When economists think about climate change, some think a lot about horse manure. Specifically, they consider the greatmanure crisis of the late 1800s, when the world’s cities relied on horses for transport to such an extent that a public sanitation disaster loomed. Fine minds set to work on a crisis that The Times of London estimated in 1894 was so dire that in 50 years every street in the city would be buried 9ft deep in horse droppings.
当经济学家思考气候变化问题时，其中一些人会重点研究马粪。具体来说，他们研究的是19世纪末的马粪大危机。当时世界各地的城市极度依赖马匹作为交通工具，以至于一场公共卫生灾难迅速逼近。1894年，伦敦《泰晤士报》(The Times)估计，50年后这场危机会变得非常可怕，伦敦的每一条街道都将覆盖9英尺厚的马粪，于是一群聪明人开始着手应对这场危机。

As it turned out, a simple solution was at hand: not new laws or policies but the motor car, a technical innovation so successful that the equine pollution problem was swiftly overcome.
结果，很快就出现了一个简单的解决方法：不是新的法律或者政策，而是汽车。这种非常成功的技术革新让人们迅速解决了马粪带来的污染问题。
The lesson is obvious for anyone worried about climate change, say economists such as Steven Levitt. In 2009’s SuperFreakonomics he and co-author Stephen Dubner used the tale to argue that technological fixes are often far simpler and cheaper than doomsayers imagine; and global warming could be addressed by so-called geoengineering, or manipulating the environment to halt rising temperatures.
史蒂文•莱维特(Steven Levitt)等经济学家表示，这给任何担忧气候变化的人提供了显而易见的教训。在2009年出版的《超级魔鬼经济学》(SuperFreakonomics)一书中，莱维特和合著者斯蒂芬•杜布纳(Stephen Dubner)利用这个故事辩称，通过技术解决问题往往比末日论者想象的简单得多，成本也低得多；可以用所谓的地球工程来解决全球变暖问题，也就是通过操控环境来遏止温度上升。
The dangerous allure of such thinking is a central theme tackled by two other economists: Gernot Wagner, an academic who works for the US Environmental Defense Fund, and Harvard professor Martin Weitzman in Climate Shock: The Economic Consequences of a Hotter Planet.
另外两位经济学家认为此类想法具有危险的诱惑力，并作为其著作的主题加以讨论：就职于美国环保协会(Environmental Defense Fund)的学者赫尔诺特•瓦格纳(Gernot Wagner)和哈佛大学(Harvard)教授马丁•威茨曼(Martin Weitzman)合著了《气候冲击：一个变暖星球的经济影响》(Climate Shock: The Economic Consequences of a Hotter Planet)。
They are right to do so. Interest in geoengineering ismounting as warming carbon dioxide emissions have continued to rise despite decades of UN climate negotiations, billions of dollars worth of renewable energy subsidies and sporadic attempts to price carbon. The failure of those efforts underlines the fact that climate change is, as the authors point out, the ultimate “free rider” problem. It is hard to get people to limit their own pollution when they bear the costs and the benefits are global.
他们这样做是正确的。人们对地球工程的兴趣逐步增长，同时尽管联合国(UN)几十年来一直举行气候谈判，人们投入了数十亿美元为可再生能源提供补贴，偶尔还会尝试碳定价，但造成气候变暖的二氧化碳排放仍在继续上升。这些努力的失败凸显出如下事实：正如两位作者指出的那样，气候变化问题最终是“搭便车”问题。当人们自己承担成本、好处却是全世界共享的时候，他们就很难限制自身造成的污染。
Geoengineering, on the other hand, is so cheap that one country alone could conceivably carry out a plan discussed by Levitt and many others: mimic the 1991 eruption of the Mt Pinatubo volcano in the Philippines, which cooled global temperatures by about 0.5C the following year, by shooting sulphur dioxide into the stratosphere to create a giant sunshade.
