Not all about the carbon

并非只有碳

Why curbing methane emissions will help fight climate change

为什么控制甲烷排放有利于应对气候变化

It's a more powerful greenhouse gas than carbon dioxide, and should be easier to control

甲烷是比二氧化碳更强大的温室气体，控制甲烷排放应该比较容易


The headline of the latest pronouncement from the Intergovernmental Panel on Climate Change (ipcc) on the physical science of climate change is the finding that, even if the world cuts emissions by more than governments are promising, it is still “more likely than not” that Earth will be 1.5°C warmer by around 2050 than it was in the late 19th century.

政府间气候变化专门委员会（IPCC）发表了关于气候变化物理科学的最新声明，其焦点是发现即使全世界的减排量超过各国政府的承诺，到2050年左右，地球温度仍很有可能比19世纪末升高1.5摄氏度。

That is important, and frightening, but hardly shocking. The aim of letting the world warm no more than 1.5°C, agreed on in Paris six years ago, is one to which many countries, notably the small-island states for which sea-level rise is an existential threat, are deeply committed. But many observers believe it stringent almost to the point of impossibility.

这很重要，也很可怕，但并不令人惊讶。在六年前的巴黎，许多国家坚定承诺将世界的温升控制在1.5摄氏度以下的目标，尤其是小岛屿国家，海平面升高关系到它们的生死存亡。但许多观察人士认为该目标太苛刻，几乎不可能达到。

Another conclusion in the ipcc report, though, may come as news to many. If carbon-dioxide emissions were the only means by which humans were changing the climate, 1.5°C of warming would have already come about. As it is, other human emissions matter, too. Among the most important are sulphate aerosols: tiny particles produced by the combustion of coal and some sorts of oil that float in the air, sully the lungs, kill millions—and also, by reflecting away incoming sunlight, cool Earth.

IPCC报告得出的另一结论可能对许多人来说是新闻。如果二氧化碳排放是人类改变气候的唯一途径，那么1.5摄氏度的温升目标早已达到了。事实上，人类的其他排放物也有很大影响。最重要的是硫酸盐气溶胶：细小的颗粒来源于碳和某些油类的燃烧，它们悬浮在空气中，损伤肺部，害死数百万人。另外，它们也能反射太阳光，对地球起到冷却作用。
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The ipcc reckons that sulphates have provided a net cooling of 0.4-0.5°C since the late 19th century, and that this is a large part of the reason why that period has seen only 1.1°C of warming. But the sulphates’ influence is on the wane. In order to improve air quality, and thereby save lives, sulphur is now removed from almost all liquid fuels at the refining stage and increasingly scrubbed from the flues of coal-fired power stations, even in China. This clearing of the air is stripping away some of the noxious cooling. Speedy reduction in fossil-fuel use will remove the rest of it—thus, ironically, allowing the effects of the carbon dioxide already in the atmosphere to be felt all the more keenly.

IPCC估算自19世纪末以来，硫酸盐使地球净降温0.4-0.5摄氏度，这是这段时期的温升只有1.1摄氏度的主要原因。但硫酸盐的影响正在递减，为了改善空气质量，进而拯救生命，几乎所有的液态燃料在提炼阶段就已脱除硫酸盐，包括中国在内的燃煤发电厂在日益脱除烟道中的硫酸盐。这种空气净化正在去除一部分有害的冷却效应，使用化石燃料的迅速减少将去除其余的冷却效应。所以讽刺的是，人们更强烈地感受到大气中现有二氧化碳带来的升温效应。

In 2006 Paul Crutzen, a pre-eminent atmospheric chemist, suggested that there might be a way to save people’s lungs while still keeping them cool. In the lower atmosphere, where industry dumps them, sulphate particles are short-lived. In the stratosphere they last much longer. Putting a relatively sparse layer of sulphates into the stratosphere could thus provide the same amount of cooling as today’s lower-atmosphere smogs while doing almost no direct harm.

