Alexander von Humboldt

Humboldt spent five years crossing Latin America with a barometer, climbing Chimborazo higher than anyone had recorded and measuring everything from ocean temperature to the blueness of the sky. Out of it came the idea that nature is a single connected web — and the first description of human-caused climate change, written in 1800 about deforestation around a Venezuelan lake.

He spent his fortune on publishing the results and died nearly poor. More species, places and features are named after him than after any other person.