The Anthropocene began seventy years ago

In 2000 Paul Crutzen, the Dutch atmospheric chemist and Nobel prize-winner, and American ecologist

Eugene F Stoermer, proposed using the term ‘anthropocene’ for the current geological epoch to emphasize the central role of mankind in geology and ecology.

Fifteen years on, several of the papers that were presented at the four-day World Economic Forum in Davos, Switzerland, last week referred to the advent of the Anthropocene era, though it is doubtful if many of the 2,500 attendees paid much attention.

Geological Epochs

So what is a geological epoch, when did the Anthropocene epoch start, and how is the Anthropocene relevant to us?

You will know about the Jurassic period when dinosaurs roamed the earth*. But do you know some of the other periods of geological time: the Cambrian, the Devonian, the Carboniferous, the Triassic, the Cretaceous? The Cambrian period started about 540 million years ago, and the Cretaceous period ended 66 million years ago. This enormous length of time is only 10% of the age of the Earth, which is 4.6 million years old.

(*The dinosaurs actually first appeared in the Triassic period, 231.4 million years ago, and were the dominant terrestrial vertebrates for 135 million years, from the beginning of the Jurassic period until the end of the Cretaceous, 66 million years ago.)

The last 66 million years is also made up of geologic periods: the Paleogene, the Neogene and the Quaternary, and to make it more complicated, the Quaternary period is made up of two epochs, the Pleistocene (2.6 million years ago to 11,700 years ago) and the Holocene (11,700 years ago to the present day). Even though human beings first appeared between 400,000 and 250,000 years ago, the Holocene, the start of which is marked by the end of the last major ice age, encompasses the rise of modern humans, all human written history, the development of major civilizations, and the relatively recent transition toward urban living. The word Holocene means ‘entirely recent’ and comes from the Greek holos, meaning ‘whole’ or ‘entire’, and –cene meaning ‘new’.

The Anthropocene Epoch

But for some time, geologists, climate scientists and ecologists have been debating whether the profound effect that the human species is having on the Earth means that we are moving from the Holocene to a new epoch, the Anthropocene (pronounced an-thropo-scene). The first use of a similar term however goes back to 1873 when the Italian geologist Antonio Stoppani  acknowledged the increasing power and effect of humanity on the Earth’s systems and referred to an ‘anthropozoic era’. Incidentally Eugene Stoermer originally coined the term in the 1980s, but never formalised it until Paul Crutzen, who had started using the term, contacted him. The name Anthropocene is a combination of the Greek roots anthropo- meaning ‘human’ and -cene meaning ‘new’.

Geologic epochs primarily refers to geologic time based on boundaries between different rock strata differentiated by fossils, which is the science of stratigraphy, and any decision on recognising the Anthropocene epoch, which is still an informal term, lies with the International Commission on Stratigraphy (ISC). The ISC set up an international Anthropocene Working Group of scientists which was ‘tasked with developing a proposal for the formal ratification of the Anthropocene as an official unit amending the Geological Time Scale’. The working group, which first met in Berlin last year, has given itself until 2016 to come up with the proposal to submit to the ISC, but this month they put forward their initial view.

The Beginning of the Athropocene

The working group has proposed that if there were to be a single date to mark its beginning of the Anthropocene epoch, it would be 16 July 1945, the date that the first atomic-bomb test took place at the US Army testing range at Alamogordo in New Mexico, as the subsequent nuclear tests left an indelible mark around the Earth due to the release of radioactive isotopes or ‘fallout’ which settled in the soil and land around the world. This event also coincided with a worldwide ‘great acceleration’ of other human activities that ushered in a new geological epoch.

However a significant minority of the working group supported alternative dates, and the group plans to bring forward a formal, evidence based, proposal in 2016. Scientists have argued for a number of different dates that mark the start of this new human epoch. One date is the start of the industrial revolution in England in the 18th century when coal became the main source of fuel, production by hand changed to production by machine, new processes to produce iron were introduced, and the use of steam power increased dramatically. Earlier dates include the invention of agriculture and the clearing of forests about 10,000 years ago, and even further back to 14,000 to 15,000 years ago based on lithospheric evidence, the exposed top layers of the earth. These latter dates would be closely synchronous with the current epoch, the Holocene.

Extinction Events

There have been at least five previous ‘global events’ in the geological record that mark the transition from one geological era to another and which resulted in the mass extinction of species. The Earth’s most severe event was the Permian-Triassic extinction event that occurred approximately 251 million years ago and about 90 % of all marine species and 70% of terrestrial vertebrate species became extinct. Many theories have been presented for the cause of the extinction such as the Earth being hit by an asteroid, a supernova producing lethal gamma radiation, or extreme volcanism. The Cretaceous-Tertiary extinction event, which occurred about 66 million years ago, is possibly better known as the dinosaurs disappeared, along with possibly 76% of all plant and animal species. It is widely accepted that the cause of the extinction was the earth being hit by an asteroid from space, an impact event, which landed in the Yucatan peninsula in south-east Mexico, which you can read more about here.

The Mid-Twentieth Century Boundary

The chairman of the Anthropocene Working Group is Dr Jan Zalasiewicz, geologist at the University of Leicester. His colleague Mark Williams in the same department is also a member of the working group and they have written a succession of papers on aspects of the Anthropocene. Together with Paul Crutzen and the other 23 members of the working party, they have just published When did the Anthropocene begin? A mid-twentieth century boundary level is stratigraphically optimal in the January 2015 issue of Quaternary Journal, which puts forward the case for the ’16 July 1945′ date:

Of the three main levels suggested – an ‘early Anthropocene’ level some thousands of years ago; the beginning of the Industrial Revolution at 1800 CE; and the ‘Great Acceleration’ of the mid-twentieth century – current evidence suggests that the last of these has the most pronounced and globally synchronous signal. A boundary at this time … can be defined by a point in time of the human calendar. We propose an appropriate boundary level here to be the time of the world’s first nuclear bomb explosion, on July 16th 1945 at Alamogordo, New Mexico; additional bombs were detonated at the average rate of one every 9.6 days until 1988 with attendant worldwide fallout easily identifiable in the chemo-stratigraphic record.

