Ozone loss was a thing even before CFCs were widely used
Ozone loss was a thing even before CFCs were widely used
在氟氯烃（CFCs）被广泛使用之前，臭氧层损耗就已经存在了
The ban on ozone-depleting substances that successfully reversed the growth of the hole in the ozone layer isn’t seen as a missed opportunity. On the contrary, the quick global response is one of the best cases of common-sense environmental action. But what if it could have been done even earlier? 成功扭转臭氧层空洞扩大的禁用消耗臭氧层物质举措，并不被视为一次错失的机会。相反，全球迅速采取的行动是常识性环保行动的最佳案例之一。但如果这项行动能更早实施呢？
The fact that chlorofluorocarbons (CFCs)—chemicals once common in aerosol cans and refrigerant loops—could destroy ozone in the atmosphere was discovered in 1974. Within just a few years, bans on CFCs began to roll out based on the projected consequences. The seasonal ozone “hole” discovered over Antarctica in 1985 pushed things along even faster, and in 1987 an international agreement was signed to phase out CFCs everywhere. A new study led by Jian Guan at MIT asks an interesting what-if question: Would it have been possible to detect this problem even sooner with today’s scientific tools? 氟氯烃（CFCs）——曾广泛用于喷雾罐和制冷循环的化学物质——会破坏大气臭氧层的事实是在1974年被发现的。仅仅几年内，基于对后果的预测，针对CFCs的禁令便开始实施。1985年在南极洲上空发现的季节性臭氧“空洞”进一步加快了进程，1987年，一项旨在全球范围内逐步淘汰CFCs的国际协议得以签署。麻省理工学院（MIT）的关健（Jian Guan，音译）领导的一项新研究提出了一个有趣的假设性问题：如果使用今天的科学工具，是否有可能更早地发现这个问题？
Beyond CFCs
超越氟氯烃
The use of CFCs started in the 1950s and ramped up through the 1960s, but they weren’t the first ozone killer to enter the picture. The industrial solvent carbon tetrachloride had been around for several decades before that. Not only do we have estimates of how much was produced for use, but records from the dense snow atop ice cores can confirm how much was in the atmosphere. This data shows that in 1950, carbon tetrachloride was about 3–4 times as prevalent as initial CFC levels. CFCs的使用始于20世纪50年代，并在60年代激增，但它们并不是最早出现的臭氧杀手。工业溶剂四氯化碳在此之前已经存在了几十年。我们不仅有关于其生产量的估算数据，冰芯顶部致密积雪中的记录也能证实大气中该物质的含量。数据显示，1950年时，四氯化碳的含量约为初期CFCs水平的3到4倍。
This would have had some impact on ozone, but detecting that effect could be difficult given that ozone levels vary naturally for several reasons. The formation of ozone (O3) is driven by the interaction of sunlight and oxygen gas (O2), it’s sensitive to the 11-year cycle in solar activity, for example. Emissions from volcanic eruptions can also cause some chemical chaos in this system. And because these processes can vary at different altitudes, just examining the total amount of ozone in a column through the atmosphere can obscure a depletion trend at a specific altitude. 这本应对臭氧产生一定影响，但由于臭氧水平会因多种自然原因而波动，检测这种影响可能非常困难。例如，臭氧（O3）的形成受阳光与氧气（O2）相互作用的驱动，并对11年的太阳活动周期非常敏感。火山喷发的排放物也会导致该系统出现化学紊乱。此外，由于这些过程在不同高度会有所差异，仅检查大气柱中的臭氧总量可能会掩盖特定高度的损耗趋势。
Current satellite data measures ozone separately in the lower, middle, and upper stratosphere, and model simulations help scientists work out the causes of any changes in these layers. This is the capability we’re imagining adding to the world of the 1950s. 目前的卫星数据分别测量平流层下层、中层和上层的臭氧，模型模拟则帮助科学家找出这些层级中任何变化的成因。这正是我们设想将其应用到20世纪50年代所具备的能力。
Early detection
早期检测
The researchers ran a climate model that includes ozone chemistry, feeding it the history of greenhouse gas emissions, ozone-depleting pollution, and natural events like volcanic eruptions. After setting the background with a few simulations starting in 1850, they ran many simulations from 1950 onward with slightly different starting atmospheric conditions to generate a range of realizations. 研究人员运行了一个包含臭氧化学过程的气候模型，输入了温室气体排放、消耗臭氧的污染以及火山喷发等自然事件的历史数据。在以1850年为起点进行几次模拟设定背景后，他们从1950年开始运行了多次模拟，通过略微不同的初始大气条件生成了一系列结果。
Detecting a trend of declining ozone depends both on how strong the trend is and on how strong the noise is. The lower and middle portions of the stratosphere respond much more strongly to things like volcanic eruptions—and we have the 1963 eruption of Mount Agung to contend with. Ozone in the upper stratosphere is much less variable, and also quite sensitive to ozone-depleting pollutants. While the effects of these pollutants are strongest at middle to high latitudes, variability is lowest near the tropics. In the model, this is actually where the ozone depletion trend emerged first. 检测臭氧下降趋势既取决于趋势的强度，也取决于背景噪声的强度。平流层中下层对火山喷发等事件的反应更为强烈——我们必须考虑到1963年阿贡火山（Mount Agung）的喷发。平流层上层的臭氧波动较小，且对消耗臭氧的污染物非常敏感。虽然这些污染物在中高纬度的影响最强，但热带附近的波动性最低。在模型中，这恰恰是臭氧损耗趋势最早显现的地方。
If we switched on our modern scientific infrastructure in 1950, ozone depletion would first be detectable (clearing the 95 percent statistical confidence bar) in the upper stratosphere over the tropics around 1957. At this point, one-half to two-thirds of the ozone-eating chlorine up there was still carbon tetrachloride rather than CFCs. Elsewhere, it would have taken a bit longer. By 1976, it would have been detectable in the lower stratosphere—including over Antarctica, where the ozone hole wasn’t actually discovered until another decade had passed. 如果我们能在1950年就启用现代科学基础设施，那么大约在1957年，热带地区平流层上空的臭氧损耗就能被首次检测到（达到95%的统计置信度）。当时，该区域内二分之一到三分之二的“食臭氧”氯元素仍来自四氯化碳，而非CFCs。在其他地区，检测到这一趋势则需要更长时间。到1976年，平流层下层的损耗也将被检测到——包括南极洲上空，而南极臭氧空洞实际上直到十年后才被发现。
So it seems that ozone depletion was technically detectable significantly earlier than its discovery, meaning we might even have intervened sooner and better prevented ozone loss. However, the researchers also point out that this kind of monitoring is currently at risk. The satellite currently measuring ozone at multiple heights in the stratosphere has been in orbit since 2004 and is well past its intended expiration date. (Last year’s White House budget proposal called for shutting it down, in fact.) Without a replacement, it will become much harder to detect future changes while they’re still small. 因此，臭氧损耗在技术上显然比其实际发现时间要早得多，这意味着我们本可以更早地进行干预，从而更好地防止臭氧流失。然而，研究人员也指出，这种监测目前正面临风险。目前用于测量平流层多个高度臭氧的卫星自2004年起就在轨运行，早已超过了预期的使用寿命。（事实上，白宫去年的预算提案曾提议将其关闭。）如果没有替代方案，未来在变化尚小时就进行检测将变得更加困难。