A compelling case for action to avoid a climatic catastrophe
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Published: November 1 2006 02:00 | Last updated: November 1 2006 02:00
Repent, for the end of the world is nigh. That is a warning one would expect to come from an evangelical preacher or an environmental doomsayer, not from a sober economist. Yet that is, in essence, what Sir Nicholas Stern, author of the British government's new report on climate change, is saying.* The tone may be sober, but the conclusion - act now before it is too late - is not.
Hitherto many economists, business-people and politicians, particularly in the US, have argued that, given both the uncertainties and the high costs of taking possibly unnecessary action, the best policy is to wait, see and, if necessary, adapt. The contribution of this report is to reverse that logic. It argues that, given these very same uncertainties and the relatively low costs of acting now, the best policy is action.
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How and how convincingly does the review make this case? The answer, I suggest, is: "Sufficiently so."
The starting point has to be with the consequences of "business as usual". The underlying scientific argument on this is straightforward. Since the industrial revolution the stock of greenhouse gases in the atmosphere has risen from the equivalent of 280 parts per million (ppm) of carbon dioxide to 430ppm. If current emission trends continue, the stock of greenhouse gases in the atmosphere could more than treble by the end of this century.
Greenhouse gases trap heat, which is why there is abundant life on earth. It is also, argue the scientists, why the earth has warmed by about 0.7°C since 1900. Should current trends continue, temperatures might rise by between 3°C and 10°C by 2100 (see chart). By the middle of this century and, so, within the life-span of many now alive, warming could be between 2°C and 5°C. Since the earth is only 5°C warmer today than during the last ice age, a change of that magnitude would be enormous.
Should the temperature rise by 5°C, there may be adverse effects on crop yields; significant rises in sea levels that threaten developing countries, such as Bangladesh, but also coastal cities, such as London, Shanghai and New York; water shortages affecting more than a billion people; mass extinctions; increasingly intense storms; and, conceivably, huge shifts in the climate system, with local cooling and intense local warming.
All this sounds biblical.
If warming is so dreadful, would a proto-Stern of 12,000 years ago have warned his contemporaries of the dire results of the looming end of the ice age? The answer to this query is presumably no. Warming can be - and, in that case was - highly beneficial. But this does not mean rapid warming would now be so. We - and the rest of life - are well adapted to today's world. While human beings cope superbly with change, the speed and scale of the potential disruption would test that ability to the limit.
Modelling work done for the review concluded the costs of climate change over the next two centuries could be equivalent to a reduction of 5 per cent in average consumption per head. This is itself equal only to the loss of two years of economic growth. But the costs of failure to act might be as much as 20 per cent of gross world product. The report compares such costs with those associated with "the great wars and the economic depression of the first half of the twentieth century". Worse, in this case, "it will be difficult or impossible to reverse these changes". Moreover, these costs would fall heavily on the poorest.
It seems simple common sense, therefore, to reduce the dangers, provided the costs of doing so are modest. Houses rarely catch fire, but few would question the wisdom of buying cheap smoke alarms.
The question is how expensive the recommended actions would be. On this the review is encouraging. The economic costs of mitigating the rise in greenhouse gas seem modest. The review estimates them at as little as
1 per cent of global gross product, though, here too, there is a range of uncertainty. One per cent is itself just a few months of economic growth.
The report argues for setting a target of 450-550ppm of carbon dioxide equivalent: anything higher, it argues, would be too risky; anything lower would be too costly. Given the trends, even achieving that target would require a massive shift (see chart). The longer change is postponed, however, the bigger the dangers and the higher the costs of forestalling them: "Delay in taking action would lead both to more climate change and, ultimately, higher mitigation costs." Given the costs and benefits estimated in the report, early action seems sensible. But that conclusion depends in part on the discount rate used. The review argues, sensibly, that there is no reason why the welfare of our generations should be intrinsically more important than those of our grandchildren. The only other reason for a high discount rate is high economic growth. But if climate change slows economic growth significantly, as seems likely, a low discount rate makes sense. Under that assumption, the case for early action becomes even stronger.
What needs to be done? Adaptation is part of the answer, partly because further warming is certain, given the concentrations of greenhouse gases already in the atmosphere. But mitigation must also be central. Fortunately, many of the technologies needed to lower greenhouse gas emissions per unit of output are known already. What also emerges from the analysis is that there is no dominant solution. A mixture of technologies will be needed, instead (see chart). Among them are: increases in efficiency; carbon capture and storage; nuclear power; use of biofuels; and domestic combined heat and power. Also important, however, is forestation.
How are such shifts to be brought about? The broad answer is through a combination of pricing of greenhouse gas emissions, investment in new technologies and regulation of energy efficiency.
This raises the biggest question of all: how is humanity to deal with what is both the biggest "market failure" ever seen and an unprecedented challenge to its capacity for large-scale and enduring co-operation. Is it imaginable that the countries of the world, with their vastly different views and interests, will rise to the collective action challenge climate change poses?
Hitherto, the answer to that question has been a resounding "no". The report may have made a case for early action. But it could easily end up as just another futile exhortation. Whether that has to be so is the question I plan to address next week.