2006年，知名大气化学家保罗·克鲁岑提出建议，可能有办法既能拯救人慢慢的肺，又能使他们保持凉爽。工业排放的硫酸盐颗粒物在低层大气中存在时间短，在平流层存在时间较长。如果将一层相对稀薄的硫酸盐喷洒到平流层，既能像低层大气中的烟雾一样提供等量的冷却效应，又几乎能够避免对人造成直接伤害。

Crutzen’s intervention spurred renewed interest in the idea of intentionally interfering with incoming sunlight, a possibility known as “solar geoengineering”. It is an interest of which the ipcc is wary. Solar geoengineering has no role in the scenarios the panel uses to talk about future climates. As a result its new report, like its predecessors, discusses the idea only in broad terms. In doing so it notes, correctly, that the idea has significant drawbacks. But it also allows that solargeoengineering might, in principle, be used to create significant global cooling much more promptly than reducing carbon-dioxide emissions ever could.

克鲁岑的干预论重新激起了人们对主动干预入射阳光的兴趣，这种可能性被称为“太阳能地球工程”。IPCC对此兴趣持审慎态度，在该工作组讨论未来气候的各种设想中，太阳地球工程没有用武之地。所以正如以前的报告那样，新报告仅仅从广义层面探讨了这一设想。IPCC正确地指出该设想存在巨大弊端，但原则上可以利用太阳地球工程为地球大幅降温，降温速度远快于二氧化碳减排。
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Both the drawbacks and the potential provide good reason for researching geoengineering more thoroughly and systematically. But it would be wrong to think it a quick, easy or necessarily desirable response. Perhaps the biggest worry is that its seeming promise would be used as an excuse for inaction on carbon-dioxide emissions. A world where geoengineering was used simply to cover up, increasingly imperfectly, the effects of ever higher greenhouse-gas levels would be a fearsomely unstable one.

弊端与潜力并存，所以有理由更彻底和系统地研究地球工程。但不要误以为这种办法简单快捷或者肯定是可取的，最大的担忧是表面上的希望会被当作在二氧化碳排放上不作为的借口。如果地球工程仅仅被用于掩盖越来越浓的温室气体产生的效应，而且这样做的弊端越来越大，那么这个世界会不稳定到可怕的地步。
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A more palatable approach to offsetting the diminishing effects of sulphate pollution, enthusiastically endorsed by the ipcc, is to redouble efforts to reduce emissions of another climate-changing by-product of human civilisation. Methane is a more powerful greenhouse gas than carbon dioxide, but one which lasts in the atmosphere for only about a decade. Reduce methane emissions and you soon reduce methane levels; reduce methane levels and you reduce global warming.

为了弥补硫酸盐污染效应的递减，IPCC积极支持的另一种可取办法是大力减少排放另一种导致气候变化的人类文明的副产品。甲烷是比二氧化碳更强大的温室气体，但它在大气中的存在时间大约只有十年。减少甲烷排放量就能降低甲烷浓度，降低甲烷浓度就能减缓全球变暖。
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Its rising atmospheric concentration shows that today’s efforts to abate methane emissions are not up to the job. Happily, there is much more that can be done. Emissions from the energy industry could be more tightly regulated almost everywhere. Because methane is valuable, some would pay for themselves. Reducing emissions from landfill sites is not terribly difficult either. Livestock would burp less with the right feed supplements. Eliminating emissions would be hard; but quite steep reductions are entirely possible.

大气中的甲烷浓度越来越高，这表明减排的力度还不够。可喜的是，可做的事情还有很多。几乎在所有的地方，能源产业的排放都应该受到更严格的监管。由于甲烷是有价值的，所以部分甲烷是有利可图的。减少垃圾填埋场的甲烷排放也不是太难。适当的饲料添加剂可减少牲畜打嗝排出的甲烷。杜绝排放很难，但大幅减排是完全可能的。

Carbon dioxide remains the heart of the climate problem. Exploring the possibilities, practicalities and dangers of solargeoengineering remains a good idea. But it is on methane emissions that progress can be made most quickly. And the world is getting ever hotter. Methane should be given priority on the agenda at the cop26 climate summit this November.

二氧化碳仍然是气候问题的核心，探索“太阳能地球工程”的可能性、实用性、风险仍是一个好主意，但可以取得最快进展的是甲烷减排。世界正变得越来越热，在即将于11月召开的第二十六届联合国气候大会上（COP26），甲烷应该被优先列入议程。