According to Will Steffen, Adjunct Professor at the Fenner School of Environment and Society at Australian National University, the evidence is now abundantly clear: “[Human] activities now rival – or in some cases exceed – the great forces of nature that have shaped the evolution of Earth’s environment over its 4.6 billion year existence”.
Professor Steffen is a member of the Anthropocene Working Group, a global research team trying to persuade the International Commission on Stratigraphy (ICS) to formally recognise that humans have tipped the planet across a new geological threshold. The ICS is like a world body of geological timekeepers who keep track of the chronological changes in the geology, climate and overall environment of planet Earth. The working group would like the ICS to acknowledge that the planet has ticked over from the current geological epoch, the Holocene, to a new one: the “Anthropocene” (a name derived from the ancient Greek words for “man” and “change”). The group has set itself a goal of generating an Anthropocene proposal for the ICS by the end of this year.
If you’d like to get a better idea of what an epoch is, or why it matters, you can check out my previous post, Holocene or Anthropocene? What’s the big deal?. As for the Holocene, it’s basically been around for the last 11,700 years and makes up an interglacial phase of the current ice age – a period of stable, warm climate in between the advances of continental ice sheets (known as glacial periods). This warm, stable Holocene climate has been very accommodating to humans all over the globe.
What Professor Steffen and his colleagues in the working group are arguing is that the conditions and markers that have characterised the Holocene period have largely been overridden by man-made changes. In a study led by Dr Colin Waters of the British Geological Survey published in the journal Science earlier this month, Steffen and colleagues compiled overwhelming evidence to support their case.
“The human signature is pervasive around the planet, but, according to the stratigraphers, some of the most prominent human markers will be radionuclides, plastics, new forms of metal like aluminium (which occurs in nature in its oxidised form) and spheroidal carbon particles (fly ash) from burning fossil fuels. These markers are being formed in both ocean and land sediments and will likely be around for millions of years,” Steffen explained.
“Humans have also very significantly changed the land cover of the planet, leaving records such as techno-fossils (tools) and real fossils (domesticated animals) as well as pollen records that show the change in vegetation due to human activities.”
The study shows several drastic environmental changes were caused by humans. Observable man-made increases in atmospheric carbon dioxide levels have changed patterns of carbon isotopes. Chemicals released into the environment by humans – such as nitrogen from fertiliser, phosphorus, or artificial radionuclides released by atom bomb explosions – have greatly perturbed the geochemical cycles. Human-synthesised materials like plastic will take thousands, maybe millions, of years to decompose. We are, quite possibly, causing the sixth mass extinction of the world while simultaneously homogenising life and directing its evolution through artificial selection. Further to this, and perhaps most significant, the sheer amount of change is comparable to that which has been prescribed to the transition of other epochs.
The research paper also puts a new start date to the Anthropocene. Initially, the Anthropocene’s proponents – such as Nobel Prize-winning atmospheric chemist Paul Crutzen, who coined the term – suggested the Industrial Revolution as the candidate for the beginning of the new epoch. According to Professor Steffen, the new data points it to the middle of last century.
“When we actually plotted the trajectory of the human enterprise and the trajectory of the Earth System from 1750 to the present, we didn’t see a smooth curve beginning from the Industrial Revolution but rather a very striking acceleration from the mid-20th century,” he said.
“Furthermore, for the Earth System parameters, we can only show conclusively that the Earth System has been pushed out of its Holocene envelope of variability after the mid-20th century.”
As with many things in science, the Anthropocene does have its critics, though. Professor Steffen explained that one major criticism related to the fact the new epoch was being proposed in ‘real time’; in other words, it has unfolded, quite literally, in the lifetimes of people alive today.
“Geologists have traditionally looked backward in time – in the strata that have been formed thousands, millions and billions of years ago, not in strata that are forming now,” he elaborated.
A related problem, according to Professor Steffen, is that some geologists simply can’t accept that one species, homo sapiens, can affect so much geological change.
“It is indeed unprecedented to see one species change the structure and functioning of the Earth System in such a short period of time,” he said. “One could argue that cyanobacteria engineered a major change in the Earth System when their metabolism changed the Earth’s atmosphere to an oxidising state (the so-called “Great Oxidation“), but this took hundreds of millions of years and was no doubt a very, very slow process compared to what is happening now.
“(However), this is almost an ideological or worldview problem because it ignores the massive amount of evidence that supports the Anthropocene concept.”
There are even controversies within those who share agreement over the existence of the Anthropocene, regarding the epoch’s starting date. Professor Steffen believed these differences in opinion somewhat aligned with the different scientific disciplines from which they came.
“Those who study human activity in the past (e.g. archaeologists) might favour earlier proposed start dates,” he explained. “I think there is a strong and growing consensus for the mid-20th century start date because it is supported by a massive amount of evidence and, by far, is the clearest candidate in terms of a demonstrable change of state of the Earth System.”
At any rate, no matter whether or not the ICS and the scientific community writ large formally adopts the Anthropocene, the implications of the data presented in the working group’s study are palpable. The environmental system within which humanity has been able to prosper and achieve unprecedented growth, during the Holocene, has been altered in a big way. For Professor Steffen, the sentiment behind the Anthropocene is that it is a planetary wake-up call. We are, in his words, “sailing into planetary terra incognita”.
“If we now look at the Anthropocene from a human-centric rather than a geological perspective, it could be (and often is) viewed as a very big challenge, if not a crisis, for human societies,” he said. “There is a very good reason for that. Agriculture, villages and cities, and the complex societies we live in today all developed during the relatively stable environment of the Holocene. The Anthropocene means that we are rapidly and decisively leaving the stability domain of the Holocene, and moving into a very different, rapidly changing state of the Earth System – the end point of this transition is not yet known.
“But there are serious, well-ground concerns that our societies of today may not be able to thrive in the rapidly changing world of the Anthropocene.”