We have never understood it. Take one square meter of soil and make it bare like this is down here,  我们从来都没有搞清楚过。像这样一平方米的土壤表面像下面这样程度的裸露着，

　　and I promise you, you will find it much colder at dawn and much hotter at midday than that same piece of ground if it's just covered with litter, plant litter.  我敢说，它会比被植被覆盖的地方，同样的大的地方，黎明的时候会冷得多，中午时会热得多。

　　You have changed the microclimate.  你已经改变了这个地方的微气候。

　　Now, by the time you are doing that and increasing greatly the percentage of bare ground on more than half the world's land, you are changing macroclimate.  现在，就像你刚才做的那样，如果世界上裸露的土地的面积快速的增长到超过了世界土地一半以上的面积，大气候就被我们改变了。

　　But we have just simply not understood why was it beginning to happen 10,000 years ago?  但是我们还是无法理解为什么这个过程一万年前就开始了？

　　Why has it accelerated lately? We had no understanding of that. 又为什么最近加快了？我们对此无法理解。

　　What we had failed to understand was that these seasonal humidity environments of the world,  我们过去不了解的是，世界上这些季节性雨水充沛的环境中，

　　the soil and the vegetation developed with very large numbers of grazing animals,  伴随着植被的蓬勃生长，

　　and that these grazing animals developed with ferocious pack-hunting predators.  数量可观的游牧食草动物也随之而来，而这些游牧的动物又引来了凶猛的猎食者。

　　Now, the main defense against pack-hunting predators is to get into herds,  游牧动物防御捕食者的主要方法是群居生活，

　　and the larger the herd, the safer the individuals.  兽群越大，个体就越安全。

　　Now, large herds dung and urinate all over their own food,  大量的兽群在自己的食物上大小便，

　　and they have to keep moving, and it was that movement that prevented the overgrazing of plants,  而它们又必须不断的迁移，这些迁移过程防止了过渡放牧的现象，

　　while the periodic trampling ensured good cover of the soil, as we see where a herd has passed. 同时定期的踩踏土壤，正如这群动物路过时发生的那样，确保了土壤表面得到了很好的覆盖。