THE ORACLE of Delphi’s trance-like state is thought to have been induced by gases seeping into her chamber through a crack in the ground. Some say methane was part of the cocktail. If true, the gas has shaped the course of civilisations at least three times: in ancient Greece when wars were waged and kingdoms fell on the strength of the Oracle’s prophecies, in the 20 th century when methane-fuelled machines helped power industrialisation, and today, when the gas is a central but under-appreciated part of the fight against climate change.
女祭司在德尔菲神庙中传达神谕时会进入一种迷狂恍惚的状态，据说是因为有一些气体通过地面的裂缝渗入她所在的内殿。有人说其中一种气体就是甲烷。果真如此，那么甲烷至少三次塑造了文明的进程：在古希腊时期，因为神谕的力量，战争爆发，一些王国陷落；在 20 世纪，用甲烷作燃料的机器推动了工业化；而今天，在对抗气候变化时，影响至关重要的甲烷没有受到足够重视。
Human activity emits far Less methane than carbon dioxide, but methane packs a heavier punch. Over the course of 20 years, a tonne of the gas will warm the atmosphere about 86 times more than a tonne of CO2. As a result methane, sometimes called carbon dioxide on steroids, is responsible for 23% of the rise in temperatures since pre-industrial times. Carbon dioxide gets most of the attention, but unless methane emissions are limited there is little hope of stabilising the climate.
人类活动排放的甲烷远少于二氧化碳，但甲烷的影响更大。20 年的时间里，一吨甲烷让大气变暖的程度大概是一吨二氧化碳的 86 倍。因此，甲烷有时被称为加强版二氧化碳，它导致自前工业时代以来的气温上升 23%。绝大部分的关注都放在了二氧化碳上，但是除非限制甲烷的排放，否则稳定气候的希望微乎其微。
Unfortunately methane emissions have been anything but stable. After briefly stalling in the early 2000 s, atmospheric concentrations of the gas started rising again in 2007. A global inventory, concluded last year, found that humans were largely to blame. Chief among the reasons for the rise are the gassy output of livestock farming (cows belch it), rice cultivation (soggy environments harbour micro-organisms that make it) and the fossil-fuel industry (pipelines and rigs leak it). Agriculture and energy each account for roughly one-third of annual methane emissions. China, America, Russia and other big energy producers and consumers are heavy polluters. Countries with lots of livestock produce a disproportionate share of farming-related emissions, too.
不幸的是，甲烷排放量一直没有控制住。在本世纪初的短暂停滞之后，大气中的甲烷浓度在 2007 年又开始上升。去年的一项全球调查得出结论，人类在很大程度上是罪魁祸首。排放量攀升的主要原因是畜牧业的气体排放（牛会释放甲烷）、水稻种植（潮湿的环境孕育了产生甲烷的微生物）和化石燃料行业（管道和钻机会泄露甲烷）。农业和能源各占每年甲烷排放量的三分之一左右。中国、美国、俄罗斯和其他大型能源生产国和消费国都是排放大户。畜牧业发达的国家也在农牧甲烷排放中占有过高的比例。
By how much do methane emissions need to fall? Carbon dioxide lingers in the atmosphere for centuries, making it hard to reduce its atmospheric concentrations. By contrast, methane has a half-life of roughly ten years, which means that it degrades quickly. If new emissions can be cut to below the rate at which old emissions deplete, the concentration of methane lingering in the atmosphere will soon fall, slowing global warming. The Intergovernmental Panel on Climate Change estimates that, to keep temperatures between 1.5°C and 2°C above pre-industrial levels, human methane emissions must drop to 35% below where they stood in 2010 by mid-century.
甲烷排放量需要减少多少？二氧化碳在大气中能存留几个世纪，因此它的大气浓度难以降低。相比之下，甲烷的半减期大约为 10 年，这意味着它的降解速度很快。如果新增排放的速度能够下降到低于既有排放消解的速度，那么大气中的甲烷浓度会很快下降，从而减缓全球变暖。联合国政府间气候变化专门委员会（Intergovernmental Panel on Climate Change）估计，要想将气温保持在比工业化之前高 1.5 到 2 摄氏度的水平，到本世纪中叶人类的甲烷排放量必须下降到 2010 年水平的 35%。
That is entirely plausible. A big step would be to stop millions of tonnes of methane from leaking out of fossil-fuel infrastructure each year, through pipes with holes, leaky valves and carelessness. Natural-gas operators will be able to sell more gas in exchange for a moderate investment in monitoring and repairing leaks. The International Energy Agency, a global forecaster, estimates that 40% of methane emissions from fossil fuels, equivalent to 9% of all human methane emissions, can be eliminated at no net cost for firms. The harder task is to reduce emissions from agriculture, but even here farmers can draw on new ideas, including developing new forms of feed for livestock, and altering how rice is irrigated.
这是完全有可能实现的。一项重大举措是防止每年数百万吨的甲烷从化石燃料基础设施里泄漏，比如通过管道孔洞和阀门的泄露，或是粗心大意引发的泄漏。如果在监测和修补泄漏方面适度投资，天然气运营商就能换来更多的天然气供出售。全球预测机构国际能源署（International Energy Agency）估算，化石燃料甲烷排放的 40%，即人类所有甲烷排放的 9%，可以在不增加企业净成本的情况下消除。减少农业排放会更困难。但即便如此，农民也可以运用一些新点子，比如开发新式畜牧饲料、改变水稻的灌溉方式等。
Natural gaps 天然裂口
Politicians and the public tend to worry about carbon-dioxide emissions and neglect the effects of cutting methane. But dealing with the gas would have a large effect rapidly and at relatively low cost. Governments are busy firming up their commitments to cut emissions under the Paris agreement, as they prepare for the COP26 climate summit in November. On April 22 nd President Joe Biden will convene his own summit. America is expected to make its targets public around that time, which will almost certainly include a pledge to reduce emissions to net zero by the mid-2000 s. It should go further and include a specific target for methane. Then other nations should follow its lead.
政客和公众往往担心二氧化碳的排放，而忽视减排甲烷的效果。但对付这种气体能够迅速产生巨大的影响，而且成本相对较低。各国政府正在加紧落实《巴黎协议》的减排承诺，为 11 月的第 26 届联合国气候变化大会（COP26）做准备。4 月 22 日，美国总统拜登要召开自己的峰会，预计美国将在这段时间前后公布其减排目标，其中几乎肯定会包括到本世纪中减排至净零的承诺。美国应该更进一步，设定甲烷的具体减排目标。之后其他国家应该跟上。