Our guide to the actions that have done the most to slow global warming 我们的行为指南已经最大限度减缓了全球变暖

　　ON SEPTEMBER 23rd 120-odd presidents and prime ministers will gather in New York for a UN meeting on climate change.  9月23日，120多位国家总统和首相将会汇聚纽约联合国总部，就气候变化议题举行会议。

　　It is the first time the subject has brought so many leaders together since the ill-fated Copenhagen summit of 2009.  这是自2009年一无所获的哥本哈根气候大会之后，国家元首们第一次为了此项议题聚会。

　　Now, as then, they will assert that reining in global warming is a political priority. 就像当时一样，他们如今也一致认为控制全球变暖是政治的头等大事。

　　Some may commit their governments to policies aimed at reducing greenhouse-gas emissions. 一些元首们也许会承诺实行以削减温室气体排放为目标的相关政策。

　　What few will say is how many tonnes of carbon dioxide these will save—because they almost never do. 但很少人能明确说出这些政策最终将减少多少吨二氧化碳排放量—因为根本没效果。

　　According to scientists, cutting carbon-dioxide emissions is an essential part of reducing catastrophic risks from climate change.  科学家表示，减少二氧化碳排放量是缓解由气候变化导致的灾难性后果的重要一步。

　　Yet governments are persistently averse to providing estimates of how much carbon a policy saves.  但政府自始至终都不愿意预估他们的政策到底能少排多少碳。

　　That may be because, in countries where climate change is controversial, 这也许是因为，在那些对气候变化仍存争议的国家，

　　it makes more sense to talk about the other benefits a scheme offers rather than its effect on carbon.  政府更愿意显示他们实行的其他福利政策是多么有效，而非低碳减排。

　　Or it may be that, in countries which are enthusiastic about renewable energy, pointing out that it may not save that much carbon is seen as unhelpful.  或者在那些热衷于再生能源的国家，指出政府政策并没有减少那么多碳排放也于事无补。

　　Or perhaps governments think climate change is so serious that all measures must be taken, regardless of cost  或者政府认为气候变化太重要了，可以不惜一切代价来完成

　　(though their overall lacklustre record suggests this is not the case). （不过总的来看，根据他们拖拖拉拉的表现，这是不可能的）。

　　Whatever the reason, the end result is that while the world's governments have hundreds of policies for tackling climate change, some of them very expensive 不管什么原因，结果就是尽管世界各个政府出台了几百条治理气候变化的政策，有的还代价高昂

　　China, America and the European Union spend 140 billion a year on subsidising renewable energy 中国、美国和欧盟每年花费1400亿补贴再生能源

　　it is hard to say which policies are having the greatest effect. 很难说哪些政策是最有效的。

　　So The Economist has made a stab at a global comparison of carbon-mitigation efforts.  因此，《经济学家》尝试制作了一张全球各国碳减排成果的比较图。

　　We have ranked 20 policies and courses of action according to how much they have done to reduce the atmosphere's stock of greenhouse gases.  图表1是结果，列出了前20个政策和行动方案以及每个政策方案的大气层温室气体的减少量。

　　We have used figures from governments, the EU and UN agencies.  我们使用了政府、欧盟和联合国各机构公布的数据。

　　As far as we know, this exercise has not been carried out before. 据我们所知，以前还没有人做过这样的比较。

　　First, a health warning: the policies and actions on our list are not strictly comparable.  首先有个温馨提示：本次列出的政策和行动方案严格来说是不可比较的。

　　Some are global, some regional and some national.  一些是全球范围的，一些是区域性或国家层面的。

　　Some are long-standing; some new.  一些是长期执行的，另一些是新政。

　　A couple are not policies at all,  有几条并不能算是政策，

　　such as the collapse of the Soviet Union, which led to the closure of polluting factories and to inefficient state farms reverting to grassland, locking up carbon. 比如由苏联解体导致的污染工厂关门、效率底下的国有农场复归草原，锁住了碳。

　　And the numbers almost all come with caveats.  这些数据都显示出了警告信号。

　　It is fairly easy to estimate how much carbon a new field full of solar cells or a nuclear-power plant saves by looking at the amount of electricity it produces in a year  很容易估算出一片新铺满太阳能板或盖满核能工厂的旷野减少了多少碳排放，只要看看它每年发了多少电就可以了；

　　and how much carbon would have been emitted if fossil fuels had been used instead, based on the local mix of coal, gas and oil.  另外，根据当地煤、气、油的混合状况也能很简单地估计出如果以化石燃料替代之，将多排放多少碳。

