经济学人下载:气候变化影响农作物产量

Moreover, there is a simple way more or less to abolish the effect of climate change on yield to date. According to William Cline of the Peterson Institute for International Economics in Washington, DC, at least 4% of the world’s grain is used to make ethanol for fuel. Most of this is doing little good for the environment, and stopping subsidies for such fuels would boost the supply of grain for feeding people on a scale similar to the hit that the past three decades of warming have provided.

此外，有一个简单的方法或多或少能够消除迄今为止气候变化对农作物产量的影响。根据皮特森国际经济研究所（位于华盛顿哥伦比亚特区）的威廉姆．克莱恩的研究，世界粮食至少4%被用于制造酒精燃料。这大部分对环境完全没有好的影响，而且停止对这种燃料的补贴将增加食用粮食的供应，增加的程度相当于过去三十年来气温升高造成的损失。

Still, in a world where more than a billion people are undernourished and the population is still growing, every little hurts. The net effects of climate and carbon dioxide, Dr Lobell and his colleagues calculate, is to make grain prices about 5% higher than they would otherwise be. Dr Lobell reckons that means about $50 billion a year. In some countries the effects are particularly large: climate change means Russian wheat yields are more than 10% down. As Mr Cline points out, growth in yields has slowed recently. And climate effects could speed up. Earlier work by Dr Schlenker has showed that plants have skewed preferences: they dislike temperatures beyond the optimum more than they dislike temperatures below the optimum, so increasing warmth can have worsening effects beyond a certain point.

尽管如此，在一个有十多亿人营养不足的世界里，而且人口一直在增加，每一点变化都是有害的。罗拜耳和其同事们计算，气候和二氧化碳的最终影响造成的损失，在粮食价格上比其它方面高出5%。罗拜耳计算，这意味着每年损失大约500亿美元。在有些国家影响特别大：气候变化造成俄罗斯的小麦减产超过10%。正如克莱恩指出的，增产最近变慢了。但是气候影响可能加速。史灵克做的早期研究表明，假象歪曲了参数选择：与不喜欢温度低于最佳点相比，他们更讨厌温度高于最佳点，因此升温可能使影响夸大超过了某一程度。

That might be keenly felt if patterns of warming shift. One of the reasons that the climate effects Dr Lobell and his colleagues have dug out of the data are not worse is that, although the planet as a whole has warmed up during the past 30 years, growing seasons in the parts of America which produce 40% of the world’s maize and soyabeans have failed to follow suit. No one is quite sure why this might be and no one knows if it will last. That climate change has not yet done very much harm may be cheering, but the past offers no firm guarantees for the future.

如果升温的模式发生变化，这种情况可能会被强烈地感觉到。罗拜耳和其同事们从这些数据中得出，气候变化不是更差的，原因之一是，尽管地球整体来讲在过去30年里气温升高，但是在美国的部分地区生长季节气温并没有升高，这些地区生产的小麦和大豆占世界产量的40%。没有人能完全确定这其中的原因，也没有人知道它是否将持续。气候和变化迄今为止还没有造成非常大的损害，这也许是件令人高兴的事，但是过去并不对未来提供可靠的保证。