The Anthropocene epoch: scientists declare dawn of human-influenced age
Experts say human impact on Earth so profound that Holocene must give
way to epoch defined by nuclear tests, plastic pollution and
domesticated chicken
Nuclear test explosion in Mururoa atoll, French Polynesia, in 1971. The
official expert group says the Anthropocene should begin about 1950 and
is likely to be defined by the radioactive elements dispersed across
Earth by nuclear bomb tests.
Photograph: AFP/Getty Images
Humanity’s impact on the Earth is now so profound that a new
geological epoch – the Anthropocene – needs to be declared, according to
an official expert group who presented the recommendation to the
International Geological Congress in Cape Town on Monday.
The new epoch should begin about 1950, the experts said, and was
likely to be defined by the radioactive elements dispersed across the
planet by nuclear bomb tests, although an array of other signals,
including plastic pollution, soot from power stations, concrete, and
even the bones left by the global proliferation of the domestic chicken
were now under consideration.
The current epoch, the Holocene, is the 12,000 years of stable
climate since the last ice age during which all human civilisation
developed. But the striking acceleration since the mid-20th century of
carbon dioxide emissions and sea level rise, the global mass extinction
of species, and the transformation of land by deforestation and
development mark the end of that slice of geological time, the experts
argue. The Earth is so profoundly changed that the Holocene must give
way to the Anthropocene.
“The significance of the Anthropocene is that it sets a different
trajectory for the Earth system, of which we of course are part,” said
Prof Jan Zalasiewicz, a geologist at the University of Leicester and
chair of the Working Group on the Anthropocene (WGA), which started work in 2009.
“If our recommendation is accepted, the Anthropocene will have
started just a little before I was born,” he said. “We have lived most
of our lives in something called the Anthropocene and are just realising
the scale and permanence of the change.”
Prof Colin Waters, principal geologist at the British Geological
Survey and WGA secretary, said: “Being able to pinpoint an interval of
time is saying something about how we have had an incredible impact on
the environment of our planet. The concept of the Anthropocene manages
to pull all these ideas of environmental change together.”
High levels of nitrogen and phosphate in soils, derived from artificial
fertilisers, could be taken as evidence of the onset of the
Anthropocene. Photograph: Pascal Rossignol/Reuters
Prof Chris Rapley, a climate scientist at University College London
and former director of the Science Museum in London said: “The
Anthropocene marks a new period in which our collective activities
dominate the planetary machinery.
“Since the planet is our life support system – we are essentially the
crew of a largish spaceship – interference with its functioning at this
level and on this scale is highly significant. If you or I were crew on
a smaller spacecraft, it would be unthinkable to interfere with the
systems that provide us with air, water, fodder and climate control. But
the shift into the Anthropocene tells us that we are playing with fire,
a potentially reckless mode of behaviour which we are likely to come to
regret unless we get a grip on the situation.” Rapley is not part of
the WGA.
Martin Rees, the astronomer royal and former president of the Royal Society, said that the dawn of the Anthropocene was a significant moment.
“The darkest prognosis for the next millennium is that bio, cyber or
environmental catastrophes could foreclose humanity’s immense potential,
leaving a depleted biosphere,” he said.
But Lord Rees added that there is also cause for optimism. “Human
societies could navigate these threats, achieve a sustainable future,
and inaugurate eras of post-human evolution even more marvellous than
what’s led to us. The dawn of the Anthropocene epoch would then mark a
one-off transformation from a natural world to one where humans
jumpstart the transition to electronic (and potentially immortal)
entities, that transcend our limitations and eventually spread their
influence far beyond the Earth.”
The evidence of humanity’s impact on the planet is overwhelming,
but the changes are very recent in geological terms, where an epoch
usually spans tens of millions of years. “One criticism of the
Anthropocene as geology is that it is very short,” said Zalasiewicz.
“Our response is that many of the changes are irreversible.”
Human activity has left a permanent layer of airborne particulates in sediment and glacial ice. Photograph: Pool/Reuters
To define a new geological epoch, a signal must be found that occurs
globally and will be incorporated into deposits in the future geological
record. For example, the extinction of the dinosaurs 66m years ago at
the end of the Cretaceous epoch is defined by a “golden spike” in
sediments around the world of the metal iridium, which was dispersed
from the meteorite that collided with Earth to end the dinosaur age.
For the Anthropocene, the best candidate for such a golden spike are
radioactive elements from nuclear bomb tests, which were blown into the
stratosphere before settling down to Earth. “The radionuclides are
probably the sharpest – they really come on with a bang,” said
Zalasiewicz. “But we are spoiled for choice. There are so many signals.”
