器直接从大气中捕集和封存碳。或将矿物质碾碎洒向陆地和大海，加快长年累月的自然风化过程，使它们与二氧化碳结合形成碳酸盐岩。

Whether any of these technologies can do the job in time is unknown. All of them are very expensive and none is proven at scale. Persuading Earth’s swelling population to plant an India’s worth of new trees or crops to produce energy, as the climate simulations require, looks highly improbable. Changing agricultural practices would be cheaper, but scientists doubt that this would suck up enough CO2 even to offset the greenhouse gases released by farming. Direct air capture and enhanced weathering use less land, but both are costlier. Though renewable energy could profitably generate a fair share of the world’s electricity, nobody knows how to get rich simply by removing greenhouse gases.

这些技术能否实现目标不得而知。它们不仅昂贵，而且未得到大规模应用。按照气候模拟所要求的，说服日益膨胀的人口种植更多树木或农作物来生产能源，看来希望渺茫。改变耕种方法成本较低，但科学家质疑该方式吸收的二氧化碳能否抵消耕种排放的温室气体。直接从空气中捕集二氧化碳和加快自然风化占地较少，但成本都很高。尽管可再生能源可为世界提供一大部分电力，但没人知道如何单靠除碳来致富。

When the need is great, the science is nascent and commercial incentives are missing, the task falls to government and private foundations. But they are falling short.

虽然需求巨大，但科学尚不成熟，市场激励机制欠缺，于是任务落到政府和私人基金会身上，但它们达不到要求。

More science would serve as a collective insurance policy against a grave threat. However, this year Britain became just the first country to devote cash to such projects; America is eyeing grants, too, despite Mr Trump. Britain’s one-off ￡8.6m ($11.3m) is footling. Roughly $15bn a year goes to research into all low-carbon technologies; that pot needs to increase, and more of it should be channelled to extracting carbon.

增加科研将成为应对巨大威胁的集体保险政策。然而，今年英国成为第一个向此类项目拨款的国家；且不论川普先生，美国也正在期待政府拨款。英国一次性拨款860万英镑（1130万美元）微不足道。每年约有150亿美元用于研究所有低碳技术；这笔资金有待于增加，将碳捕集方面投入更多资金。

Another form of climate denial

否认气候变暖的另一种形式

A big market for CO2 would provide an extra incentive to mine it from the atmosphere. But its uses are still limited. If regulators forced industries that cannot convert to electricity, such as aviation, to use synthetic fuels rather than fossil ones, demand for the CO2that is the raw material for those fuels could increase greatly. The industries, though, would resist.

庞大的二氧化碳市场会为从大气中捕集碳提供额外激励机制，但用途仍然有限。针对航空等无法改用电力的行业，如果监管机构不能迫使它们用合成燃料替代化石燃料，二氧化碳作为化石燃料的原料，需求量可能激增。但这些行业会抵制合成燃料。

If the market will not provide an incentive, governments could. The case for a proper price on carbon (this paper has favoured a tax) is strong. Its absence is one of the reasons carbon capture and storage has not taken off as a way of reducing emissions from fossil-fuel plants; the kit needed can double the price of electricity. Yet, setting a price high enough to encourage negative emissions would asphyxiate the economy.

如果市场不提供激励机制，政府会提供。政府有充分理由制定合理的碳价（本刊倾向于碳税）。碳捕集与封存未能成为化石燃料发电厂的减排方式，原因之一是缺少合理的碳价；它能使电价提高一倍，但制定高价来促进负排放会扼杀经济。

Subsidies are another option. Without them, renewables would have taken longer to compete with fossil fuels. But they are wasteful. Germany has lavished $1trn on low-carbon electricity, and even then still depends on fossil fuels for over half its power. Still, governments could offer a reward for every tonne of CO2 that is extracted and stored. In theory such a bounty should be paid from a fund bankrolled by countries according to their cumulative historical emissions (top comes America followed by Europe, with China rapidly closing the gap). In practice no mechanism exists to get them to cough up.

另一种方式是提供补贴。如果没有补贴，可再生能源本会花费更长时间与化石燃料竞争。但可再生能源耗资巨大，德国已经为低碳电力耗资1万亿美元，即便如此仍有一半电力依靠化石燃料。但是，政府可以为每吨捕集和封存的二氧化碳提供奖励。理论上，应根据各国的历史累积排放量出资建立基金，由基金提供奖励（最大出资方当属美国，其次是欧洲，及差距快速缩小的中国）。可实际上，没有一种机制能迫使各国出资。

Indeed, facing the shortcomings of Paris is beyond most governments. Under Mr Trump, America is not prepared to reduce the flow of emissions, let alone the stock. But the problem would not magically be solved even if America returned to the fold. Many rich countries say they are already doing their bit by cutting emissions more steeply than developing countries. In fact, taking carbon dioxide from the atmosphere is not an alternative to belching out less greenhouse gas. It is necessary in its own right. Unless policymakers take negative emissions seriously, the promises of Paris will ring ever more hollow.

事实上，多数政府面对《巴黎协定》的缺陷无能为力。在川普先生的领导下，美国不准备减少排放，更别提减少碳总量了。但即使美国重返协定，问题也不会迎刃而解。许多发达国家认为已经尽到责任，减排力度超过发展中国家。事实上，从大气中捕集二氧化碳不能取代绿色气体减排，减排本身是必要的。除非决策者重视负排放，否则巴黎承诺将更加纸上谈兵。