|
The global environment 地球环境 Boundary conditions 边界条件 The idea of planet-wide environmental boundaries, beyond which humanity would go at its peril, is gaining ground 地球环境边界条件的概念正在为人们所普遍接受。超过这个边界，人类将面临生存危机 Jun 16th 2012 | from the print edition of The Economist 译者：dqzxf PULL a spring, let it go, and it will snap back into shape. Pull it further and yet further and it will go on springing back until, quite suddenly, it won’t. What was once a spring has become a useless piece of curly wire. And that, in a nutshell, is what many scientists worry may happen to the Earth if its systems are overstretched like those of an abused spring. 当您拉开一根弹簧，然后松开时，弹簧就会啪地一声复归原来的形状。下一次将弹簧拉得更长一些，它会照样弹回。依此而行，每次都拉得更长一点，弹簧每次也都依然弹回；但直到您拉伸到某一次时，弹簧会突然就失去了弹性。这根昔日的弹簧变成了一根卷曲的废铁丝。简而言之，许多科学家担心的就是，如果地球的各个环境系统就像这根弹簧一样承受了超过限度的拉伸，则地球的命运就会如这根弹簧一样。 One result of this worry, in the autumn of 2009, was the idea of planetary boundaries. In the run-up to that year’s climate conference in Copenhagen a group of concerned scientists working under the auspices of the Stockholm Resilience Centre, in Sweden, defined, in a paper in Nature, what they thought of as a safe operating space for human development—a set of nine limits beyond which people should not push their planet. 正是出于这种担心，在2009年秋，诞生了地球环境边界条件的概念。在那年的哥本哈根全球气候大会召开之前，一组对此感到不安的科学家在瑞典斯德哥尔摩应变中心的资助下，在《自然》杂志上发表一篇文章，对他们认为是人类发展的安全运作空间进行了界定。这个界定由一组共9项极限条件所组成。超过了这些极限值，人类就将失去他们的地球家园。 The nine areas of concern were: climate change; ocean acidification; the thinning of the ozone layer; intervention in the nitrogen and phosphate cycles (crucial to plant growth); the conversion of wilderness to farms and cities; extinctions; the build up of chemical pollutants; and the level of particulate pollutants in the atmosphere. For seven of these areas the paper’s authors felt confident enough to put numbers on where the boundaries actually lay. For chemicals and particulates, they deferred judgment. 这9项边界条件涉及的领域有：气候变化；海洋酸化；臭氧层变薄；对植物生长至关重要的氮与磷酸盐循环的妨碍；荒野变为农田与城市的转化率；物种的灭绝；化学污染物的积聚以及大气颗粒污染物的浓度。这篇文章的作者们认为，在这些领域中有7个可以设置具体的边界值。对此他们有足够的自信。而对于化学污染物积聚与大气颗粒污染物浓度这两项指标，他们稍后将提出具体的边界值。 Since then, the idea of planetary boundaries has taken root. It crops up repeatedly in GEO-5, the United Nations Environment Programme’s new assessment of the world. The High-Level Panel on Global Sustainability, which reported recently to Ban Ki-moon, the UN’s secretary-general, gave the idea pride of place. And Planet Under Pressure, a big scientific conference held recently in London, made boundaries central to the message it sent to Rio 20, the UN environmental summit that opens in Brazil on June 20th. 自那以后，地球环境边界条件的概念就扎下了根。在“联合国全球环境展望”第5版中（GEO-5），这个概念被多次提及，颇为出人意外。“全球可持续发展高级别小组”（High-level Panel on Global Sustainability）最近向联合国秘书长潘基文提交了一份报告。报告中这个概念被置于醒目的位置。最近在伦敦召开了一个规模庞大的科学大会：重负下的星球（Planet Under Pressure）。大会将地球环境边界条件的概念作为会议的核心信息传达给“里约 20”。“里约 20”是定于6月20日在巴西召开的联合国环境高峰会议。 Don’t fence me in 不要将“我”禁锢住 Planetary boundaries provide a useful way of thinking about environmental change, because in many cases they give scope for further change that has not already happened. That has brought the concept friends who are not normally persuaded by environmental thinking, as well as green enemies who will brook no compromise. But the concept has numerous drawbacks. The actual location of the boundaries is, as their proponents acknowledge, somewhat arbitrary. That is partly because of the incomplete state of current knowledge, but it may remain so however much anyone knows. Some boundaries might be transgressed without irreversible harm occurring. Some may have been drawn around the wrong things altogether. And some academic opinion holds that spectacular global change could come about without breaking through any of them. 