Welcome to the age of the Anthropocene

Is the “Anthropocene” an exercise in geological bureaucracy or something sociologically more significant? PROFESSOR TIM NAISH explains.

Pressure is mounting on the guardians of the Geological Time Scale, the International Union of Geological Sciences (IUGS), to formally recognise a new epoch in Earth’s history.

Welcome to the age of the “Anthropocene”. This is to be known as the period of geological history in which human activities left an indelible imprint in the layers of sediment currently forming on the floor of oceans and lakes, and in the snow and ice accumulating in glaciers and ice sheets.

The Anthropocene will end the 11,700 year long reign of the Holocene Epoch, often referred to as the “goldilocks period” of equable climate, during which we enjoyed a very pleasant average global temperature of 14 degrees Celsius – not too cold, not too hot, but just right for human civilisation to flourish.

But hold on, doesn’t it take a lot to end a geological period?

An asteroid crashing into Mexico was required to extinguish the dinosaurs that ended the Cretaceous Period, 65 million years ago. And a major ice age in the Northern Hemisphere was required to start the Pleistocene Epoch 2.5 million years ago, which as it happened also coincided with the origin of our species, Homo sapiens.

So, has our species really done enough to change geological time?

Geologists subdivide the geological history of our planet into units of time extending back to its origin 4.543 billion years ago. Several criteria must be met by the “stratigraphic police” at the IUGS before a new epoch of geological time can be ushered in.

Critically, the new time unit must be recognisable in Earth’s rock layers on the basis of a physical or biological feature marking its beginning, which can be accurately dated and easily recognised in other parts of the world.

Global recognition is the key. As a species, we have been leaving isolated archeological evidence of our existence and activities in the geological record since our origin. But it wasn’t until radioactive fallout from atomic bombs in the mid-1940s that the first widespread evidence with global coverage was recorded in snow and ice cores, lakes and bogs, corals and speleothems.

The so-called “chemical bomb spike” marks the beginning of the “great acceleration of the mid-20th Century”, when globally synchronous changes started occurring to our planet’s climate and ecosystems. These changes are unusual in the context of the last 10,000 years and directly attributable to human impacts.

So what are they? We know from measuring ancient air bubbles in ice cores from Antarctica that the present level of carbon dioxide is unprecedented in the last 800,000 years and unprecedented in other geological evidence over the last 3 million years.

The rise in carbon dioxide to today’s level of 400 parts per million has mostly occurred in the last 100 years as a consequence of our use of fossil fuels and has driven Earth’s average temperature up by almost 1C. Earth’s temperature is now well outside the variability of the last 2000 years.

The warming has produced dramatic physical changes to the surface of the Earth. The area of Arctic summer sea-ice has retreated by 50 per cent, the polar ice sheets are melting, virtually all the world’s glaciers are shrinking, the ocean is warming to a depth of 4000m and sea-level has risen by 20cm.

With anthropogenic global warming, these changes are predicted to continue and in some cases accelerate. The only future scenario with a chance of keeping our climate within the dynamic range of the Holocene Epoch, and some would argue the last 3 million years, is the target signed up to in the Paris Climate Agreement late last year, which requires immediate and aggressive carbon dioxide emissions reductions to limit warming to 1.5 to 2C.

While Paris was a major diplomatic achievement, the real concern is that the “intended nationally determined contributions” pledged in Paris, including New Zealand’s, will not get us there. In fact the tabled emission reductions put us on track for a planet that will be closer to 3C warmer.

A recent meeting in Geneva, convened by the Intergovernmental Panel on Climate Change (IPCC), scoped a study to look at how global warming could be limited to 1.5C. Low-lying coastal nations requested this be done as part of the Paris agreement, concerned 2C was not a safe “guard rail” for them. I returned with the sobering realisation that we will be at 1.5C within the next 10 years.

Looking further into our future, the most recent IPCC report said it is virtually certain Earth will be unable to trig­ger widespread glaciation during the next 1000 years.

Climate models indicate that cooling into the next ice age, expected to occur naturally during the coming millennia, will not happen if CO2 concentration remains above 300 ppm. This to me is one of the clearest indicators that we have not only entered the Anthropocene, but we are there to stay. Our species has already pushed Earth’s climate off is natural trajectory of the last 800,000 years and possibly the last 3 million years.

Large-scale chemical perturbations to the cycles of carbon, nitrogen, phosphorus and other elements are also occurring. These, combined with climate change, are causing unprecedented changes to biodiversity.

Species have evolved to live within certain temperature ranges. When these are exceeded and a species cannot adapt to the new temperatures, or when the other species it depends on to live cannot adapt, for example its food supply, its survival is threatened.

Climate change alone is expected to threaten with extinction approximately one quarter or more of all species on land by the year 2050, surpassing even habitat loss as the biggest threat to life on land.

Many of these biological and physical changes are geologically long-lasting and some are effectively irreversible.

So in a million years’ time, when geologists drill through the layers of sediment on the ocean floor, what will the geological evidence of the Anthropocene look like?

The array of signals in the strata may include plastic, aluminium and concrete particles, artificial radionuclides, elevated levels of heavy metals, changes to carbon and nitrogen isotope patterns, fly ash particles and black carbon, and a variety of fossilised biological and non-biological remains.

In 2003, the former Astronomer Royal, Sir Martin Rees, put the chances of civilisation coming to an end in the 21st century as high as 50-50 in his book Our Final Century.

Though controversial at the time, his concern was not just destruction, but self-destruction. The 20th century, he points out, was the first in which humanity’s chance of self-destruction shot up above the eschatological background noise.

Certainly within the geological community the case is progressing to see the Anthropocene formally adopted in the timescale. At the 35th International Geological Congress in South Africa earlier this month, a working group set up to consider the question voted 34 to 0 that the Anthropocene was real in a geological sense.

So is this just an exercise in geological bureaucracy or something philosophically and sociologically more significant?

That changing climate, natural catastrophe and species before us have left their signature recorded in geological time is nothing new.

What concerns me is I am a member of the first species to have developed the capacity to reshape in a geological instant the physical and biological future of the planet we live on.

It is a tremendous responsibility that all of us who are now living in the age of the Anthropocene carry into the future.

Professor Tim Naish is director of the Antarctic Research Centre at the Victoria University of Wellington.

http://www.stuff.co.nz/science/84522636/welcome-to-the-age-of-the-anthropocene

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