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By Howard Falcon-Lang Royal Holloway, University of London
Human civilisation developed in a cosy cradle.
Over the last 11,700 years - an epoch that geologists call the Holocene -
climate has remained remarkably stable.
This allowed humans to plan ahead, inventing agriculture, cities, communication
networks and new forms of energy.
Some geologists now believe that human activity has so irrevocably altered our
planet that we have entered a new geological age.
Start Quote
Simply put, our planet no longer functions in the way that it once did
End Quote Jan Zalasiewicz University of Leicester
This proposed new epoch - dubbed the Anthropocene - is discussed at a major
conference held at the Geological Society in London on Wednesday. Yet some
experts say that defining this "human age" is much more than about
understanding our place in history. Instead, our whole future may depend on it.
The term, the Anthropocene, was coined over a decade ago by Nobel Laureate
chemist, Paul Crutzen.
Professor Crutzen recalls: "I was at a conference where someone said something
about the Holocene. I suddenly thought this was wrong. The world has changed
too much. No, we are in the Anthropocene. I just made up the word on the spur
of the moment. Everyone was shocked. But it seems to have stuck."
But is Professor Crutzen correct? Has the Earth really flipped into a new
geological epoch - and if so, why is this important?
Back to the beginning
Dr Jan Zalasiewicz of the University of Leicester is one of the leading
proponents of the Anthropocene theory. He told BBC News: "Simply put, our
planet no longer functions in the way that it once did. Atmosphere, climate,
oceans, ecosystems they're all now operating outside Holocene norms. This
strongly suggests we've crossed an epoch boundary."
Atomic weapons test DOE Early atomic bomb tests have left a tell-tale signature
in soil
Dr Zalasiewicz added: "There are three ideas about when the Anthropocene began.
Some people think it kicked off thousands of years ago with the rise of
agriculture, but really those first farmers didn't change the planet much.
"Others put the boundary around 1800. That was the year that human population
hit one billion and carbon dioxide started to significantly rise due to the
burning of fossil fuels in the Industrial Revolution," he explained.
"However, the really big changes didn't get going until the end of the Second
World War - and that's another candidate for the boundary."
To formally define a new epoch, geologists must show how it can be recognised
in the layers of mud that will eventually form rocks. As it turns out, there is
enormous practical advantage in fixing 1945 as the beginning of the
Anthropocene.
"1945 was the dawn of the nuclear age," explained Dr Zalasiewicz. "Sediments
deposited worldwide that year contain a tell-tale radioactive signature from
the first atom bomb tests in the States".
So, thousands of years from now, geologists (if any still exist) will be able
to place their finger on that very layer of mud.
Extraordinary times?
Nonetheless, the choice of 1945 for start of the Anthropocene is much more than
just convenient. It coincides with an event that Professor Will Steffen of the
Australian National University describes as the "Great Acceleration".
Professor Steffen told the BBC: "A few years ago, I plotted graphs to track the
growth of human society from 1800 to the present day. What I saw was quite
unexpected - a remarkable speeding up after the Second World War".
In that time, the human population has more than doubled to an astounding 6.9
billion. However, much more significantly, Professor Steffen believes, the
global economy has increased ten-fold over the same period.
"Population growth is not the big issue here. The real problem is that we're
becoming wealthier and consuming exponentially more resources," he explained.
Rainforest slash and burn agriculture AFP/Getty Humans have made a dramatic
impact on many of the planet's ecosystems
This insatiable consumption has placed enormous stresses on our planet. Writing
in the prestigious journal Nature, Professor Steffen and colleagues recently
identified nine "life support systems" essential for human life on Earth. They
warned that two of these - climate and the nitrogen cycle - are in danger of
failing, while a third - biodiversity - is already in meltdown.
"One of the most worrying features of the Great Acceleration is biodiversity
loss," Professor Steffen said. "Species extinction is currently running 100 to
1000 times faster than background levels, and will increase further this
century."
Members of public walking along Canal Street levee, New Orleans Much of the
city of New Orleans is already below sea level
"When humans look back the Anthropocene will probably represent one of the six
biggest extinctions in our planet's history." This would put it on a par with
the event that wiped out the dinosaurs.
But perhaps more alarming is the possibility that the pronounced global warming
seen at the start of the proposed Anthropocene epoch could be irreversible.
"Will climate change prove to be a short-term spike that quickly returns to
normal, or are we seeing a long term move to a new stable state?" asked
Professor Steffen. "That's the million dollar question."
If the Anthropocene does develop into a long-lived period of much warmer
climate, then there may be one very small consolation: the fossil record of
modern human society is likely to be preserved in amazing detail.
Dr Mike Ellis of the British Geological Survey told BBC News: "As a result of
rising sea level, scientists of the future will be able to explore the relics
of whole cities buried in mud".
Preserved buildings
In New Orleans, large areas of the city are already below sea level. The
disastrous combination of rising sea level and subsidence of the Mississippi
Delta on which it is built suggest that it will succumb at some point in the
future.
Although the Intergovernmental Panel on Climate Change (IPCC) predicts less
than a metre of sea level rise over the next 90 years, more than five metres of
sea level rise is possible over the coming centuries as the Greenland and West
Antarctic ice caps melt.
One application for exploring the changing coastlines of the Anthropocene world
is Google Flood. It allows users to raise sea level by up to 14 metres and zoom
into street level to see the effects.
Plastic bottles washed up on beach at Prestwick, Scotland Humans are likely to
leave behind many markers of their presence, including plastic waste
Sea level rise of this magnitude will mean that the lower storeys of buildings
will be preserved intact. Such "urban strata will be a unique, widespread and
easily recognisable feature of the sedimentary deposits of the human age", Dr
Ellis commented.
Geologists of the future may also hunt for other, more unusual, "markers" of
the Anthropocene epoch, such as the traces of plastic packaging in sediments.
But geologists like Dr Mark Williams from the University of Leicester hold much
more serious concerns: "One of the main reasons we developed the Anthropocene
concept was to quantify present-day change and compare it with the geological
record," he explained. "Only when we do so, can we critically assess the pace
and degree of change that we're currently experiencing."
Dr Williams added that while the Anthropocene has yet to run its course, "all
the signs are that the human age will be a stand-out event in the 4.5 billion
year history of the Earth".