* The economics of Climate Change,
www.hm-treasury.gov.uk 环境灾难离我们有多远？
作者：英国《金融时报》首席经济评论员马丁?沃尔夫(Martin Wolf)
2006年11月3日 星期五
忏
悔吧，因为世界末日就在眼前。听到这句话，你可能认为这是福音派信徒或环境末日论者的警告，不会想到它出自一位冷静的经济学家之口。然而，这基本上就是英国政府最新气候变化报告*作者尼古拉斯?斯特恩爵士(Sir Nicholas Stern)的意思。他的口吻可能还算冷静，但结论却不然：马上行动，否则就太迟了。
许多经济学家、商界和政界人士（尤其在美国）一直辩称，由于存在诸多不确定性，而且采取可能不必要的行动会带来高昂的成本，因此，最好的政策就是等待、观望，并在必要的情况下“适应”气候的变化。这份报告的贡献，就是要推翻这种逻辑。报告强调，鉴于同样的不确定性，且马上行动的成本相对较低，因此，最好的政策是行动。
这份报告如何证明这一点？可信性有多高？我认为，答案是“足够可信。”
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首先一点，就是“一切照旧”的后果。关于这一点的科学论证相当简单。自工业革命以来，大气中的二氧化碳浓度已从280ppm（百万分之280）升至430ppm（百万分之430）。如果按照目前的排放趋势发展下去，到本世纪末，大气中的温室气体含量可能会增加两倍多。
温室气体保留热量，这是地球生命得以生存的原因。科学家强调，这也是地球气温自1900年以来已升高约0.7摄氏度的原因。如果延续当前的趋势，到2100年，地球气温可能会升高3至10摄氏度（见图）。到本世纪中叶，即现在许多人的有生之年，气温可能会升高2至5摄氏度。这种幅度的变化是巨大的，因为与上一个冰川期相比，现在的地球温度也仅仅高了5摄氏度而已。
如果气温升高5摄氏度，可能会对农作物生产造成不利影响；海平面将大幅上升，不仅会威胁孟加拉国等发展中国家，也会危及伦敦、上海和纽约等沿海城市；水资源将出现短缺，受影响人口超过10亿；大量生物将会灭绝；将出现越来越强烈的风暴；气候系统也肯定会发生巨大变化，一些地区将变冷，另一些地区将急剧变暖。这些后果听上去都像是《圣经》中的灾难。
如果气候变暖是如此可怕，那么，1.2万年前的“斯特恩”会警告他同时代的人，关注冰川时期即将结束的可怕后果吗？这个问题的答案想必是否定的。气候变暖可能非常有利（1.2万年前就是如此）。但这并不意味着现在的气候迅速变暖也是如此。我们（以及其它生命）很好地适应了现在的气候。虽然人类的适应能力非常强大，但气候变化的速度和潜在破坏的规模将考验人类的极限。
为这次气候变化评估而进行的模型分析工作得出结论认为，未来两个世纪，气候变化的代价可能相当于人均消费减少5%。这仅仅相当于损失了两年的经济增长。然而，如果不采取行动应对气候变化，代价可能高达世界生产总值的20%。报告将这些损失与“20世纪上半叶重大战争和经济危机”的相关成本进行了比较。更糟的是，对于气候变化而言，“这些变化很难逆转，或者不可能逆转”。而且，这些代价将主要由最贫困人口来承担。
因此，如果行动的成本如此合理，那么，降低危险似乎是简单的常识。房屋很少失火，但没人反对花一点小钱购买烟雾报警器。
问题在于，建议采取的那些行动到底需要多少成本。在这方面，报告的结论相当鼓舞人心。降低温室气体排放量增长速度的经济成本，似乎颇为合理。报告估计，尽管其中也存在很多不确定性，但这项成本占全球总产出的比例仅有1%，仅相当于几个月的经济增长。
报告建议，为二氧化碳等温室气体的大气浓度设定一个目标，建议设在450ppm至550ppm：如果目标浓度太高，气候风险就会过高；如果目标浓度太低，需要付出的成本就会太大。鉴于当前的趋势，即便达到这个目标也需要付出巨大努力。然而，我们拖延的时间越长，危险就越大，对抗这些危险的成本也越高：“拖延采取行动的时间，将导致更大的气候变化，最终造成更高的治理成本。”鉴于报告中估计的成本和好处，提早行动似乎是明智的。然而，这个结论在一定程度上取决于所用的贴现率。报告明智地指出，从本质上讲，我们这一代的幸福没有理由比我们后代的幸福更重要。贴现率较高的唯一一个其它原因，是较高的经济增长率。然而，如果气候变化令经济增长大幅放缓（似乎有这种可能），那就应该采用较低的贴现率。如果这样，提早行动的理由就更加充分了。
我们需要做什么？答案之一，就是学会适应，部分原因是温室气体已在大气中，气候肯定会进一步变暖。然而，采取治理措施也很重要。幸运的是，人们已经研发出很多能够降低单位产出温室气体排放量的技术。报告也指出，在这方面，还没有一个权威的解决方案。我们需要把多种技术结合起来，包括：提高能效；碳捕捉及封存；核能；生物燃料的使用；以及适用于家庭取暖的热电联产(CHP)。同样重要的是植树造林。
如何促使人们采取这些措施呢？广义的答案是，将温室气体排放权定价、新技术投资和能效监管结合起来。
这就引出了一个最大的问题：面对这个有史以来最严重的“市场失灵”，面对这个前所未有的、对人类大规模持久合作能力的挑战，人类将如何应对？观点和利益存在巨大分歧的世界各国有可能联合起来，应对气候变化带来的挑战吗？
迄今，对这个问题的回答一直是响亮的“不”。这份报告可能提出了一个提早行动的理由。但它很可能最终也是一次无用功。是否一定如此，我将在下周分析。