地球环境边界条件的概念为人类思考环境变化问题提供了一种有效的手段。在许多情况下，人们都可以借助这种手段预先觉察到地球环境尚未出现的变化。这是一个很少考虑环境问题的朋友们可以接受的概念；同时这又是一个能与激进环保主义者达成妥协的概念。但这个概念尚有众多的缺陷。正如这个概念的倡议者们所承认的那样，给出的边界值有些武断。其部分原因是人类目前的知识水平所限，但人们不知道这种状况还要持续多长的时间。也许有些边界值被突破却不会引发不可逆转的灾难；而有些边界条件的设定则很可能是选错了对象。一些学术观点认为，即使这些边界条件全都没有被突破，地球环境也很可能发生巨变。 The latest criticism comes from the Breakthrough Institute, a determinedly heterodox American think-tank that focuses on energy and the environment. Among the points made in a report it published on June 11th, two stand out. The first is that the idea of boundaries does not focus enough on the distinction between things with truly global effects and those that matter primarily at a local or regional level. The second is that the planetary-boundaries group derives most of its limits by looking at conditions during the Holocene—the epoch since the end of the most recent ice age, in which human civilisations have grown up. Both of these criticisms have merit. 最近的批评声来自突破研究所（Breakthrough Institute）。这是一家持坚定的非主流观点的研究机构，专注于研究能源与环境问题。在这家机构于6月11日发表的报告中，有两个观点非常引人注目。第一个观点是，地球环境边界条件的概念并没有在真正造成全球影响的事物与那些基本上只是造成了局部或地区性影响事物的区分上给予足够的关注。第二个观点是，提出地球环境边界条件这个概念的科学家们所设定的极限值，大都依据对全新世地球状况的考察而得出。这个地质年代始自最近一场冰川期的结束，而人类文明正是在这一时期发展起来的。这两个批评观点都值得我们深思。 For things that clearly do have the springlike quality of shifting irreversibly if pulled (or pushed) too far, like the collapse of ice sheets or the melting of permafrost, a boundary system that seeks to stop you getting too close to the threshold seems as sensible as a safety rail is on a parapet. There is good reason to believe that parts of the climate do behave this way, and thus need railing off. But of the nine boundaries, only three apply to systems where the boundary setters really believe there is a global threshold: the climate; the acidity of the oceans; and the ozone layer. Some of the other six may have local thresholds, but for the most part their global effects are simply the aggregate of the local ones. 一根弹簧如果拉伸（或压缩）过度就会产生不可逆的变化。对于那些明显具有弹簧这样特性的事物，如冰架的崩塌或永久冻土带的融化等，地球环境边界条件就像安装在女儿墙上的安全栏杆一样非常有益，可以让人类不要过于逼近危险的临界点。人们有充分的理由相信，部分气候现象已经在向这个临界点逼近，因而有必要设置安全栏杆。但在这9项边界条件中，设置者们相信真正具有全球性临界点的环境系统只有气候、海洋的酸化程度与臭氧层这3项。其他6项中，一些可能有区域性临界点，但大多数系统的全球性影响都只不过是区域性影响的集合而已。 Confusing the two might, in the Breakthrough Institute’s view, result in poor policy. Concern over a planet-wide nitrogen limit, for example, could lead to people forgoing the benefits that fertilisers offer the poor soils of Africa on account of harm done by their over-application in China. 突破研究所的报告指出，混淆了这两者的区别，将会导致错误政策的出笼。例如，由于中国过度使用氮肥而带来危害，就对全球范围内氮元素的使用进行限制，其结果将导致人们放弃使用氮肥。这样一来，非洲贫瘠的土地也就无法受益于这种肥料了。 The institute’s other criticism is the implicit assumption that because mankind came of age in the Holocene, therefore Holocene conditions are optimal for the species now. There are indeed reasons to believe some aspects of the Holocene were optimal. It was a time of climatic stability and, in the temperate regions of the Earth, clemency. The Breakthrough criticism agrees that climate stability is a good thing. It points out, though, that there is little evidence things like the behaviour of the nitrogen cycle or the phosphate cycle in the Holocene were particularly well-suited to humans. The fact that people have used industrial chemistry to short-circuit the nitrogen cycle, by making fertilisers out of nitrogen in the air at a rate which greatly exceeds what natural systems can manage, has real environmental effects. Nitrate-rich run-off, for example, can wreck the ecology of lakes. But if these effects could be managed, then it is not clear that the amount of nitrogen being drawn out of the air would, of itself, be a problem. 