Dawning of age of Anthropocene

Is the ‘Anthropocene’ an exercise in geological bureaucracy or something sociologically more significant? 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 sediment forming on the floor of oceans and lakes, and in 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.

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, bogs and corals.

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 Antarctic ice cores 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.

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, 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 is up 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