　　But as Paul Joskow of the Massachusetts Institute of Technology has pointed out, the standard “levelised” calculations,  然而，正如麻省理工学院的Paul Joskow指出的那样，标准的“水平化计算”

　　which divide the total amount of power a plant will produce over its lifetime by its total lifetime cost, are a poor way to compare fossil fuels and renewable energy. 即用一座工厂整个使用年限所耗费的成本除以其产生的全部功率值，并不是一种比较化石燃料和再生能源的好方法。

　　Other measures have problems, too.  其他的测量方法也有问题。

　　Take the effects of fuel-efficiency standards.  以燃料效率标准为例。

　　Would companies have curtailed their cars' emissions anyway to sell more of them to cost- and mileage-conscious drivers?  司机对成本和公里数很敏感，公司会为了向他们销售更多汽车而减少汽车排量么？

　　And how much has better fuel efficiency encouraged drivers to drive farther? 更高的燃料利用率又在多大程度上鼓励了司机多开车？

　　A further complication is that many policies have benefits beyond—or indeed closer to hand than—those they offer in terms of climate.  更加复杂的是，很多政策所带来的好处不仅仅是治理气候。

　　Burning less coal saves lives in the near future as well as reducing climate risks in decades to come.  燃烧更少的煤炭可以在不远的将来挽救很多生命，也能减少未来几十年内气候变化带来的各种危机。

　　Saving forests preserves wildlife, not just carbon. 拯救森林不止是控制碳排放，也能保护野生动物。

　　So our table should be treated with caution.  所以这次谈判应该谨慎对待。

　　It is only safe to say that one policy is better than another in climate terms if it beats it by a wide margin. 只有当某个政策提供了更多的回旋余地，才能说它是更好的。

　　As it happens, though, there are some very wide margins to be found.  正好，我们还有很多潜力有待发掘。

　　One policy stands head and shoulders above all others.  有一个政策尤其值得注意，

　　And it is one that few people other than climate-policy specialists will have thought of in this context:  尽管除了环境政策研究专家以外其他人很少考虑到这一点：

　　the Montreal protocol, a 1987 agreement to phase out substances such as chlorofluorocarbons (CFCs) used in air conditioners, refrigerators and so on.  在蒙特利尔议定书中，一份1987年签订的协议要求逐步淘汰空调、电冰箱等家电中的氯氟化碳成分。

　　It was enacted to limit the damage such substances were doing to the ozone layer, a goal which it has achieved. 这项协议意在防止此类物质继续损害臭氧层，目前这个目标已经达成。

　　Like carbon dioxide and many other gases emitted by industry and agriculture—methane and nitrous oxide,  氟氯化碳就像二氧化碳和其他被工业农业排放出来的气体

　　for example—CFCs are greenhouse gases.  （例如甲烷和一氧化二氮）一样，都属于温室气体。

　　And they are extremely potent ones, causing thousands of times more warming per molecule than carbon dioxide does.  它们破坏力巨大，每分子所产生的热量比二氧化碳要高几千倍。

　　That means stopping CFC production,which was in the range of millions of tonnes a year,delivered a climate benefit equivalent to cutting carbon-dioxide emissions by billions of tonnes. 这也就是意味着每年停止产生数百万吨的氟氯化碳给缓解气候变化带来的好处，相当于减排数十亿吨二氧化碳。

　　Guus Velders of the Dutch National Institute for Public Health and the Environment  荷兰国家公共健康和环境研究所的Guus Velders

　　has compared the warming effect that would have come about if the emissions of such chemicals had continued to grow at the rate they were growing before the protocol with what has come about thanks to their banning.  估算了如果这些化学气体按照协议书禁令出台之前的速度排放所带来的温室效应：

　　The net effect is equivalent to that of a whopping 135 billion tonnes of carbon dioxide.  其净排量相当于1350亿吨二氧化碳，

　　That is more than twice today's total annual greenhouse-gas emissions,  比现在每年排放的温室气体总量（500亿吨）

　　which are equivalent to about 50 billion tonnes of carbon dioxide (carbon dioxide itself makes up about three-quarters of that, with methane, nitrous oxide and some gases used in industry making up the rest).  的两倍还要多,二氧化碳占温室气体排放量的四分之三，其余的是甲烷、一氧化二氮和其他工业气体。

