He had barely started across Venezuela before he was alerted by the falling water level in the idyllic lake of Valencia. This, he came to realize, was caused not only by the siphoning of streams for irrigation but also by the felling of the surrounding forests.
Humboldt, Wulf writes, “was the first to explain the fundamental functions of the forest for the ecosystem and climate: the trees’ ability to store water and to enrich the atmosphere with moisture, their protection of the soil, and their cooling effect. He also talked about the impact of trees on the climate through their release of oxygen. The effects of the human species’ intervention were already ‘incalculable,’ Humboldt insisted, and could become catastrophic if they continued to disturb the world so ‘brutally.’ ”