Defining the Anthropocene – What is the Age of Man?

An artist's impression of a baffled orangutan.The Age of Man

We, humans, have driven environmental changes on a scale that is unique in Earth’s history.  Human-driven biological, chemical and physical changes to the Earth’s system are so great, rapid and distinct that they may characterise an entirely new epoch – The Anthropocene.

The word ‘Anthropocene’ has entered the scientific and popular literature, as a vivid expression of the degree of environmental change on planet Earth caused by humans.  In 2000, scientists Paul Crutzen and Eugene Stoermer used the concept to denote the ever increasing influence of humans on Earth.

 

A Great Acceleration

Once upon a time, exploitation of resources was limited mostly to firewood and muscle power.  Prior to the Industrial Revolution, global human population was around 300 million in the year 1000 AD.  Five hundred years later, it was 500 million.  In 1750 AD, the global population was still only a mere 790 million.

A drawing depicting the Earth's geological timescale from the Archean to the Holocene strata.Although human remains and artefacts are rare from this time, other indicators such as the presence of seeds and pollen from woodland trees and plants, followed by pollen from crops shows how humans cleared large areas of woodland for agriculture.  Soil was exposed to weathering in deforested regions and this is seen in pulses of sediment, which collected in valley bottoms.  Mineral resources were dug from the ground and the landscape began to change, but on a local scale.

Archaeological and fossil evidence seen in Holocene geology show how human activity increased.  Lead pollution is found in polar ice caps and peat bog deposits from Greco-Roman times (around 2110 years BP) onward (Dunlap et al., 1999).  The time prior to the advent of major mechanisation, industrialisation and expansion in the use of fossil fuels was termed the ‘Pre-Anthropocene’ by Steffen et al., 2007.

An etching of a river city in the Industrial Era.
A city at the start of the Industrial Area, around the 1800s.

From the beginning of the Industrial Revolution (c. 1750 to 1850) to the present day, global human population has climbed rapidly.  Our current global population is currently estimated to be 7 billion (United Nations, 2011), and it continues to rise. 

The exploitation of coal, oil, and gas in particular has enabled planet-wide industrialisation, construction, and mass transport.  The period from around 1800 to 1945 was termed ‘The Industrial Era’ by Steffen et al., 1997.

Humans have caused a dramatic increase in erosion of the land surface and changes in sedimentation, through agriculture and construction, and also by other activities such as the damming of most major rivers.  As well as these physical changes, the signal of chemical pollutants and radioactive waste that we have accumulated over the past 200 years will leave a signal that stretches into the distant future, and one which would be identified by geologists millions of years hence as identifying the Anthropocene.  In recognition of the rapid modification by humans of the landscape through industrialisation and urbanisation from 1945, Steffen et al., used the term ‘The Great Acceleration: Stage 2 of the Anthropocene’.

The combined human driven changes to the Earth’s chemistry, biology and physical environment, including its rocks and soils, has the potential to leave a unique signature buried in the ground.

 

A photograph showing a deforestation web in the mountains of Jambi, in Sumatra, Indonesia.
Deforestation web in the Mountains of Jambi Sumatra, Indonesia.

Earth System

The Earth system is the sum of our planet’s interacting physical, chemical, and biological processes.  It includes the land, the oceans, the atmosphere and the frozen poles.  It takes in the grand natural cycles through which vital elements like carbon, nitrogen, phosphorus and sulphur circulate around the planet, the movement of water between sea, sky, rivers and ice, and the imperceptibly slow events deep beneath our feet that create and destroy continents and oceans.

Living things are part of the Earth system too.  Ocean plankton absorb carbon dioxide from the air to make their shells.  After death, their bodies sink to the seabed, where that carbon remains locked up for millennia in layers of sediment that are slowly compressed to make limestone.

A photograph showing a river dam in Glen Canyon, Arizona.
Large dams such as Arizona’s Glen Canyon Dam can block the seaward trek of more than 90 percent of the sediment carried by a river. Source: phschool.com

Humans are no exception.  Not merely an outside force disturbing the natural order of things, human beings are an integral part of the Earth system ourselves.  But as our societies have grown, the impact of our actions has increased too.  We are now among the main causes of environmental change.

The amount of greenhouse gases varies naturally in the atmosphere, but levels of carbon dioxide and methane are now higher than at any time in the last one million years – possibly even 15 million.  Our great dams are trapping giga-tonnes of sediment, our farms are draining aquifers.  In many places, this is happening faster than they can refill.  Our appetite for land is clearing enormous swathes of forest.

We, humans, are remaking the Earth system itself.  But we don’t know where this will lead.

 

A black and white photograph of the Trinity test fireball at Los Alamos.
The Trinity Test Fireball seen 16 milliseconds after detonation on July 16, 1945 in Socorro, New Mexico. The viewed hemisphere’s highest point in this image is about 200 metres (660 ft) high. Source: Los Alamos Laboratory

A Planet Transformed by Humanity

The team, which was tasked with defining the so-called Anthropocene, says humanity’s impacts on Earth will be visible in sediments and rocks for millions of years into the future.

Published in Science magazine, the latest report by the Anthropocene Working Group is an update on the panel’s investigations.  The Anthropocene Working Group has 37 members – the majority of them now agree that we are living in an interval we should call the ‘Anthropocene’.  There is discussion as to whether it should be a formal or informal unit, but a specific definition is being sought after.