　　Durwood Zaelke of the Institute for Governance and Sustainable Development, a think-tank, says that if CFCs were uncontrolled the annual figure would be 8 billion tonnes higher.  “治理和可持续发展智库”的Durwood Zaelke表示，如果氟氯化碳的排放未受控制，则每年会多排放80亿吨。

　　The Montreal protocol has had nearly as big an effect as all the rest of our list put together. 蒙特利尔协议书的效果比其他所有协议的总和还要显著。

　　Trailing some way behind the Montreal protocol is a small group of measures 蒙特利尔协议书之后的其余各项措施

　　not really climate policies—that have been responsible for avoiding between 4% and 7% of greenhouse-gas emissions.  不完全是气候政策—也减少了4%~7%的温室气体排放。

　　According to the International Atomic Energy Agency, nuclear power avoided the production of 2.2 billion tonnes of carbon dioxide in 2010 根据国际原子能机构的研究，核能在2010年减排了22亿吨二氧化碳

　　that is, emissions would have been 2.2 billion tonnes higher if the same amount of electricity had been produced by non-nuclear plants.  即如果由非核能工厂发电，二氧化碳将增加22亿吨。

　　Energy from dams and other hydroelectric sources avoided 2.8 billion tonnes  大坝和其他水利发电减排了29亿吨二氧化碳

　　(though emissions of methane from the reservoirs behind some of those dams mean the net effects were less than that).  （如果计入大坝后面蓄水库里产生的甲烷，则净减排量要少一些）。

　　Between them they generated 6,000 terawatt-hours of electricity in 2011, compared with 450TWhrs for wind and less than 60TWhrs for solar.  这些在2011年共发电6000太瓦时，相比之下，风力发电贡献了450太瓦时，太阳能发电则为60太瓦时。

　　The high rate at which new wind and solar capacity is being built will eat into this lead, but it will take some time to overturn it. 风能和太阳能发电会占有越来越高的比重，但这还需要时间彻底扭转目前的趋势。

　　The other item in this group is something of a cheat.  另一项政策则不太切题。

　　In 2007 Su Wei of China's foreign ministry said that his country's one-child policy,  在2007年，中国外交部的苏伟表示，从 20世纪70年代到本世纪头十年的中期，

　　by reducing the number of births between the late 1970s and the mid-2000s by 300m, had reduced carbon emissions by 1.3 billion tonnes in 2005  中国的出生人口因独生子女政策减少了3亿，到2005年，碳排放量因此减少了13亿吨

　　(because there were fewer people to consume goods which generated greenhouse gases in their production).  （因为生产商品的过程往往产生温室气体，人越少，消耗商品越少）。

　　Taking this argument further, one could say that the fall in global fertility since 1960 cut emissions even more.  按照这个说法进一步思考，可以说，1960年后全球生育率的下降为减排做出的贡献更大。

　　That is not exactly a climate policy.  那压根不是气候政策。

　　But it is a reminder that greenhouse gases are powerfully influenced by factors far beyond the scope of climate-change policies. 但是，这表明温室气体排放量会受到非气候变化政策因素的强烈影响。

　　Three other lessons emerge.  三个教训值得学习。

　　First, policies to slow or reverse deforestation are more important than one might expect.  第一，减缓或逆转森林伐木的政策比预想更重要。

　　Trees absorb carbon as they grow and release it when they are cut down.  树木生长时能吸收二氧化碳，被砍伐时则会释放二氧化碳。

　　According to a recent study in Science,  据《科学》一项新研究表明，

　　declining deforestation in Brazil meant that the country produced 3.2 billion tonnes less atmospheric carbon dioxide between 2005 and 2013  巴西实行减少森林砍伐的政策后，2005年到2013年间，

　　than it would have if the tree-felling had continued unabated.  其排放到大气中的二氧化碳比不实行政策前少了32亿吨。

　　That is 400m tonnes a year.  年排放量为4亿吨。

　　The slowdown in deforestation in tropical countries is one of the reasons that the conversion of forests to farmland now accounts for only 11% of greenhouse-gas emissions globally, much less than 20 years ago. 林地转耕地的温室气体排放量现在仅占全球总排放量的11%，比20年前少了很多，而热带国家森林开伐的节奏放缓是缘由之一。

