Not all about the carbon

并非只有碳

Why curbing methane emissions will help fight climate change

為什么控制甲烷排放有利于應對氣候變化

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強大的溫室氣體，控制甲烷排放應該比較容易


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.

政府間氣候變化專門委員會（IPCC）發(fā)表了關于氣候變化物理科學的最新聲明，其焦點是發(fā)現(xiàn)即使全世界的減排量超過各國政府的承諾，到2050年左右，地球溫度仍很有可能比19世紀末升高1.5攝氏度。

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.

這很重要，也很可怕，但并不令人驚訝。在六年前的巴黎，許多國家堅定承諾將世界的溫升控制在1.5攝氏度以下的目標，尤其是小島嶼國家，海平面升高關系到它們的生死存亡。但許多觀察人士認為該目標太苛刻，幾乎不可能達到。
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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報告得出的另一結論可能對許多人來說是新聞。如果二氧化碳排放是人類改變氣候的唯一途徑，那么1.5攝氏度的溫升目標早已達到了。事實上，人類的其他排放物也有很大影響。最重要的是硫酸鹽氣溶膠：細小的顆粒來源于碳和某些油類的燃燒，它們懸浮在空氣中，損傷肺部，害死數(shù)百萬人。另外，它們也能反射太陽光，對地球起到冷卻作用。

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世紀末以來，硫酸鹽使地球凈降溫0.4-0.5攝氏度，這是這段時期的溫升只有1.1攝氏度的主要原因。但硫酸鹽的影響正在遞減，為了改善空氣質量，進而拯救生命，幾乎所有的液態(tài)燃料在提煉階段就已脫除硫酸鹽，包括中國在內的燃煤發(fā)電廠在日益脫除煙道中的硫酸鹽。這種空氣凈化正在去除一部分有害的冷卻效應，使用化石燃料的迅速減少將去除其余的冷卻效應。所以諷刺的是，人們更強烈地感受到大氣中現(xiàn)有二氧化碳帶來的升溫效應。

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，知名大氣化學家保羅·克魯岑提出建議，可能有辦法既能拯救人慢慢的肺，又能使他們保持涼爽。工業(yè)排放的硫酸鹽顆粒物在低層大氣中存在時間短，在平流層存在時間較長。如果將一層相對稀薄的硫酸鹽噴灑到平流層，既能像低層大氣中的煙霧一樣提供等量的冷卻效應，又幾乎能夠避免對人造成直接傷害。

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.

克魯岑的干預論重新激起了人們對主動干預入射陽光的興趣，這種可能性被稱為“太陽能地球工程”。IPCC對此興趣持審慎態(tài)度，在該工作組討論未來氣候的各種設想中，太陽地球工程沒有用武之地。所以正如以前的報告那樣，新報告僅僅從廣義層面探討了這一設想。IPCC正確地指出該設想存在巨大弊端，但原則上可以利用太陽地球工程為地球大幅降溫，降溫速度遠快于二氧化碳減排。

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.

弊端與潛力并存，所以有理由更徹底和系統(tǒng)地研究地球工程。但不要誤以為這種辦法簡單快捷或者肯定是可取的，最大的擔憂是表面上的希望會被當作在二氧化碳排放上不作為的借口。如果地球工程僅僅被用于掩蓋越來越濃的溫室氣體產生的效應，而且這樣做的弊端越來越大，那么這個世界會不穩(wěn)定到可怕的地步。

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.

為了彌補硫酸鹽污染效應的遞減，IPCC積極支持的另一種可取辦法是大力減少排放另一種導致氣候變化的人類文明的副產品。甲烷是比二氧化碳更強大的溫室氣體，但它在大氣中的存在時間大約只有十年。減少甲烷排放量就能降低甲烷濃度，降低甲烷濃度就能減緩全球變暖。

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.

大氣中的甲烷濃度越來越高，這表明減排的力度還不夠。可喜的是，可做的事情還有很多。幾乎在所有的地方，能源產業(yè)的排放都應該受到更嚴格的監(jiān)管。由于甲烷是有價值的，所以部分甲烷是有利可圖的。減少垃圾填埋場的甲烷排放也不是太難。適當?shù)娘暳咸砑觿┛蓽p少牲畜打嗝排出的甲烷。杜絕排放很難，但大幅減排是完全可能的。

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.

二氧化碳仍然是氣候問題的核心，探索“太陽能地球工程”的可能性、實用性、風險仍是一個好主意，但可以取得最快進展的是甲烷減排。世界正變得越來越熱，在即將于11月召開的第二十六屆聯(lián)合國氣候大會上（COP26），甲烷應該被優(yōu)先列入議程。