Jan 8, 2016 by

For over a decade, both climate activists and scientists have used one word to describe the mass-level changes humans are causing on Earth: Anthropocene. But whether or not this word actually describes a real, measurable geologic time period has been the source of major scientific debate.

Now, a new study is adding fuel to that debate, finding that human influence on the environment changed the planet so dramatically that the world recently moved into a new geological epoch. In other words, there’s scientific proof that we’re living in the Anthropocene, the study’s researchers say.

In the study, published Thursday in the journal Science, the international Anthropocene Working Group states that the man-made Anthropocene epoch is distinct and likely starts in the mid 20th century, as human influence on the planet increased dramatically when the nuclear age began.

“The paper that has just been released … is in effect saying we also think we know what level of hierarchy this [Anthropocene] unit is. We think it’s an epoch level,” said Colin Waters, co-author and secretary of the working group, in an interview with ThinkProgress. “The reason for that is the scale of the changes being every bit, if not greater than, the changes that happened in the beginning of the Holocene.”

Humanity is formally living in the Holocene Epoch, and has being doing so for about 11,700 years. In the past, geologists have divided Earth’s time based on continental movement, or major shifts in climate and fossil evolution. Evidence for these changes have to be measurable around the world at a similar scale, and that’s been proven traditionally through rock, sediments or ice records.

Waters and other authors of the study — which gathered data from multiple other studies — said the amount of data available identifies various so-called signatures that can be found worldwide in a similar time and scale. This makes the case for the Anthropocene and its proposed starting date compelling, some authors said.

“It’s the things like the novel materials we’ve seen in the last 60 years,” said Waters, a principal geologist at the British Geological Survey. “It’s the way that the atmospheric geochemistry, the CO2 and the methane (have) changed dramatically in the last 60 years. It’s the general contamination from nitrates and phosphates, heavy metals, all the things that we looked at seem to show a very dramatic change in the mid 20th century.”

Graph based on data from the U.S. Geological Survey.

Graph based on data from the U.S. Geological Survey.

CREDIT: Dylan Petrohilos

These signatures, according to the report, are a product of accelerated technological development, rapid growth of the human population, and increased consumption of resources. All these brought an unprecedented increase in use of metals, minerals, fossil fuels, and fertilizers, as well as a transformation of land and sea.

“The way we view the concept isn’t about the presence of humans, or isn’t about the mere presence of human legacy on the landscape,” said Alexander Wolfe, co-author and adjunct professor of the Paleobiology Department of Biological Sciences at the University of Alberta. “[It’s] about humans actually beginning to control wholesale the physics, the chemistry and the biology of the planetary whole.”

Humans have collectively affected the Earth’s dynamics so the physical, chemical and biological conditions of the environment is inherently less stable, and different in the Anthropocene when compared with the Holocene, Wolfe said. Even the movement of man-made concrete is comparable to the movement of tectonic plates in the past, he said.

Although scientists say humans have dramatically influenced the planet, not all geologists feel the Anthropocene group has built a case with this new study — or with the ones they’ve published in the past.

“I think most geologists would immediately agree that the impact of humans has been very important in the environment, and it’s increasingly of importance. So there’s no doubt about that,” said Philip Gibbard, a geologist from the University of Cambridge who read the article and is familiar with the group’s research. “But where we as a geological community are concerned is, you know, is it necessary to create a formal division of geological time in order to in a way reflect that.”

Gibbard, leading Paleoclimatologist William Ruddiman, and many others say that trying to place the beginning of the Anthropocene so close to the present is questionable, even if the basis is the dramatic increase of human activity of the 20th century.

“Many of those activities are not likely to be preserved in the geological record,” said Gibbard. “And also we have to say to what extent are those things going to be anything more in the future than just a sort of blip.”

And then there’s the idea that humans started changing the planet via deforestation, agriculture, and other activities thousands of years ago.

“Humans have been actually interfering with their natural environment — and it’s a perfectly normal thing to be doing by the way — since about 14,000 years ago or more in some cases,” said Gibbard.

Jan Zalasiewicz, a co-author of the study and paleobiologist at the University of Leicester, said the roots of the Anthropocene may reside nearly 14,000 years in the past. But he noted in an interview that agriculture, deforestation and other man-made environmental changes “took place over a long period of time, and occur at different times across the world.”

The Anthropocene Working Group’s study provides a case for including the Anthropocene as an epoch, but it’s still unknown whether it will officially become one. Right now, Anthropocene is not an official unit within the rigorous geological time scale that virtually all science follows. Including it would require screenings and a final decision falls on a scientific governing body called the International Commission on Stratigraphy. The process is long and meant to be tedious (the Holocene was accepted after decades of debate). The scientific community could begin the formal process of evaluation later this year.

If the Anthropocene became an official epoch, it would be groundbreaking not just for its relevance in society, but because up until now all geological epochs have been recorded thousands or even millions of years after they happened. The Anthropocene as a geological epoch could also be an inspiring symbol and further proof of scientific consensus around climate change, and would codify a term widely used in the climate change community.

The case for the Anthropocene is largely based on identifying the so-called golden spike — a fixed way to measure a change from Holocene to Anthropocene. Some authors reached by ThinkProgress said the detonation of the first atomic bomb in 1945 and the worldwide measurable radiation that followed and persists in the environment is a good benchmark for the beginning of the epoch.

Waters, like Wolfe and Zalasiewics, said that there are also many other signatures around the 1950s that are good candidates to establish a boundary dividing the Holocene and the Anthropocene.

“It could be the sudden presence of plastic appearing in your sediments. It could be the first appearance of pulverized fuel ash from big thermal power stations. It can be fall out from nuclear detonations,” said Waters. “All of these things sort of happened around the mid 20th century.”

And yet even some authors and members of the 36-person Anthropocene Working Group are unconvinced that the 1950s provide the evidence to mark a change in epoch. This shows the divergent opinions that exist and previews the uphill battle that the concept has to withstand as it goes through the long and formal process of scientific evaluation. It resembles, too, albeit in a much more grounded way, how divisive climate change can be within disciplines and experts that otherwise agree on humanity’s dangerous influence on the environment.

“The evidence that the Earth has been transformed profoundly and permanently by humans is incontrovertible. I think almost everybody agrees on this,” said co-author Erle Ellis, an environmental scientist at the University of Maryland, Baltimore County. “But the question of exactly when did this happen, why this happen, how this happen, isn’t so settled.”

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