　　The other reason for deforestation's dramatically reduced share of total emissions, though, is that industrial emissions of carbon dioxide have continued to grow rapidly.  导致森林砍伐二氧化碳排放量占比大幅下降的另一个原因在于，二氧化碳的工业排放量持续快速上涨。

　　The rise is not as fast as it might have been.  增长速度与预期有差异。

　　Rules that make vehicles more efficient and improve the energy efficiency of buildings and appliances have done more than might be expected.  提高交通工具使用效率以及提高房屋与电器的能源效率的政策比预期更有效。

　　America has been setting standards for vehicle greenhouse-gas emissions and fuel efficiency since the mid 1970s;  20世纪70年代起，美国为交通工具的温室气体排放以及燃料效率制定了标准。

　　the current rules are forecast to reduce carbon-dioxide emissions by 6 billion tonnes in 2012-25, meaning by about 460m tonnes a year.  当前的政策可以预测，2012-2025年间，二氧化碳排放量将减少60亿吨，相当于一年排放4.6亿吨。

　　America's Department of Transportation reckons that overall such rules have reduced carbon-dioxide emissions by a cumulative 14 billion tonnes.  美国交通部估计，总体来说，这些政策已累计减少二氧化碳排放量140亿吨。

　　Europe's equivalent regulations for passenger cars and light trucks do less (European vehicles were more efficient to start with) but are still respectable;  欧洲针对轿车和轻型货车出台的类似政策，减排量不如美国（欧洲的交通工具之前更有效率），但依然显著。

　　being adopted by overseas manufacturers who want to sell cars in Europe gives them an unquantified extra clout. 这些政策也适用于想在欧洲卖车的海外制造商，这部分影响力无法量化。

　　New EU rules on the design of boilers and water heaters are expected to save 136m tonnes of carbon dioxide a year within six years.  欧盟针对锅炉以及热水器设计的新规定，有望在六年内将年碳排放量减少1.36亿吨。

　　China's Development Research Centre and the World Bank say  中国发展研究中心及世界银行表示，

　　that on the basis of 2010 figures energy-efficiency targets for Chinese state-owned enterprises save about the same amount;  根据2010年的数据，中国国有企业的能源效率目标也减少了相当量的碳排放，

　　that scheme has recently been much expanded. 并近日计划扩大这一目标。

　　Subsidies for solar and wind power do less than you might expect, considering the attention they receive.  以太阳能及风能补贴政策受到的关注度来看，其表现低于预期。

　　The European Environment Agency calculates that between mid-2008 and 2012, what it calls changes in the carbon intensity of energy  欧洲环境署估计，在2008年中期到2012年，被其称为能源碳强度

　　(mainly, the rise in renewables) accounted for a third of the decline in carbon-dioxide emissions in the EU.  （主要指可再生能源的增加）引起的变化占欧盟减排量的三分之一。

　　Emissions fell 350m tonnes in that period, so renewable policies seem to be responsible for about 30m fewer tonnes of carbon dioxide a year,  在此期间，排放量下降3.5亿吨。因此，可再生能源政策可以解释约3300万以下的减排量，

　　making them less effective than energy-efficiency measures. 这使得此项政策不如能源效率政策有效。

　　A separate calculation by Germany's environment ministry puts the figure for Germany alone at 100m tonnes in 2012.  另一个由德国环境部估计的数据显示，在2012年，仅德国的可再生能源政策产生的减排量就达1亿吨。

　　But even if the EU estimate is only half what it should be, renewables would still fall short of other carbon-mitigation policies.  但是，即使欧盟的估计仅为实际的一半，可再生能源政策的减排效果也远不如其他减排政策。

　　They are also extremely pricey.  这些政策的成本也很高。

　　The cost of Germany's Energiewende (its transformation to a renewables-based electricity system) is 16 billion (21 billion) a year.  德国的能源转型成本（以新能源为基础的电力系统改革）是每年160万欧元（210万美元）。

　　The cost of helping developing countries phase out CFCs under the Montreal protocol was just 2.4 billion all-told from 1990-2010.  1990-2010年间，德国根据蒙特利尔议定书，帮助发展中国家逐步淘汰氟氯碳化物的总成本仅24亿美元。

