The Earth has entered a new age-the Anthropocene-in which humans are the most powerful influence on global ecology. The accelerating pace of energy use, greenhouse gas emissions, and population growth has thrust the planet into a massive uncontrolled experiment. The Great Acceleration explains its causes and consequences, highlighting the role of energy systems, climate change, urbanization, and environmentalism. Human dependence on fossil fuels inaugurated the Anthropocene. Before 1700, people used little in the way of fossil fuels, but over the next two hundred years coal became the most important energy source, and by 1900 coal and oil accounted for seventy-five percent of energy use. This allowed far more economic activity and a higher standard of living, but it also created far more ecological disruption. Three-quarters of the carbon dioxide humans have contributed to the atmosphere has accumulated since World War II ended, and the number of people on Earth has nearly tripled. So far, humans have altered the planet's biogeochemical systems without consciously managing them.
If we try to control these systems through geoengineering, we will inaugurate another stage of the Anthropocene. Where it might lead, no one can say.
J. R. McNeill is University Professor in the Department of History and School of Foreign Service at Georgetown University. Peter Engelke is a Senior Fellow at the Strategic Foresight Initiative at the Atlantic Council in Washington, DC.