Three years ago, the University of Vermont in Burlington began to experiment with a few nudges towards a healthy, sustainable lifestyle. First, in 2012, campus outlets and the company operating the vending machines were required to make sure that at least 30 per cent of the drinks on offer were wholesome stuff such as vegetable juice, low-fat milk and water. A few months later, selling bottled water on campus was banned outright. The aim, pushed hard by student campaigners, was to encourage students to fill reusable bottles with tap water instead.

三年前，位于伯灵顿的佛蒙特大学(University of Vermont)开始尝试一些推进健康、可持续生活方式的“轻推”(nudge)举措。首先，在2012年，校园商店和经营自动售货机的公司被要求确保它们提供的饮料中有至少30%是健康饮品，比如蔬菜汁、低脂牛奶和水。几个月后，校园里彻底禁售瓶装水。这一举动的目标是鼓励学生用自来水灌入可重复使用的饮水瓶、以代替瓶装水，学生倡导者也努力推动这一目标的实现。

So, how did the Vermont experiment go? A study by Elizabeth Berman and Rachel Johnson (of the University’s own Department of Nutrition and Food Sciences) was recently published in the American Journal of Public Health. The researchers found that “per capita shipments of bottles, calories, sugars and added sugars increased significantly when bottled water was removed...As bottled water sales dropped to zero, sales of sugar-free beverages and sugar-sweetened beverages increased.”

那么，佛蒙特大学这一尝试的结果如何？该校营养与食品科学部的伊丽莎白伯曼(Elizabeth Berman)和蕾切尔约翰逊(Rachel Johnson)最近在《美国公共健康杂志》(American Journal of Public Health)上发表了一项研究。两位研究者发现，“瓶装水没有了以后，瓶子、热量、糖和添加糖的人均消耗量都显著增加了……随着瓶装水销量降至零，无糖饮料与含糖饮料的销量都增加了。”

In other words, the policy backfired with both barrels. Students didn’t switch to tap water, they switched to the likes of Coke and Diet Coke instead. All this would be just an amusing curiosity — one more example of student campaigners who are all heart and no brains — if it weren’t for the fact that more mature policy makers often commit similar blunders on much broader canvases. We would do well to learn some lessons from the University of Vermont’s experience.

换句话说，该政策在两个目标上都适得其反。学生们并未改喝饮用自来水，而是改喝可口可乐、健怡可乐之类的饮料。如果不是更多成熟的政策制定者在更广阔的领域经常犯同样错误的话，这一切只不过是有趣的奇闻异事，成为学生倡导者一腔热血但是不动脑子的又一个例证。我们最好从佛蒙特大学的例子中汲取一些教训。

The first lesson is that when it comes to saving the planet, people focus on what they can see. Type “environmental impact of concrete” into a search engine and you are likely to see a page filled with scholarly analysis pointing out that the impact is very large indeed, because cement production releases vast volumes of carbon dioxide. Type “environmental impact of bottled water” instead and your search results will be packed with campaigning groups seeking to persuade you to change your ways.

第一个教训是，当谈到拯救地球时，人们专注于自己能看到的事。在搜索引擎中键入“水泥对环境的影响”，你可能会看到整个搜索结果页面上全都是各种指出水泥对环境的影响确实很大（因为水泥的生产过程释放出大量二氧化碳）的学术分析。再键入“瓶装水对环境的影响”，搜索结果肯定全都是各种活动团体试图说服你改变生活方式。

This is understandable: I can’t do much about concrete but I can stop drinking bottled water. But being a logical target for campaigners is not the same as being a logical target for policy action.

这是可以理解的：我对水泥生产无能为力，但我可以停止喝瓶装水。但作为活动人士的目标合乎逻辑，不等于它作为政策行动的目标也合乎逻辑。

The second lesson is that we often struggle to deal with multiple goals. The University of Vermont wanted to reduce the flow of plastic water bottles to landfill but also wanted to encourage students to be healthy. There’s a clear conflict between these goals. Water is as healthy a drink as you can find, yet that was exactly what the University of Vermont was banning from vending machines. Wishful thinking provides a resolution — if everyone just drank tap water then there would be no problem. But wishful thinking is not an excuse for setting no priorities.