另一方面，地球工程的成本非常低廉，可以说单个国家就能实施莱维特和其他许多人讨论过的一种方案：模拟1991年菲律宾皮纳图博(Pinatubo)火山的喷发。那次火山喷发向平流层喷射了大量二氧化硫，制造了一个巨大的遮阳罩，使全球气温在接下来的一年里大约降低了0.5摄氏度。
The cost could be lower than that of cutting emissions, say Wagner and Weitzman, while the impact could be huge — which, they argue, means geoengineering turns the standard economics idea of climate change on its head, from a “free rider” to “free driver” problem.
瓦格纳和威茨曼表示，地球工程的成本的确可能比减排低，而影响却是巨大的——他们认为，地球工程彻底颠覆了经济学上对气候变化的标准看法，从“搭便车”问题变成了“随便开”问题。
But the risks of such geoengineering are myriad — from ozone depletion to fast-rising temperatures should Mt Pinatubo-style techniques ever stop — because the underlying emissions causing warming would continue.
但这种地球工程存在诸多风险，从臭氧层破坏到一旦停止皮纳图博式的做法就会导致气温快速上升，因为引发气候变暖的潜在排放仍将持续。
A further obstacle to reducing emissions is the lack of certainty about precisely how much warming they will cause. This is another theme of Climate Shock, a title chosen to highlight one widely misunderstood aspect of climate change: it is not enough merely to stabilise annual emissions. They have to be slashed to near zero to bring down C02 concentrations, which in 2013 rose to 400 parts per million, well above the 280 ppm of pre-industrial times.
减排的另一个障碍是，对碳排放引发气候变暖的程度缺乏明确认知。这是《气候冲击》一书论述的另一个主题。作者之所以选择这个标题，是为了强调一个被广泛误解的气候变化问题：仅仅稳定年度排放量还不够。要降低碳浓度，碳排放量必须被大幅削减至接近零排放的程度。2013年碳浓度已经升至400ppm，远高于工业时代前280ppm的水平。
Dissecting the latest scientific findings about how much global temperatures are likely to rise as C02 in the atmosphere doubles, the authors conclude there is about a 10 per cent chance of temperatures eventually exceeding a catastrophic 6C. Homeowners take out insurance policies against devastating fires that are almost always less likely than this.
如果大气中的二氧化碳含量翻倍，全球气温可能会上升多少？两位作者仔细分析了最新的科学发现。他们的结论是，现在气温升幅大约有10%的几率最终会超过6度，而气温上升6度就会引发巨大灾难。房主会投保预防毁灭性大火，而实际上出现这种大火的几率几乎总是低于10%。
The correct economic solution has been well understood for years, they argue: stop subsidising fossil fuels by about $15 a ton of C02 globally, and create a price of at least $40 a ton. But Climate Shock advises economists to stop demanding a global carbon price and start working on more politically possible solutions, such as fuel economy standards. That sounds dull compared with geoengineering. But it is also infinitely safer.
多年来，人们已对经济方面的正确对策了如指掌，他们主张停止在全球征收每吨约15美元的碳税（那样是在补贴化石燃料），碳价至少应提高至每吨40美元以上。但是《气候冲击》一书则建议经济学家不要再制定全球碳价，开始探寻更偏政治的可能解决方案，比如制定燃油经济标准。与地球工程相比，这样的举措听起来有些枯燥，但它也安全得多。
This is not a book for people deeply versed in climate policy, few of whom will find its contents remotely shocking. For the intelligent lay reader wanting a lively, lucid assessment of the economic consequences of global warming, however, it is well worth reading.
这本书不是为那些深谙气候政策的人准备的，他们不会觉得这本书的内容多么令人震惊。这本书对全球气候变暖的经济影响进行了生动而清晰的评估，对于那些想要一览此类内容的聪颖的一般读者，该书非常值得一读。
The writer is the FT’s environment correspondent
本文作者是英国《金融时报》环境记者
Climate Shock: The Economic Consequences of a Hotter Planet, By Gernot Wagner and Martin Weitzman, (£19.95, $27.95)
《气候冲击：一个变暖星球的经济影响》(Climate Shock: The Economic Consequences of a Hotter Planet)，赫尔诺特•瓦格纳与马丁•威茨曼合著，售价19.95英镑/27.95美元