Heated debate激烈的争论.doc

Heated debate激烈的争论The costs of climate change can be mitigated if economic activity moves in response如果经济活动能够相应调整的话，那么气候变暖的代价可能会有所降低。WHEN Superstorm Sandy roared ashore in late October and the lights of lower Manhattan went out, New Yorkers were given a stark vision of a possible future. Climate-change science is still a realm of great uncertainty but there is consensus that the planet is warming dangerously and that people are to blame. A recent report commissioned by the World Bank warned that the world is on track to have a global mean temperature that is 4C above pre-industrial levels by 2100. If so, sea levels could rise by between half a metre and a metre by the end of the century, threatening hundreds of millions of people in coastal cities. Other regions would face the threats of droughts, bigger storms and changing rainfall patterns. That entails not just human costs but economic ones, too.今年十月末，当超级风暴桑迪咆哮着登陆，曼哈顿下城一片乌黑时，纽约人就应该清楚地意识到他们未来出现这种情况的可能性。气候变化科学这个领域仍旧充满着很大的不确定性，但是至少有一个共识，那就是地球正在变暖，很危险，而这一切都是因为人类的原因。一份由世界银行委托进行的研究报告警告说，到2100年，世界平均温度将比工业化前上升4C，而现在全世界正在通往这个目的地的道路上前进着。如果真的这样，到本世纪末，海平面将会上升0.5米到1米，这对那些居住在海滨城市的人们来说是个巨大的威胁。而其它地区将会面临干旱，大风暴和降雨方式改变的威胁。这不仅让人类损失惨重，经济也会受到严重影响。The question that preoccupies Klaus Desmet of the Universidad Carlos III in Madrid and Esteban Rossi-Hansberg of Princeton University in a new NBER working paper* is whether there are ways to manage the impact of changing weather patterns by moving the location of economic activity. They note that roughly 90% of global production uses just 10% of available land. If that 10% is threatened, activity may at least theoretically shift to bits of the 90% made more hospitable by climate change.是否有什么方式可以通过改变经济活动的位置，来管理天气模式改变产生的影响呢？马德里卡洛斯三世大学的克劳斯-德斯米特，和普林斯顿大学的埃斯特班-罗西-汉斯伯格，在一份新的国家经济研究局工作报告中也详细分析了这个问题。他们在报告中写道，全球近90%的生产是在可用土地的10%上完成的。如果这10%的土地受到了威胁，从理论上来说，经济活动至少可以转移到由于天气变化而更适宜生产的另外90%的土地上。Messrs Desmet and Rossi-Hansberg build a model economy, and then batter it with different temperature increases to see how it reacts. In their benchmark analysis, they allow people to move around as they like in response to these changes. In extreme scenarios freedom of movement doesnt make much difference: temperatures reduce global agricultural productivity to near zero, “implying the end of human life on Earth”. But in more moderate scenarios, rising global temperatures improve agricultural productivity in northerly climes. Welfare losses are small because there are big movements of people northward. A relatively small temperature increase (by the models standards), of 2C at the Equator rising to 6C at the North Pole, causes a shift in the average locations of agricultural and manufacturing activity of about ten degrees of latitude by the end of this centuryroughly the distance between Dallas and Chicago, or Frankfurt and Oslo.德斯米特先生和罗西-汉斯伯格建立了一个经济模式，然后将温度升高到不同高度对它进行打击，以观察模式的反应。在他们进行基准分析时，他们允许人们，如果喜欢这些变化可以四处走动。在极端情况下即温度让全球农业生产率接近于零时，这时候也“意味着地球上人类生命的终结”，所以移动并没有产生太大的变化。但是在较为适中的情况下，全球温度的上升提高了北方气候条件下的农业生产率。因为大规模的北上迁移，所以经济繁荣的情况只受到了些许的影响。相对较小温度的增加（按照模式标准），比如赤道温度上升2C，北极上升6C，那么到本世纪末，就会引起北纬10C附近地区大约位于达拉斯和芝加哥之间，或者是法兰克福和奥斯陆之间的区域-农业和制造业活动的平均位置的变化。Restrictions on movement dramatically increase welfare costs, however. The authors modify the model by introducing a rigid border at the 45th parallel, which runs through the northern United States and across southern Europe, with roughly 1 billion people living above the line and 6 billion below. The model finds that rising temperatures actually benefit the northern section of the globe. Agricultural productivity grows and northern manufacturers enjoy more trade with the throngs that mass just south of the border. Welfare in the south falls, by contrast, by about 5% on average relative to the no-warming case. The model is simplistic, of course, but it suggests that limits on migration have a big effect on the costs of global warming.然而，对活动的限制却极大地增加了社会福利的成本。试验者通过在北纬45C限定了一条严格的边界线贯穿美国北部，横穿欧洲南部，那里大约有10亿人在这条边界线的北方，而有60亿人在南方-调整了经济模式。通过这个模式，发现温度上升让北半球地区受益不小。不仅农业生产率提高上，而且北方的制造商们与那些聚集在南方边界地区人们的贸易往来也更加繁荣。相比于气候没有变暖的时候，南方的经济增长平均下降了5%。当然，这个模式很简单，但是它显示，限制移民对全球变暖成本有很大的影响。Unfettered migration is obviously a lot more likely within countries. But even then, wouldnt it matter if people left a really productive place for somewhere less dynamic? Real output per person in the New York area is some 70% higher than in Buffalo, for instance; a New Yorker fleeing upstate may suffer a large income loss. Matthew Kahn of the University of California, Los Angeles, reckons that this, too, is manageable. In his book “Climatopolis”, Mr Kahn points out that the productivity of rich places often has little to do with unique geographical advantages. Instead, cities profit as magnets for skilled workers attracted by other skilled workers. New Yorks financial wealth stems not from its port but from its brimming community of firms and workers.很显然，国家内部无限制的移民更容易。但是即使那时，如果人们离开一个真正适合生产力发展的地方，而去一个欠缺活力的地方也没有问题吗？纽约地区的实际人均产出比布法罗高出了70%，打个比方说，一名逃离纽约北部的人可能会遭受到很大的收入损失。洛杉矶加州大学的马修-肯认为，这也是可以解决的。在他的“气候城邦”一书中，他指出，那些发达地区的生产率与该地区独特的地球优势几乎没什么关系。相反，城市效应对技术工人来说就像磁铁一样充满吸引力，而这又吸引了其它地区的技术工人。纽约的金融财富并不是来自于它的港口，而是来自于充满企业和工人的社区。Mr Kahn argues that as the climate warms, vulnerable areas like lower Manhattan will become less desirable relative to rival centres: midtown Manhattan, New Yorks suburbs, or Chicago. Rational workers and firms should assess the risk of floods or the like and migrate, raising the productivity of the destination locations as they arrive. The move wouldnt be costless. Investors in lower Manhattan property would suffer large losses, for example. Yet Mr Kahn says there could also be gains, as activity shifts from cities with an out-of-date capital stock (like New Yorks ageing i