The Great Acceleration of Human Activity

Another member of the Anthropocene Working Group is Professor Will Steffen of the International Geosphere-Biosphere Programme in Stockholm and co-author of one of the reports presented at Davos, The trajectory of the Anthropocene: The Great Acceleration which was published in the January 2015 issue of the journal Anthropocene Review. He said:

The start of the nuclear age also coincided with the post-war economic expansion around the world which led to what scientists have called the ‘great acceleration’ of human activity. It is difficult to overestimate the scale and speed of change. In a single lifetime humanity has become a planetary-scale geological force

The Consequences of the Great Acceleration

The Anthropocene however is not just a scientific term. It is something that is relevant to all of us. The consequences of the ‘great acceleration’ of human activity on the earth’s biodiversity and on its climate are very evident.

Species Extinction

Human activities have accelerated the rate of species extinction. Whilst the exact rate is controversial, it is possibly 100 to 1000 times the normal background rate of extinction. In just the oceans, a 2010 study published in Nature found that marine phyto-plankton – the vast range of tiny algae species accounting for roughly half of Earth’s total photosynthetic biomass – have declined substantially in the world’s oceans over the past century. Since 1950 alone, algal biomass decreased by around 40%, probably in response to ocean warming – and the decline has gathered pace in recent years.

On land, wildlife populations have halved in the last 40 years according to a report by the World Wildlife Fund (WWF) and the London Zoological Society (ZSL) in September 2014. Wildlife and their habitats are destroyed by agriculture, logging, pollution, and by the damming and diverting of rivers. Animal numbers are decimated by humans killing them for food in unsustainable numbers, by hunting and shooting them for pleasure, and by the introduction of invasive species. According to a study by an international team of scientists Defaunation in the Anthropocene in the journal Science in July 2014, the current loss and decline of animal species, which is associated to human activity, is contributing to the early stages of a sixthmass biological extinction event. This includes a 45% decrease in the number of invertebrate animals such as beetles, butterflies, spiders, and worms in the past 35 years, during which time the human population has doubled.

Increase in Atmospheric Carbon Dioxide

Human activity has led to an increase in atmospheric carbon dioxide. During the glacial–interglacial cycles of the past million years, natural processes have varied CO₂ by approximately 100 parts per million (from 180 ppm to 280 ppm). By 2013, net emissions of CO2 produced by humans have increased atmospheric concentration of CO₂ by a comparable amount from 280 ppm (Holocene or pre-industrial ‘equilibrium’) to approximately 397 ppm. This change is especially significant because it is occurring much faster, and to a much greater extent, than previous, similar changes. Most of this increase is due to the combustion of fossil fuels such as coal, oil, and gas, although smaller amounts are due to industrial production and land-use changes like deforestation. This will have led to more extreme weather, changes in patterns of rainfall, changing river levels, changes in the ocean currents, rising sea levels due to the melting of ice sheets and glaciers, and increased desertification.

There are other irreversible and detrimental changes being made to the Earth by human activity from fossil fuel extraction, mining for minerals, huge infrastructure projects, heavy industry plants, for example.

These are just the effects of human activity on the earth, not on the human race.

The Effects of Human Activity on Ourselves

The current and likely future consequences of human over-population and over-consumption for humans themselves are just as severe: food shortages due to too many people, water scarcity due to increasing use for irrigation and by heavy industry, soil degradation, water and land pollution due to overuse of fertilisers, conflicts over land, increased migration, land grabs, insufficient housing, dwindling mineral resources, and adverse effects on health from food derived from intensively reared animals or due to air pollution from transport.

Sixth Mass Extinction

According to Elizabeth Kolbert in her new book The Sixth Extinction: An Unnatural History, the human species is now at the same point as when the 10 km (6 mi) asteroid that landed in the Yucatan Peninsula 66 million years ago, an event that wiped out not just the dinosaurs, but most plant and animal species. So it is not just other animals that are facing a sixth mass biological extinction event, we are too.  Our effect on the Earth is not as spectacular or as instantaneous as an asteroid, but in geological terms it might as well be. Elizabeth Kolbert says that if all human civilisation were to end now, then in 100 million years time, everything that we had built, if spread evenly and compressed, would in the geological record amount to a layer of sediment ‘not much thicker than a cigarette paper’.

For a species that has been around for less than 1% of 1% of the earth’s 4.5 billion-year history, Homo sapiens has certainly put its stamp on the place, and now we’ve even got a name for it.

Postscript

Writing in the 11 March 2015 issue of the journal Nature (issue 7542), Simon Lewis, an ecologist at University College London, and Mark Maslin, a geologist at Leeds University propose that a potential marker for the start of the Anthropocene could be the noticeable drop in atmospheric CO2 concentrations between 1570 and 1620, which is recorded in Antarctic ice cores. They link this change to the deaths of some 50 million indigenous people in the Americas, mostly from infectious diseases brought by European colonists. 65 million hectares of agricultural land were abandoned, and the re-growth of forests in their place led to a pronounced dip in carbon dioxide levels. At the same time, Europeans transferred animals and plants between continents, including maize, which in the early 1600s left the first traces of fossilised New World pollen in European marine sediments. Dr Lewis said:

In a hundred thousand years, scientists will look at the environmental record and know that something remarkable happened in the second half of the second millennium. …. Historically the collision of the old and new worlds marks the beginning of the modern world.