突破研究所在这份报告中还提出了其他含蓄的批评意见。他们认为，由于现代人类是在全新世进化成熟的，因此全新世的环境状况对现今的物种而言是最适宜的。人们确实有理由相信，在某些方面全新世的环境状况是最佳选择。在这段地质年代里，气候相对稳定。在地球的温带地区，气候温暖宜人。突破研究所的批评者们也同意气候稳定是件好事。然而该研究所的报告指出，并没有证据证明，全新世的氮圈或磷酸盐圈的作用方式等特别适合人类生存。人类利用化工生产的方法来缩短氮循环的周期，利用空气中的氮来生产氮肥，其速率远远超过了大自然的运作规律，对环境产生了实实在在的影响。例如，富含硝酸盐的地表径流能够破坏湖泊的生态平衡。但如果人类能够控制这些影响，则无法断定从空气中提取氮的数量达到多少时才会成为问题。 This is, at bottom, an argument about the nature of the Anthropocene—the age of man. Many scientists feel that human interference in the way the Earth works is now so great that the Holocene is history and a truly separate Anthropocene has dawned. The planetary-boundaries idea seeks to constrain the Anthropocene within the norms of the Holocene. The Breakthrough Institute, by contrast, argues for ordering things according to a calculation of the needs of human welfare, rather than just aping what has happened in the past. There is no doubt as to which of the two approaches is more prudent, and prudence always has a constituency. There is plenty of room for debate as to which is more plausible, or practical. 这实际上是在争论人类世（人类地质年代）的性质。许多科学家感到人类对地球的影响巨大，全新世已经成为过去，一个真正独立的地质年代——人类世已经开始。而地球边界条件的概念是想将人类世禁锢于全新世的范畴之内。与之对照，突破研究所认为，应该根据人类福祉的需要通过计算来确定规范，而不应西颦东效地模仿地球史上已经出现过的状态。这两种方法中哪一种更为谨慎，对此人们没有疑义。而谨慎行事的方法总是能得到大多数人的支持。但哪种方法更有道理，或更实际可行，则尚需人们通过大量的争论来得出结论。 Independence declaration 独立宣言 Another problem for the idea of planetary boundaries is the assumption that they are independent of each other. That seems unlikely, and if they are not then a crisis might arise even if no single boundary were transgressed. On June 7th Nature, which likes to get its oar in before big international powwows like the ones in Copenhagen and Rio, published a review of evidence that this may be happening. It suggested that the Earth may be approaching a “tipping point” past which simultaneous changes—to land use, climate and more—driven by an ever larger, ever richer human population, push the system into a very different state from its present one, with climate zones changed permanently, ecosystems functioning differently, and so on. 地球环境边界条件这个概念的另一个问题就是假定所有的边界条件都是相互独立的。这一点似乎不大可能成立。若果真如此，则可能出现任何单一边界条件的极值都没有被突破，但却爆发了一场全球性环境危机的情况。在6月7日出版的《自然》杂志上刊登了一份证据审查报告，其结论是这种情况很有可能出现。在如哥本哈根世界气候大会与“里约 20”这类声势浩大的国际会议召开之前，这份报告就像一颗投入水中的石子，激起了阵阵涟漪。这份报告认为，地球可能正在接近一个“临界点”。越过这个临界点，就会出现土地使用、气候等方面同时出现的变化。人口数量的不断增长与人类生活的不断富足都在推动着这种变化，将地球的环境系统推入到一个与现今非常不同的状态。气候带会持续改变；生态系统功能也会不断变化。各方面的变化不胜枚举。 A sudden shift is plausible. Small ecological systems, such as lakes, often switch states in this way and there is no obvious reason why a large system like the Earth should not do likewise. And according to Anthony Barnosky of the University of California, Berkeley, one of the Nature review’s main authors, a combination of changes, each itself within the planetary boundaries, could still trigger such a change of state. （地球环境）很可能出现突然的变化。既然如湖泊一类较小生态系统的状态经常出现这样的突然变化，那么如地球一类大型生态系统自然也会如此。没有什么明显的理由能说明它们为什么不会产生这样的变化。