【英语生活】加快引进“碳价格”

Euan Murray grew up on a sheep farm in southern Scotland; now he is in charge of “carbon footprinting” for corporate clients of the Carbon Trust. “If I ask my old man, ‘What's the carbon footprint of a sheep?' he looks at me as though I'm mad,” he explains. “But he can tell me the stocking density, what he feeds the sheep, and he can answer those questions as part of running his business.”

Quite so. Carbon footprinting, the study of how much carbon dioxide is released in the process of producing, consuming and disposing of a product, is all about the specifics. This is a refreshing change from the politics of climate change, which is all about the generics. We hear promises from our leaders of big change in the future, without any credible plans right now.

I first approached Murray to ask him about the climate change impact of a cappuccino. Loyal readers may recall that a year and half ago, I wrote about the question, pointing out that meeting any of these grand targets in a sensible way would require billions upon billions of small decisions. The cappuccino's climate change impact depends on whether the café is double-glazed, the decisions the staff and I take to get there, the diet of the methane-producing cow that produced the milk and the source of power for the espresso machine. Last week I pointed out that there are around 10 billion products in a modern economy; that means that the problem of reducing carbon dioxide emissions is “simply” the problem of reducing carbon dioxide emissions from a cappuccino, 10 billion times over.

In the case of the cappuccino – or at least, a typical, generic cappuccino – the climate change impact probably comes from the milk. I say “probably” because we don't know for sure. Murray's best guess was based on his work on milk chocolate. Milk makes up one-third of a chocolate bar by mass, but is responsible for two-thirds of the climate-change impact of the entire production and consumption process. Switching to espresso might be in order; so, too, might a different diet for the cows. It is hard to make generic recommendations, though: even the particular soil on which the grass grows on which the cows feed alters the climate change calculus.

The carbon-footprinting process often produces surprises. An environmentally conscious consumer in the crisps aisle of the supermarket will probably be thinking about packaging or “food miles”. The Carbon Trust reckons that about 1 per cent of the climate impact of a packet of crisps is from moving potatoes around. The largest single culprit is the production of the nitrogen fertiliser, and half of the climate impact in general takes place at the agricultural stage. The point is not that agriculture is always the problem, but that it is very hard for a well-meaning consumer to work out what the green purchasing decision actually is. For this reason, the Carbon Trust has a carbon labelling scheme. The trouble is that many consumers simply do not care enough to pay more or choose a less enjoyable product simply because of the low carbon label.

A government role is necessary, then, but it is even harder for governments to regulate such fine details. All this is why economists continue to advocate some kind of carbon price, which would give an incentive to everyone involved in these complex supply chains to trim carbon dioxide emissions. A modest and credible price for carbon is slowly becoming the conventional policy wisdom. It is a shame we still don't have it.

尤安•默里(Euan Murray)在苏格兰南部的一个牧羊场长大；目前他在英国碳信托有限公司(Carbon Trust)为企业客户管理“碳足迹”。“如果我问我父亲，‘羊的碳足迹有多少？'他会盯着我，好像我神志不清似的，”默里解释道。“但他能够告诉我养畜密度，羊的饲料是什么，他可以将这些问题作为其企业经营的一部分来解答。”

的确如此。碳足迹研究的是在某一产品的生产、消费和处理过程中，二氧化碳的排放量，关注的完全是细节问题。相较于充斥着泛泛之谈的气候变化政治主张，这是个令人耳目一新的转变。执政者向我们承诺，未来会发生重大改变，但眼下却拿不出任何可信的方案。

最初我和默里联系是为了讨教一杯卡布奇诺咖啡对气候变化的影响。忠实的读者也许还记得，一年半以前我曾写过这个问题，指出要切实地实现任何一个宏伟的目标，都需要无数微小决定的共同作用。这杯卡布奇诺对气候变化的影响，取决于这杯咖啡是否浇了双层糖浆、我和同事们决定如何前往咖啡馆、制造甲烷的奶牛的饮食结构、以及咖啡机的电力来源。上周我撰文指出，在一个现代经济环境中，大约存在100亿件产品；这意味着，二氧化碳减排问题，“不过”是减少一杯卡布奇诺的二氧化碳排放量，再乘以100亿的问题。

就卡布奇诺而言——至少是一杯标准的普通卡布奇诺——对气候变化的影响很可能来自牛奶。我说“很可能”，因为我们并不肯定。默里最合理的猜测基于他对牛奶巧克力的研究。按重量计算，牛奶在一块巧克力中仅占三分之一，但却要为整个生产和消费过程对气候变化造成的影响负三分之二的责任。改喝浓咖啡或许是正确之举；给母牛换一换饮食可能也会有用。不过，很难提出一些通用的建议：就连母牛所吃牧草所生长的那块土壤，也会改变气候变化的计算方法。

产生碳足迹的过程常常带来意外发现。在超市里摆放薯片的架子前，一位具有环境意识的消费者很可能考虑的是包装或“食品里程”(food mile)的问题。但英国碳信托公司计算，一包薯片所产生的气候影响中，约1%来自马铃薯的运输过程。而罪魁祸首则是氮肥的生产，总体而言，有一半的气候影响都发生在农耕阶段。关键不在于农业总是问题所在，而是好心的消费者很难弄清楚，到底什么才是绿色采购决定。为此，英国碳信托公司推出了一项碳标志计划。但问题是，许多消费者对此根本不够在乎，不愿仅仅为了一个低碳标志，就多花钱或选择不那么中意的产品。

因此，政府有必要参与进来，但政府要监管如此细微的具体问题，难度更大。这正是经济学家不断提倡引进某种碳价格机制的原因所在，这种机制将激励这些复杂供应链牵涉到的每一个人积极减排。给碳排放制定一个适中且可行的价格，正慢慢变成普遍的政策意见。我们仍未将其付诸实际，真是太遗憾了。

译者/何黎