Other spikes being considered as evidence of the onset of the
Anthropocene include the tough, unburned carbon spheres emitted by power
stations. “The Earth has been smoked, with signals very clearly around
the world in the mid-20th century,” said Zalasiewicz.Another candidate to be considered as evidence of the Anthropocene is
plastic pollution. Photograph: Dimitar Dilkoff/AFP/Getty Images
Other candidates include plastic pollution, aluminium and concrete
particles, and high levels of nitrogen and phosphate in soils, derived
from artificial fertilisers. Although the world is currently seeing only
the sixth mass extinction of species in the 700m-year history of
complex life on Earth, this is unlikely to provide a useful golden spike
as the animals are by definition very rare and rarely dispersed
worldwide.
In contrast, some species have with human help spread rapidly across
the world. The domestic chicken is a serious contender to be a fossil
that defines the Anthropocene for future geologists. “Since the mid-20th
century, it has become the world’s most common bird. It has been
fossilised in thousands of landfill sites and on street corners around
the world,” said Zalasiewicz. “It is is also a much bigger bird with a
different skeleton than its prewar ancestor.”
The 35 scientists on the WGA – who voted 30 to three in favour of
formally designating the Anthropocene, with two abstentions – will now
spend the next two to three years determining which signals are the
strongest and sharpest. Crucially, they must also decide a location
which will define the start of the Anthropocene. Geological divisions
are not defined by dates but by a specific boundary between layers of
rock or, in the case of the Holocene, a boundary between two ice layers
in a core taken from Greenland and now stored in Denmark.
The domestic chicken is a serious contender to be a fossil that defines
the Anthropocene for future geologists. Photograph: Alamy
The scientists are focusing on sites where annual layers are formed
and are investigating mud sediments off the coast of Santa Barbara in
California and the Ernesto cave in northern Italy, where stalactites and
stalagmites accrete annual rings. Lake sediments, ice cores from
Antarctica, corals, tree rings and even layers of rubbish in landfill
sites are also being considered.
Once the data has been assembled, it will be formally submitted to
the stratigraphic authorities and the Anthropocene could be officially
adopted within a few years. “If we were very lucky and someone came
forward with, say, a core from a classic example of laminated sediments
in a deep marine environment, I think three years is possibly viable,”
said Zalasiewicz.
This would be lightning speed for such a geological decision, which
in the past would have taken decades and even centuries to make. The
term Anthropocene was coined only in 2000, by the Nobel prize-winning
scientist Paul Crutzen, who believes the name change is overdue. He said in 2011:
“This name change stresses the enormity of humanity’s responsibility as
stewards of the Earth.” Crutzen also identified in 2007 what he called
the “great acceleration” of human impacts on the planet from the mid-20th century.
Despite the WGA’s expert recommendation, the declaration of the
Anthropocene is not yet a forgone conclusion. “Our stratigraphic
colleagues are very protective of the geological time scale. They see it
very rightly as the backbone of geology and they do not amend it
lightly,” said Zalasiewicz. “But I think we can prepare a pretty good
case.”
Rapley also said there was a strong case: “It is highly appropriate
that geologists should pay formal attention to a change in the signal
within sedimentary rock layers that will be clearly apparent to future
generations of geologists for as long as they exist. The ‘great
acceleration’ constitutes a strong, detectable and incontrovertible
signal.”
Evidence of the Anthropocene
Human activity has:
Pushed extinction rates of animals and plants far above the
long-term average. The Earth is on course to see 75% of species become
extinct in the next few centuries if current trends continue.
Increased levels of climate-warming CO2 in the atmosphere at the fastest rate for 66m years, with fossil-fuel burning pushing levels from 280 parts per million before the industrial revolution to 400ppm and rising today.
Put so much plastic in our waterways and oceans that microplastic
particles are now virtually ubiquitous, and plastics will likely leave
identifiable fossil records for future generations to discover.
Doubled the nitrogen and phosphorous in our soils in the past
century with fertiliser use. This is likely to be the largest impact on
the nitrogen cycle in 2.5bn years.
Left a permanent layer of airborne particulates in sediment and glacial ice such as black carbon from fossil fuel burning.
Another candidate to be considered as evidence of the Anthropocene is
plastic pollution. Photograph: Dimitar Dilkoff/AFP/Getty Images
Other candidates include plastic pollution, aluminium and concrete
particles, and high levels of nitrogen and phosphate in soils, derived
from artificial fertilisers. Although the world is currently seeing only
the sixth mass extinction of species in the 700m-year history of
complex life on Earth, this is unlikely to provide a useful golden spike
as the animals are by definition very rare and rarely dispersed
worldwide.
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