根据加州大学的安东尼·巴诺斯基（Anthony Barnosky）和《自然》杂志上报告的作者之一伯克利（Berkeley）的看法，即使地球生态系统的所有单项指标没有突破地球环境边界条件的极限值，多项系统的变化叠加后依然可以触发这样的状态改变。 That would be a bad thing. Even if the ultimate result were an Earth that is still hospitable to mankind, the transition could be catastrophic. But the existence of plausible bad futures within the boundaries raises the obverse question: are there good futures outside them? In particular, might it be possible to finesse the most famous boundary of all, the one governing greenhouse warming and climate change? 这可能是一个坏消息。即使这种状态改变的最终结果是地球上仍然适合人类居住，状态改变的过程就可能是人类的一场巨大灾难。但环境指标没有超出边界值仍然可能出现灾难性后果的可能性又导出了一个反向问题：超出了边界值后人类是否还能有光明的未来？特别是，对于控制温室气体预警与气候变化最重要的边界条件而言，能否灵活设置其边界值？ The planetary-boundaries team, slightly confusingly, defines this boundary in two different ways. One is a limit on carbon dioxide, the main long-lived greenhouse gas, of 350 parts per million (ppm) in the atmosphere. The other is a limit on “radiative forcing”—the increase in energy delivered to the surface of the Earth over time, largely as a consequence of extra greenhouse gases—of 1 watt per square metre above pre-industrial levels. Either way, the climate boundary is one that already lies squarely in humanity’s rear-view mirror. This reflects the view of some on the planetary-boundaries team, such as James Hansen of the Goddard Institute for Space Studies, that today’s climate is already beyond the point which can guarantee long-term survival for things like the Greenland ice sheet, the demise of which would raise sea levels by seven metres. 提出地球环境边界条件这个概念的科学家们用两种不同的方法定义了环境边界条件，这有点令人困惑不解。一种方法是限定二氧化碳这种长久以来对引发温室效应的起主要作用的气体的数值。其限定极值为：大气中每百万个气体颗粒中有350个二氧化碳颗粒（ppm）。另一种方法是限定“辐射强迫”（radiative forcing）的数值。“辐射强迫”是指一段时间内射入到地球表面的能量增值，大体上是温室气体增加带来的结果。相对于工业化前的水平，辐射强迫的极值定为每平方米1瓦特。无论采用哪一种方法，气候边界条件都正好直接面对人类的后视镜。这是提出地球边界条件这个概念的科学家中部分人的观点。如戈达德太空研究所（Goddard Institute for Space Studies）的詹姆士·汉森（James Hansen）就持这种看法。他们认为现在的气候已经超出了临界点，但很多事物却长久地存活了下来。格陵兰的冰川就是如此。如果这个冰川消融了，则地球的海平面将上升7米。 If the planetary-boundaries scientists really have got their sums right, the greenhouse-gas situation looks hopeless. From today’s position of carbon-dioxide levels pushing 400ppm and going up about 2ppm a year, a carbon-dioxide level of 350ppm can be reached only by going to zero emissions and then spending a long time—centuries, in all likelihood—sucking CO2 out of the atmosphere and putting it back underground by various means. 如果提出了地球环境边界条件这个概念的科学家们计算的正确，则温室气体的状况看起来令人绝望。目前大气中的二氧化碳高达近400ppm，而且还在以每年2ppm的速度增长。如果要想将大气中的二氧化碳降到350ppm的水平，就必须在漫长的时间内做到二氧化碳零排放，这一过程很有可能需要数百年时间。而且要采用所有可能的方法将二氧化碳从大气中分离出来，将它们重新埋入地下。 Force majeure 不可抗力 Greenhouse gases are, however, only a problem because of their effect on radiative forcing. If that could be reined back inside the boundary by other means, then the CO2 limit would no longer pertain. And that might be possible by spraying reflective particles into the upper atmosphere, to bounce sunlight back into space. 然而，由于温室气体对辐射强迫的影响，它与辐射强迫是同一个问题。如果借助其他手段能将辐射强迫控制在限定值内，则对二氧化碳的限定就不再起作用了。而在高层大气中喷洒反光颗粒，将阳光反射回太空的方法就可能实现对辐射强迫的控制。 Such a radical scheme would have all sorts of disturbing side effects, with political ones quite possibly outweighing environmental ones. It is by no means clearly the right thing to do. But it might be. And it certainly serves to show that, although the Earth may have boundaries, thinking about how to help it should not. 这样一个激进的方案很可能产生各式各样令人烦恼的副作用。对各种政治问题的考量很可能会超过环境问题。虽然目前还无法断定这个方案确实正确可行，但并不能排除其可行性。能够肯定的是，这样一个方案说明，尽管地球也许有各种不能超越的边界，但思考如何来帮助她却可能没有止境。 |
|
|
