Crutzen wrote up his idea in a short essay, “Geology of…

““Crutzen wrote up his idea in a short essay, “Geology of Mankind,” that ran in Nature. “It seems appropriate to assign the term ‘Anthropocene’ to the present, in many ways human-dominated, geological epoch,” he observed. Among the many geologic-scale changes people have effected, Crutzen cited the following: • Human activity has transformed between a third and a half of the land surface of the planet. • Most of the world’s major rivers have been dammed or diverted. • Fertilizer plants produce more nitrogen than is fixed naturally by all terrestrial ecosystems. • Fisheries remove more than a third of the primary production of the oceans’ coastal waters. • Humans use more than half of the world’s readily accessible fresh water runoff. Most significantly, Crutzen said, people have altered the composition of the atmosphere. Owing to a combination of fossil fuel combustion and deforestation, the concentration of carbon dioxide in the air has risen by forty percent over the last two centuries, while the concentration of methane, an even more potent greenhouse gas, has more than doubled. “Because of these anthropogenic emissions,” Crutzen wrote, the global climate is likely to “depart significantly from natural behavior for many millennia to come.””

— Elizabeth Kolbert