　　The Amazon Fund, which has done much to fight deforestation in Brazil, has mostly been funded by the Norwegian government at a cost of just 760m over 11 years. 在巴西，奋力对抗森林砍伐的亚马逊基金会主要得到挪威政府的资助，11余年的成本仅为7.6亿美元。

　　Over the next few years, the relative weights of all these policies will change.  在接下来的几年，所有政策的相对权重会发生变化。

　　Nuclear energy is being phased out in Germany and may not recover to its pre-Fukushima heights in Japan.  德国会逐步废除核能，日本对核能的重视程度也可能无法恢复到福岛核泄漏之前的水平。

　　Although it is growing in China, its share of worldwide electricity generation—currently about a seventh—is likely to decline.  虽然在中国，核能政策的权重在不断增强，但其在世界范围内的发电份额—约七分之—可能下降。

　　The same may be true of hydropower.  水力发电可能也面临一样的遭遇。

　　The share of solar and wind power, on the other hand, will rise as costs fall and capacity increases (installed capacity for these renewables doubled in 2012-14). 另一方面，由于成本下降、容量增大（这几类可再生能源的装机容量在2012-2014翻倍）太阳能和风能的份额可能会增加。

　　The Economist asked Climate Action Tracker, a group of scientists who study emissions policies and actions, to calculate the policies likely to have the biggest impact in 2020.  本刊邀请来自气候行动追踪组织一群研究排放政策和行动的科学家，估计2020年最可能产生最大影响的政策。

　　Their findings, in chart 2, suggest that the influence of the EU's renewables regime will grow considerably,  他们的结果（如图2）表示，虽然欧洲依然达不到零碳排放能源系统的要求，

　　though Europe will still be far from the zero-carbon energy system greens long for.  欧盟可再生能源制度的影响力会大幅增强。

　　Chinese efforts to boost renewables and energy efficiency are also likely to start bearing a lot more fruit.  中国推进可再生能源以及能源效率的政策也很可能产生更多的成效。

　　So, they think, could the UN's Clean Development Mechanism (CDM), which finances greenhouse-gas reduction measures in developing countries to offset emissions in rich ones. 因此，他们在想，资助发展中国家温室气体减排措施的联合国清洁发展机制是否可以补偿发达国家的排放量。

　　These estimates work on the basis of current policies.  这些估计都是基于当前的政策。

　　But one possible new measure would make a big difference.  但是，一项合理的新政策将会有重大意义。

　　Hydrofluorocarbons (HFCs) are ozone-friendly replacements for CFCs, and are one of the fastest-growing greenhouse gases,  氢氟碳化物不破坏臭氧层，是对氟氯碳化物的替代品，也是增长最快的温室气体之一。

　　having risen 40% since 1990.  1990年后，其排放量增长了40%。

　　Emissions of HFCs are unrestricted, though CDM investments are used to reduce them in some cases.  清洁发展机制曾投资减少一定程度的氢氟碳化物量，但其排放量仍不受限制。

　　If the Montreal protocol were quickly amended to include them, says Mr Zaelke,  Zaelke表示，如果蒙特利尔议定书经修正后包含了这些内容，

　　it might do almost as much for greenhouse-gas emissions in the next 35 years as it did in 1990-2010. 今后35年的温室气体排放量将达到1990-2010的水平。

　　Saving the equivalent of some 130 billion tonnes of carbon dioxide so cheaply would be a big win.  以如此低的成本减少约1300亿吨二氧化碳排放量意义重大。

　　But it is still only a tenth of what would need to be done to ensure that the temperature in 2100 is no more than 2C higher than it was at the time of the Industrial Revolution 但是，若要保证2100年地球温度与工业革命时期相比不超过2C

　　the limit that the countries of the world have committed themselves to.  各国承诺的指标，其工作只完成了十分之一。

　　Without the measures listed in chart 1 emissions might be equivalent to almost 70 billion tonnes of carbon dioxide a year, rather than 50 billion.  如果没有表1列出的各项政策，年碳排放量大约为700亿吨，而不是500亿吨。

　　But even the lower number is too high to meet the stated goal, and the overall trend is up, not down.  但即使碳排放量减少，对于完成既定目标来说，排放量依然很高，而且，碳排放量的总趋势还在增加而不是减少。

　　World leaders gathering in New York are not only being vague about their climate policies. They are being dilatory, too. 聚集在纽约的各国领导，不仅对其气候政策界定不清，行动上也不够积极。翻译：杨诗露；校对：黄梅