This week in Science, a short commentary by William Ruddiman and colleagues challenges the idea that scientists should recognize an Anthropocene epoch as having begun in the postwar era. They argue that this date does not recognize the massive human alterations to biomes that began well before the development of agriculture and accelerated during the Holocene:
Selecting 1945 as the start of the “Anthropocene” would implicitly omit these extensive agricultural and early-industrial alterations. Does it really make sense to define the start of a human-dominated era millennia after most forests in arable regions had been cut for agriculture, most rice paddies had been irrigated, and CO2 and CH4 concentrations had been rising because of agricultural and industrial emissions? And does it make sense to choose a time almost a century after most of Earth's prairie and steppe grasslands had been plowed and planted? Together, forest cutting and grassland conversion are by far the two largest spatial transformations of Earth's surface in human history. From this viewpoint, the “stratigraphically optimal” choice of 1945 as the start of the Anthropocene does not qualify as “environmentally optimal.”
Those who favor defining an “Anthropocene” epoch want us to recognize that industrialization caused global effects, for example, chemical changes to soil composition, changes in the proportions of atmospheric components, introduction of radioisotopes to the biosphere, massive replacement of tropical forest by monocultures, construction of massive dams, and a great acceleration in the rate of extinction of species worldwide. But many of these processes began much earlier in time, at or before the dawn of agriculture. Moreover, many of the processes important in the early industrial era actually began to reverse after 1945. For example, many long-dammed rivers have been freed during the last seven decades, while a vast area of North America once cleared for farming has now become secondary forest. And even the postwar era has not been static: Radioisotopes spiked during the heyday of atmospheric atomic testing, but have markedly declined since then.
Ruddiman and colleagues extend this argument and point to a deep problem with the Anthropocene concept: It cannot be distinguished from the Holocene. The processes that humans have deployed within the last seventy years have, at some scale, defined all of human history.
The Anthropocene concept is mostly about politics, and not at all about geology. It does raise an important question for academic geology, and a timely one: To what extent can the major transitions in Earth’s history be described by discrete causes? With the Holocene and Anthropocene, we are talking about differentiating causal effects that have unfolded across a mere 10,000 years. Probably in no other case in Earth’s history can we hope to attain such temporal resolution on the processes that led to faunal turnover and broad-scale biotic change. Even with the Cretaceous-Tertiary boundary, where the hypothesis of an impact-mediated extinction is very well supported, the overall pattern of extinction and biotic turnover may have taken longer than the Holocene.
Ruddiman and colleagues suggest a solution:
Despite differing views, the term “Anthropocene” is clearly here to stay. One way forward would be to use the term informally (with a small “a”). This approach would allow for modifiers appropriate to the specific interval under discussion, such as early agricultural or industrial. In this way, we could avoid the confinement imposed by a single formal designation, yet acknowledge the long and rich history of humanity's environmental transformations of this planet, both for better and for worse.
In other words, allow the Anthropocene concept to shape academic discussion, without letting it into the textbooks as a formal equivalent of Holocene. This lets us recognize the ways that human activity have come to shape the planet, and likewise recognizes that no single inflection point can suitably distinguish human from natural effects.
I haven’t entirely decided what I think about the Anthropocene concept. So far, most of the Anthropocene boosters have seemed to be mostly concerned with public relations, not building new scientific insights. They have largely ignored the capabilities of early farmers, not to mention things like the intentional management of grassland ecosystems with fire by ancient Australians and New World peoples. We have been shaping Earth to our will for many thousands of years, which should be obvious to anybody familiar with archaeology. The geologists proposing the Anthropocene concept have seemed oblivious to this record.
I do like that the Anthropocene concept recognizes that feedback from biotic processes (including human activity) may have caused major transitions in Earth’s history. It would be interesting to examine how much the Holocene resulted from human activity—for example, in contrast to earlier Pleistocene interglacials. I would like to see this aspect of the science grow.
Ruddiman WF, Ellis EC, Kaplan JO, Fuller DQ. 2015. Defining the epoch we live in. Science 348:38-39. doi:10.1126/science.aaa7297