经济学人下载:气候变化影响农作物产量

But there are caveats. For example, the analysis does not track changes over time in the areas being farmed, using instead a crop map from around 2000. And many agronomists hold that relying on year-to-year yield changes for modelling exaggerates the damage due to longer climate shifts. Farmers will tend to adapt. That said, subtler effects of climate change such as more sudden rains and particularly hot days with disproportionate effects on yield are left out, which might mean the study underestimates the effects.

但是需要做一些说明。例如，这一分析没有追踪现已被耕种地区的产量随时间的变化，反而使用的是2000年前后的作物分布图。很多农学家认为，依靠逐年同比的产量变化建模，夸大了较长时间气候变化引起的损害。那样农民将会适应。这说明，诸如较为突然地降雨等气候变化的较微弱的影响，和特别热的天气对产量的很大的影响被忽视，这可能意味着研究低估了影响。

Some people will be surprised, even dismayed, that comparatively modest climate changes are already doing measurable damage. But in context, it is quite small. Yields have been going up around the world despite the warming climate—and over 29 years those increases swamp the estimated global reductions due to climate. The sort of loss that climate change inflicts in a decade is often the sort of gain that better farming brings in a year. What is more, for wheat the increasing level of carbon dioxide that is changing the climate also makes photosynthesis easier, which should have increased yields enough to wipe out perhaps half of the climate-related loss (maize, which photosynthesises in a different way, is thus the bigger loser of the two in net terms).

有些人将感到吃惊甚至惊愕，因为不太大的气候变化已经造成了重大的损害。但是在上文中，这种损害相当小。尽管气候变暖，但世界各地的农作物产量一直在增加——而且29年来的这种增产超过了估计的由于气候变化造成的全球减产。十年里气候变化造成的减产，经常与一年里由于耕种技术改进带来的增产相等。而且，对小麦来讲，一直影响气候的CO2的含量增加也使光合作用更为容易，这将使产量增加到足以抵消大约一半的与气候有关的损失（玉米的光合作用方式不同，因此按净额计算受损较大）。

Then there is a point made by Richard Tol of VU University Amsterdam: farm yields show the worst of the situation. Easily achievable improvements in roads, markets and other things can increase the availability of food a lot even if farm yields stop rising. And people can adapt, at least to lowish levels of change; indeed the study provides evidence to help them do so as it shows which crops in a given country are the most affected by global warming. So Malthus looks beatable even when he sits astride the apocalyptic horse of climate change.

接着阿姆斯特丹自由大学的理查德．套耳指出一个要点：农作产量指示着最坏的情形。即使农作物产量停止增长，在公路、市场和其它方面容易取得改进能够使食物的有效利用大大增加。而且人们至少能够适应相当小的变化；的确，当研究表明在一个被考察的国家里哪一种农作物受全球升温影响最大时，研究提供的证据有助于人们去适应。因此即使马尔萨斯骑在预示气候变化大灾难的高头大马上时，看起来他也被击败了。