書評 氣候變化的解決之道

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.

當經濟學家思考氣候變化問題時，其中一些人會重點研究馬糞。具體來說，他們研究的是19世紀末的馬糞大危機。當時世界各地的城市極度依賴馬匹作爲交通工具，以至於一場公共衛生災難迅速逼近。1894年，倫敦《泰晤士報》(The Times)估計，50年後這場危機會變得非常可怕，倫敦的每一條街道都將覆蓋9英尺厚的馬糞，於是一羣聰明人開始着手應對這場危機。

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.

結果，很快就出現了一個簡單的解決方法：不是新的法律或者政策，而是汽車。這種非常成功的技術革新讓人們迅速解決了馬糞帶來的污染問題。

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•萊維特(Steven Levitt)等經濟學家表示，這給任何擔憂氣候變化的人提供了顯而易見的教訓。在2009年出版的《超級魔鬼經濟學》(SuperFreakonomics)一書中，萊維特和合著者斯蒂芬•杜布納(Stephen Dubner)利用這個故事辯稱，通過技術解決問題往往比末日論者想象的簡單得多，成本也低得多；可以用所謂的地球工程來解決全球變暖問題，也就是通過操控環境來遏止溫度上升。

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.

另外兩位經濟學家認爲此類想法具有危險的誘惑力，並作爲其著作的主題加以討論：就職於美國環保協會(Environmental Defense Fund)的學者赫爾諾特•瓦格納(Gernot Wagner)和哈佛大學(Harvard)教授馬丁•威茨曼(Martin Weitzman)合著了《氣候衝擊：一個變暖星球的經濟影響》(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.

他們這樣做是正確的。人們對地球工程的興趣逐步增長，同時儘管聯合國(UN)幾十年來一直舉行氣候談判，人們投入了數十億美元爲可再生能源提供補貼，偶爾還會嘗試碳定價，但造成氣候變暖的二氧化碳排放仍在繼續上升。這些努力的失敗凸顯出如下事實：正如兩位作者指出的那樣，氣候變化問題最終是“搭便車”問題。當人們自己承擔成本、好處卻是全世界共享的時候，他們就很難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，可以說單個國家就能實施萊維特和其他許多人討論過的一種方案：模擬1991年菲律賓皮納圖博(Pinatubo)火山的噴發。那次火山噴發向平流層噴射了大量二氧化硫，製造了一個巨大的遮陽罩，使全球氣溫在接下來的一年裏大約降低了0.5攝氏度。

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.

瓦格納和威茨曼表示，地球工程的成本的確可能比減排低，而影響卻是巨大的——他們認爲，地球工程徹底顛覆了經濟學上對氣候變化的標準看法，從“搭便車”問題變成了“隨便開”問題。

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.

但這種地球工程存在諸多風險，從臭氧層破壞到一旦停止皮納圖博式的做法就會導致氣溫快速上升，因爲引發氣候變暖的潛在排放仍將持續。

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.

減排的另一個障礙是，對碳排放引發氣候變暖的程度缺乏明確認知。這是《氣候衝擊》一書論述的另一個主題。作者之所以選擇這個標題，是爲了強調一個被廣泛誤解的氣候變化問題：僅僅穩定年度排放量還不夠。要降低碳濃度，碳排放量必須被大幅削減至接近零排放的程度。2013年碳濃度已經升至400ppm，遠高於工業時代前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.

如果大氣中的二氧化碳含量翻倍，全球氣溫可能會上升多少？兩位作者仔細分析了最新的科學發現。他們的結論是，現在氣溫升幅大約有10%的機率最終會超過6度，而氣溫上升6度就會引發巨大災難。房主會投保預防毀滅性大火，而實際上出現這種大火的機率幾乎總是低於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.

多年來，人們已對經濟方面的正確對策瞭如指掌，他們主張停止在全球徵收每噸約15美元的碳稅（那樣是在補貼化石燃料），碳價至少應提高至每噸40美元以上。但是《氣候衝擊》一書則建議經濟學家不要再製定全球碳價，開始探尋更偏政治的可能解決方案，比如制定燃油經濟標準。與地球工程相比，這樣的舉措聽起來有些枯燥，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.

這本書不是爲那些深諳氣候政策的人準備的，他們不會覺得這本書的內容多麼令人震驚。這本書對全球氣候變暖的經濟影響進行了生動而清晰的評估，對於那些想要一覽此類內容的聰穎的一般讀者，該書非常值得一讀。

The writer is the FT’s environment correspondent

本文作者是英國《金融時報》環境記者

Climate Shock: The Economic Consequences of a Hotter Planet, By Gernot Wagner and Martin Weitzman, (£19.95, $27.95)

《氣候衝擊：一個變暖星球的經濟影響》(Climate Shock: The Economic Consequences of a Hotter Planet)，赫爾諾特•瓦格納與馬丁•威茨曼合著，售價19.95英鎊/27.95美元