第二个教训是，我们往往很难同时应对多个目标。佛蒙特大学既想减少需要填埋的塑料水瓶的数量，又想鼓励学生培养健康的生活方式。这两个目标存在明显的矛盾。喝水最健康，但佛蒙特大学恰恰禁止自动售货机出售瓶装水。一厢情愿的思维方式提供了一个答案——如果每个人都干脆喝自来水，问题就解决了。但一厢情愿的思维方式并非放弃设定优先顺序的借口。

We see this sharply in the debate over nuclear power. We want to reduce the greenhouse gas emissions that result from burning fossil fuels. We also want to avoid radioactive waste and the risk of radiation leaks. In response to a genuine policy dilemma, politicians have tended to plump for wishful thinking every time, typically involving wind turbines.

在关于核能的辩论中，我们更清楚地看到了同样一幕。我们想减少燃烧化石燃料带来的温室气体排放。我们也想避免放射性废料以及辐射泄漏的风险。在回应这一真正的政策两难时，政客们每次都倾向于选择一厢情愿的思维方式，通常都涉及风力涡轮机。

The third lesson is that the much-vaunted notion of “nudging” doesn’t always help navigate a complicated policy maze. Nudging means using default options, information design and similar techniques to achieve policy goals. It can be very successful. But careless nudges are no more welcome in public policy than at a domino-toppling event. If you pick a questionable target (bottled water) and fudge a key policy dilemma (the environment vs health) then nudging isn’t going to solve your problems.

第三个教训是，备受吹捧的“轻推”概念并不总能帮助我们走出政策迷宫。“轻推”意味着使用默认的选项、信息设计以及相似的技术来实现政策目标。它可以很成功。但粗心的“轻推”在公共政策领域不比它在推倒多米诺骨牌的游戏中更受欢迎。如果你选择了一个有问题的目标（瓶装水）并随随便便制造出一个重要的政策困境（环境vs健康），那么“轻推”将不会解决你的问题。

So what can be done? One approach is to try to reach policy goals with the help of market signals. The classic example of this is a carbon tax, levied on fossil fuels to reflect their carbon-dioxide emissions. The advantage of this approach is that it encourages everybody at any stage of production or consumption to take actions that reduce emissions, because those actions will save them money. A truck manufacturer might develop a cleaner engine, a logistics company might find a more efficient delivery algorithm, and the final consumer might decide to consume a little less.

那么，我们能做什么呢？一种方法是，设法在市场信号的帮助下达成政策目标。这方面的经典例子是碳税——以化石燃料为对象、按照其二氧化碳排放量征收。这种方法的优点在于，它鼓励处于生产或消费任何阶段的每个人都采取行动减少碳排放，因为这样做可以省钱。卡车制造商或许会开发出更清洁的发动机，物流公司可能会找到更高效的投递算法，而终端消费者可能会决定少消费一些。

The idea of using the price system to solve environmental problems is widely accepted by economists but, alas, it finds itself stranded in the policy doldrums. Ponder this: the Pope recently argued that climate change was a grave problem but he opposed market-based responses. Meanwhile the US Republican party likes market-based responses but isn’t so convinced about climate change.

利用价格体系解决环境问题的理念得到经济学家们的广泛认同，但可惜的是，这一理念自身被困在了政策内耗之中。思考一下：教皇最近称，气候变化是一个严重问题，但他反对基于市场的应对措施。与此同时，美国共和党喜欢基于市场的措施，但并不怎么相信气候变化真实存在。

One other advantage of using environmental taxes is that people can decide on their own priorities. A lot of what we do has consequences for the planet — including breathing — and so part of the problem we face is deciding what is worth doing anyway.

采用环境税的另一个好处是，人们可以决定自己的优先顺序。我们的很多活动（包括呼吸）都对地球产生影响，因此，我们面临的部分问题在于决定什么事值得去做。

Perhaps it is time for a confession. I am writing this column on the hottest July day recorded in British history. At my left hand is a glass of chilled sparkling water, and next to the glass is a plastic bottle to top it up. If there had been a tax on that bottle, it is a tax I would willingly have paid.

或许我该坦白一下了。我正在英国历史上有记录以来7月最炎热的一天写这篇专栏，我左手边是一杯冰镇苏打水，玻璃杯旁边是一个塑料瓶，用来把杯中的苏打水加满。如果这个瓶子需要交税的话，这税我愿意交。