Simon Lewis: The Anthropocene

We live in epoch making times. I mean this literally, rather than as a tool to dramatise our seemingly perpetual global economic crisis or latest political scandal. Long spans of time are described by geologists as eons, eras, periods, and epochs. An epoch therefore describes a unit of geological time. The end of the last glaciation, some 11,000 years ago, saw the transition from the cool Pleistocene to the warmer Holocene. This relatively stable epoch saw humans turn to agriculture and our population rise considerably. Now geologists, ecologists and climate scientists, myself included, are stating that we have entered a new and much less stable geological epoch: the Anthropocene.

Just as changes to the Earth’s orbit, volcanic eruptions and asteroid impacts in the distant past have set the world on radically new courses, humanity itself has now become a collective force of nature.

The evidence is all around us. Human activity has put carbon dioxide into the atmosphere altering the climate globally. To put this in context, human activity is adding carbon dioxide to the atmosphere at a rate faster than at any time within the past 66 million years.

Extinction rates are at least 100 times higher than background rates, as we edge towards the sixth mass extinction in Earth’s history. Previous extinctions, such as that which wiped out the dinosaurs 66 million years ago, are joined by a human-induced loss of life.

These is little debate amongst scientists that the actions of humans today are altering the planet in ways that rival important events in Earth’s 4.6 billion history. But formally a geological definition of the Anthropocene requires a beginning. This is contentious. So, one strand of my research asks, when did the Anthropocene begin? This requires locating a long-term, preferably near permanent change to the Earth, and a marker of such a change in geological deposits.

Mark Maslin (Professor of Physical Geography, at UCL) and I have recently proposed a clear start date and formal definition of the Anthropocene.

We argue that the Anthropocene began with the irreversible exchange of species between the New and Old Worlds following the 1492 arrival of Europeans in the Americas. The resulting global networks of trade led to a rapid, repeated, cross-ocean exchange of species, which is without precedent in Earth’s history. It provides an unambiguous event after which the impacts of human activity became global and set Earth on a new environmental and evolutionary trajectory. These evolutionary impacts are one of the few irreversible human impacts likely to be measureable millions of years into the future, the usual duration of an Epoch.

A formal beginning, a boundary maker or ‘golden spike’ in geology-speak, is the clear drop in atmospheric carbon dioxide, centred on 1610, due to the arrival of Europeans in the Americas. This arrival led to the deaths of about 50 million indigenous people, most within the sixteenth century due to disease. The resulting near-cessation of farming across the continent and the re-growth of forests removed enough carbon dioxide from the atmosphere to produce a pronounced dip in carbon dioxide seen in Antarctic ice core records. The temporary sharp decline in carbon dioxide fits the formal geological requirement of a dated global environmental change that is captured and preserved in a natural material. The resulting temporary global cooling marks the last globally cool moment before the long-term warmth of the Anthropocene.

This time-period also marks the emergence of the modern world, and a new social system, a capitalist world-economy, with far-reaching global environmental impacts including those of today. Our research suggests that a 1610 CE date provides both a geologically and historically coherent definition of the Anthropocene.