A majority of the group are moving towards the mid-20th Century for the start of this new epoch.  In due course, the group is expected to produce final recommendations.

The researchers are working towards a formal classification of the new epoch.  An open question is the start date.  Some panel members think could be the 1950s – a decade which marks the beginning of the “Great Acceleration”, when the human population and its consumption patterns suddenly speeded up, and coincides with the spread of ubiquitous new “techno materials”, such as aluminium, concrete and plastic.

The 1950s also covers the years when thermonuclear weapons tests dispersed radioactive elements across the globe.  Their long-lived activity will still be apparent to anyone who cares to look for it hundreds of millennia from now.

The first photograph ever taken of the Earth from space in 1966.
Earth photographed from deep space for the first time by Lunar Orbiter 1 on August 23, 1966.

The paper looks at the magnitude of the changes that humanity has made to the planet.  Have there been sufficient changes to significantly alter the nature of the sediments now being accumulated at present?  Are they distinctive from the existing Holocene Epoch that started at the end of the last Ice Age? 

At the heart of its findings is that humanity’s impacts on Earth should now be regarded as pervasive and sufficiently distinctive to justify a separate classification.  According to British Geological Survey scientists,  the case has been made.

Ultimately, it will be down to the International Commission on Stratigraphy to accept – or not – the “Anthropocene Epoch”, as an additional unit in the official time scheme used to describe the planet’s 4.6 billion years of history.

 

A diagram of interconnected Earth systems.
Earth Systems are all interconnected…

Thresholds, Boundaries, and Tipping Points…

The Earth is a complex interconnected system.  Although the very complexity of a system can confer a remarkable stability to it, such systems are also susceptible to abrupt and rapid changes.  Seemingly trivial changes in conditions can lead to unexpectedly swift and profound results.

As scientists learn more about how our planet works, both now and in the past, they are increasingly aware of the existence of environmental ‘tipping points’ – points of no return.  These are thresholds beyond which environmental change becomes hard to stop.

Many of these arise from feedback loops – vicious circles, in which changes that are small in their own right make future changes more likely.  For instance, global warming is causing the carbon stored in polar soils to be released into the atmosphere, triggering further warming and releasing even more soil carbon.

Scientists are still trying to understand exactly where these tipping points lie, and what risks they pose.  But even given the remarkable resilience of the Earth system, it’s increasingly clear that we’re heading into dangerous territory.  Human society needs a stable environment.  If things change too much or too fast, many societies may be unable to cope.

Two images of the hole in the ozone layer over Antarctica in 1982 and 2011.
Ozone depletion over Antarctica, almost 30 years apart. Source: British Geological Survey

But we are causing rapid changes in many areas.  This has led a team of scientists to suggest nine critical boundaries we need to stay within to avoid unacceptable environmental degradation with serious consequences for societies, suggesting that we are close to or beyond at least four of them:

  • carbon dioxide CO2 concentration, 

  • ozone O3 depletion,

  • N2O concentration,

  • CH4 concentration,

  • climate change,

  • water use,

  • biodiversity loss,

  • nutrient pollution,

  • land degradation.

 

Worryingly, we are also getting close to several other suspected tipping points.  All these thresholds are interconnected, thus crossing one makes it easier to cross the others.  On the one hand, the clearing of large parts of the Amazon rainforest could affect weather patterns, while endangering water supplies on the other.

 

Welcome to the Anthropocene!

A photographic illustration of the great acceleration in human population growth.
It is difficult to overestimate the scale and speed of change.  In a single lifetime, humanity has become a planetary-scale geological force…

The evidence is increasingly obvious to us all, from satellite images of global transformations to local extinctions of butterflies, to our increasing up-close-and-personal experiences with extreme weather events.

Earth scientists divide time according to marked shifts in Earth’s state.  Nevertheless, it’s a difficult and novel task for geologists who must try to determine a start date for an era whose palaeontology and geology are still being created.  Indeed there is no handy stripe in the rock layers to mark the Anthropocene yet.

Recent global environmental changes suggest that Earth may have entered a new human-dominated geological epoch, the Anthropocene.  Here we review the historical genesis of the idea and assess anthropogenic signatures in the geological record against the formal requirements for the recognition of a new epoch.  The evidence suggests that of the various proposed dates two do appear to conform to the criteria to mark the beginning of the Anthropocene: 1610 and 1964.  The formal establishment of an Anthropocene Epoch would mark a fundamental change in the relationship between humans and the Earth system.

”When reality is changing faster than theory suggests it should, a certain amount of nervousness is a reasonable response”

The Economist

 

An animation showing graphical representations of the global change in rates of atmospheric CO2 concentration, atmospheric CH4 concentration, ozone depletion, tropical rainforest and woodland loss, damming of rivers, water use, coastal zone nitrogen flux, species extinction, total real GDP, telephones, motor vehicles, international tourism. All of which are on the increase.

Overwhelming the Forces of Nature

The mid-20th Century marks the beginning of the global Great Acceleration – a useful marker both scientifically and because it represents the great social changes that have occurred.

Almost all of us now carry digital communications devices.  We have air miles, TiVo and Nectar points.  We can look back at our own planet from space.  It is the evolution in human society that created this environmental planetary change.  And the way human society develops will shape this new age of man for decades and centuries to come.

Welcome to the Antropocene!