经济学人下载:气候变化影响农作物产量

David Lobell and Justin Costa-Roberts, of Stanford University, and Wolfram Schlenker, of Columbia University, first put together temperature and precipitation figures for the parts of the world where four staple crops—wheat, maize, rice and soya—are grown. Those four crops, between them, account for about 75% of the calories people end up eating, although a lot of the soya is fed to animals first.

斯坦福大学的戴维德．罗拜耳、扎斯汀．考斯特-罗伯特和加利福尼亚大学的沃尔夫然姆．史灵克，首次将世界上以小麦、玉米、稻子和大豆作为主要农作物的部分地区的气温和降水量结合在一起。他们共同研究发现，尽管很多大豆首先被用来喂牲畜，但人们最终所吃的热量有75%是这四种作物提供的。

It turns out that during the seasons in which crops grow, these arable areas had on average become significantly warmer in the 29 years after 1979. Some bits of Europe that grow wheat, for example, have heated up by a couple of degrees since 1980. The researchers then assembled models of how the yields changed from year to year, and against the longer trend, to find changes linked to temperature and rainfall that are independent of improvements through better farming. Finally they compared today’s yields with what their models say yields would have been with today’s farming but in the 1980’s climate.

研究发现，从1979年以后的29年里，在农作物的生长季节，这些可耕作面积的气温普遍越来越暖。例如，自1980年起，一些种植小麦的欧洲地区气温上升了两度。为了发现与气温和降水有关的产量变化，并且是不依赖于农耕方法的改进引起的变化，研究人员接着建立了产量逐年同比变化的模型，并与更长的趋势相对照。模型显示，产量变化除了1980年与气候变化有关外，可能与现在的耕作方法有关。最后，他们将现在的产量与模型显示的产量相对照。

Popping corn
夸大得象爆玉米花

For both wheat and maize, the results, published this week by Science, were negative. Globally, wheat yields are down 5.5% compared with what they would have been with no climate change, and maize yields are down 3.8%. For soya, some places saw improvements, some saw damage, with no real net effect on the global scale. For rice, warming brought a clear benefit for crops at higher latitudes and some losses in warmer places. Temperature played a bigger role than precipitation. The results seem to fit with previous studies into such effects in individual countries.

研究发表在本周的《科学》杂志上，对小麦和玉米来说，结果是否定的。在全球范围内，与没有气候变化的条件下相比较，小麦产量下降5.5%，玉米产量下降3.8%。大豆则某些地方增产，某些地方减产，没有真正相同的全球范围的影响。对稻子来说，气温变化对较高维度地区明显有益，而对较温和的某些地区则有损害。气温比降水造成的影响更大。这一结果似乎符合以前做过的关于在单个国家里这种影响的研究。